Marli Miller GEOLOGY 102 Final Exam Study Guide
Marli Miller GEOLOGY 102 Final Exam Study Guide 102
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This 16 page Study Guide was uploaded by Chloe Nightingale on Monday March 14, 2016. The Study Guide belongs to 102 at University of Oregon taught by Marli Miller in Winter 2016. Since its upload, it has received 20 views. For similar materials see in Geology at University of Oregon.
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Date Created: 03/14/16
Deserts Absence of water and vegetation cover de nes a desert how De ned by land receiving less than 10 inches of rain a year How does this absence of water affect physical vs chemical weathering rates Soil development Leads to very slow rates of chemical weathering slow rates of physical weathering and very thin soil development Leaching as a type of dissolution causes salts to be deposited on land 1 Rainwater soaks into the ground and dissolves some salt and calcite 2 Warms up water rises back to surface and evaporates Dissolved material is left behind Desert Varnish as a time dependent process the darker a surface the longer it s been exposed l Airborne dust settles on the rock 2 Microorganisms extract Mn and Fe from the dust and deposit it on the rock 3 The longer the process goes on the darker the rock becomes Make sure you know the main causes for desert landscapes How do rain shadow deserts form 1 Warm dry air picks up moisture instead of dropping rainfall 2 Relates to atmospheric circulation 3 Rain shadow deserts form when air rises and cools over mountains cool air can t hold much moisture On the other side of the mountain air sinks and warms picking up moisture on the land Erosion in deserts Water wind gravity Water is the most important factor Why 1 Water Flash oods are very effective at moving material because of a lack of vegetation 2 Wind Carries material in dust and sand Ventifacts and sand dunes 3 Sand dunes De ation hollows wind has removed the sand Why are ash oods common in deserts There is a lack of vegitation Wind erosion carries material as bed load and suspended load Gravity talus and rock avalanches Rock falls rock avalanches talus aprons or talus cones Ventifacts A desert rock whose surface has been faceted by the wind De ation hollows De ation is he process of lowering the land surface by wind abrasion Mesas A large attopped hill in an arid region Buttes A medium sized attopped hill in an arid region Role of resistant and lessresistant rock in shaping the landscape What determines how resistant a rock is to erosion Sand dunes A relatively large ridge of sand built up by a current of wind or water cross bedding typically occurs within the dune Alluvial fans A gently sloping apron of sediment dropped by an ephemeral stream at the base of a mountain in arid or semiarid regions Playas The at typically salty lake bed that remains when all the water evaporates in drier times forms in desert regions Salt lakes Glacial Geology Pleistocene Ice age gt 25 Ma 10000 y a Glacier Body of ice that moves under the in uence of gravity Alpine glacier Mountain glaciers high altitude steep gradients typically much smaller than regular glaciers Continental glacier High altitude and low relief ice sheets Movement of Glaciers occurs by basal sliding and internal deformation ow How do crevasses indicate glacial movement How deep to they go Why Ice Budget on a glacier Determines how far a glacier can move Zones of Accumulation and ablation Accumulationgtloss and accumulationltloss Equilibrium line What happens to the equilibrium line during advance or retreat How does advance or retreat of a glacier take place Basal sliding Glacier slides on its base Internal ow Pressure increases with depth inside a glacier and the ice can deform without breaking Happens because of the placement of continents more land at high altitudes leading to colder winters ocean currents bringing warm or cold water to speci c places and earth s orbital uctuations Glacial Erosion takes place by abrasion and plucking How do abrasion and plucking occur Also much weathering by frostwedging Abrasion Rocks embedded in ice cause abrasion leading to smoother surfaces Plucking Ice freezes into bedrock glacier moves Roche moutonee A glacially eroded hill that becomes elongate in the direction of ow and asymmetric glacial rasping smoothes the upstream part of the hill into a gentle slope while glacial plucking erodes the downstream edge into a steep slope Ushaped valleys A steepwalled valley shaped by glacial erosion into the form of a U Cirques Bowl shaped area at the head of a glacier alpine erosion Horns Peaks surrounded by cirques Headwalls Cliffs behind cirques Aretes Ridges separating cirques Hanging valleys A glacially carved tributary valley whose oor lies at a higher elevation than the oor of the trunk valley Don t forget glacial polish and striations Glacial polish A polished rock surface created by the glacial abrasion of the underlying substrate Striations Linear scratches in rock Glacial Deposition Main materials are till outwash loess Till Material deposited directly by the glacier unsorted no bedding makes moraines Outwash Sediment deposited by streams below the glacier Moraines Formed by will get younger toward the cirque sediment pile Till forms moraines lateral medial terminal recessional Lateral A strip of debris along the side margins of a glacier Medial A strip of sediment in the interior of a glacier parallel to the ow direction of the glacier formed by the lateral moraines of two merging glaciers Terminal The end moraine at the farthest limit of glaciation Recessional The end moraine that forms when a glacier stalls for a while as it recedes Drumlins A streamlined elongate hill formed when a glacier overrides glacial till Kettle lakes A circular depression in the ground made when a block of ice calves off the toe of a glacier becomes buried by till and later melts Erratics A boulder or cobble that was picked up by a glacier and deposited hundreds of kilometers away from the outcrop from which it detatched Other Effects of Pleistocene Glaciation Outburst oods Missoula Floods as example loess lowered sea levels Ice loading and rebound Pleistocene lakes The glacial lake Missoula grew broke through the ice and caused catastrophic ooding Ice loading an rebound leads to the depression of crust beneath ice crust sags from the weight of the glacier Lowered sea level Coastline moves outwards to the edge of continental shelves lowering the ultimate base level leading to increased erosion Seen in drowned river valleys Multiple advances and retreats during the Pleistocene Marine record more complete than land record Evidence for less than 4 on land 2030 in ocean Because less erosion takes place in the ocean than on land How big were the temperature changes between glacials and interglacials What explains them Milankovitch Cycles Variations in orbital shape aXis angle wobble of aXis Tilt ranges from 225 to 245 less colder Precession The wobble of the aXis AXis leans away from the sun in the winter and toward it in summer Role of Greenhouse Gases Trap long wavelength radiation escaping from Earth to space make life on earth possible with heat Process 1 Sun sends short UV wavelength radiation that reaches and warms earth 2 Earth reradiates long wavelength infrared radiation into space 3 C02 and other greenhouse gases absorb some of the outgoing infrared radiation Coastal Geology Understand how waves evolve as they approach the shore The lower part of the wave slows down when the bottom touches land Movement decreases and then ceases at 12 the wavelength Wave energy focuses on headlands and less intense on embankments Wave refraction Causes erosion extremely high water pressures and abrasion by suspended sediment Active vs Passive continental margins Active Rocky coasts with sandy intervals lots of uplift with exposed rocks Passive Sandy coastline movement of sand parallel and perpendicular to the coastline Rocky Coastlines Headland erosion produces sea arches sea stacks wavecut platforms sea cliffs Dominated by erosion driven by waves and mass wasting Wave cut benches can be uplifted and preserved as marine terraces evidence for ongoing uplift and active margins Differential erosion produces many of the more interesting features including blowholes sea caves Uplifted marine terraces allow us to calculate rates of tectonic uplift about 412 inches 1000 yrs Sandy Coastlines Movement of sand restricted by headlands and rivers Tidal ats where the tidal range is very broad at Sand is always moving perpendicular and parallel to the beach Swash has more water and more power than the backswash because of infiltration Carries and up and perpendicular Longshore drift produces sand spits and baymouth bars Barrier Islands An offshore sand bar that rises above the mean highwater level forming an island Geology Midterm Definitions Rock A coherent naturally occurring solid consisting of an aggregate of minerals or less commonly of glass Cement What bonds rocks mineral material that precipitates from water and lls the space between grains Clastic Rocks that are held together by cement Crystalline Rocks Whose crystals interlock with one another rocks that originate as a continuous mass Bedrock Rock that is still attached to the earth s crust Outcrop An exposure of bedrock Igneous rocks Rocks that form by the freezing of molten rock They cool and crystalize to form a liquid state Lava extrusive and magmaintrusive Extrusives are nely grained and intrusives are not Examples Intrusivegranite and extrusive basalt Sedimentary rocks Rocks that form by either the cementing together of fragments broken off preexisting rocks or by the precipitation of mineral crystals out of water solutions at or near the Earth s surface Bedded Can be clastic broken particles biogenic precipitated from biological activity or chemical precipitated through chemical processes Examples Sandstone limestone or rock salt Metamorphic rocks Form when preexisting rocks change character in response to a change in pressure and temperature conditions Foliated layers Does not involve melting Usually crystalline and found at mountain belts and subversion zones Equant Same dimensions in all directions Inequant Dimensions are not the same in all directions Bedding The layering of sedimentary rocks Foliation The layering of metamorphic rocks Hand specimen A stsize piece of rock Lithosphere Consists of the crust plus the top cooler part of the upper mantle behaves rigidly oats on the asthenosphere Asthenosphere Relatively soft layer composed of warmer mantle that can ow slowly when acted on by a force convects like water in a pot on the stove The continental lithosphere is much thicker than the oceanic lithosphere The continental lithosphere oats at a higher level because it is composed of lower density felsic and intermediate rock Lithosphere plates Plates that eXist because the lithospheric shell contains a number of major breaks There are 12 major plates and also microplates Plate boundaries Breaks between plates Earthquakes Vibrations caused by shock waves that are generated where rock breaks and suddenly slips along a fault occur in narrow and distinct belts Active margins Plate boundaries Passive margins Not plate boundaries continental crust is thinner here and sediment covers it up Continental shelf The surface of the sediment covering passive margins broad and shallow Fish hang out here Divergent boundary Plates move apart from each other Transform boundary Plates slide sideways past each other Convergent boundary Plates plates move toward each other and one sinks beneath the other Relative age The age of the rock in respect to another Numerical age Age of a rock in years Principle of uniformitarianism Physical processes that operate in the modern world also operated in the past at roughly the same rates Responsible for forming geologic features preserved in outcrops Principle of original horizontality Layers of sediment when first deposited are fairly horizontal because sediments accumulate on surfaces of low relief in a gravitational field Principle of superposition In sedimentary rock layer each layer must be younger than the one below Principle of lateral continuity Sediments generally accumulate in continuous sheets within a given region Principle of cross cutting relations If one geologic feature cuts across another the feature that has been cut is older Principle of baked contacts An igneous intrusion bakes surrounding rocks so the rock that has been baked must be older than the intrusion Principle of inclusions A rock containing an inclusion fragment from another rock must be younger than the inclusion Geologic history The succession of events in order of relative age that have produced the rock structure and landscape of a region Fossil assemblage The group of fossil species The principle of fossil succession Extinction is forever Once a fossil disappears at a horizon in a sequence of strata it never appears higher in the sequence Index fossils Fossil species that are widespread but survived only for a relatively short interval of geologic time Angular unconformity Rocks below an angular unconformity were tilted or folded before the unconformity developed Nonconformity Sedimentary rocks overlie generally much older intrusive igneous rocks andor metamorphic rocks The igneous or metamorphic rocks underwent cooling uplift and erosion prior to becoming the substrate on which new sediments accumulated Disconformity The boundary between a new sequence of sediment and the old sediment below it Isotopic dating Using measurements of radioactive elements to calculate the numerical ages of rocks Geochronology The study of numerical ages Radioactive decay The process isotopes undergo when they re unstable converting them to another element Parent isotope The isotope that undergoes decay Daughter isotope The element that emerges after decay Halflife How long it takes for half a group of parent isotopes to decay Isotopic dating techniques Find unweathered rocks separate the minerals by crushing extract parent and daughter isotopes by dissolving the minerals in acid analyze the parentdaughter ratio with a mass spectrometer Closure temperature The temperature below which isotopes are no longer free to move Radiometric dating Dating geologic events in years by measuring the ratio of parent isotopes to daughter product atoms Relative age The age of a geologic feature in relation to another Main Points How to distinguish rocks Grain size Dimensions of the grains in a rock measured in mm or cm Composition Proportions of the different chemicals making up the rock Texture Arrangements of the grain in the rock Layering De ned by bands or grains that trend parallel to each other Names of rocks usually come from the dominant component making up the rock the region where the rock was rst discovered or is abundant the root word of Latin origin or the traditional name used by the people in an area where it is found Steps in studying a rock Identify a rock Develop a hypothesis for how it formed Make a very thin slice thickness of human hair Observe under a petrographic microscope illuminates a thin section Identify the grain and its orientation Make a record of the image using a camera through the microscope the picture is called a photomicrograph The rock cycle Material can enter when magma rises from the mantle Refer to diagram in notes The material that makes up any type of rock can turn into any other type of rock given the right combination of processes These processes are 0 Weathering erosion Lithi cation Transformation of loose sediment into solid rock Burial High temperature and pressure Melting Cooling OOOOO O O Crystalizing Uplift and erosion Metamorphism Changing of a rocks chemical composition by reactions with hydrothermal uids Volcanism Geologic time scale Diagram in notes Vi Precambrian Paleozoic Phanerozoic Mesozoic Phanerozoic Cenozoic Phanerozoic wig ra 439 vi ra 4 ra 439 vi Weathering and erosion Weathering The breakdown of material at the Earth s surface The surface has less pressure lower temp oxygenrich atmosphere and acidity in waters Mechanical weathering O O O O O Reduces the size of rocks and depends on properties Frost wedging Water seeps into frozen rock and ice makes it expand Crystal growth Rock absorbs water water evaporates crystals grow and crack rock Thermal expansion Enlargement of crystals due to heat Chemical bonds are weakened Mechanical exfoliation Overlying rocks apply pressure expand upon erosion Biological disturbance Tree root growth animals burrowing Abrasion Scraping and sculpting by loose particles such as glaciers rivers and wind Chemical weathering O Alters the composition of the rock typically occurs through the ow of water Natural rainwater is slightly acidic Dissolution Water removes mass in solution uses carbonic acid and acid rain to dissolve the rock Hydrolysis Granite materials are altered to clay minerals by H and OH Oxia ation Elements lose electrons when combined with oxygen Iron oxides are formed Factors that affect chemical weathering Surface area of minerals contact time with water strength of chemical bonds biological in uence and climate moisture and temperature Mass wasting types Mass wastings are natural hazards move along the rock cycle control the height of mountains have socioeconomic impacts and have biological functions Types of mass wasting types are determined by the types of material velocity and environment or setting Caused by convergent margins collisional orogeny rifts volcanoes human deposition sea level drop and displacement Triggered by rainfallsnowmelt shocks earthquakes undercutting and strength loss due to weathering or vegetation change Intact rock is very strong fractures decrease strength Gravitational forces vs frictional forces Frictional forces provide stability Creep Slow continuous process that occurs on soilmantled slopes Driven by freezethaw cycles and biological disturbances Slumping Headscarp that fractures at the top and folds at the toe with a bench like deposit Hummocking terrain like a golf course with a discrete failure surface Flows Mixture of rock soil and water Velocity varies with steepness speed and material 0 Earthflows Highly vicious and slow moving deeply weathered soil and rock Deposits on moderate slopes o Debris flows Course grained materials with a low viscosity more water Deposits on gentle slopes o Mudflows Finegrained material with a very low viscosity Deposits on gentler slopes o Lahars Volcanic ash and water that s eruption or rain related with scalding lobes Rockslia es Travel as coherent mass initiate along a plane of weakness Roe falls Loose rock on steep cliffs with a very high viscosity l60mph i r K K K r Water properties Two hydrogen atoms bound to an oxygen with a bond angle of 1060 creates a polar molecule Bonds to other water molecules via hydrogen bonds Water has these special properties Capillary action High surface tension remains liquid over a wide range of temperatures Is a powerful solvent has a high heat capacity has latent heat of vaporization is denser than ice Plate tectonics The lithosphere is broken up into plates that move over the asthenosphere Convergent margins Subduction zones one plate is more dense than the other and slides under Divergent margins Formed at midocean ridges Ocean oor spreads apart and forms a ridge New basalt erupts at the divergent margin and fills the gap making new ocean oor Transform faults Link other plate boundaries and connect and support unconnected ridges The PN W subduction zone divergent margin and transform fault Hypothesis Scientific theory K K K GEOLOGY MIDTERM 2 Rivers Drainages and drainage networks evolving from sheet wash to channels that grow by headward erosion Shape of a river pro le drainage networks watersheds divides Continental divides Great Basin Begins with sheet wash water owing like a sheet Irregularity causes increased erosion Small channel develops Channel grows by headward erosion Development of tributaries o Watershed The area drained by a given trunk stream 0 Divide A ridge or other topographic feature that separates two adjacent drainage basins It is an imaginary line that separates two different directions of surface water ow 0 Headward er0si0n Takes place at steeper areas 0 C 0ntinental divides A continental divide is a mountainous ridge on a continent On one side of the divide all the water generated from snowfall feeds into rivers that ow to an ocean bay or sea The rivers on the other side of the divide feed into a different ocean bay or sea 0 Great Basin Western US no drainage to ocean 0 River prO le o Drainage networks Shape of drainage network how does it relate to the bedrock below 0 Concept of base level 0 Marks a local elevation below which the river channel above it can t erode Ephemeral vs permanent streams what are they and how do they relate to groundwater o Ephemeral Only ows after rainfall events 0 Permanent Has a base that is below the water table and ows all year typically found in temperate climates River Discharge what is it and how do we figure it out Why is it important 0 Rivers and sediment transport dissolved load suspended load bed load How does the grain size of each of these types vary How does bed load actually move 0 Dissolved 0ad Dissolved sediment o Suspended 0ad Sediment is ne grained and suspended in the water 0 Bed 0ad Dragged and pushed along the bottom of the channel coarse grained moved by saltation or bouncing and rolling Deposition and erosion of sediment o Er0si0n occurs when a river load is below its capacity 0 Depositian occurs when it s above its capacity How does water velocity and thus a river s carrying capacity vary across a meander bend 0 Fast water and erosion on the outside and slow water and deposition on the inside How does watertransported sediment alluvium change downstream from its source 0 Sediment becomes ner grained more rounded rich in quartz resistant to chemical weathering What happens to a river s gradient discharge and velocity downriver from its source 0 Discharge increases 0 River gradient decreases 0 Velocity increases River types and environments Alluvial fans braided rivers meandering rivers oodplains deltas oxbows abandoned channels meander bends meander cutoffs tributaries distributaries lakes know all those terms and what they are 0 Alluvial fans fan or coneshaped deposit of sediment crossed and built up by streams If a fan is built up by debris ows it is properly called a debris cone or colluvial fan 0 Braided rivers o Meandering rivers o F l00dplains o Deltas o Oxbcws o Abandcned channels 0 Meander bends o Meander cuto fs o Tributaries o Distributaries o Lakes Erosion of Waterfalls as example of headward erosion o Waterfalls and boulders that drop down from the top erode the cliff underneath creating an overhang Rivers and Flooding When and why do rivers ood What causes them Besides their damage how are they bene cial o Caused by heavy rainstorms prolonged heavy rains dam breaks and snowmelt 0 Bene ts Replenishcs soil by depositing negrained sediment on oodplains ush out toxins Seasonal vs ash oods and representation on hydrographs 0 Seasonal rainy seasons expected temperate climates wide area 0 F laslz oods Sudden extreme brief small area localized arid climates How have oods changed as the landscape has become more urbanized 0 Flood frequency is assessed by annual probability and recurrence interval which are related to each other by a simple equation What does each mean 0 Annual prcbability means the probability of ooding in a given year 2 002 chance of ooding in the given year 0 Recurrence interval The average number of years it takes for a ood to occur Flood Control measures levees channeling dams each has bene ts each has drawbacks o Levee Arti cially deepens the channel Can make things worse by moving the ood downriver Can also promote a false sense of security 0 Channeling Lining a channel with concrete or cutting off meander bends Floodwaters can move out more quickly A problem because water goes downriver without buffering Adverse impact on environment 0 Dams About 75000 in the US Hold oodwaters back Support irrigation recreation and hydropower Problems with short life eXpectancy 2050 years increased erosion downriver because it lls with sediment River has unful lled carrying capacity Ecology effected Dams can fail City planning using oodplain maps help us live with oods 0 Flood control on the lower Mississippi River its long term effects especially on the delta and the relation of the Mississippi to the Atchafalaya o Groundwater Make sure you know the meaning of the saturated zone and water table 0 Saturated zone Where the pores are lled 0 Water table How does groundwater move through the saturated zone 0 Sinks into the zone of saturation ows along curving lines from high to low hydraulic head discharges to stream Hydraulic head hydraulic gradient porosity primary and secondary permeability o Hydraulic head The top of the water table 0 Hydraulic gradient How steep the water table is 0 Primary porosity Measure of the rock s original porosity 0 Secondary porosity Porosity that came after the rock was formed caused by faulting fracturing etc o Permeability Ability of the rock to let water move through it Depends on the interconnectedness of the pores and the natural conduits fractures etc The coarser the grain size the more permeable the rock Order of permeability least to most Shales siltstone sandstone conglomerates Controls on porosity and permeability o Aquifers and Aquitards con ned and uncon ned aquifers o Aquifer Rock or sediment with high porosity and high permeability C0n ned Doesn t have passage to surface Uncan ned Open to land surface 0 Aquitard Impedes the ow of water low permeability Wells and springs meaning of artesian locations of springs 0 Well Hole that goes down to the water table 0 Spring Occurs when the water table intersects the land surface 0 Artesian Well that rises above the water table 0 Lacatian 0f springs Discharge zones fault zones juxtaposing an impermeable layer water perched on an aquatard at intersecting fractures and at alluvial fans Groundwater as a resource 0 West offlze middle 100th meridian in the US agriculture needs groundwater 0 Renewable but takes time to replenish and is being used at a faster rate than it s being recharged 0 High plains aquifer Covers most of South Dakota Kansas Oklahoma and much of North Dakota and North Texas Varies from 2001000 feet thick and is being depleted at about 2 feet per year Groundwater makes up 30 of Earth s freshwater so heavily utilized as a resource When pumping exceeds recharge wells develop a cone of depression can lower water table 0 Cone ofdepressian Extraction is greater than recharge and the water table lowers ASR Aquifer Storage and Recovery becoming increasingly important 0 Takes surplus surface water and injects it into the aquifer o In the PNW during warm winters precipitation comes as rain which makes for surplus water Mesa Verde Colorado as an example of surface and groundwater resources 0 Springs and alcoves form at the top of aquitards o Scattered shale lenses intrude on sandstone Karsts Landscape dominated by dissolution of limestone or other easily soluble rock Weakly acidic groundwater can dissolve limestone Caves typically form below the water table but get decorated by speleothems above the water table How 0 Water percolatcs through the cave roof forming stalactites o Stalactitcs drip forming stalagmites on the ground below them 0 They can merge to form columns Besides caves and speleothems what s a speleothem anyway what other features are typical of karst o Spelcothems are mineral deposits formed from groundwater within underground caves Stalactitcs and stalagmitcs are types of these 0 Other types Cave shapes are typically in uenced by features in the bedrock typically those that in uence permeability
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