Exam 2--lectures and book notes
Exam 2--lectures and book notes ISP 203B
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This 33 page Study Guide was uploaded by Jordyn on Friday February 27, 2015. The Study Guide belongs to ISP 203B at Michigan State University taught by Tyrone Rooney in Fall2014. Since its upload, it has received 445 views.
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Date Created: 02/27/15
EXAM 2 REVIEW Tsunami lecture March 11 2011 magnitude 9 earthquake struck off coast Vertical movement of ocean oor pushed water into waves 10m high tsunami waves swept ashore 20 min after tsunami sirens Waves carried away everything in path Disabled cooling system of Fukushima nuclear reactors resulting in meltdown and radioactive contamination 0 Generators couldn t take the water Tsunamis should not be called quottidal wavesquot Tsunamis can be generated from earthquakes from vertical oor movement submarine landslides submarine volcanic eruptions and asteroid impacts Form 0 Undersea earthquakes rocks slowly ex as plates movehappens every 230 to 400 years in this area 0 15m is maximum vertical slip before the plates would break 0 Almost physically impossible to generate a M 10 earthquake because plates would break 1960 Chile earthquake caused this tsunami in Hilo Hl 3rOI or 4th wave is commonly the highest Typical waves 0 Driven by wind 0 Particles travel in circular motion that fades downward 0 quotTouch bottomquot at depths less than half wavelength Tsunami waves 0 Enormous wavelength 0 quotTouch bottomquot everywhere in ocean 0 Velocity depends on water depth shallower the water the slower the wave moves the deeper the water the faster the wave moves 0 Deep water move as fast as a jet liner Tsunami in open ocean 0 Small waver heights 1 m Average wavelength 360 kilometers Period 3O minutes apart Velocity 500 mph Best place to go in tsunami is deep water If the average wave height of a tsunami is only 1m then how does it cause such devastation Wavelength increases as it gets closer to shore As wave approaches shore it slows down due to friction Compresses the water from a broad wave into a tall wave Sumatra tsunami damage 0 Tsunami was catastrophic in top 10 physical disasters in the last century most were oods o Waves carry debris Boats cars shredded buildings eroded soil vegetation 0 Multiple waves rst wave is NOT the largest o Bulge on upper plate one northeast dropped The earthquake moved about 2000kmquot3 of water about 5 to 10 m 0 Large source area most within 2 hours 0 North Sumatra coast had less than 15 minutes Velocity of a tsunami wave 0 Depends on water depth CgDquotO5313DquotO5 C velocity in meters per second D depth in meters g gravitational acceleration lndia plate sinks under Burma Plate Overlying plate bends then nally slips in an earthquake How large was the Sumatra slip zone 0 Similar to the Cascadia subduction zone 0 Rupture time 9 minutes Long term water quality problems too much salt in water US at risk allusion islands or Chile smaller impact Chile earthquake destroyed the Hilo Hawaii waterfront Coastal subduction zone earthquake and tsunami 0 Compression of continental margin 0 Locked margin buckles 0 Finally slips major earthquake 0 Large displacement of water tsunami 1 00000 Paci c NW subduction zone 0 Occasional giant earthquakes generate giant tsunami Chapter 5 tsunami March 11 20111 mag 9 earthquake struck the coast ofjapan People stood on a four story roof and were waist deep under water Tsunami generation Tsunami means harbor wave in Japanese referring to the fact that the waves rise highest in where they are focused into bays or harbors Tsunamis are most commonly generated by earthquakes Earthquake generated tsunami Movement of ocean oor on reversethrust fault on subduction zone and occasionally a normal fault Subduction zone usually the oceanic lithosphere typically goes underneath the continental lithosphere Coastal bulge the region above a subduction zone in which the overlying continental plate exes upward before slip on the subduction zone causes a major earthquake 0 Same way a piece of paper bulges upward if you pull its far edge toward you Height of a tsunami depends on the magnitude of the shallowfocus earthquake area of the rupture zone rate and volume displaced or offset on a fault Vertical movement of a fault causes displacementnot horizontalstrike slip A major tsunami forms somewhere along the paci c ocean roughly once a decade once every 20 years a 30 m high wave hits Tsunami generated by volcanic eruptions Volcanic processes can displace large bodies of water Tsunamis generated by volcanic eruptions are usually catastrophic but are poorly understood Krakatau in 1883 35 min after eruption a series of waves high as 30m attened the coastline of Sundai Atlantis theory cone of eastern Mediterranean island volcano collapsed Tsunami from fastmoving landslides of rock falls Fast moving landslides or rock falls enter ocean can displace huge tsunami Higher falls displace more water Created 150m high tsunami in Lituya Bay Alaska Submarine landslides occur underwater can also generate a tsunami Could be major subduction zone earthquake in the Caribbean Tsunami can also occur in large deep lakes ake Tahoe broad shelf of lake sediments collapsed some time after the last icing glaciers from the last ice age Tsunami from volcano ank collapse Flanks of many oceanic volcanoes including Hawaii and canary islands Atlantic ocean apparently collapse on occasion and fall into the ocean resulting in tsunamis thousands of cubic meters high Volcanoes such as the ones that make up the Hawaiian islands grow from the sea oor for 200000 to 300000 years before breaking the sea level 0 Then build lava shield 0 Mega land sliding occurs near the end of the shield building stage Debris avalanche a fast moving avalanche of loose debris that ows out a considerable distance from its source One per 100000 years Tsunami from asteroid impact 1km asteroid colliding with earth one every million years Supersonic speeds and wave high into the atmosphere Tsunami movement Wave can be described by its wavelength height and period Wavelength the distance between two waves Period time the time between the passage of two successive wave crests Tsunami wave heights in the open ocean are small The average wavelength of a tsunami wave is 360km A ship wouldn t notice such a gentle wave in deep sea Winddriven waves only feel the bottom of the ocean near shore Tsunamis slow because their circular motions at depth drag even more strongly on the ocean bottom Tsunami on share In some cases tsunamis may appear much like ordinary breaking waves at the coast except their velocities are much greater Some tsunamis are a rapid rise of sea level Coastal effects As tsunami waves approach the shore the mouths of rivers and coastal bays funnel the waves and raise their height Tsunami waves curve progressively to face toward the shore December 12th 1992 magnitude 75 earthquake in Indonesia generated a tsunami in the Flores sea 0 1000 people died in small island of Babi 2 Costal geography of other regions can protect them from tsunami islands that are surrounded by coral reefs Runup Runup the height the wave reaches as it rushes onshore It varies depending on distance from a fault rupture Runup is usually 510m high above normal tide level Water levels can change rapidly as much as several meters in a few minutes Waves will typically run up onto shore in a direction perpendicular to the orientation of the wave crest Trimline way to see evidence of a past tsunami line across mountainside where tall trees upslope are bordered by distinctly shorter trees downslope Pe od The arrival of a giant wave is usually followed by others that are bigger than the rst A wave traveling 760 kmhr wavelength 200km arrive every 15 min 1946 people in Hilo Hawaii assumed the danger passed and went outside and were swept by second wave Time between tsunami waves is often more than a half hour Tsunami hazard mitigation Coastal developments that orient streets perpendicular to waves tend to survive better than those aligned parallel to the shore o Allows waves to penetrate further as dissipate Tsunami barriers provide some protection can be overtopped or destroyed Tsunami warnings Tsunamis are most likely to occur within minutes to hours after earthquake Warnings are perfected for far eld tsunami many regions failed to invest until AFTER the 2004 tsunami Paci c tsunami warning system buoys on bottom of ocean Tsunami watch issued when magnitude 7 or grater is detected somewhere around the paci c ocean Tsunami warning if a signi cant earthquake is identi ed from the buoy system the watch is upgraded to a warning Paci c tsunami warning system was tested when Tonga subduction zone had a quake and there was a warning sent out from Hawaii but Hawaiian population had only about 10 minutes to respond Some radio stations didn t interrupt their station to send out a warning Surviving a tsunami A nearby earthquake allows almost no time for of cial tsunami warning Get to high ground or inland IMMEDIATLEY Moving inland will help because the speed energy and height dissipates quickly inland Even when wave slows its too fast to outrun Take cover from falling objects Never go to the shore to watch a tsunami Don t return to the shore after the rst wave Stay turned on radio and tv Future giant tsunami Will effect north America in near future 0 Subduction zone in paci c northwest o Flank collapse of shield volcano of Hawaii 0 Flank collapse of shield volcano on canary islands in Atlantic ocean near Africa Paci c north west tsunami 40000 summer residents visit Oregon and have no clue it is such a tsunami hazard First indication risefall in sea level Kilauea Hawaii potentially catastrophic ank collapse Frequency of these events seem unclear f slump collapses possibly triggered by an earthquake it could have catastrophic waves 100m high We hope next event wont be any time soon but we will have no way of knowing Canary islands potential catastrophe in coastal cities across the Atlantic Most recent collapse was 170000 years ago Average collapse of 100000 years may be long but isn t unlikely to happen Since east coast is very populated and not very prepared it could be awful Volcanoes lecture Cascade range volcanoes are active 0 Until 19705 cascade range volcanoes thought to be extinct or dormant Rule of thumb if volcano had signi cant glacial erosion it had not erupted since end of last ice age and probably wouldn t erupt again 0 Located western north America 19141921 eruptions of Mount Lassen Northern California seen as exception 0 With the understanding of plate tectonics came realization that cascade range volcanoes sit over active subduction zone therefore volcanoes are potentially active 0 Active volcano is one that is likely to erupt again 3 O Portage lake volcanic upper peninsula extinct volcanoes o Volcanologists don t consider volcanoes to be dormant only active or extinct on geologic time scale 0 Cascades oceanic crust subducting under continental Mt St Helens o What caused Mt St Helens to eventually erupt earthquake not buildup of gas 0 Outcome coarse material deposited close ne material was deposited far from the mountain 0 May 18th 1980 Erupting magma releases more pressure on magma below steam expands and escapes as ash erupts Release magma bubbles in the magma expand Soda bottle don t see as many bubbles until you release the pressure and take the top off If the bubbles are unable to escape they make an explosion Whole forest down preserved Which of the hazards of volcanoes kills more people than anything else 0 Lava ows 0 Ash ows 0 Ash falls ash lands on roofs and collapse 0 Landslides o Mud ows correct Mud ows are dangerous because people don t see them coming snow melted and mixed with ash and created a mudslide and was like a concrete mixture moving quickly Mud ows move down valleys during eruptions o Eruptions generate rainstorms and melt snowice 0 Rain falls on ash on the slopes 0 Wet ashmud ows Long after eruption heavy rains can reactivate and create more mud ows 61 people were dead or missing Columbia river mudslide People with some experience are more dangerous than people with none Mt Rainier has a potential to erupt Intro to volcanoes generation of magma o Volcano coneshaped hill or mountain formed at vent from which molten rock or gases reach earths surface and erupt o Magma molten rock BEFORE it erupts Basalt magma brown to black low viscosity ows well water like around 50 silica fewer silica tetrehedra Andesite magma intermediate around 60 silica behaves honey Rhyolite magma white or pale shades high viscosity around 70 silica rigid frameworks of silica tetrahedra behaves like tar Magma rises through crust because less dense than surrounding rocks Magma sometimes breaks off and incorporates pieces of adjacent rocks Magma chamber mass of molten magma that rises though earths crust often erupting at surface to build volcano where magma may reside for a period of time o Lava magma AFTER it reaches earths surface 0 Volcanoes only form at settings where magma is generated at depth and can rise to surface 0 No two volcanoes are exactly alike 0 No two eruptions exactly alike even same at volcano 0 Events of eruption depend on How uid magma is viscosity Krakatoa Indonesian volcanic island oudest noise ever made on earth heard all the way in Australia Quality of water vapor other volcanic gases volatiles Type and amount of magma volume 0 From size and slopes of volcano can infer magma composition volatile content 0 Type of volcano re ects eruptive style associated hazards risks 0 Volcano types 0 Shield volcano Hawaii largest volcanoes on planet but will never notice them 0 Shield volcanoes Persistent basalt eruptions of low viscosity basalt eventually build gently sloping pile of thin ows Supposed resemblance to roman shield Flows characterized by low viscosity low volatile content broad and gently sloping sides large to giant volumes 4 Lava does not ow from peak but from three eruptive rifts radiating from central summit o Mauna Loa and Kilauea basalt giants over a oceanic hot spot Most shield volcanoes are associated with hotspots 0 Three stages of activity Long series of eruptions below sea level building broad base of volcano little strength Basalt lava ows build main mass of volcano As volcano moves off hotspot smaller and less frequent eruptions o Mauna Loa and kilaueo basalt giants over an oceanic hotspot Activity at Kilauea moved form Kilauea crater to Pu u O o cater on east rift Southern ank of Kilauea has broken along a rift and is slowly sliding toward ocean Impending eruptions announced with swarms of small shallow earthquakes harmonic tremor of magma movement in ation of volcano summit Rarely dangerous exception of hot gas surge that killed some of King Keoua s army in 1790 0 Mount Etna Sicily Largest continental volcano on earth Most active volcano in Europe except Stromboli Flank eruptions have build three radial ridges like Hawaii s Cinder cones on ridges erupt cinders and lava ows Continuous eruptions include some violent subplinian episodes Cinder cones 0 Also from basalt Characterized by small size low viscosity steep sides moderate volatile content Sometimes referred to as mono genetic single events Lava and cinders erupt from vent fall around in loose steepsided pile Usually erupt only over one short period few months to few years Build pile of cinders 100200m high followed by basalt ow from base Basalt material degrades to from fertile soil 0 Event fountains lots of magma into the air Stratovolcano Large steepsided cone Characterized by moderate volume and size moderate to high viscosity and slope moderate to high volatile content 0 Moderateviscosity magma lava ows solidify 0 Large eruptions of ash and blocks build cone close to vent Mostly in coastal chains above subduction zones Eruption behavior intervals vary dramatically Lava domes usually in strtatovolcanoes or by themselves Rhyolitic volcanoes characterized by small to moderate size high magma viscosity steep anks low to moderate volatile content 0 Rhyolite magma emerge slowly with little steam to solidify in a large dome 0 Extremely viscous magma within may continue to rise forcing pieces of dome to break off Broken pieces may tumble downhill as a pyroclastic ow Overtime form loose rubbery steep slopes Generation of magma o Distinction between liquid solid and gas 0 Substances change from one to another with change in temperature andor pressure 0 Melting temperature depends on pressure and availability of water The melting temperature of a rock depends on depth and amount of water Rock may melt by 0 Increase in temperature Decrease in pressure 0 Addition of water shifts melting curve to lower temperatures 0 000000 Earth e eerreee Sulbduetiiemzene i eee green arrewe err cliegran l Selid linereeee preeeere I heating I riee i e eeeee A 7 ereeeure decrease e additien ef water 7 jclerereeeed melting 3 tEl l lpE39l f tlLllFE Deep EDIE EDIE i reee 1400 EMS Temperature PC Where does magma come from the mantle it is made from a subducting plate under another How do you generate magma from the mantle o Decrease the pressure 0 If want to make a rock melt you need to decrease the pressure at a constant temperature or increase the temperature at a constant pressure 0 Increased pressure increased the boiling pointdecreased pressure decreases the boiling point 0 If you release pressure in a pressure cooker you have an explosion 0 When you increase the pressure you prevent it from melting need to DECREASE the pressure Environments of magma formation Spreading centers 0 Convection causes asthenosphere to rise most spreading centers are at oceanic ridges o Lithospheric plates rift apart 0 As asthenosphere periodtite rises pressure drops and it melts to form basalt magma 0 Melt is lower density than surrounding rock so the basalt rises and erupts onto the ocean floor Subduction zones 0 Increase in temperature downward o Boil off water from subduction zone add water to hot rocks above subduction zone causes melting of basalt magma o Basalt magma rises heats continental crust causes melting to form graniterhyolite magma o Added water decreases melting temperature of rocks Mantle plume o Rising column of hot solid peridotite mantle o Melts to form basalt magma as pressure decreases Hawaii 0 Under a continent the basalt melts continent to form rhyolite magma Yellowstone o Plume is where hotspots are 39T l B i39ll Eihereete e ee ef the eern men m llm er law 5 i lNEIEEilI E Till Dl EIlE Hil iEM L E Sl ULT Elli i z Tl M L Tl EFl llEl iTlElN l TE 4 lFl ll i llTE ieee 7 7739 Ellie eeeeee 777 397 WW eieeeef 7 777quot eel enrl peeeiil ligh emery Ueler Blane E Bf grail gram and Ether Pale mime itemting while girlie eeiilew ll39Ii39E39l Inerllele eelere Eempeeiilem Megneeiem iren elm eeleiumriel39l Sredeeelrel e P eieeeium elel eilieemli Silica eeeieni e 531 Emir e ree Temperature ii 1 DEF re lED J C rellme ie red ihei Ereeieieeel m BEEF and 900 dull red little water re rite rit lunleee magma 39ilelelilee emieiiniese gjreunlglweier May remain ifirerie eriel re a Eerierellii were weiew39 eigni39lieenl terhen Lil iriltilif Eruetetl materiel Meeily fleee ileee Enigma m5 Erma rmgim nm leleeily eeli Which magma is likely to form a taller volcano 0 High silica Which would be least explosive 0 Low silica Viscosity resistance to ow 0 High viscosity magmas are thick and pasty o Depends on chemical composition internal arrangement of atoms and molecules 0 Silica tetrahedra bonds are strong gt rigid silicate structures gt higher viscosity 0 Differences in viscosity mainly due to differences in amount of silica 0 Higher percentage of silica gt higher viscosity Magma properties and volcanic behavior 0 Temperature affects viscosity 0 As magma cools more bonds form between atoms and molecules gt magma becomes more Viscous 0 Temperature of 11001200 degrees Celsius basalt lava pours downhill spreads across at ground 0 Temperature of 800900 degrees Celsius rhyolite magma erupts with dull red heat Rhyolite magmas o Are cooler than basalts Magma properties and volcanic behavior 0 Volatiles dissolved gasses in magma 0 Water vapor carbon dioxide other gases 0 Water at high temperatures of magma expands violently to form steam when reaches low pressure near earths surface 0 At 20 km depth rhylotite magma can hold 2 water vapor o Thicker the magma is the harder it is to loose bubbles in a non explosive way At earths surface magma can hold almost no gas comes out of solution and forms bubbles Magma properties and volcanic behavior Volatiles dissolved gases in magma Bubbles of volcanic gas can escape easily from low viscosity basalt magma Bubbles of volcanic gas remain trapped in high viscosity rhyolite magma Rhyolite magma explodes into clouds of steam foamy pumice and white rhyolite ash Volume determines magnitude of an eruption Viscosity and volatile determine eruptive style How thick is the magma and how much carbon dioxide is there Composition and volume of magma in subduction zone depend on Rate of subduction Temperature and water content of descending slab Composition temperature and water content of overlying crustal rocks Ease with which magma can rise through crust other intangible factors Volcanic eruptions and products 0 Characteristics of volcanoes size steepness and eruption products depend on Magma volume Viscosity volatile content 0 Eruption products include Lava Pyroclastic materials ash pumice pyroclastic ow deposits re material means pieces of volcano that explode Lahar volcanic mud ows warm mud ows Ashacid raid volcano ash mixes with water 0 Sulfur dioxide with water sulfricacid 000000 0 O annoralizodl Products of 1ulollioonoes P WDELAETIE lii39il lTEPlli39i39il iI iEH L illi PllFi39lllEE EITHER lFFi l iElil39lENTE Li39jilHi39JiFiE Fmii quotl l Mam magma that aims raginoiito anti Soot of olioiiioo W r motion blown outoi a 1ioloorio Voloanio ash and minor liatn39ionto iroi io tried EFiiiiTioii aiiiandmo Earns J i t J W Mai to depos ited by a pgrroolaotio clownslooe WIIII39T water lmudflowoi ouriooo 39 flow or by airfall ooh Fl l lrLll l KEIFIlj raiii froir39i Iooa loan 9 mm r39l1 llj l39ll39lIL lll llo l lilillSUllLllllUS quot 1 P J V i ooh to lens 3 cm aoiooo H GENERAL oooohoronishooto or Angular lo rounded unooriotl partiooo lioin moo lo Largai Homo ii ia q L13 lrolo3ii lroiii olrier iiolnanio rocks on the oi it hit 3911 GH lli AGTEHIET HES lJi EJl iE39Jll juiiilJloo oi iolooi39ir boulders iiiEH Non explosive eruptions lava ows 0 Basaltic magma usually erupts as lava ow 0 May spill out from central crater or pour from rift 0 Hawaiian type lava 7 Pahoehoe smooth ropy or billowy surface Aa rubbly and clinkery surface very sharp edges Explosive eruptions pyroclastic materials 0 Fragments of solidi ed magma from explosive eruptions o More viscous greater gas content gt more likely to explode 0 As it approached surface steam bubble froth trapped in viscous magma expands to form dome of glassy bubbles pumice Explosion is caused by the bubble Bubbles continue to expand pumice bursts into pyroclastic ash particles and volcanic gases Finer fragments of pyroclastic material deposited as airfall ash Heavier pyroclastic fragments may collapse downhill as pyroclastic ow falls side ways and can wipe out a whole city Travels distances up to 20 km at high speeds Destroys everything in path 0 Ash and pyroclastic deposits on ank pf volcano may mix with water from rain of volcano may mix with water from rain or melted snow to form lahar or mud ow 0 Ash cloud rolls over pumice if ash mixes with water it will make steam explosions Ash and pumice falls 0 Volcanic ash is composed of bits of pumice o Largest ash particles fall near vent o Smallest ash particles remain suspended in stratosphere for years and are carried around world blocking radiation from sun After 1815 eruption of mount Tamora Indonesia quotyear without summerquot Ash particles are suspended in a cloud of steam that cools and condenses falls in ashy rain volcanic weather Heavy Ioa ng of ash on roofs when mixed with water causes roof collapse Serious health problems from inhaling ash for those with existing respiratory illness Problems for cars hinders visibility clogs air lters Serious problems for aircraft causes loss ofjet engine power Monitoring systems now warn of potential eruptions but radar can not detect ash clouds Engine converts the glass back into lava 1982 Malaysia to Australia ight ew into ash cloud lost all four engines fell 7000m before engines restarted 1989 and 2009 eruptions of Mt Redoubt in Alaska affected ights and closed Anchorage airport 2010 ash cloud from Iceland eruption blanketed Europe closing airports and grounding ights for days April 17th 8pm eruption airplanes didn t y economic cost of shutting down aircrafts 0 Looks like ash fall on top then the ow underneath with blocks of pumice underneath Distribution of ash picture 0 Ash fall evenly covers hills and valleys 0 Surge lateral blast thicker in valley thin on hills 0 Ash ow thick in valleys essentially absent on hills Lenses of ash compressed and fused Welded to form solid gas Ash ows can be hot enough to melt the ash to for streaks of black obsidian welded ash Surge lateral blast layers are often crossblended Volcanic mud ows o Mud ows form when ash combines with water Pours down sides of stratovolcanoes at high speeds with consistency of wet concrete Similar to deep oodwaters spread over lower slopes picking up objects in path Can be triggered by eruption of volcano covered in ice or snow or by heavy rain Icy to boiling temperature hot mud ow called lahar Most stratovolcanoes emit steam from summit from snow or rain melt water heated by volcanoes hot interior Hot groundwater further weakens already unstable stratovolcano making enormous mud ows more likely o Mud ows from mount Rainier have buried valleys where many communities now sit Poisonous gases 0 At depths of more than few kilometers pressure keeps gas dissolved At surface gases absolve come out of solution Increasing column of escaping gases near volcano can warn of impending eruption Gas in atmosphere forms aerosols gt volcanic smog vog Carbon dioxide uncolored and odorless wont know its there until too late O 0000 00000 O 0000 0 0 0 1986 in Cameroon magmatic carbon dioxide bubbled out of Lake Nyos swept downhill through several villages as river 50m thick 16km long think the water ipped and the carbon dioxide stuck in the ground was released it stumbled down the side of volcano killed everything n the path that breathed oxygen Killed more than 1700 people 3000 cattle small animals Carbon dioxide from long valley calderas in eastern California has killed huge areas of trees Non related earthquake C02 enters throughout the ground and when trees start to die unexpectedly its usually from CO2 Other volcanic gases include sulfur dioxide hydrogen sul de chlorine compounds uorine Hydro uoric acid eats your bones when produced in volcano and breathe in is very dangerous 1783 eruption of Laki in Iceland appears to have injected enough uorine into the atmosphere to kill several thousand people in Iceland and Europe Explosive eruptions Giant continental calderas 0 DO 0000 0 Rhyolite volcanoes characterized by high magma viscosity high volatile content gently sloping anks Yellowstone National Park typical giant rhyolite caldera Erupt rhyolite in enormous volume mostly explosively until magma chamber has emptied enough for ground surface to collapse in creating depression in landscape N43 magma lling magma chamber may create resurgent dome Eruptions are infrequent at intervals of hundreds of thousands of years Can inject enough ash volcanic gas into upper atmosphere to change climate DEADLY LAHAR mount Pinatubo Philippines 1991 Andesitic volcano 90 km from manila Previous 400 years no eruptions Philippine volcanologists and US Geologic survey began monitoring volcano Geologic mapping showed 600yearold pyroclastic ows across densely populated areas and Clark Air Force Base Frequency of earthquakes increased moved higher in volcano Volume of sulfur dioxide emissions increased Occasional small pyroclastic ows swept down from volcano Major eruption seemed imminent within two weeks Evacuation recommended for area within 10 km of summit Lava dome began growing harmonic tremor increased Evacuation recommended for area within 30 km of summit Plinian eruption began june 12th with huge plume of steam and ash towering 3540 km Ash layers 30 cm thick blanketed region Typhoon Yunya s intense rain mixed with ash to collapse roofs form lahars Twenty million tons of SO2 combined with water in atmosphere to make droplets of sulfuric acid re ecting on incoming ultraviolet radiation Mean global temperatures dropped up to 1 degree Celsius Spectacular sunsets for few years 58000 people evacuated 350 people killed mostly from ash collapsed buildings Later 932 people killed by disease Timely warning and broad evacuations saved tens of thousands of lives Long periods between collapse caldera eruptions santorini Greece Now appears as ring of islands along rim of submerged caldera Twelve major explosive eruptions in last 360000 years about one in every 30000 years Caldera collapse followed by growth of new andesite volcano up to next eruption and collapse Approx 1620 BC 0 Series of catastrophic plinian eruptions of rhyolite ash and pumice culminating in caldera collapse 0 Eruptions may have lasted weeks 0 Area buried under several tens of meters of pumice and ash 0 Town of Akrotiri destroyed possible source of Atlantis legend 0 Modern town of Thera built into caldera wall Future eruptions of giant caldera volcano 0 Yellowstone Typical giant rhyolite caldera Eruptions occurred 2 million 13 million and 640000 years ago 9 Resurgent caldera eruptions by far largest most destructive of all volcanic eruptions nothing comparable in historic time 1000 times volume of 1980 Mount St Helens eruption Multiple calderas Ash from most recent eruption covered much of north America If such an eruption occurred today Destruction or transportation communication energy systems throughout US Huge volumes of ash in atmosphere would block sunlight lower temperatures gt agricultural disaster and famine Since 1870 thermal areas getting hotter resurgent bulges in caldera rise and fall over time Will erupt again but know one knows when Tectonic environments of volcanoes 0 0000 0 Plate boundaries are common locations of change in temperature pressure or water content Most volcanoes are along plate boundaries subduction zones or spreading zones Other volcanoes are above hotspots not at plate boundaries Very few volcanoes at continentcontinent collisions or transform boundaries Spreading zones typically have peaceful eruptions Subduction zones typically have violent eruptions Spreading zones 0 Midoceanic ridges as in paci c or Atlantic eruption basaltic lavas onto adjacent ocean floor Little threat or signi cance to humans except in Iceland where midAtlantic ridge extends above sea level Fissure along center of Iceland opens and erupts every few hundred years most recently in 1783 0 At oceanic ridges periodite from mantle rises to partially melt and form basalt magma o Basalt lava erupting into water forms pillow basalt 0 Flood basalt ows on continents have volumes hundreds of times bigger than ordinary basalt ows covering thousands of square kilometers 0 Continental rifts Basin and range in Nevada Rio Grande Rift in New Mexico Ease African Rift zone spread much more slowly than oceanic rifts produce less magma Lava erupts along riftzone faults Forms small volcanic cinder cones 0 Locations where oceanic plates slide under oceanic or continental plates 0 Widespread most active volcanism 0 Most spectacular most hazardous 0 Cold ocean oor lithosphere descends into warmer mantle o Ocean oor rocks contain water that begins to boil off at depths of about 100 km 0 Water rises into mantle rocks under overlying plate changes melting temperature 0 Mantle periodite melts to form basalt magma o Basalt magma rises through overlying crust can melt granitic rocks to form rhyolite magma o Basaltic magma and rhyolite magma may mix to form andesitic magma 0 Water still contained in andesitic or rhyolite magma may cause it to erupt violently Hotspots 0 Far fewer in number but large in volume 0 Within tectonic plates at random locations 0 Active hotspot volcano lies at end of series of older inactive volcanoes 0 Source of magma is in relatively stationary asthenosphere under moving lithospheric plate 0 Hotspot under oceanic lithosphere Basalt magma from mantle in perioditie Peaceful eruptions o Hotspot under continental lithosphere Basalt magma mixes to form rhyolite or andesitic magma Dissolved water in magma drives explosive eruptions Chapter 6 volcanoes tectonic environments and eruptions Cascade range volcanoes are active Subduction zones are associated with earthquakes and overlying volcanoes so cascades are active although covered in glaciers 0 0 Active volcano likely to erupt again Dormant not erupted for hundreds or thousands of years Several cascade volcanoes are probably active Glacier Peak Mt Rainer Mt St Helens Mt Adams Mt Hood Three Sisters Mt Shasta and Mt Lassen have all erupted in the last 200 years Introduction to volcanoes Generation of Magmas Volcano usually coneshaped hill or mountain formed at a vent from which molten rock called magma or magmatic gases reach earths surface and erupt 10 Lava once magma reaches the earths surface it is considered magma Solids are in a tight bond so they rarely move Liquids are loosely held together by a exible bond As temperature and pressure change substances undergo a change from one state to another If you decrease the pressure on a hot solid rock it may expand and melt into a liquid then expand even more to vaporize into a gas Melting temperature depends on pressure and the availability of water 0 Hot rock deep within earth may melt if the temperature rises pressure falls or water is added addition of water shifts the melting curve to a lower temperature 0 Newly formed magmas may crystalize by cooling or loss of water before reaching the surface As long as the column of magma is less dense than the surrounding rock the magma will oat in it Magma chambers are large masses of molten magma that rise through earths crust often erupting at the surface to build a volcano Slight rise or tilt in the ground surface may indicate an expanding magma chamber Magma properties and volcanic behavior What happened during an eruption depends mainly on how uid the magma is viscosity the quantity of water vapor and other volcanic gases it contains volatiles and the type and amount of magma that erupts its volume Viscosity Refers to how uid magma is high viscosity magmas are thick and pasty low viscosity magmas are thinner and more uid 0 Viscosity depends on chemical composition 0 Most abundant atoms in a magma are oxygen and too a lesser extent silicon and aluminum 0 All silicate rocks including common volcanic rocks have silica tetrahedral silica atom surrounded by four oxygen atoms Bonds are strong so hard to break silicate structures are rigid 0 Higher percentage of silicamore viscous the magma o Basalt black or brownish black and its magma is about as uid as cold molasses dark magmas have fewer silica tetrahedral 50 silica Calcium magnesium or iron make it so uid 1100 degrees Celsius to 1200 decree Celsius Little water content unless magma encounters water 0 Rhyolite comes in white or pale shades of gray yellow pink green and lavender its extremely viscous Contain lots of silicon atoms 70 Potassium and silicarich 800900 degrees Celsius Generally contains more water content Mostly ash eruption o Andesite intermediate falls between basalt and rhyolite dark shades of gray green and other intermediate colors 60 silica Lava and ash eruption Volatiles refer to the dissolved gasses it contains 0 Water is the most abundant Under volcanic conditions water exists mostly in water vapor and instantly ignite anything ammable in its path 0 Carbon dioxide is second most abundant has little in uence on the explosive nature of eruption 0 Pressure holds in any dissolved water so the amount of water a magma can contain decreases where the rock pressure is lower 0 Magmas that contain little water erupt quietly o Magmas with large amounts of dissolved water are likely to explode unless uid enough to let steam zz quietly o Rhyolite magmas produce 010 water by weight Volume determines size or magnitude of an eruption 0 Effects size of lava ow as well as the volume areal extent and time span of ash eruption o For rhyolite and andesite explosions volume of fragmented material depends on volume of magma reaching earths surface viscosity and proportion of dissolved gas 0 Dissolved gas tends to rise toward top of eruption o The upper third of magma chamber erupts explosively and the rest of the magma stays underground or little may erupt as lava ow later in the eruption process 0 Subduction zone volcano depends on subducting rate temperature and water content of overlying crustal rocks ease with which the magma can rise through the crust and other intangible factors Tectonic environments of volcanoes 11 Plate tectonic environments are common locations for change in temperature pressure or water content spreading zones and subduction zones are most common Spreading zones Oceanic oor riftsspreading zones paci c and Atlantic erupt basalt lavas that spread out on the adjacent ocean oor 0 Don t provide much hazards to humans except in Iceland because the midAtlantic ridge extends above sea level 0 A ridge crest makes a broad valley that follows an angle walls move a few centimeters apart per year Pillow basalts a chilled skin of solid basalt forms on the outside of the ow then the molten basalt within bursts and pours out into a new direction the result is a pile of basalt cylinders pillow basalts ook like a pile of oversized pillows in dull shades of greenish to brownish black Floodbasalt simply giant lava ows with volumes of several hundred cubic kilometers more than 100 times of ordinary basalt ows Continental rifts such as basin range of Nevada Rio Grande rift of New Mexico and East African rift zone move apart much slower than oceanic rift zones so decrease in pressure at slower rate Subduction zones Oceanic plate slides under continental plate Cold oceanic lithosphere collides with descends under warm low density oceanic oor or continental rocks the descending oceanic plate or slab slowly heats up and at depths of 100km or so begins to boil off some of the water begins to boil off some of the water which rises into continental crust When mantle peridotite melts it makes basalt magma Subduction zone volcanoes are a composition of basalt andesite and rhyolite Magmas are commonly generated at a depth of 100km Usually contain water making bubbles so the eruptions are violent Hotspots Fewer in number but generally produce large volumes of volcanoes Grow within tectonic plates at what appear to be random locations Dry periotite magma produces quiet eruptions Little basalt magma makes it all the way to the crust but the intense heat melts the silica rich continental crust that new magma rises to erupt at the surface Volcanic eruptions and products Nonexplosive eruptions lava ows Most basalt magmas don t explode because they re uid and contain modest amounts of gas manly water and carbon dioxide Lava ow basalt magma spill out of volcano and spill out down the sides Crater where the lava spills out from or a depression as ash blasts out or pour from a spreading crack or rift on the ank of the cone Hawaiian type lava where uid basalt lava ows dominate eruption o Pahoehoe have smooth ropy or billowy surface generally Develop on lavas rich in steam and other volcanic gases Ropy when uid lava drags a thin cooling skin into small wrinkles or folds 0 People walking across recently erupted but solidi ed lava ows risk breaking through a think crust and falling into molten lava 0 Because of low viscosity basalt ows spread out easily and solidify in gentle slopes o Aa basalt lavas charged with less steam and other gasses crystalized rubbly clinkery surface Runs slower so makes thicker ows Explosive eruptions pyroclastic materials Pyroclastic material Fragments of solidi ed magma from explosive eruptions More vicious and greater gas content make it more likely to explode Pumice glassy bubbles made from froth expanding Volcanic ash when bubbles burst after they expand and the magma rises ash consists of mostly curving shards of ash When pumice bursts into ash steam escapes and whole mass explodes Ash may rain from eruption or be blown downwind as airfall ash o Pyroclastic ow when heavier parts of the ow could collapse onto ank volcano 0 Can also spill directly downslope directly from the crater rim 0 Can travel distances of 20km in few cases much further destroying everything in their path Lahar volcanic landslide if ash and fragment deposits on a volcanoes ank soak up suf cient water from rain or snow the mixture may pour downslope March 18th 2007 partial collapse of Mt Raphehu s crater rim on north island of New Zeeland released large lahar o Seepage through crater following several days of heavy rain caused its collapse which released about 13 million mquot3 of water owing at 2500 mquot3sec in a valley 7 km downstream Area is uninhabited so little damage 12 Mount Pinatubo Phillippines 1991 VEI 6 Size of ash eruption depends on many factors including amount of magma magma viscosity and its wa tervapor content Erupting steam commonly moves between 400 and 700kmhr but may exceed speed of sound Bombs steam explosions can throw large blobsblocks of magma as far as 5km to 10km smaller particles drift further downward Styles of explosive eruptions Volcanic explosive index VEI crudely quanti es eruption size volume and violence Hawaiian eruptions are most frequent and least violent Phreatic and phreatomagmatic eruptions Phreatic eruptions are violent streamdriven explosions generated by vaporization of shallow water in the ground a nonvolcanic lake a crater lake in a volcano or shallow sea 0 Steam dominates magma isn t erupted Maar broad bowl shaped crater encircled by a low rim that commonly rises only slightly above the surrounding terrain Phreatomgagmic eruption if magma incorporates ground water Waterrich eruptions can be extremely dangerous phreatic and phreatomagmatic Erupting column of steam and ash can collapse and create a base surge that sweeps rapidly outward hot sand and rock fragments can sandblast and kill people Strombolian eruptions o Stromboli off west coast of Italy fed by magma that interacts with groundwater or seawater o Fluid nature of magma is generally associated with mild eruptions Vulcanian Eruptions o Vulcano island off north coast of Sicily fed by viscous andesite magmas that are rich in gas Ash falls may dominate but pyroclastic ows and lateral blast eruptions can develop with the ash fall Pelean eruptions Mount Pelee erupted in the West Indies in 1902 obliterated town of st pierre Pelean eruptions characterized by giant ash columns that collapse to form incandescent pyroclastic ows 1902 Sides of expanding dome collapsed to form hot searing block and pyroclastic ows Plinian eruptions Great eruptions of Vesuvius in 79AD and mt St Helens 1980 Larger than pelean eruptions pilian eruptions can be catastrophic for any nearby population Silica rich ash ash falls accompany incinerating proclastic ows Caldera collapse of the magma chamber formed by ejections of large volumes of magma 0 Mt Mazama crater lake Oregon 7700 years ago should actually be called caldera lake 0 Krakatau Indonesia 1883 o Tambora Indonesia in 1815 Craters formed by smaller eruptions at eruptive vent where vent is evacuated by violent eruption Difference between crater and caldera isn t size it s the mechanism of depression formation Types of volcanoes Based on height size and slopes of ank can infer the magma composition that produced in its volatile content Shield volcanoes Persistent bashousalt eruptions of very uid basalts within a small area eventually build a gently sloping pile of think ows Low viscosity low volatile content broad and gently sloping sides and large to giant volumes Most lava from shield comes from three broad equally spaced ridges that radiate outward from the volcano summit forming rift zones Gravity pulling on the anks of these edges causes a slight spreading which causes rifting of the spreading crest Largest volcano on earth mauna loa in Hawaii rises 9450m above base on sea oor and 4270 km above water Others Newberry volcano in central Oregon and medicine lake volcano in central California Mauna Lea and Kilauea Basalt Giants over an oceanic hotspot Mauna Loa Hawaii s largest volcano has erupted 33 times since 1843 Mauna Loa and Kilauea exhibit the mildest eruptions with VEIs of 0 to 1 Oceanic hotspot volcanoes go through 3 stages of activity 0 First a large series of eruptions below sea level that build the broad base of the volcano great heap of volcano with little mechanical strength 0 Second main stage volcanoes produce basalt lava ows that build the main visible mass of the volcano 0 Last stage as volcano moves off the hotspot eruptions become smaller and less frequent Kileauea came after Mauna Loa Kileauea produces much smaller eruptions and looks like a big edge on Mauna Loas southeastern ank Most of Kileaueas eruptions are along rift zones that radiate from the summit 13 Has erupted 60 times since 1832 Kilaueas eruptions produce mostly basalt There is hazardous sulfur dioxide in vog Mt Etna Sicily Italy Catalina 3315m high Etna stands on an unstable base of soft muds deposited from sea water onto oceanic crust Flank eruptions from rifts that divide the volcano into 3 large pie slices have built three radial ridges similar to hawaiin volcanoes Sometimes have eratic violent episodes July 22 1998 one crater produced an eruption 10 km high Plinian eruptions happen sometimes Cinder cones Also basalt but are characterized by their small size low viscosity steep sides and moderate volatile content Erupt where rising basalt magma encounters nearsurface groundwater and escaping steam coughs cinders of bubbly molten lava out of a vent or summit crater When water in ground dries up a single basalt lava ow pushes up from the base Along faults basalt rises to feed lava ows and where it encounters water it ashes into steam to build cinder cones Next eruption in area will probably build a new cinder cone where water is present rather than reactivate an old one Most people evade the rain of glowing cinders as result usually only destroys property Stratovolcanoes Stereotypical volcano large steep sided cone over a subduction zone characterized by their moderate volume and size moderate viscosity and slope and moderate to high volatile content Aka composite volcanoes Slope of ank of stratovolcanoes consists of two factors 0 Magma has moderate viscosity so lavas are not especially uid they ow only on moderately steep slopes before they cool and solidify 0 Escape of dissolved volatiles through viscous magma typically causes large eruptions of ash and broken rubble that concentrate near vents and tumble to form slopes of about 30 degrees this builds the cone higher near the vent Ex cascades Mt Vesuvius in Italy Mount Fuji in Japan Generally 75 and 200 km inland trends parallel to the oceanic trench Usually being growing with a tall basalt shield and then build a tall andesite cone on that base Finally may erupt dacite or rhyolite could make a large eruption and kill their andesite cone An absence of activity for tens of thousands of years doesn t indicate that a volcano is inactive Lava Domes Are rhyloitic volcanoes characterized by their smalltomoderate size high magma viscosity steep anks and lowtomoderate volatile content Generally form at the crest or in the anks of stratovolcanoes They emerge slowly and quietly expand over months or years Single lava dome may erupt only once though it may be replaced by another dome as magma below continues to rise Sometimes as magma in the throat of the volcano solidi es and the magma under pushes it extruding the magma in to a pyroclastic ow Giant continental calderas Continental calderas are rhyolite volcanoes characterized by highviscosity and high volatile content but gently sloping anks due to a predominate ash content spread over large areas Yellow stone will erupt rhyolite typically in enormous volume pyroclastic ows cover tens of thousands of square km Also long history in Santorini Greece Volume of magma typically in the range of hundreds to more than a thousand cubic kilometers Eruption opens calderas then lls with rhyolite ash Resurgent dome magma rises beneath lled caldera The amount of ash in atmosphere would cause drastic climate change Chapter 7 Volcanoes Hazards and Mitigation May 18th 1980 mount st Helens o Bulge in north ank had been growing for weeks Dynamite keg with the fuse lit Volcanic hazards Number of deaths are based on those living in close proximity and the eruption product Pyroclastic ows kill most ash ows kill few Some cases casualties are caused by misjudgment or politically motivated decisions by authorities Lava Flows Downslope where lava is no longer red it is still hot enough to ignite wood if it doesn t burn it is often buried and overwhelmed by the ow 14 Trees in lava either char on the outside of later rots away leaving a cast of the tree trunk Commonly advance at 1 ms at vent and slow to 110th that when cools pose little threat to humans Vesuvius especially uid alkalirich lava ow killed 3000 people in 1631 0 Also bad in 1805 when traveled twice the speed of an Olympic sprinter Pyroclastic ows and surges Pyroclastic ow a mixture of hot volcanic ash and steam that pours downslope because it is too dense to rise Aka ash ow Usually occurs when rapidly erupting steam carries a large volume of ash in a column that rises high above the volcano when steam slows part of the column collapses and the column of ash pours down the ank of the volcano glowing hot pyroclastic ows incinerating everything ammable in their path 0 Deadly pyroclastic ows Mt Pelee Martinique 1902 People engulfed in pyroclastic ow face certain death unless they re near outer edges in car or building Surge highspeed ashrich shock wave can race across ground ahead of pyroclastic ow 0 Commonly originate as lateral blasts of ash and steam in the rst stage of an ash ow eruption 0 Some may hug ground and wipe out forests kill almost everything they meet with heat abrasion and impact 0 Surges leave dunes of ash 0 Both steam and ash in the hottest pyroclastic ows are hot enough to glow in the dark Welded ash harden sheet of ash Travel distance of pyroclastic ow is related to density and quantity of pyroclastic material produced in a particular eruption Pyroclastic ows pour downslope worst place to be is the bottom of a valley Pyroclastic ows are too dense to rise into the air only part of the main ow will have particles dense enough to sink into water so it can travel over water 1902 pyroclastic ow Mt Pelee and continued off shore to capsize and burn boats anchored in the harbor Ash and pumice falls Volcanic ash composed of bits of pumice less than 2mm across light enough to drift some distance in the wind Ash erupts into a column air Ash particles are suspended in a cloud of steam that condenses into water droplets as it expands and cools then falls like snow Fine ash is carried high into the atmosphere and may spread around the world Tambora volcano Indonesia April 1815 blew an immense amount of ash into the upper atmosphere Can drop temperatures shorten growing season and create famine 20cm of ash is enough to collapse a roof less than that if required in warm regions Wet ash is much heavier than dry ash Volcanic weather weather created by volcanic ash eruptions that can produce rain Head out of ash plume by heading perpendicular to the wind ash on the ground or in the air can cause serious health problems Breath through approved mask and if not available breath through wet cloth Fine dust areas eyeglasses are better than contacts Ash causes slippery driving conditions especially when wet Headlights cannot see through falling ash rear end collisions are common due to lack of visibility Ash and aircraft Aircrafts can freeze up and stall when enter ash cloud June 1982 Malaysian aircraft ew into ash cloud all engines failed and fell 7000m before crew could restart engines Ash enters jet intakes melts and coats fuel injectors and turbine vanes 2010 eruption along mid Atlantic ridge in Iceland shut down air traf c for 6 days Disruption cost 200 million per day in lost revenue Volcanic mud ows Volcanic mud ows happen when ash combines with water primarily on stratovolcanoes and pours down on their anks at high speeds with a consistency similar to very wet concrete Can be triggered by the eruption of a volcano covered in ice or snow that is rapidly melted or mobilized by hot ash 1985 Nevado del Ruiz Columbia Lahar hot mud ow or any volcanic mud ow or debris ow Eruption may cause thunderstorms and rain and can make mud ow even if the volcano isn t erupting Stratovolcanoes pose a very high mud ow risk because they are unstable piles of lava Mount Rainer poses serious mud ow risk like many stratovolcaones consists of weak material 15 0 Every 500 years a large mud ow reach as far as 100km from mount rainier Best way to avoid mud ows is to avoid the bottoms of stream valleys that drain away from volcanoes unfortunately most towns develop in valley bottoms and that s where mud ows follow when they move downslope 0 Don t outrun mudslide climb up valley side run back into forest away from channel is a goodidea Poisonous gasses Gasses emitted by volcanoes can pose a hazard to people animals and trees Increasing volume of escaping gases commonly proceeds an eruption Vog volcanic fog made by volcanic gases and aerosols gas reacted with sunlight moisture and oxygen Carbon dioxide is deadly in high concentrations because its heavy because odorless and colorless can suffocate people without warning 0 1986 Cameroon West Africa 0 C02 bubbled out of lake Nyos 0 An air mix of 10 c02 can kill people Sulfur dioxide also dangerous gas acrid smell and chocking effect 0 Results with oxygen to make sulfur trioxide Some volcanoes expel poisonous hydrogen sulfate 0 Hydrogen sul de settles into depressions and can quickly kill people Vog droplets are small enough to be retained in lungs where degrade function and compromise immune system Vog can produce acid rain Hawaii may unintentionally drink toxins in rainwater Predicting volcanic eruptions Examining ancient eruptions Not possible to predict exactly when a volcano will erupt or if it will erupt at all Past volcanic activity can help understand patterns of reoccurrence Paleovolcanology interpreting deposits from prehistoric eruptions and reconstructing a record using age dates on plant material charred in past eruptions or dates on the volcanic rock themselves Tuff rock from ash after deposition Ashfall tuff is distinctly layered also distinctly layered on hills Pyroclastic ow tuff is unlayered at least near the vent mostly in valleys little in hills Exposed rock on a volcano rarely provide a complete record because rock erosion Is the volcano still active Yellowstone 2002 geyers that were inactive for a long time dormant became active Eruption warnings volcano precursors Hard to predict what a volcano will do in the next few days or weeks Mt Vesuvius near maples ltaly seismograph records of volcanic earthquakes have been used to infer magma movement Harmonic tremors low frequency rolling ground movements that proceeds many eruptions Many frequent small earthquakes can lead to eruption not always reliable Changes in surface temperatures of volcanoes and the steam the erupt can be another indication of eruption Small changes in summit elevations and slope steepness associated with eruptions have been observed at some Japanese volcanoes and at a Kilauea volcano in Hawaii Titmeters instruments that measure changes in the slope of a volcano Also GPS can show change in position to show summits rise As magma rises toward the surface steam and other gases are released look for sulfur None are a sure sign of volcano but can tell authorities and see what they do with them USGS predicted mount St Helens but some people didn t leave because personal freedoms Local loggers and timber companies didn t close because of loss of income Mitigation of Damage Controlling lava ow Attempts to slow or divert lava ow have brought only partial success Diverts to another part Warning of mud ows Mud ows kill thousands of people living on lower slopes of volcanoes Automatic detection systems detect when weather when temperature sensors detect movement of hot mud ow Residents might have only 30 min to leave Populations at risk Vesuvius and its neighbors Northern part of European plate slides under southern Europe plate making Alps and drives chain of volcanoes in Italy Mt Vesuvius Long series of major eruptions AD 79 killed 15 population of Pompeii and Herculaneum 16 Area around Vesuvius has gone through cycles of volcanic destruction and rebuilding As far as anyone knows Vesuvius could explode at anytime Long pause since last eruption means the next one could be largest since 1631 Pyroclastic ows would reach populated areas in 5 to 7 minutes after eruption Disaster prevention relies on early detection Campi egre Unquestionably active resurgent caldera within the western suburbs of Naples 2 million people live on the floor of the caldera Eruptions came at intervals of 50 to 70 years extremely high level of volcanic activity especially for a giant rhylotic caldera volcano Past eruptions dumped ash 1m high on Naples Potential death toll for eruption here is frightening hard to imagine workable evacuation plan Cascades of western north America Stratovolcanoes above active subduction zone Cities by cascade are far enough to provide suf cient warning with exceptions to national parks national monuments national forests and wilderness areas Also mud ows hazards from weather over paci c Mount Rainer Largest highest and most spectacular volcano in the line of cascades National park so prevents people from coming too close Last erupted in 1840 Probably not inactive Biggest threat is path of mud ow likely to pour down broad valleys could reach speeds of 100kmh Mount st Helens 1980 was known to be the most active volcano in the range Had been quiet since 1957 USGS issued hazard warnings 2 years before eruption 0 Didn t provide speci c time and area so many precautions weren t taken by people Mount Hood 75km east of Portland Oregon hasn t erupted since 1790 2 major eruptions in past 2000 years Mud ow risk toward Portland and hood river Three sisters Lesser known tri volcano west of bend Oregon Spring 2002 16km wide bulge Mt Mazama crater lake Was an enormous andesite volcano that covered a large area of southwest Oregon 7700 years ago thought to have destroyed itself in giant rhyolitic eruption Released at least 35 times as much magma as amount St Helens Mazama 5 peak simply sank into caldera o It is lake made by collapse of itself 1000years ago a smaller volcano grew on the oor Not great danger because not a lot of people and there are a lot of evacuation routes Mt Shasta Jean Francois saw erupting volcano in 1786 Second tallest volcano in cascades 4318m high Young volcano Produced small quantities of rhyolite in its most recent eruptions usually andesite Seismograph detect 5 waves near volcano Only few lava ows holding it together If collapsed would endanger 1 million people Mount Lassen Oversized lava dome of dacite that descents from a long history of volcanic violence Had little indication for potential eruption May 30th 1914 northern California produced a large steam cloud and a lot of booming noises May 19th 1915 the north slope collapsed sending a mass of hot blocks racing down over a 10 square km area at the base of the eruption May 22nOI steam cloud created mud ow Continued to make clouds until 1921 Area near Lassen is not very populated so will not have a huge effect A look ahead Opportunities for volcanic catastrophe to people are property are greater than ever with growing populations and fertile soils near active volcanoes The chance of dying in an eruption is small enough that most people ignore the hazard The collective death toll and devastation from volcanoes is small in comparison to earthquakes landslides and floods remains of a volcanic catastrophe Chapter 8 landslides 17 Mass gravity landslides Topography and gravity Glacier became unstable because summer time Rain can destabilize the land same with earthquakes Main features of a landslide picture Main Fssiurss f a rstsltirlsll sill v s urinal fju39i39 lfil l39i sii 39 A T snsytsss 7 w Tissssstss Ef EH3quotK 7 77 sgss H 39 swarms quot rIi Iira 1995 La Conchita slide of Santa Barbra o Avocado orchard on top added too much water 0 La Conchita destroyed houses below coastal cliffs of Santa Barbra 0 Houses destroyed south end of the 1995 La Conchita landslide no one killed so people stayed 0 Second landslide from same scarp January 10th 2005 same house 10 people killed would you continue to live in this town Landstes 0 Any object on a slope will end to move down the slope due to gravity 0 Force mass x acceleration mass of rock amp soil x 98 msecquot2 This force acts vertically Shear stress 0 Downslope gravity force Shear strength 0 Internal friction o Cohesion 0 Can the rock handle the strength put on it Gravityinternal friction helps it from falling downslope picture Psrt sf Gravity is piullng sbjsst dwnspsl Hisrmal stress hilarity 0 Factors that would increase the risk of a landslide 0 Increase angle of slope increases the shear stress 18 o Decreases friction 0 Increase mass of block Force weight can be the same but how much is perpendicular to the force Overview of factors that in uence slope stability 0 Slope Angle of repose 0 Moisture content Reduces friction pushes grains apart Frost heave expansioncontraction 0 Grain size and composition Ex expanding clays o Vegetation can increase friction in shallow slides o Earthquakes shaking Angle of repose 0 Material slides if steeper than the angle of repose o Finer rounder particles gentler slope 0 Composition Clays often slide Sand fairly stable Gravel stable 0 Shape Round less stable 0 Sand builds up on dunes then slides down the slip face at angle of repose 0 Some dunes landslide in patches add to much sand at time and it breaks Age of the slope has no effect on if it will slide High angle of repose rocks don t fall as easy Talus slope big rocksboulders source and talus around below them 0 Largest boulders typically reach the bottom of a talus slope or rockfall 0 Small rocks get caught in spaces between large rocks as they tumble 0 Large rocks easily roll over areas of smaller rocks to reach bottom of slope The effect of water on land sliding 0 Surface tension of a lm of water holds grains together more water pushes them apart 0 Water pressure at depth pushes grains apart 0 Unsaturated grains Held together by water surface tension Good for holding surface together First place water goes is to make a coat around the grains 0 Saturated grains Sand grains moved apart by water Surface tension of water quotsticksquot grains together 0 Think lm of water adhering to sand 0 Water lls narrow necks between grain o Partly drained pores Pressure on water 0 Higher pressure at base of sand than at the top of the sand water lls the space to much and then forces the grains apart Water lls spaces between loose grains in the ground below the level of the sharply de ned water table exposed in a gravel road cut in Glacier National Park Build sandcastles close to water Will be more compacted in the morning when the dew is still there Which would increase slope stability 0 Add weight to the base of the slope Don t add weight on top steepened slope add water build with loose full Classic hazard elements of a typical rational landslide 0 House with water added by roof and drive way drains septic system and drain lled and leaking swimming pool How to reduce landslide risk 0 Drain hillslopes Reduces weight and increases friction at base of slope Remove portion of slope that is likely to slide Avoid undercutting steep slopes Bolt slope together 0 Avoid developing areas with high slide risk Drain slop and install retaining wall Water drain will push back the water table and reduce risk of landslides Highway Remove potential slide material if road cut is necessary on unstable slope 0 Rock bolts cables anchored in stable rocks deeper and will hold slope together 19 000 Common landslide triggers 0 Large rain storms water 0 Development water slope steepened load 0 Natural erosion undercuts slope steepened o Earthquakes shaking also shaking from other landslides and can shake another part of the rock 0 Volcanic eruption water new loose material Washington state collapsed after trees were cleared took away trees added water Earthquakes dislodge some landslides Earthquakes can rearrange grains excess water gt liquefaction 0 Shake it and it rearranges then excess pore water carries load of overburden Liquefaction zone upward ow of water Clays and clay behavior 0 Clays absorb water and expand can weaken rock even lift it o Feldspars most abundant minerals in rocks weather to form clay minerals with structures that can lead to landslides o Kaolinite weak positive and negative charges soft and weak structure soaks up water 0 Smectite forms from volcanic ash with open structure between layers that lls with water swelling soils 0 Quick clays watersaturated muds in marine bays estuaries old saline lakebeds that are especially prone to collapse and ow when disturbed Mixture of ne slit clay grains and water in tiny pore spaces Flakes deposited in random orientation give mass total pore space of 50 or more f loose arrangements is disturbed by earthquake or by heavy load on top quick clay lique es and ows almost like water for few minutes until water escapes then mass becomes stable and will not ow again Common along northern coasts of Canada Alaska Europe 0 Clay grains with salty water can be unstable Before collapse quothouse of cardsquot with water in between After collapse much less pore space the water is displaced o T es of mass movement Tabla 3amp1 Eil Ei ti n EFF M3555 M v am ts Material Type Heels DEE3n Emlltenl Debris Meetly 32 mm Sell l 12 mm Fall HidcltFall ehris fall Earth Fall lepple Reel tepple Debrie tdpple Earth temple Slide retatidnal Slump Debris glide Earth glide Elide trenslatidnel Health slide Gehrig Elll ll Earth slide Elllii39 fl39o quot glide lateral regentsiding Hm It ewesid Debris gumad Faerh sewed Fitsw R tlt Flew Debris ew Earth Flew o Magnitude 77 earthquake on subduction zone off Peru triggered landslide 130 km away on mount Nevados Huscaran highest mountain in Peru 0 Which of the following could cause a landslide o Flush fresh water through a clay saturated with salty water 0 Debris avalanches 0 Mass rock that falls but does not disintegrate will travel shorter distance mechanism for travel of debris ows debated o Cushion of compressed air beneath ow Major debris avalanches scoured ground beneath them so could not have moved atop cushion of air 0 May ow as uid composed of rock fragments suspended in air Acoustic uidization if air can not escape spaces between fragments 0 Common types of landslides o Rotational Load at toe holding back movement small amount larger amount large amount advancing toe collapses Tree roots don t penetrate deep enough to hinder movement Trees point toward head scarp Center of rotation is parallel to top of the slope 20 o Translational Loose material on slope moves above solid bedrock Some tree roots may penetrate deeply enough to hinder movement Tristle Utah slide 1983 most expensive landslide blocked river and made lake and had to relocate a whole town Puerto rice 1985 heavy rainfall in tropical storm probably with direct sewage discharge into the ground What else can be done to minimize danger and damage from landslides o Recognize already that are prone to sides 0 Don t build or buy a house there don t build a road there if there is an alternative 0 Don t do anything that may increase the danger of a slide Zion NP close to the site of the October 2011 rockslide almost destroyed a home and killed the owner Laguna beach CA 1978 landslide and then built houses on landslide and 2005 slid again Rocks on bottom of slope stabilize from rotational landslide A tragic case of slope failure landsliding in response to reservoir lling o Vaiont dam northeast ltaly built in 1963 o Filling a reservoir can trigger a slide Added water to sides of slope because water table stays same height and it lls the reservoir and makes the sides more likely to slip 0 When rock slipped the water ew over dam and it broke from displaced water wave took over town Flank collapse from stratovolcanoes mount Shasta 0 Sides of volcano fell off and spread 43 km northwest from mount Shasta 0 East coast at risk of ank collapse canary islands Lateral spreading slides due to liquefaction of sands Mud ow more water than a debris ow 0 All sizes of fragments from mud to sand to boulders all mixed with lots of water 0 Mud ow is different from a debris ow in that a mud ow is water saturated If you see a debris ow or mud ow heading down a valley toward you what should you do run to the side of the valley and upslope October 2005 hurricane Stan mud ows Mexico amp Guatemala Rock falls generate jagged rocks along the base Debris ows 0 Sand to boulders with lots of water 0 Boulders oat to top 0 Water steeps out from between large rocks Signs of debris ow trees slanted high levee and big boulders o Rocks lodged in tree branches 0 Bark battered off tree up high 0 Note also that the bark had been burned in a forest re before the debris ow Debris ow often begin with a small landslide snowmelt picked up water downvalley to develop into a debris ow that destroyed several houses at the base of the mountain slide Grain size and water distribution in a debris ow 0 Turbulent muddy water 0 Smaller fragments in viscous watersaturated matrix 0 Boulders with less water Debris ow often begin with small landslides and develop into ash oods Landslides wet gt debris ow lots of water gt ash ood mostly water Northern Venezula 1999 ash ood and debris ow What can be done to minimize debris ow destruction 0 Build engineered debris ow basins 0 Clean these basins after debris ows ll them avoid building below these collection basins LA CA Soil creep 0 Slow downslope movement especially near the ground surface 0 Freezethaw Effects on a slope Trees bent downslope but try to maintain upward growth 0 Rock layers bent downslope o Trampling soil by animals 0 Burrowing animals tunnels collapse 0 Evidence for creep Broken walls 21 Tilted objects Bent trees Chapter 8 landslides and other downslope movements Unstable hills October 1978 a landslide destroyed 24 homes in Laguna beach heavy rainfalls in the previous winter soaked the ground and months later caused high water pressure within the soil permitting it to slide Next year the homes were rebuilt in 2005 a new slide destroyed 19 homes on the same slope from the heavy rain in the winter Forces on a slope Downslope ground movement is a natural part of landscape evolution Creep natural process to pull a rock down a slope The ability of a slope to resist sliding depends on the total driving force pulling it down versus the resisting force holding it up Driving force consists primarily of the force of gravity working on the weight of the material pulls it down Resisting force consist of the strength of the material and the friction holding it in place holds it back Slope steepness material weight and moisture content all play roles that determine when a slope will fail Slope and load Relationship between slope and load is a key factor in slope failure 0 Slope angle the angle of the slope as measured down from the horizontal 0 Load the weight of material on a slope Increasing load will increase the likelihood of slope failure The steeper the slope the greater the driving force and the greater the likelihood that the slope will fail Angle of repose maximum stable slope for loose material sand its 3035 degrees but wet sand will stand almost vertically Frictional resistance and cohesion Frictional resistance the resistance to downslope movement of a ow or landside depends on the angle O of the slope and the load L of the body The mass will slide or the slope will fail when the force F exceeds the frictional resistance f Anything that reduces the friction on the slope will increase the likelihood of slope failure Cohesion C is an important force holding soil grains together it is the attraction between small soil particles that is provided by the surface tension of water between the particles 0 Results from the static charge attraction between minute clay particles the surface tension attraction of water between grains or the strong chemical bonds of a cementing material 0 Surface tension the effect by which the grains of sand are held together by the thin lms of water between them Most particles have tiny static charges on their outer surfaces For somewhat larger grain sizes the thin lms of water between grains hold them together through cohesion Water and sand castles or hard to separate two wet boards The surface tension attraction of water in a narrow space pulls the glass to the countertop Cohesion is like a weak glue that can be overcome if the sliding force is large enough When the ground is saturated with water there is a buoyancy effect that also decreases the mass pushing against the slope Slopes fail When a driving force is large enough to overcome both the force from a resisting mass and the friction along the surface as well as the cohesion strength of materials Over time slopes adjust to nearequilibrium values controlled by the local environment that is they re ect the slope material climate and thus the water content of the soil Slope material Clay and shale are the most likely to slide Moisture content The amount of water between grains determines what effect the water will have on the strength of a slope Small amount of water provides cohesion and helps hold grains together too much eliminates cohesion and pushes grains apart Pore spaces spaces between grains 0 Loose solids have from 1045 pore space Water tabe amount of water in the soil higher water tables increases pressure in the pore spaces 0 When the weight of water is above a certain point it pushes mineral grains apart 22 0 When the ground is fully saturated water will ooze out of the surface signaling an increased likelihood of slope failure Internal surfaces Most solid rocks such as granite basalt and limestone are inherently strong and unlikely to slide but these rocks are especially prone to slide if their zones of weakness are angled downslope Daylighted beds layers inclined less steeply than the slope so that their lower ends are exposed at the surface Internal surfaces that dip at gentler angles than the slope of a hill 0 Rock layers dipping about parallel to a slope with their edges coming to the surface are said to daylight o Often exposed at their lower ends by a road cut or stream make ideal zones for slippage only friction can keep from slipping Clays and behavior Some rocks or rock materials contain clays that absorb water and expand thereby weakening the rock and even lifting it Feldspars the most abundant minerals in rocks Chemical weathering of all minerals consists primarily of their reaction with water 0 As they weather feldspars lose most or all of their calcium sodium and potassium while their aluminum silicon and oxygen reorganize into clays Kaolinite and Smectite clays that can lead to landslides Kaolinite common clay mineral formed by weathering and which may contribute to land sliding does not expand when wet 0 Have no overall charge but have weak charges on top and weak charges on the bottom 0 Form by weathering in warm wet environments 0 Individual kaolinite akes do not absorb water and do not expand when wet but overall structure is soft and weak soaks up water Smectite soft quotswellingquot clay that forms by alteration of volcanic ash swells when wet and becomes extremely slippery It is prone to land sliding and can deform houses built on it akes have an open structure between their molecular layers which when lled which water causes them to expands aka swelling soils 0 Water has virtually no strength almost any load will cause layers to slide easily over other layers 0 Smectite forms readily by weathering of volcanic ash so soils with old volcanic ash tend to be extremely slippery and prone to landslides when they are wet Quick clays watersaturated mud deposited in salty water and tends to consist of randomly oriented of clay with large open spaces between the akes If the salt is ushed out the akes are unstable and may easily collapse and ow almost like water 0 Silt and clay grains are so ne that water cannot move through the tiny pore spaces quickly enough to escape o The mass has a total pore space of 50 or more 0 House of cards 0 Because tiny clay akes have negative charges the positive charges in the water hold the combination together 0 Liquefaction process in which watersaturated sands jostled by an earthquake rearranges them into a closer packing arrangement The expelled water spouts to form sand Liquefaction occurs as grains settle into a closer packing arrangement with a lower porosity Can also occur on a at surface where it does not cause a slide but can still collapse buildings 0 Quick clays make dangerous risks for any foundation Vibrations caused by an earthquake pile driver or heavy equipment can cause failure of quick clays o Rissa Norway 1978 farmer piled soil at the edge of a lake thereby adding a small loadlt triggered a quickclay slide Causes of landslides Slope equilibrium involves a balancing relationship between slope angle and load You can destabilize equilibrium by changing the slope undercutting loading upper part of slope removing vegetation or moist conditions instability or earthquakes Oversteepening and overloading Balance between the forces acting on a slope can be upset by making the slope steeper or by increasing the load on the slope Load can be increased by adding material to the top or taking some away at the toe Slope angle increased when ll is added above or when slopes are undercut below Oversteepening of a slope increases likelihood of slope failure happens through erosion excavation or adding ll 0 Highway 1 along coast of central California frequently closed due to steep landslides 23 People build on top of steep slopes to have views of sea lakes or rivers these slopes are undercut by waves Some mountains are stable until are dug at to build homes or yards undercut slope above and overload slope below A section of coastal cliff at the edge of Puget Sound near Seattle collapsed crushing and burying a home and family on the narrow strip of beach Adding water Water increases the load on the slope and reduces its strength In addition to rainfallslopes in wet climates are generally prone to landslides Human leaking water from sewer pipes cracked swimming pools prolonged watering of lawns of crops will raise water table La conchita California January 10th 2005 soft weak and porous sediments not cemented into rocks avocado orchard and heavy winter rains soaked slope with water killed 10 people 0 People decided to stay and on December 22nOI 2010 another slide a few blocks north Filling reservoir behind damn can also raise water table Removal of vegetation from a slope will permit more water infiltration because brush and trees remove water by evaporation from their leaves and takeup of water through their roots South west Washington state 2007 heavy rainstorms triggered 730 landslides Overlapping causes When multiple factors occur is when the greatest catastrophes occur Mt Pinatubo Philippines 1991 mud ows accompanied major tropical typhoon hit area during eruption Types of downslope movement Landslides and other downslope movements are generally classified on the basis of material type movement type and rate of movement Debris coarser than 2 mm earth or soil is ner than 2 mm Rates depend on many factors including slope steepness grain size water content thickness of the moving mass clay mineral type and amount of clay Styles of movement falls from cliffs topples slides lateral spreads and flows Among the most common of these are rockfalls rock slides talus debris slides debris ows earth ows mud ows and snow avalanches Rockfalls A rock mass that falls from a steep slope develop in steep mountainous regions marked by cliffs with nearly vertical fractures or other zones of weakness Factors that favor rock falls include cliffs or steep slopes of at least 40 Rocks that are most likely to cause rock falls are those that break easily into fragments granite metamorphic rocks and sandstone Taulus coarse angular rock fragments that fall from a cliff to form a coneshaped pile banked up against the slope fanshaped piles of rock fragments banked up against the base of a cliff 0 Individual rocks especially large boulders may bounce or roll well away from the base of the slope Denver great Plains no build zones USGS Even in areas of relatively subdued topography and horizontal sedimentary layers cliffs or high road cuts can be prone to rockfalls Strong layers of sandstone or thick beds of limestone often break on vertical fractures Roads often follow the base of precipitous cliffs or are built by excavating high road cuts that destabilize original slopes Colorado landslides are most common in areas ofJurassic and Cretaceousage marine shales interlayered with stronger sedimentary rocks Shale most abundant sedimentary rock found at basin Rockfall runout Runout distance rock fall will travel including that beyond the base of the slope generally related to the height from which a rock falls as well as its mass Large blocks high on a cliff have more potential energy than smaller rocks and thus roll faster and farther Larger blocks roll easily on the slope39s smaller material and keep going Potential energy m x g x h When rock falls its potential energy becomes its kinetic energy highest velocity is near bottom of the fall Kinetic energy 12 m x vquot2 Fastmoving rockfalls can run out for distances greater than the height of an original slide scarp Very large rockfalls can run out horizontally as much as 5 to 20 times their vertical fall Debris avalanches Debris avalanches Rockfalls in which a material breaks into numerous small fragments that ow at high velocity as a coherent stream Many of the largest and most destructive landslides in recorded history started as ordinary rockfalls that developed into debris avalanches 24 Yungay Peru on May 31 1970 Mt Nevados Huascaran fell from the peak at the top of the photo and raced down the valley to bury the town of Yungay o Survivors recalled that the strong wind arrived first followed by ying rocks then a huge wave of wet debris with a quotrolling confused motionquot 0 Buried entire city of yungay o Eyewitness accounts indicate that the total time from the earthquake to the ow39s arrival at Yungay 14 km downslope was approximately 3 minutes Fluidization process of changing a soil saturated with water to a uid mass that ows downslope 0 May work if air cannot readily escape the small spaces between rock fragments during the extremely brief period of movement 0 Rockfalls composed of small grains should be more subject to uidization than those composed of coarser particles The air brie y supports the fragments and lubricates their ow Rotational slumps Rotational Slump Homogeneous cohesive soft materials those that lack a planar surface that guides landslide movement commonly slide on a curving slip surface concave to the sky One of the most common landslide types The surface curves because at the top of the moving mass gravity pulls it straight down Farther downslope the mass is also pushing outward toward the open air where less load pushes down 0 Headscarp vertical part of the slip surface 0 Toe lowest farthest extent of a landslide 2005 Laguna beach landslide rotational slump The lower part of the slip surface commonly dips back into the slope provides some resistance so movement ultimately stops Engineers can estimate whether a rotational slump will move by calculating the forces on a slope Center ofrotation found by projecting perpendicular to any exposed part of that surface They may also drill holes through a landslide to find the slip surface at depth If the driving mass is large enough to overcome the force from the resisting mass the friction along the potential slip surface and cohesion then the slide will move Translational Slides Translational slides a landslide with a slip surface approximately parallel move on existing weak surfaces that lie more or less parallel to a slope Compared to a rotational slump a translational slide is shallow which is demonstrated by the fact that trees slip down the surface and remain vertical rather than rotating with the sliding surface Translational slides are especially dangerous because they often move faster and farther than rotational slumps February 17th 2006 Philippines buried village of Guinsaugon Lateral spreading slide lf loose waterrich sands or quick clays are present at shallow depth then liquefaction or collapse may send the mass moving downslope Soil Creep Soil creep slow downslope movement nearsurface soil or rock caused by numerous cycles of heating and cooling freezing and thawing burrowing animals and trampling feet 0 Slow downslope movement of surface soils and weak rock involves nearsurface movement and is not especially dangerous Rates of movement decrease at greater depth because most driving processes operate close to the surface When the soil expands it moves out perpendicular to the slope when it shrinks it moves more nearly straight down under the pull of gravity Trees that stand straight but with their bases curving back into a slope socalled pistolbutt trees have trunks that initially grow upward but become tilted downslope by creep Bedrock layers can bend downslope Soi ucton near surface downslope movement where water saturated ground freezes to great depth 0 Soggy near surface layers ooze downslope Snow avalanches Rapid downslope movement of snow Conditions for avalanche formation depend upon slope steepness weather temperature slope orientation north or south wind speed and direction vegetation and conditions within the snowpack Snow avalanches are often triggered by human actions 0 A skier crossing a slope can add enough load to trigger a snowpack failure weight and vibration of snowmobile is likely to trigger failure Steep slopes of 30 to 45 are most prone to avalanching but avalanches can occur on much gentler slopes given the right weather conditions 25 New snow is one risk factor for avalanches A heavy snowstorm adds a load of loose snow to a slope conditions favored by skiiers Higher temperatures during a spring day can melt grain surfaces enough to fill any pore spaces with water Unstable layers are also formed when hoar frost on the surface is buried by new snow Wet snow that freezes covered by newer drier snow leaves a weak boundary prone to sliding Also can be triggered by strong winds Windblown snow in a cornice is tightly packed and heavy it can easily break off and avalanche downslope The orientation of a slope is also a factor in assessing avalanche risk Northfacing slopes that remain in shadow all day in the winter are dangerous because they don39t warm enough during the day to cause the localized melting and refreezing that helps solidify a snowpack A fresh avalanche on an adjacent slope facing the same direction and with a similar slope is a very dangerous sign The greatest danger for mountain skiers or snowmobile riders occurs when their weight triggers an avalanche while crossing a ridgecrest cornice or avalanche chute Surviving an avalanche The first rule in avalanche safety is to avoid travelling alone in avalanche country If you must cross a dangerous slope do so one at a time testing the edge of the open slope carefully first If you are caught in an avalanche and you are not near the surface as the snow slows take a deep breath to expand your chest so you have room to breathe later and punch out an air space around your face Conserve energy by not panicking and yell only when rescuers are almost on top of you snow rapidly dampens sound waves The quickest way to find a buried victim is through avalanche transceivers carried by each member of a ski party and always set to transmit Time is critical because if the person is dug out within 15 minutes they have a 90 chance of surviving In the next 15 minutes the chance drops to 50 and after another 90 minutes there is virtually no chance Hazards related to landslides Can be triggered by storms and ooding or by earthquakes and volcanic eruptions Earthquakes If a slope is at all unstable an earthquake is likely to send it downslope Even without water sudden shaking may trigger failure Earthquakes below magnitude 4 trigger few landslides 1959 magnitude 73 West Yellowstone earthquake for example triggered the massive Madison landslide and rockfall Of all the different downslope movements an earthquake may trigger debris avalanches and rapid soil ows make up less than 1 Earthquakes cause failure of unstable slopes among the most susceptible are recently raised marine terraces composed of soft wet clays and associated sediments Many accounts of earthquakes include reports of sand spouting from the ground or surfacing in big sandboils evidence for liquefaction When some earthquake waves pass through soil saturated with water the sudden shock jostles the grains causing them to settle into a more closely packed arrangement with less pore space A loosely packed sand with 45 porosity might collapse to about 30 porosity Failure of landslide Dams Any moderately fastmoving landslide can block a river or stream to create a dam when landslide dam fails it can be catastrophic Of those dams that failed roughly a quarter eroded through in less than a day half failed within 10 days and some lasted for a long time 0 Size height and geometry of a dam o The material making up a dam o The rate of a stream ow and how fast a lake rises o The use of engineering controls such as the excavation of arti cial breaches arti cial spillways or tunnels Mud ows debris ows and earth ows create many natural dams that block rivers quickly are not high are composed of noncohesive material and breach soon after formation Most landslide dams fail because the water behind them over ows and erodes a spillway that drains the lake may not happen if the dam consists of large rocks and is so permeable that the lake drains by seepage instead of through an over ow spillway The higher the water level and the greater the volume of water behind the dam the higher the ood level will be downstream Lake Waikaremoana the largest landslidedammed lake in New Zealand 26 1928 the St Francis higharch concrete dam north of Los Angeles failed while the reservoir was being lled because it was built on the toe of a large Pleistocene landslide in schist bedrock Mitigation of damages from land sliding Few insurance policies cover them or any other type of ground movement Landslides in the United States cost more than 2 billion and 25 to 50 deaths per year Worldwide landslides have caused an average of 7500 deaths per year over the last century and 20 billion per year Record of past landslides A record of past landslides indicates that future landslides are likely Building a road across constructing a building on or removing material from the base of such hummocky topography would be unwise Old landslides can be reactivated by any of the processes that initiate new landslides that is adding water steepening the slope undercutting the toe or removing toe material loading the upper part of a slope removing vegetation or earthquakes If the conditions are appropriate for landsliding preexisting slip surfaces can reactivate Landslide hazard maps Best strategy is to avoid building in places prone to landslides Geographic Information System GIS o In the GIS approach the area of concern is mappedEach polygon is chosen as having consistent internal attributes such as slope concaveupward curvature soil texture and depth ease of slope drainage slope facing direction type of vegetation bedrock type length of roads within the polygon and presence of slope failures High risk landslide areas Steep slopes and clearly mountainous areas Local slopes that exceed the local angle of repose 3040 degrees on a hillside Areas where large amounts of rainfall or snow melt enter the ground Locations where shallow slides commonly develop at the interface between bedrock and the loose colluvium that covers it 0 Locations of pervious shallow landslides of any size Shallow slides are more likely to develop on slopes with sparse vegetation and a lack of significant tree roots to hold shallow material in place June 2011 when the North Carolina legislature debated funding for mapping slope hazards in mountainous parts of the state some argued that homeowners and homebuyers deserve to know whether a property is at risk homebuilders and real estate agents didn t want this Engineering solutions Engineers can sometimes restore the balance among forces to keep a slope stable Can add load to the lower part of the slide to resist movement To stop a slope from moving highway engineers sometimes pile heavy boulders on the toe area to increase the resisting mass loading toe area Rock cliffs or slopes can be sprayed with a cement mixture called shotcrete or gunite to restrict water access Drape wire mesh to prevent falling of rocks on buildings or highways Drill in rock bolts to stabilize slope Removing water from soil can increase its strength making it less likely to slide Evaportranspiration water removal involving trees and shrubs taking up water from the soil through their roots dries soil Shrubs and trees that grow prolifically adjacent to streams or lakes use great quantities of water Planting trees or shrubs that use large amounts of water can help stabilize a slope If soil has low permability perforated pipes can be inserted and water drains into the pipes and trickles down into the surface A more expensive approach is to dig deep trenches in the slope with a backhoe line the trenches with geotextle fabric cloth that permits water but not sediment to flow through then backfill them with coarse gravel 0000 Chapter 9 Lecture Caves and Sinkholes Caves commonly develop in limestone Sinkholes subsidence and swelling solids 0 Some sedimentary rocks salt gypsum and limestone are soluble in water 0 Florida is on limestone so prone to sinkholes The ground over solution cavities can sink into those opening sometimes slowly sometimes suddenly 0 Ground water over the cavern collapses not the cavern itself Some clays swell when they get wet They can deform those buildings over them Underground caverns reach surface sink hole forms What would you do if this was your house sink hole move belongings and get expert advice 0 Window into ceiling can become bigger 27 Sediments spall into cavity Rain water carbon dioxide carbonic acid in water Carbonic acid reacts with limestone to form calcium bicarbonate soluble in water ushes away hard water What happens in a limestone cavern 0 Water percolates through fractures in limestone 0 Like icicles water drips and connects to make column o If break limestone stalactic could take centuries to reform Formation of karst terrain dissolved limestone pinnacles china What is the main substance in ground water that helps it dissolve limestone carbonic acid formed from carbon dioxide in air mixed with rainwater Drilling can cause collapse Ground penetrating radar o It can detect objects changes in material and voids and cracks Pennsylvania coal mines and don t know where it is can collapse buildings over old industrial activity Allentown Pennsylvania 1994 sinkhole opened up under of ce building Land subsidence mostly caused by extraction of groundwater or petroleum from porous soils or sediments or by drainage of water from organic or clayrich soils Ground water pumping in California s central valley increased from 1915 through 1960 very sunny not much water desert Pumping caused declines in groundwater levels Land surface subsided until water was imported recharge the groundwater 1963 Excessive groundwater pumping in SW Arizona caused ground ssures Differential subsidence Open lt1 inchevent Great lakes contract cant make pipe line from great lakes to Arizona Oil pumping can also cause land to drop Why does Venice Italy have canals for gondolas and boats instead of normal streets for cars extraction of groundwater below the city caused subsidence of the city below sea level 1996 Venice ood The leaning Tower Pisa in Italy is curved because it started leaning when it was built Swelling soils opposite problem to subsidence o Expandable clays swell when wet to deform overlying buildings and roads 0 Damages amount to more that 4 billion per year in the US Amount of clay is how much it will swell Smectite is a clay mineral that swells when it gets wet Water soaks in between the layers of atoms Popcorn clay swelled up and dried out Thick soils that sticks to rims of car smectite swelling soils Volcano ash makes swelling soils Or when you add water to the ground when you add different amounts of water to different parts of theland Permafrost 1 foot deep ground is still frozen Build building on stilts Chapter 9 sink holes land subsidence and swelling soils Sh nki Sink h ng ground For more than 100 years groundwater has been critical for agriculture mining and municipal uses in the Phoenix and Tucson areas of southern Arizona groundwater supplies are drawn down more quickly than they are being replenished In many respects earth is water planet roughly 71 of earths surface is covered in water less than 1 is readily available fro use as freshwater ground water provides about 40 of public water supplies and 80 of public water use As the water table lowers the ground above sinks and sometimes collapses oles Sink holes a ground depression caused by collapse into an underground cavern Especially in limestone terrains of the eastern United States the ground may suddenly collapse leaving sinkholes that are tens to hundreds of meters across Not only can sinkholes damage houses and roads but they can drain streams lakes and wetlands Processes related to sink holes Common sedimentary rocks are soluble able to be dissolved typically in water allowing them to dissolve which poses hazards to those living above them Salt and gypsum often called evaportes are highly soluble Limestone and other carbonate rocks are slowly soluble in acidic rainwater Caverns a large natural underground cave or tunnel most commonly in limestone Also used for a soil cavern developed over a limestone cavern 0 Form as carbonate rocks near the water table dissolve in groundwater 28 Limestone dissolves when water droplets in the atmosphere take in carbon dioxide to form weak carbonic acid Slightly acidic rain falls and percolates through soil and sediment down to the bedrock Bedrock is limestone calcium carbonate the acidic water slowly reacts with the limestone along fractures dissolving it to widen cracks and leave cavities The reaction between acidic water and limestone occurs more rapidly under warm moist conditions caverns and sinkholes are most common in tropical or subtropical climates Limestone can dissolve above at and below the water table 0 Above the water table acidic water running down through fractures slowly widens them 0 Below the water table cavities can rapidly widen if horizontal bedding surfaces are open enough to conduct large amounts of water Staactites caverns that hang from the roof and staagmites when they grow from the oor Caverns found high on hillsides above a current water table suggest that the water table has dropped Limestone bedrock near the water table dissolves along fractures to create an uneven and potholed upper surface Karst rages top of limestone exposed at the surface resulting from dissolution by acidic rainfall and groundwater The ground is often marked by sinkholes and caverns o The best known of these are in the Guilin and Kunming areas of southwestern China Types of sinkholes Dissolution minerals or rocks dissolving in water 0 Where the soil cover is thin and highly permeable acidic groundwater seeps through it and dissolves the underlying limestone along fractures o The overlying soil can slowly percolate or ravel down into the fractures to create a surface depression 0 These depressions are shallow and not generally dangerous Cover subsidence gradual depression of the roof material over an underground cavity 0 Where tens of meters of sandy and permeable sediment exist on top of limestone bedrock o Depressions generally form gradually Cover collapse collapse of the roof material over an underground cavity often a soil cavern over a limestone cavern 0 Where overburdern overlying sediments contains signi cant amounts of clay this cover is more cohesive and less permeable o This can allow a soil cavity to grow large and unstable leading to the sudden collapse of its thinning roof 0 The lack of warning makes these steepsided sinkholes destructive and dangerous Cover collapse sink holes open with littleno warning February 25 2002 collapse at a road intersection in Warren County Kentucky storm water funneled underground at three corners of the intersection and caused further solution and instability in a limestone cavern underground Areas that experience sinkholes Approximately 55 of Kentucky is on limestone weathering to karst largest and most famous caverns in the united statesMommoth Cave National Park Sinkholes are prominent in Florida ice sheets melted during ice age and sea level rose so the water table rose Fluctuations of the groundwater level can contribute to sinkhole formation More sinkholes tend to form during dry seasons or when excessive pumping drops groundwater levels Areas with the greatest potential for sinkholes are those where surface water tends to percolate into the ground 0 This potential is greatest where the water table lies below the tops of limestone caverns allowing for unsupported open space in cavities above the water level Acidic rainwater percolating down through those fractures slowly dissolves and widens limestone Soil above the limestone cracks may intermittently break apart to form a progressively enlarging cavity Pennsylvania sinkholes are typically 1 to 6 m in diameter and fractures seldom enlarge to form underground caverns Areas With the least potential for sinkholes are those Where water is being discharged to the surface A large water ow can quickly ush soil from above fractured limestone to form large sinkholes August 13 2006 an 18 m wide by 23m deep sinkhole collapsed under one end of a home in Nixa just south of Springfield Missouri Sinkholes are abundant in the Karst Plain in southwestern Missouri and most appear to be covencoHapse Sediments such as salt and gypsum also produce karst landscapes and underlie large areas of the United States 29 Insurance for sinkhole collapse is not covered in many homeowner policies though it may be covered by payment of an additional premium Florida law however requires authorized insurers to cover catastrophic ground cover collapsequot Land subsidence Land subsidence settling of the ground in response to extraction of water or oil in subsurface soil and sediments drying of peat of formation of sink holes Occurs when the ground settles due to changes in uid levels underground In coastal areas subsidence can sink communities closer to sea level and leave them more vulnerable to ooding This lowering of the ground surface is caused by a variety of human activities including extraction of groundwater drainage of organic or clayrich soils and thawing of permafrost Mining Groundwater and Petroleum The most common causes of land subsidence is the pumping of water or petroleum out of the ground In areas where the amount of water being taken out for drinking exceed the precipitation this is considered groundwater mining o A similar effect can also result from pumping of underground supplies of oil and gas Withdrawal of water from the pore spaces of loosely packed sand grains permits them to pack more tightly together and take up less space 0 Because sand grains cannot be pushed apart into a more open structure once their pore space has collapsed Large water withdrawals can cause permanent reduction of aquifer capacity and subsidence of the ground 0 Silicon valley and San Francisco Bay the southern half of the Central Valley of California the Long Beach area south of Los Angeles southern Arizona the Texas Gulf Coast region near Houston and Venice Italy 0 San jose San Fran Bay ground water pumping was slowed because subsidence of 80cm in 4 years 0 In the Houston area oil and gas were produced early along with groundwater 1m subsidence in this area leading to coastal ooding 0 Wilmington and Long Beach just south of Los Angeles 19405 with pumping of groundwater at the naval shipyard and later with oil extraction 0 1958 when the California Subsidence Act was passed groups of property owners in the Los Angeles area injected water underground to repressurize the pore spaces and stabilize the rate of ground subsidence cannot be reversed once occurred Groundwater can be a renewable resource unless amount taken out exceeds what is replenished 0 Sustainable use policies can help maintain this balance Drainage of Organic Soils Subsidence can also be caused by draining organicrich soils such as peat The semiarid Sacramento San Joaquin valley of central California produces quarter of food for united states and heavy pumping of ground water for crop irrigation lowered water table causing decomposition subsidence threatens agricultural production Florida Everglades was drained decades ago for farming causing almost 2 m of subsidence Many major river deltas are now sinking at an alarming rate caused by reduced sediment loads related to upstream dams and placement of levees that prevent ood overwash as well as extraction of groundwater oil and gas If fresh water is pumped out of a well faster than it can be replenished by rainfall the salty water mixes with the water drawn from the well making the well water unusable The Netherlands is most vulnerable to subsidence because this small country lies on the delta of the Rhine and Meuse rivers and onequarter of the country lies below sea level During the dry season the water table drops so soils dry out and the peat oxidizes and settles Drying of clays Clay soils can be particularly prone to subsidence when they dry out Compression of marine clays by the Leaning Tower of Pisa39s load has caused the tower to lean Since its completion the 56mhigh Leaning Tower had sunk 2 m into the ground and was nearly 4 m off vertical Much of Ottawa Ontario is built on the notorious Leda clay Landslides throughout the St Lawrence River valley and its tributaries have involved the Leda clay Thaw and ground settling Geothermal gradient refers to the fact that the temperature at the surface of the earth increases with depth 0 Rocks deep in the earth are hotter Permafrost condition where water in the ground remains frozen all year 30 In other northern climates or high mountain areas such as the Alps and Tibet where average temperatures remain below freezing the ground is frozen all winter but a meter or two of the surface called the active zone may thaw for two months in summer Forest fires or removal of vegetation for construction can also lead to thawing of permafrost When permafrost thaws water runs out of the frozen ground causing the ground to settle and ow downslope usually shallow Buildings that were solidly anchored on the ice settle and twist out of shape 0 Modern buildings are often raised off the ground so that cold air can circulate under a heated building minimizing the possibility of permafrost thawing Nome Alaska Thermosphon device to keep ground cooler One strategy long used in building roads and railroads is covering the permafrost with crushed rock to promote heat loss in winter and minimize heat access in summer Swelling soils Swelling soils a soil that expands when wet generally a soil that contains smectite the swelling clay o Semctite soft quotswellingquot clay that forms by alteration of volcanic ash swells when wet and becomes extremely slippery It is prone to landlsiding and can deform houses built on it popcorn clay Mountain West region all of the Great Plains much of the broad coastal plain area of the Gulf of Mexico and the southeastern states and much of the Ohio River valley The annual cost in the United States from swelling soils exceeds 44 billion highways and streets account for approximately 50 of this total These minerals form by weathering of both aluminum silicate minerals and glass in volcanic ash Expansion and contraction of soils causes the cracking of foundations walls chimneys and driveways also if adjacent areas swell at different rates The problem appears when rainfall snowmelt yard watering and sometimes a leaking underground pipe wets the clay Homes built on smectite clays can experience problems because of different moisture conditions on separate parts of a property The ground receiving more moisture expands while the ground receiving less moisture contracts deforming and cracking buildings Effects can be minimized by preventing water access to the soil removing the expanding near surface soils or sinking the foundation to greater depth The double sec freeway at the east edge of the San Francisco bay collapsed in 1989 loma prieta earthquake Why it was built on soft mud What are two main causes of tsunamis subductionzone earthquakes and landslides into the ocean Which of the folo wing submarine faults cannot cause tsunami waves strikeslip faults What is the average speed of tsunami waves in the deep ocean 700800 kmhour Tsunami waves nearing the open coast slow down because they drag more on the shallower Bottom than in the deep ocean What type of event has repeatedly generated very high tsunami waves in coastal fjords of southeastern Alaska a large rock fall into the fjord When an object vibrates with a large amplitude cause by the introduction of energy at or about the natural frequency of the object the result is know as Resonance What is the most dangerous location for a tsunami hazard a bay with sandy beach at its end What are the approximate times between tsunami waves crests 1035 mins How are tsunami waves in the Atlantic Ocean likely to be generated by collapse of the ank of an oceanic island volcano In the Pacific North west what is the mot distinctive edidence of a prior tsunami event a layer of sand with no internal structure over peat What two main facots result in more violent eruptions more water and higher viscosity of the magma How does pahoehoe lava differ from aa lava pahoehoe is ropyIooking and aa is clinker Bassat magma typicaly erupts in what form Ia va ows What are the two most abundant gases in magmas water vapor and carbn dioxide Prosecutions related to the aquia earthquake are proceedingon the basis of false reassurances to the public Which of the two main volcanic gases is heavier than air collects in low areas and can asphyxiate people or animals if it is high concentrations carbon dioxide What is the dominant mechanism by which melt is generated at mid oceanic ridges decompression At what point does all molecular motion cease 0 degrees k Why does basaltic magma rise through the largely granitic crust basaltic magmas are less dense than the granite crust What is magma that is forcefuly ejected into the atmosphere as particles pryoclastic 31 Why do shield volcanoes have very gently sloping sides their basalt ows have low viscosity so the la va solidi s as gentle slopes What can cause What to separate from a waterbearing basaltic magma to driven eruption a decrease in pressure as the magma rises can cause water to separate What is a surge a high speed violent ashrich shock wave Follow the may 1980 eruption of mount st helens washingtion thousands of tres lay on the ground all parallel to one another Why a lateral blast at the beginning og the eruptio blew them all down in contrast to an old ash ow deposit an old ashfall tuff does not include Which of the folo Wing big pieces of pumice that oat to the top of a layer Crater lake formed from mount mazama by a large eruptive event that resulted in magma extraction and a caldera collapse The dark fiamme of the welded tuff are likely formed by welding of glassy pumice What is the most serious threat of volcanic ash clouds to jet aircraft fusing of volcanic glass to jet engine components The angle of repose for dry sand is degrees 3045 Old landsides are not normally reactivated by piling heavy rocks on the lower part of the slope Why does earthquake shaking of watersaturated sand often lead to ground settling The shaking of sand leads to closer packing of grains Why does raising groundwater levels often lead to slope failure it increases the water pressure in the pose spaces between the grains pushing them farther apart Why does the top of a rotation slide tilt back into the slope the slide mass rotates on a circular cuning surface so everything on it rotates backward 32 The largest earthquake in the historical record occurred off the coast of Chile on May 22 1960 and produced a tsunami which killed more than 2000 people Pillow basalts form as a result of basaltic lava erupting in water The Tambora volcano in Indonesia erupted in April 1915 and released large amounts of ash and Sulfur Dioxide into the atmosphere resulting in Cooler temperatures around the planet The death toll from the 1902 St Pierre Martinique earthquake was approximately 29000 Most were cremated or suffocated by lahars The town of Armero Columbia was destroyed by lahars Mt St Helens is the Cascades volcano most likely to erupt Feldspar rich rocks are more likely to form clays that will weaken slopes and encourage landslides Rotational slumps form along curved slip surfaces and consist of homogeneous cohesive soft materials The lling of a reservoir behind a newly completed dam caused a catatrophic mountainside collapse in 1963 and produced the Vaiont Slide in Italy 33
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