Study Guide for Exam #2
Study Guide for Exam #2 GSC 110D
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This 11 page Study Guide was uploaded by Amanda Hillegass on Thursday March 19, 2015. The Study Guide belongs to GSC 110D at University of Miami taught by Terri Hood in Spring2015. Since its upload, it has received 170 views. For similar materials see The Earth System (lecture) in Geology at University of Miami.
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Date Created: 03/19/15
GSC 110 Dr Terri Hood Exam Date 3252015 Study Guide for Exam 2 1 Sedimentary Rocks and Weathering a Sedimentary Rocks i Rocks formed atnear the earth s surface from fragments or dissolved pieces of preexiting rocks aka sediment ii These make up 1 of earth 5 mass and 80 of ea rth s surface b Steps in Formation of Sedimentary Rocks i Weathering in situ in place chemical alteration and mechanical breakdown of rocks during exposure to elements of weather ii Erosion breakdown and transportation of particlesrocksoil by moving waterairice iii Transportation movement of erodedweathered rock constituents iv Deposition settling out of sediment from transporting medium v Lithi cation conversion of sediment to sedimentary rock c Weathering i This occurs by two types of processes physical and chemical weathering 1Physica Weathering mechanical weathering breaking of rock into smaller fragments 2Types a JointsJointing i Naturally formed cracks in rock ii Can occur in onemany directions often caused by pressure release due to removal of overburden overlying material 1 Ex Exfoliation igneous rocks large granite plutons split into onionlike sheets in direction parallel to surface 2 Ex Sedimentary rocks tend to form verticaljoints these quotbedding planesquot l rectangular blocks b Frost Wedging i Happens where water periodicaly freezes and thaws due to expansioncontraction Ex temperate climates high altitudes iiWater in joint freezes pushes sides apart 1 Ex quotOld Man in the Mountainquot rock face in New Hampshire collapsed May 2003 because of heavy rains followed by freezing temps overnight c Salt Wedging i In ariddry climates salt precipitates in poresjoints of rock growth of salt crystals causes wedge effect honeycomb weathering because it makes rounded hollows d Root Wedging i Plant roots grow into joints pushing them open because they are looking for water and a way to anchor the plant e Thermal Expansion i Exposure to intense heat or to hotcold cycles causes rocks to spall outer layers breaks off in small sheets 3 Chemical Weathering aContact with airwater solutions altersdestroys minerals in rock bHappens faster in warm wet conditions like the tropics and slower in places like a desert or near the poles c Minerals differ in their susceptibility to chemical weathering i Ex within silicate minerals ma c are the most susceptible because of fewer silica tetrahedral links iiWhy quartz sand beaches are so common d Chemical Weathering i Common reactions involved are 1Dissolution dissolving into ions like salts carbonate materials aEx Effects of acid rain on marble 2Hydrolysis quotwater looseningquot original mineral H20 lions clay minerals aReleases elements that plants use so its common in sols 30xidation Ex pyrite 02 l iron oxides almportant if minerals were formed under reducing conditions ii Organisms can promote chemical weathering by directly attacking minerals or indirectly creating conditions which speed weathering iii In reality both chemical and physical weathering work together 1Physical weathering speeds up chemical weathering because breaking up a mineral increases the surface area which increases the rate of chemical weathering 2 Chemical weathering speeds up physical by attacking individual minerals making them weakerand more likely to fall apart iv Both kinds of weathering happen faster at edges and corners of blocks because more surface area is exposed l creates rounded sha pes Without any movement e Differential Weathering i Different rock types vary in their susceptibility to weathering ii Causes some rocks unitslayers to last longer while others are preferentially destroyed iii Can also depend on climate 1Ex Limestone is susceptible to chemical weathering but resistant to physical weathering 2 Soil Formation and Fertility a b c Soil Formation and Fertility i Regolith loose material between solid bedrock and ground surface ii Soil uppermost part of regolith which has undergone reactions with rainwater and addition of organic matter from decomposing animals etc iii Soils typically have different layers l quotsoil profile iv Upper zone of leaching rainwater percolating downward dissolves minerals v Lower zone of accumulation ions dissolved from above precipitate new minerals Factors affecting Soil nature and Fertility i Dissolution of minerals present in soil release nutrients used by plants 1 Composition of bedrock bedrock that contains many elements used by plants more fertile soils than ones that don t a Ex underlying basalt fertile soil Hawaii b Ex underlying limestone infertile soil South Florida c Ex underlying salt deposits toxic soil saline deserts in American Southwest 2Cimate wet tropical climate l rapid dissolution of minerals and leaching of plant nutrients les fertile soils most innate fertility is found in biomass dead trees 3Age of Soil how long minerals have been subjected to dissolution aOlder what Sold for soil millions of years i Only quartzclaysiron oxides left red clay soil fertile ex Georgia bYounger thousands tens thousands years i quotGoodquot minerals still around releasing nutrients fertile ex Illinois Indiana less more Erosion i Breakdown and transport of particles of rocksoil by moving waterairice water moves most material ii Vegetation signi cantly reduces soil erosion because roots hold soil in place and reduce soil erosion 1Deforestation and tiling increased soil erosion iii Steps being taken to reduce soil erosion 1 Contour plowing aPowing elds along contour lines lines of equal elevation bLooks like a lot of tiny steps reduces speed of water running downhill and thus reduces carrying capacity c Most important in areas with a steepersope 2Riparian forests aForests along river edges stabilize river banks water runs clearer less sediment load 3Reduce human activities in marginally stable areas aAllow ok areas to recoup and become healthy again instead of destroying them Ex Sahel in Africa d Types of Sedimentary Rocks i Clastic Sedimentary Rocks 1Created from solid pieces of previouslyexisting rocks cemented together 2quotClastsquot individual mineral grains or fragments of rock that have all four processes of sedimentation to make them into pieces 3Lithi cation involves aCompaction burial pressure of overburden squeezing out water and air bCementation precipitation from groundwater of mineral into pore spaces between grains 4Clastic rocks are classi ed based on grain size composition and grain shape sharpness of their edges farther fragments are transported more rounded Grain Size Rock Very Coarse pebble boulder size angular Breccia Rounded Conglomerate 0 Both are high energy transport 0 Because Conglomerate is rounded its always traveled farther than breccia Coarse sand size often mostly quartz Sandstone Fine silt Carried by lower energy water Sitstone Very Fine quotfine claysize Shale ii Biogenic Sedimentary Rocks quotlifeproducedquot 1 Biochemical aMade of CaC03Calcitearagonite polymorphs shellsskeletons of onceliving pantsanimals ex chalk limestone bExample components animals mollusks foraminifera salt water protists plants coccolithophores c Made of amorphous SiOz Chert i Ex mostly made of frustroles shells of diatoms or radiolarians 2 Organic aMade of altered organic material naturally produced C H and 0 compounds ex amberand coal b Amber i Fossilzed tree resin that was originally produced by certain conifer tree species in response to wounding ii Buried in sediments after millions of years amber iii Intermediate phase lt100000 yrs copal which is burned as resin iv Colorappearance depends on type of tree that produces resin conditions of burial and age v Most famous sources 1 Baltic Sea in Scandanavia 2 Dominican Republic in Caribbean younger lighter color 3 Chemical Sedimentary Rocks a Rocks formed by precipitation of minerals out of water solutions i Evaporites formed from evaporation of salty water like the Dead Sea 1 Can be a larger scale economic climatelandmark feature 2 Ex of larger scale evaporate deposits ancient Lake Bonneville 3 Drying of Mediterranean Sea a Building Aswan dam found 15 km deep canyon under present Nile River b Evaporations gt Fresh Water input c Global cooling drop in sea level below Straights of Gilbraltar isolating Med Sea from Ocean Their exchange kept salinity of Med Sea constant and prevented complete evaporation d Med Sea dries up multiple times 655 mill yrs ago leaving salt deposits gt 2km thick under present Med Sea ii Carbonates 1 Abiotically precipitated calcitearagonite 2 Change in conditions causes solution to be supersaturated precipitation a Ex Travertine i Cave deposits limestone ex Luray Caverns Virginia ii Stalactite hangs from ceiling iii Stalagmite comes up from ground iv Column joined stalactite and stalagmite b Ex OoidsOolite i Ooids eggshaped carbonate grains precipitated from seawater on warm shallow carbonate platforms currently they form in Bahamas ii Oolite quoteggrock limestone made out of cemented ooids freshwater iii Miami Oolite limestone underlying much of South Florida iv Ooids precipitated during last interglacial period when South Florida was underwaterand were cemented together after sea level dropped during the last glacial period 3 Metamorphic Rocks and Introduction a Metamorphic Rocks i Meta change quotmorphquot form ii Rock that has changed from its original form into a new one in response to increased temperaturepressure without melting iii This can create 1Metamorphic mineral assemblages minerals that need high P T to form ex garnets 2Foliation parallel surfaceslayers produced b Agents of Metamorphism i Heat 1Can cause recrystallization form new crystals from old because bonds break easily 2Under higher temps atoms migrate solid state diffusion l similar to sliding grid picture puzzle 3Can cause compositional banding without melting the material 4Ex Contact Metamorphism intruding igneous magma heats up surrounding rock and doesn t melt it aZone of thermal metamorphism around pluton metamorphic aureoe bHighest temp minerals are closest to intrusion ii Reaction with hot waterchanges rock 1Hydrothermal Solution metasomatism quotchange bodyquot 2Happens at midocean ridges convection cells draw in cold water altering new rock after formation 3Dissolved ions carried away by hydrothermal solutions often precipitate as veins iiiPressure 1ncrease pressure denser mineral structure 2Ex Stishovite very dense polymorph of quartz found only in impact craters 3Normal earth interior conditions rocks subjected to increased P andT 4A given mineral has certain P T when it is stable and will stay in its from inde nitely quotstability eldquot on PT diagram 5lf TP changes to conditions outside this eld the atoms in it will redistribute into a new mineral 6Ex AIZSiO5 polymorphs ivDifferential Stress 1Pushpull in one direction is greater than another usually push preferred mineral orientation l foliation 2Common Foliated Rocks aSlate result from lowgrade metamorphism of shale dense breaks along foliation bSchist intermediate grade has recrystallized mica can recrystallize into garnets cGneiss highgrade compositionallybanded metamorphosed just before melting 3Nonfoliated Metamorphic Rocks aQuartzite metamorphosed quartz sandstone many shades sugary look strong bMarble metamorphosed limestone interlocking calcite crystals highly preferred for carving statues because of interlocked crystals l breaks alongthrough boundaries more control over surfaces softer Why delicate folds of clothhair can be carved c Index Minerals i Metamorphic minerals with PT stability elds used to de ne metamorphic grade Low PT low grade and vice versa ii Ex Metamorphic zones in New England 4 KNOW ROCK CYCLE DIAGRAM FROM CLASS 5 Part III Tectonic Activity Volcanoes a Volcanic Eruptions i Volcano from Mediterranean island Vulcano ancient Romans thought eruptions happened when Vulcan god of re stoked his forges to make weapons for the gods b Products of Volcanic Eruptions i Lava Flows viscosity resistance to ow depends on composition of lava high silica high viscosity Basaltic l Andesitic l Rhyolitic Less Silica more silica Magma Source Continent Oceanic Mantle Increasing SiOz more resistance to ow Increasing amount of volatiles more explosive behavior 1Can predict behavior of volcanoes 2Ma c lava ows aHave different Hawaiian names based on nature of ow i Pahoehoe uid ropy texture warm surface when moving faster iiAa rubbly blocky texture ow moves are surface has solidi ed breaks into angular fragments tends to pile up on itself slower 3Both are ma c in composition low viscosity low SiOz ow readily 4lntermediate composition ows more viscous 55iicic high SiOz ows most viscous can plug volcano and doesn t even make it to the surface sometimes aEx Obsidian quickly cooled silicic lava no crystalline structure ii Pyroclastic debris re pieces 1Fragmented material thrown from a volcano that s solid when it lands can form cinder cones 2Subdivided according to size aBlocks basketball to g size volcanic bombs if streamlined bCinders marble to plum size aka lapilli looks like melon balls c Smallest size volcanic ash i Most produced during volcanic eruptions ejected upwards into the atmosphere eventually falling out ii If ash makes it into the upper atmosphere stratosphere it can encircle the globe iii Larger eruptions put so much ash into the stratosphere that it partially blocks the sunlight lowering global temperatures quotvolcanic Winter iv Mount Pinatubo Philippines 1991 v Tambora Indonesia 1815 1 1816 quotYear without a summerquot in Northern Hemisphere famine in EuropeChina 2 Spectacular sunsets Turner paintings 3 Gloomy days Mary Shelley wrote Frankenstein vi Eruption 11 mya in Idaho 1 Covered half ofNorth America with more than 6ft of ash vii Flying through volcanic ash can seriously damagedown jets 1989 eruption of Redoubt volcano in Alaska downed a 747 viiiRadar doesn t see volcanic ash but satellites do est volcanic ash advisory centers VAAC s in 1995 ix Eruption of volcano in Iceland AprilMay 2010 Eyjafjallajokull 1 Early eruptions mostly lava turned into large quantities of ash carried by upper level winds towards Europe 2 Closed many airports largest disruption there since WWII 3 Positive spectacular ashgenerated lightning displays xSometimes ash mixes with other material and moves in a different manner 3 Pyroclastic Flow aAsh mixes with air forming superheated fastmoving avalanche nuee ardente French for quotglowing cloudquot bEx Eruption ofMount Pelee 1902 Martinique West Indies i Slammed into capital St Pierre 2 minutes laterwith ony2 of 28000 people survived c Ex Vesuvius 79 AD Bay of Naples Italy i Buried cities of Pompeii and Herculaneum in pyroclastic ows 4Accumuation of pyroclastic debris aTephra unconsolidated pyroclastic debris bTuff pyroclastic debris welded together 5Lahar volcanic mud ow aAshdebris mix with water often melted from snow during eruption bForms slurry thick watery mixture c Flows down valleys or river channels at speeds up to 50 kmhour dSets like concrete once it stops moving iiiVolcanic Gases 1Up to 10 by volume of magma s composition 2Main gases aH20 bC02 can kill by suffocation i Ex Lake Nyos Cameroon 1986 1 Gases build up under sediment and create river of carbon dioxide under lake crate on top of volcano 2 Killed 1700 people and all animals plants unaffected c 502 sulfur dioxide i Converts to sulfuric acid ii Ex Souffriere Hills Montserrat 1998 gave off 1000 tons of SOzday dH25 hydrogen sul de rotten egg smell i Instanty toxic at concentrations greater than 01 shuts down respiratory and central nervous systems 3Gases trapped in cooling lava make vesicles cavities in rock ex pumice volcanic glass with so many vesicles that some oats ivokulhlaup Icelandic 1Glacial outburst ood caused by volcanic eruption under a glacier 2Typical sequence of events aEruption melts large volume of water bWater is initially trapped by surrounding ice and topography c It eventually nds its way out in a dramatic large scale event can be far from starting eruption 3Places with large glaciersvolcanoes Antarctica and Iceland c Architecture and Shape of Volcanoes i Conduit for magma ow vertical pipe chimney or long crack ssure ii Products lavapyroclastic debris accumulate around chimney to make a cone with a crater at the top iii If magma chamber collapses after eruption can form a caldera very large circular depression w at oor iv If new eruptions start after caldera forms can form a resurgent dome new cone in caldera d Volcano Types i Shield Volcano broad gentle dome form from low viscosity ma c ows ex Hawaii ii Cinder cone cone shaped pile of tephra iii Stratovolcanocomposite volcano alternates layers of tephralava subduction generated classic volcano shape ex Mt Fuji iv Relative Size Shield Composite Cinder Cone Largest Smallest e Erosion of Volcanoes i Cinder cone erodes fastest ii Lava ows in other 2 cause them to last longer iii Ex Sutters Butte CA 6 Volcanic Prediction a Mount St Helens Washington i Part of Cascade Mtn Range series of activedormant volcanoes that are subduction generated due to Juan de Fuca plate ii Active has erupted in recent recorded history iii Dormant dormer to sleep still has magma in chamber underneath iv Extinct lava source gone v Bulged rounded pro le day before eruption vi Most damage caused by lateral blast explosive gases in magma chamber build up and cause initial forceful blast to happen laterally due to preferential bulging half the volcano failed and exploded sideways vii Explosion was predicted b Yellowstone quotSupervolcanoquot i Such a large magma chamber it s a supervolcano located over continental hotspot that s been active for 16 million yrs ii Last eruption 600000 yrs ago ejected240 cubic miles of debris iii Collapse of giant magma chamber creates a 28x47 mile caldera almost hafof Yellowstone iv Signi cant ash deposits as far away as Missouri northern Mexico c Eruption Prediction i Weekmonth prediction of impending eruptions is possible because of warning signals 1lncreased heat ow magma mobbing near surface melting snowice can trigger oodslahars 2Change in shape upward bulging Mt St Helens bulged 15 mday before eruption can monitor in ations via satellite imagery 3Earthquakes magma moving up through country rock l earthquakes which get stronger and closer to surface as magma rises weeksdays before eruption 4 GasSteam Emissions escape from magma or heat up groundwater composition of gases can change as magma rises d Controlling Volcanic Hazards i RiskAssessment de ne area around volcano in the path of lava ows pyroclastic ows and lahars river valleys starting at volcano slopes are especially dangerous ii Evacuation Plan iii Diverting Flows Flow channels Japanese town with volcano erupting 100200Xyr Freezing in place Icelandic Port town of Heimay e Positive Aspect of Volcanic Activity i Geothermal Power 1Nonpolluting source of energy takes advantage of earth s internal heat 2Feasible only where geothermal gradient is high change in temp with depth l near magma chambers magma heats groundwater aCan be pumped and run through pipes to heat housesspas Iceland bWhen it rises it decompresses and becomes steam which is used to generate electricity with turbines ex Geysers geothermal eld California ii Formation of economicaly signi cant deposits 1ncludes precious metals and gemstones iii Creation of fertile soils 1Weathering of volcanic rocks creates fertile soil 2Ex Indonesia volcanic island chain most naturally fertile soil in the world
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