GEO 101-007 Exam 5 Study Guide
GEO 101-007 Exam 5 Study Guide GEO 101-007
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This 10 page Study Guide was uploaded by Jennifer Gintovt on Sunday November 22, 2015. The Study Guide belongs to GEO 101-007 at University of Alabama - Tuscaloosa taught by Dr. William Lambert in Summer 2015. Since its upload, it has received 104 views. For similar materials see The Dynamic Earth in Geology at University of Alabama - Tuscaloosa.
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Date Created: 11/22/15
Chapter 17 The Geology of Deserts Deserts De ned to be lack of rainfall not high temperature 0 Cold deserts less than 20 C 68 F 0 Hot deserts gt35 C 95 F 0 Hottest recorded temperature Libya 58 C 136 F Typically less than 25 cm of rainfall per year 0 Alabama receives about 140 cm of rainfall per year Vegetation less than 15 of surface Cover about 25 of land surface Sahara Desert Africa is Earth s largest desert A region so arid that it contains no permanent streams except for those that m water in from elsewhere and has very sparse vegetation cover But before we continue Warm air can hold large amounts of moisture water As the air cools water vapor condenses and leaves the air as precipitation typically rainfall Cold air is relatively dry What causes air to cool 0 Forcing the air up to a higher elevation mountains 0 Contact with cold ocean currents 0 High latitudes poles less sunlight and cold oceans 5 Types of Deserts Subtropical 0 Warm moist air rises at tropics air cools as it rises and produces tropic rainfall dry air moves north and south at high altitude and cools air sinks around 2030 latitude and soaks up moisture as it warms up near the earths surface Rainshadow 0 Air picks up moisture from the ocean as the air moves up and over coastal mountains it cools and the moisture is released as rainfall Once over the mountain the dry air soaks up moisture Coastal near cold ocean currents 0 Cold ocean water cools air thus reducing the air s ability to hold moisture dry air blows onto land creating coastal desert Continental interior 0 For large continents air loses its moisture as rainfall and reaches the interior of the continent very dry e g Gobi Desert Polar o Caused by combination of atmospherically circulation delivering cold dry air and cold ocean water limiting moisture in air Weathering and Erosional process in deserts Physical weathering o Rocks may split along joints cracks Chemical weathering 0 Small amounts of moisture dew or rainfall seep into rocks and leach dissolve out certain elements which causes the rock to become brittle Desert Varnish A dark rustybrown coating of iron oxide and magnesium oxide that accumulates on the surface of the rock The exact cause is poorly understood but may involve microorganisms leaching out iron and magnesium from dust that coats moist rock to from Fe and Mg oxides Petroglyph 0 Drawings formed by chipping into the desert varnish of rocks to reveal the lighter rock beneath Lag deposit Weathering and Erosional processes in deserts Lag deposit 0 The coarse sediment left behind in a desert after wind erosion remover the c A lag deposit develops when wind bows away finer sediment leaving behind a layer of coarser grains FIGURE 178 l t i39 M t Vt lt39W PlMW39H 1quot 1Wquoti litl Time1 TimeZ ner sediment 7 Ventifact 39 I o A desert rock whose surface has been quot 39I faceted surface smoothed by wind 39 39 39 Facet 39 39 Did facet New39i ce abraSion the Windblow39i sano abrados the The wmd shifts mmcturm face of a 39ock fO39mIng a facet and a view facet towns De ation o The process of lowering the land surface by wind abrasion A ventifact from top Dry Valleys of Antarctica Desert Deposits Talus o A sloping apron of fallen rock along the base of a cliff I Caused by weathering and gravity falling rock simply piles up Alluvial fan 0 A gently sloping apron of sediment dropped by an ephemeral stream at the base of a mountain in arid or semiarid regions Playa o The at typically salty lake bed that remains when all the water evaporates in drier times forms in desert regions Salt Lake 0 A lake with high salinity due to high rates of evaporation and no outlets for the water forms in desert regions Sand dune o A relatively large ridge of sand built up by the current of wind Desert Landscapes Mesa 0 A large attopped hill with a surface area of several square kilometers in an arid region Cliff Scarp retreat o The change in the position of a cliff face caused by erosion Butte o A mediumsized attopped hill in an arid region Chimney 0 An isolated column of strata in an arid Cuesld region Cuesta 0 An asymmetrical ridge formed by tilted layers of rock with a steep cliff on one side cutting across the layers and a gentle slope on the other side the gentle slope is parallel to the layering Desert Pavement o A mosaiclike stone surface forming the Rewam ground in a desert layer Desert Problems ESQTS39SW 0 Deserti ca on a Asyu unelnc ndges called cuestas develoo whele strata ma legIOH o The process of transforming nondesert we quotOI mommaquot areas into desert I Process can occur within just a few decades I Caused by natural droughts over population over grazing careless agricultural practices and diversion of water supplies I Eg 1993 Dust Bowl in Midwestern US Caused by overpopulation in the midwest poor agricultural practices too much plowing and drought Many people lost farms and were displaced The timing was unfortunate as it occurred during the Great Depression Chapter 12 Riches in Rock Energy and Mineral Resources The Sun energy Capacity to do work How much energy is stored in fossil fuels 1 barrel of oil 42 gallons 1667 kilowatthours 40 hours of pedaling per week 52 weeks per year for 801 years 1667 kilowatthours Energy and Resources Energy 0 The capacity to do work to cause something to happen or to cause change in a system Resource 0 Any material that can be of use either to make something or to provide energy Two types of resources Energy resources 0 A resource which can be used to produce heat and electricity or move machines Mineral resource 0 A resource which provides natural inorganic chemicals from which products can be manufactured Sources of energy Sun 0 Solar energy resulting from nuclear fusion reactions in the sun can be converted directly into electricity using solarenergy panels or used to heat water Gravity o Gravitational attraction between Earth and Moon causes tides water movement can be converted into electricity turbines Solar energy and gravity 0 Solar radiation heats both air and water resulting in wind and owing water after rain that can turn turbines Photosynthesis 0 Solar energy builds bonds in plants and the energy is released when these bonds are broken wood being burnt Chemical reactions 0 Inorganic chemicals that can burn to produce light and energy TNT hydrogen fuel cells Fossil fuels 0 Solar energy is stored up in organisms from long ago oil gas and coal are examples Nuclear fission o Splitting of certain atoms releases vast amounts of energy nuclear power plants nuclear submarines Earth s internal heat 0 Geothermal energy that can drive turbines heat within the Earth increases temperature of ground water Oil and Gas Oil and natural gas consist of hydrocarbons Hydrocarbons 0 Organic chemicals made of chainlike or ringlike molecules made of carbon and hydrogen atoms I Hydrocarbon type natural gas gasoline oil tar is a function of chain length How are hydrocarbons formed Hydrocarbon formation 0 Source rock I A rock organicrich shale containing the raw materials from which hydrocarbons eventually form 0 Kerogen I The waxy molecules into which the organic material in shale transforms when reaching 100 C At higher temps kerogen turns into oil 0 Oil shale I Shale containing 1530 kerogen misleading name 0 Oil window I A narrow range of temperatures under which oil can form in a source rock 90160 C o l60225 C natural gas 0 gt225 C graphite Hydrocarbon Reserve A known supply of oil and gas held underground not all rocks contain oil So we simply drill into source rock to extract oil Actually no Reservoir rock 0 A rock that contains or could contain an abundant amount of easily extractable oil and gas these rocks have high porosity and high permeability Porosity o The total volume of empty space pore space in a material usually expressed as a percentage Permeability o The degree to which material allows uids to pass through it via an interconnected network of pores and spaces Trap 0 A trap is a geologic configuration that accumulates and holds oil andor gas underground needs source reservoir and seal rocks 39 Seal rock 0 A relatively impermeable rock such as shale salt or unfractured limestone that lies above a reservoir rock and stops the oil andor gas from rising further FIGURE 123 Initially oil resides in the source rock Because it is buoyant relative to groundwater the oil migrates into the overlying reservoir rock The oil accumulates beneath a seal rock in a trap Present Temporary storage Transport will 391quot W li igiliii 39i 115 39i Past Types of Traps Anticline Trap Fault Trap Saltdome Trap Stratigraphic Trap Seal rock Reservoir rock Source rock a Anticline trap Oil and gas rise to the crest of the fold b Fault trap Oil and gas collect in tilted strata adjacent to the fault Faults Seal rock Reservoir rock Source rock c Saltdome trap Oil and gas collect in strata on the flanks of the dome beneath salt Seal rock Reservoir rock Stratigraphic quot pinchoutquot Source rock d Stratigraphic trap Oil and gas collect where the reservoir layer pinches it out Oil Exploration and Production Edwin Drake 0 He and his team were the first to ever drill into the Earth and extract oil on Aug 27 1859 Since then 2D seismic view 3D seismic view Oil Rigs Other types of hydrocarbons Natural gas Tar sands oil sands and oil shale Gas hydrates Environmental impacts of hydrocarbon use Green house and other dangerous gases are released into the atmosphere Oil spills Global warming 0 Etc A black brittle sedimentary rock that burns consists of elemental carbon mixed with minor amounts of organic chemicals quartz and clay 0 Coal and Oil do NOT have the same composition or origin Coal Formation Organic debris that eventually become coal come Ranks of Coal fr m l n m r O p a t zite ngnlte Subbltumlnous Bituminous AnthraCIte AS 563 level 363 a coal Swamp mlgrates Inland 7000 BTUlb 9000 BTUlb 12000 BTUlb 15000 BTUlb and the swamp s deposits are eventually buried by other strata 39 n A layer of peat accumulates beneath a swamp Upon burial the peat becomes lignite After further Formation Conditions gt burial lignite alters to form bituminous coal Low T P 399 T39 P Coal is found in sedimentary beds interlayered with Time of Formation gt other strata sandstone shale and limestone C gt Lowest Grade Highest Grade U 8 Coal U 8 Coal Environmental impacts of coal use Gases O C02 0 Sulfur gasesacid rains Mercury 0 It is part of the composition of the coal 0 Mercury is released easily because its compounds are volatile Ash 0 Contains trace metals such as selenium and uranium which leach wash out once ash is deposited Coal mining hazards Mining coal underground is dangerous mines collapse and miners have lung problems from breathing the coal dust Gas explosions often end tragically Nuclear power and energy Nuclear power plant 0 A reactor heats water which produces highpressure steam The steam drives a turbine that in turn drives a generator to produce electricity A condenser transforms the steam back into water Nuclear fusion 0 Fusing two light atoms into a heavier atom I Takes place in stars I Despite occasional claims of cold fusion this has never been replicated on earth Nuclear fission 0 Breaking heavy unstable atoms mostly 235U apart by subjecting them to a controlled ux of neutrons What does this have to do with geology 238U is most common 235U has to be concentrated through enrichment which is expensive Ancient streambed gravel deposits have the highest concentrations of uranium Environmental impacts of nuclear power Fukushima nuclear disaster in March 2011 0 Problems related to violent earthquake and related tsunami Nuclear power plants produce hazardous waste 0 No one wants the waste nearby 0 Where do we put it o How long should it be stored Geothermal energy obstacles faced Not a widespread energy source only feasible to drill in certain areas where heat is near the Earth s surface High installation costs Too much use can cool local rock and reduce steam production Dangerous gases can be released Most cost ef cient to provide energy for local area however station site may be in remote area Other energy sources Solar limitations Wind limitations Hydroelectric limitations Hubbert s Peak Hubbert39s Peak Oil Production 0 peak oil production Bill ions Peak oil discovery v end of r oul based economy Hubbert 39 N r geophysicist 2000 2100 0 peak oul production occurs when Pnce 0f 0quot the rate of producnon is equal to S10095 on the rate of consumption In 1956 Hubbert predicted that global oil production would reach maximum around the year 2000 and trigger an energy crisis with power blackouts and rising costs of energy and fuel
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