Geology Lectures 11 and 12
Geology Lectures 11 and 12 Geol101
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This 0 page Class Notes was uploaded by Shelby Green on Thursday March 10, 2016. The Class Notes belongs to Geol101 at Clemson University taught by Dr. Coulson in Spring 2016. Since its upload, it has received 32 views. For similar materials see Physical Geology in Geology at Clemson University.
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Date Created: 03/10/16
3816 Lecture 11 Deserts Geology in the News Cores being taken from the Atlantis massif Providing insight into the origins of life on Earth and perhaps on other planets Former Clemson geology student is one of the researchers Class of 2014 Why do we care Cover extensive areas and are growing 20 of all land is desert Another 15 is semiarid semidesert What is a desert Temp does not de ne a desert l some deserts are actually very cold regions Lack of rainfall is the key to de ning a desert less than 10 inyr quali es a desert Semiarid is a little more than that but not much more The 10 Largest Deserts kmz Antarctic Antarctica 14 000 000 Sahara Africa 9 000 000 l almost same size as the US Greenland Arctic 2 000 000 Gobi desert Asia 1 125 000 Empty Quarter Middle East 650 000 Kalahari desert Africa 580 000 Compare Great Sandy Desert Australia 414 000 South Carohna 82000 Karakum Asia 350 000 Taklamakan desert Asia 344 000 TeX S 678000 USA 9800000 Namib desert Africa 310 000 Distribution of Deserts Found in certain latitudes Red areas 30 degrees NS latitudes Hadley Cells cause cold dry air here Yellow areas rain shadow effect causes desert in left upper US tectonic in uence in middle Asia Mongolia area center is far from coastline continental size effect causes desert here Polar regions Antarctica gets very little snowfall each yr 39 Seale h1 latitude Principal regions of hatdeeerts 7 El mm znna mi 39 39IJE39IIEII 323 km Prlnmpal regions of temperate deserts mg Enwm dfa B lanni r Incquot Weathering in Deserts Little water little chemical weathering Water important for weathering reactions Weathering in deserts rely on oxygen amp iron oxides Slow chemical weathering bc it relies on quot Desert Erosion Water still an important player Big Storm events rare but do occur No vegetation to constrain it Arroyoshallowdry stream beds Do not hike in arroyo l ash oods are a real threat Wind Erosion Wind can only move relatively small particles Wind has low density and low viscosity Particles gt than 006 mm in diameter hard to erode All the small particles eroded by sand can still add up to a huge volume eroded Ex Sahara Desert 250500 million tons of dust are transported to the Atlantic every yr Can be seen by space example to right De ationthe process of moving the nest grain sediment quot 39 Pavementssurface of desert looks more and more cobbley as a result of de ation the bigger particles left behind Deflation Concentration of larger pebbles Desert pavement I Only about 20 of all desert areas are covered in sand Desert Features Ventfacts any object that has been signi cantly reshaped by wind 0 Little particles hit bigger objects l the more the impacts occur the more reshaped the bigger object becomes slow process One side will be drastically different than the other Can happen to plants cacti or rocks etc Wind Direetien In reeled Surfeee Alluvial Fans sediment fan that form at the end of arroyo o Sediment carried through arroyo until it gets deposited at the end 3913tji nr39nd Paya lakes aka playas isolated lakes in desert regions that aren t attached by any creeks and rivers 0 Form in any kind of depression kind of like a runoff pondI 0 Rings of material forms around edges Mineral material that precipices out of the water as if evaporates Useful when searching for small mineral deposits lnseberg big bodies of rock that tend to be out in atfeatureless areas 0 Note the iceburg of the desert o lgneous rocks formed below the surface as a pluton l the sediment around the pluton eroded away and left the massive rock behind Arches natural bridges 0 Result of localized erosion o Arches Natl Park Utah has over 2000 arches Formation o Weatheringerosion attacked the weak cracks o Localized erosion Dunes Wind deposits of sand Initiated by surface irregularities that disrupt wind ow Saltationall the sand is jumpingskimming along the surface of the ground 0 Originates from Spanish word quotsaltarquot which means quotto jumpquot Types of Dunes 5 different types Important factors Variance in wind direction Sand availability Vegetation 1 Barchan dunes Standardmost common type of dune Strong crescent shape 0 Two ends up the crescent called the horns illn39l 39l1l39gl Inn t n aiiala h Horns always pointing downward direction the wind is going 2 Transverse Dunes Merges Barchan dunes 0 Need a ton of sand supply 0 Wind direction is perpendicular to the crests tiltEar Dune5 3 Linear Dunes Aka longitundinal Long but relatively straight 0 Wind direction can change slightly Not a lot of sand availability 4 Star Dune Wind direction varies a lot Look like a star 5 Parabolic Dune U or V shaped steep curve Vegetation Horns point the direction the wind is coming from o Vegetation prevents the wind from blowing the horns faster Summary A Barretrains o Parabolic dunes E TFEWEVETEE dili eg El Longitudinal dunes sails Deserti cation Process of an area becoming a desert Sahara expanding south about 30 miyr 1 billion people in atrisk areas 1 in 7 people Risk assessment map below Global Desserli cuton quotti lllrrmrmbfi ily Hut 7 9 m V WIIHF In Why is it occurring 1 Tectonics 30 degrees latitude touches a lot of land areas 2 Climate Change Temp increasing so evaporation rate is higher Water levels drop 3 Human Activity Over grazing of livestock Cutting trees down What can we do about it 1 Change livestock practices l move herds around more frequently 31016 Lecture 12 Glaciers Geology in the News 0 The amount of water owing into Earth s interior found to strongly correlate to active faults W Effects of Glaciers Sea Level Risks Florida 0 As glaciers have been melting other species are I being affected 0 EX polar bears are losing their habitat Sealevelchange Melt all glaciers sea level rise of 65 m about 200 ft In the diagram all the hot colors are at risk of being ooded Glaciers trap huge amounts of water PoeGlaaal39 Sea Level Rise l 123 5 8 12 20 35 BUBD quotquot29 HeightAbOVE Sea Levelllm 39 Santa Catarina eel Rilede Janelilre a i 39 Senegal new MEIWEIE39FMEE m V 5 quot Malaeea Elrlalte l 39 quot upper Deana WED Auelifalla Jamaica a T ahllllr l quot10quot HuanPenllnleula l 39 39 Laet Glacial Maximum gt H IllL 39 39 39 39 Eea Level Change m Ballrbatleel 125 quot lmaerbwnd e 39 ls 311ndaNielnamEhelf mar 24 e ea llS 1e la 112 a e 4 2 n Thaueanae af Yeare Age Coastline during Ice Age Light blue above water a lsostatic depression the crust underneath the glacier warps downward due to glaciers weight Some places like in E Antarctic ice sheet has caused up to 25 km of isostatic depression As the crust is adjusted the mantle has to adjust beneath it Glacier E tfsuhsi e 1 39quot39 3llEI u C 31n r E3ZIIIll Crust rebound lt mantle will readjust to try and atten back out Affects weathering processes and what not at the surface Alters thermohaline circulation Density decreased speed of process slowed down discussed in precious lecture Drinking water and irrigation THEHMDHALJNE CIRCULATIDN GREAT QCEAN CURRENT 3013 y places us glaciers as a water source Ex Washington gets 47O billion gallons of water from a glacier per yr NOTE Melting glaciers do not provide MORE drinking water The glacier gets smaller every year so there is less and less ice to melt Glacier Basics Glacier Ice has to pile extremely thick at least 50 meters of 150 ft and begin moving downhill due to the pull of gravity lce on Earth Currently covers 9 of Earth s land area Antarctica 85 Greenland 10 lce on Antarctica exceeds 4200 m 25 miles in max thickness l amount of weight of the ice is tremendous Forming a GlaCier Glacierice formation Granular snow densemore compact snow Firn denser denser pelets of snow build up Glacial ice rn slowly compacts into Denser than ice from a freezer Requires time to allow the build up to happen cold enough that the snowice stays around yr round so that the glacier can accumulate over the years amp precipitation required to add more material Types of Glaciers 1 Valley Glaciers aka Mountain Alpine Glaciers that will form ll in valleys 0 Not exclusive to polar regions 0 EX Mt Kilimanjaro Africa about 20000 ft 2 Continental Glacier ice sheets 0 Covers entire landscapes 0 Exclusive to polar regions Greenland and Antarctica Glacial Advance and Retreat Accumulation the part of the glacier that is getting bigger Makes the glacier appear to be advancing bc its adding material Ablation the glacier is melting faster than its adding Makes the glacier appears to be retreating bc its losing material Firn Line the melting and adding balance out no change Granular snow nneof cciumullaitiun gt Equilibrium Line lFirn Line I quot rim of Ablation Glacial Movement 0 Speed varies 0 Center of the glacier moves faster than the sides The ice closer to the wall of the valley is affected by friction 0 Anything you stick in the ice is going to move along with the ice Explorers trying to mark their territories during exploration of Antarctica had to learn the hard way lol 0 Type of Movement 1 Plastic ow a gt50 m thick ice at the base of the glacier becomes more ductile b Each individual ice crystal is being squeezed downhill i Slow process 2 EE39E slip a A little lm of liquid water accumulated inbetween the glacier and the ground i Liquid forms because of the pressure its under has nothing to do with temp b Liquid minimizes friction and glacier moves faster i Like a slip and slide Glacier Feature QJMQJm Crevasse massive cracks seen at the surface of a glacier 0 Surface cracks as its base moves ductile like and it moves more brittlelike Glacial Erosion o Abrasion sediment gets picked up and carried within the glacier so when the glacier comes to a stop and melts the sediment gets depos ed o Glaciers often full of dirt and rock 0 Pucking big chunks of sediment that glaciers transport 0 Water under glacier gets caught in cracks of crust freezes and breaks pieces of crust off of one side of hill Glacial ice 2 lam high South west Plu lted boulders Bedrock Erosive Features 0 Striations thinstraight lines that have been carved into the surface of bedrock o Carved from glaciers 0 Ushaped Valleys steep walls but round valley 0 Hanging Valley little Ushaped valley that is elevated with in another valley Photoclr nLEmlk s featurerapids to identify hanging valley Cirque Vly big bowl shae valley 0 Tarns lake trapped in the middle of a cirque o Horn sharp point shaped by multiple valley glaciers carving down all sides of the mountain 0 Arete ridge of rock coming down the side of mountain 0 Wall left inbetween two valley glaciers o Roche Mountonnee big body of rock that appears to be a small cliffhill o Asymmetrical occurring from plucking o Gentle side steep side 0 EX glacier coming from SE to NW Glacial Ice plucking movement Glacier Glacial Sediment Deposits o Erratics o Boulders deposited by glacier Often out in the middle of no where Till o Poorly sorted pile of sediment Rocks boulderssandgravel combined Outwash o Sediment that has been carried by the melted water of glacier and gets sorted as it ows Better sorted Loess o Smallest particles best sorted sediment from glaciers that have been eroded by wind Tend to make up soil great for agriculture Ex Indiana 0 NOTE Make sure to keep the depositional features and erosional features separate in your mind Depositional Features o Moraines ridge of sediment that extends along one edge of glacier 0 As ice melts around its edges sediment falls out and forms ridge along the glacier 0 Can sometimes form in the middle of glacier Tend to be more straight and narrows 0 Made out of till deposits l poorly sorted o Eskers ridge of sediment formed under the glacier where the owing water underneath has deposited some of the sediment o More wavy than moraines 0 Made out of outwash deposits l better sorted o Drumin looks similar to a mountanee an erosional feature made of solid rock but drumlin is a depositional feature that is merely a pile of loose sediment if f o The glacier moved toward the gentle slope and came from the side of the steep slope opposite movement than a mountanee 39 1 Re 22 mils nglaCIer gmaraine Kames small hillsmounds of sediment 0 Usually form as glaciers breaks up and smaller blocks of ice are left behind and as that block melts it forms its own hill of sediment o Kettle lakes melted water from ice blocks that were left behind is trapped in impressions of the surface 0 Minnesota is the quotland of the kettle lakesquot
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