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This 97 page Class Notes was uploaded by Asha VonRueden on Friday October 2, 2015. The Class Notes belongs to GLY 1101 at Appalachian State University taught by Scott Marshall in Fall. Since its upload, it has received 116 views. For similar materials see /class/217681/gly-1101-appalachian-state-university in Geology at Appalachian State University.
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Date Created: 10/02/15
O I A Hiddeh Reeewe Gtohhdwatet MUCh 0f the glzowba1 H20 regides below Centralpivot irrigation utilizing groundwater Jordan the surface of the Eatth m What geologists refer to as groundwater Aithough in the subsurface has a large impact on society and the features thatwe see On the surface of the tEat th Greundwaier Why d0 We Care f e Groundwater 39is an important resource Drinking water fOr people and livestock InigatiOn Industry 6 1t ghasbezen fused The Underground Reservoir Some precipitation enters the subsurface via infiltration Soil properties and vegetation govern in ltration rate In ltrated water adds to soil moisture and groundwater Soil moisture wets the soil Some is Wicked up by roots some is evaporated The Underground Reservoir Some in ltrated water percolates to a deeper level 0 It is added to water that lls subsurface void spaces 0 This is groundwater 900640000 Only a very small amount of the 9 3 9 55 global groundwater flows in subterranean rivers gr vge 39 F or lakes i e b O o Vesicular basalt Most groundwater resides in pores small open spaces within rocks Porosim refers to the total volume of a rock that is empty space and is usually quoted as a percentage e g rock A has 25 porosity Therefore the porosity of a rock is the percentage of the rock that is empty space Porosity greatly varies between different rock types A Poorly sorted Conglomerate Unconformity Primary vs Secondary Porosity 7 7 39 VP Tgt39 ary porosify Priman Porosity 7 This is the v porosity of the rock after it rst lithi esforms based on the spaces between grains sity Secondary p r 7 Fine grained sediment has a lower porosity because the little grains can fill in the spaces 7 Crystalline rocks have very low primary porosity Secondary Porosity 7 New pore space created in the rock at some time after the rock formed 7 Eg Joints Faults Dissolution 7 Because of secondary porosity any rock could potentially have some porosity PorOSItV VS Permeabllity If solid rock completely 1 surrounds a waterfilled pore then the water cannot ow For groundwater to ow pore spaces must be interconnected The ability of a rock to allow a uid to ow through an interconnected network of pores A is called Permeabil 39 a r If a rock has a high porosity it does not necessarily have a high permeability The pores must have interconnected conduits 7 Eg porous cork is nearly impermeable Permeability depends on 7 Number of available conduits 7 Size of conduits 7 Straightness of conduits b Aquifers and Aquitards Hydrogeologists distinguish between rocks that transmit water easily and rocks that do not easily transmit water Aquifer A rock that easily transmits water Aquitard A rock that does not transmit water easily ie retards water motion Aguiclude A rock that does not transmit water at all UncontmedAguiter An aquifer that has direct access to the surface of the Earth Can be quickly recharged by meteoric water and Permeability ConttnedAguiter An Unconfined aquifer aquifer that is trapped below an aquitard Aquitard Confined aqulfer Low porosity and permeability Hydrogeologic Zones Unsaturated ZoneVadose Zone The portion of the subsurface where some of the pores are lled with only air Saturated ZonePhreatic Zone The portion of the subsurface where the pores are completely lled with water Water Table The boundary between these two zones HOW deep does the saturated zone g0 Hydrogeologists are not sure At some depth lOZOkm water is utilized for metamorphic reactions 7 V Unsaturated zone Vadose zone L Capillary fringe i D 39 4 g Soil V Moisture sticks to grain surfaces air pockets remain Bedrock or sediment Topography of the Water Table The water table is not a flat surface that never changes It may have seasonal oscillations wet dry seasons and rise and fall Underneath mountains and hills the water table follows a similar but subdued shape Water table H111 seai v ii 5 Perched Water Tables A locally present aquitard may create a Perched Water T able a localized phreatic zone saturated above the regional water table Can form springs if there is topography 39cohrin aaquifez39 Recharge and Discharge Groundwater ows downward in areas of Recharge and upward in areas of Discharge But what causes groundwater to ow Hydraulic Head A measure of the potential energy available to drive the ow of a given volume of groundwater Groundwater ows from locations of high hydraulic head to low hydraulic head Drainage divide Ground v water ow path l Infiltration Hydraulic Head and Hydraulic Gradients In an unconfined aquifer hydraulic head can be thought of being due to the weight of the water above it Similar to air pressure Water will always ow from regions of high head to regions oflow head In a confined aquifer the hydraulic head is more complex Hydrogeologists measure hydraulic head by drilling holes into the ground and measuring the level to which water fills the hole The rate at which groundwater flows is determined by the HVdr lliC Gradient which is the change in head from one location to another along the flow path To calculate discharge a French engineer Henry Darcy coined 11 12 what we now call Darcy s Law Rain EL D h If you know the hydraulic Drillhole 1 I gradient Ahj the hydraulic conductivity K and the area through which the water is owing A you can calculate the discharge by quot xbrillhole 2 Q KAhjA Sometimes we simplify this and say that Discharge Slope of Water Table Permeability How Fast Does Groundwater Flow Water in an ocean current 3 kmhr Water in a river up to 30 kmhr Groundwater 001 14 mday 4500 myr Why so slow Conduits are very curved and small so groudwater must ow in a very crooked path and friction with conduit walls slows it down Hydrogeologists measure ow in some regions by injecting a dye radioactive element or bacteria all types of tracers and monitor its movement Some groundwater may emerge after months or years but some may not emerge for thousands to tens of thousands of years 100 km Groundwater 1 km ow path Wells How We Get To Groundwater Since water is important to society access to groundwater is important We access groundwater through wells and springs where groundwater percolates out at the surface of the Earth An ordinary well penetrates to a depth below th water table where an aquifer allows access to owing water We then either pump it out right or manually pull up the water below Well Drawdown amp Cones of Depression When a well is drilled to access an aquifer drillers like to make the well as shallow as possible to save 53 If a well pumps out water faster than it is replaced by normal groundwater ow it draws down the water table in what is called a Cone of Depression Cones of depression can make nearby wells temporarily dry So when drilling a well drillers must consider both the ow rate in the aquifer and the pumping rates of nearby wells Artesian Wells In some places groundwater does not need to be pumped out of a well if water freely ows out of the well it is called a owing artesian well To see why this happens lets look at a city water supply and water towers Cities first pump water from the local aquifersource into a high reservoir tank This high tank is connected to the houses in town by a network of underground pipes The pressure in the elevated tank provides the push to make water rise out of the pipes of town The level to which the water will rise is called the Potentiometric W Potentiometric Water leve1 Therefore the water surface Standpipe in tank company doesn t have to pump water to your house just to the raised tower So if you are on city water you are likely getting it because you have an artesian connection to the city water main water we Artesian Wells in Nature An artesian well can occur in nature when a well penetrates a con ned aquifer that is under great pressure If the potentiometric surface is above ground the well will be a owing artesian well If the potentiometric surface is above the water table but below the ground it will be a non owing artesian well r v 5 Potentiometrlc surface r Flowing Standpipe Aquifer Non owing artesian well artesian well Springs What Conditions Cause Them to Form Syring A location where groundwater is discharged from the ground The various conditions shown here cause a spring to form Recharge Discharge Impe rmeable layer Fractures C Springs What Conditions Cause Them to Form The various conditions shown here cause a spring to form Artesian springs f Joint Perched water table Note that an Artesum Sgrlng 1s a natural feature while and artesian well is drilled by man Oasiserage or Geology Folded aquifers and faults can cause an Oasis to form These are important stops for people traveling across the Sahara Faults can bring deep water up to the surface of the Earth forming a hot spring Fault trace Sand region Recharge region Karst Landscapes and Grundwater Groundwater can f 7 j quot 0 13 dissolve calcite 39 39 39 39 bearing rocks such as limestone Caves form ust When C02 mixes below the water water is makes a weak table acid called carbonic acid that speeds this process Over time changes in the water table may form complex networks of caves If a large cave becomes near to the surface of the Earth usually by erosion it can collapse forming a sinkhole Terrain dominated by sinkholes is called Karst Landscape or Karst T opographp Old caves empty speleothems grow Water table sinks new caves form Caves collapse karst landscape develops New caves get bigger How Does Groundwater Flow Through Limestone Although limestone is Joint set 1 nearly impermeable it is commonly jointed Joint set 2 o The joints provide a secondary porosity and allow groundwater to flow through Bedding ll More soluble bed Less soluble bed Groundwater In nite or Finite 0 Although on scales of tens of thousands of years groundwater is renewable if usage is high it can be a big problem on scales of years to hundreds of years An Industrial well lowers the water table and dries up a river Flowing river b Industrial pumping Groundwater Problems Large wells can change the direction of tank groundwater ow moving contaminants into unsafe places Home water supply well Septic i 4 1quot Regional groundwater ow Contaminant West East Contaminated Large water supply irrigation well Contaminant plume has changed flow direction Groundwater Problems Saltwater is more dense than freshwater so it stays below the fresh water table ereb1 Salty Fresh groundwater groundwater Pumping and drawdown can cause saltwater in ux into what would naturally be freshwater aquifers Groundwater Problems Saltwater in ux is a huge problem in Florida Gulf of Mexico Gulf of Mexico Water ow Q Saltwater intrusion El Urban area El Nonswampland E Swamp I Mangroves Canal Groundwater Problems gym v V 0 Groundwater pressure holds grains POWPEH O O O C of rock apart When water is removed the once wet layer may become compacted D causing subsidence above the 1 7 J A aquifer V Ground cracks fissures and scarps Heavy 7 i i irrigation Aquifer has become thinner r r AVA 0159 391 Air filled pores collapse grains pack together more tightly S 81m amp P10 0 Pessible waterrelated features on Mars The Geoloov 0t R1111111110 V ter em 39ermmz39ng 7 AI 39 mqr have had Streams in 1178 pa lsl Flood 7 an V In 39 gt imm 1 Malayalam ving Wm is W J3 quotAll of the water is part of the hydrologic cycle 7 It starts out in the atmosphere falls as rainsnow is collected into streams and eventually empties into oceans 7 Ocean water evaporates and the cycle repeats Stream Morphology Water Table The boundary defining the subsurface realm where water completely fills cracks and pores Surface Water All water on the surface Groundwater All water that is stored below the ground in soil and rock 31 Forming Streams Running water begins as Sheetwash a film of water a few mm thick like water on a road Sheetwash erodes its substrate the solid base layer it rests upon The rate of erosion depends on velocity strength of substrate and amount of vegetation strength of substrate Eventually the sheetwash forms a channel in the weaker portions of the substrate and the channel is eroded deeper with time by Downcutting eventually forming a stream As ow increases Headward Erosion ie erosion in an upstream direction occurs because ow is faster at the entry to the channel With passing time other Tributaries may link together to a main Trunk Stream Sheetwash New channel Time Headward erosion lengthens Channel V Tributaries Trunk stream Drainage Networks Volcano lnterconnecting tributaries form a Drainage Network They come in several avors Resistant ridge C Rectangular Trellis Drainage asms and Divrdes The area drained by a system of tributaries is called a Drainage Basin Catchment 0r Watershed o A high ridge that separates one water shed from another is called a Divide Divide Divides and Watersheds in the US Watersheds exist in a variety of scales Tiny tributaries Continental rivers Large watersheds Feed large rivers Section continents Continental divides separate ow to different oceans Mississippi River basin limit Drainage divide 39 Arctic Ocean Pacific 1 I Ocean Mississippi Basin Continentai h RIVer divide E Gulf f y Mexico Permanent vs Ephemeral Streams Some streams ow all year and some do not Permanent stream Permanent Stream A stream that has a base that is below the water table and so it ows all year Usually found in temperate climates Ephemeral Stream A a stream that only ows after rainfall events The water y Y Dry wash eventually ows into the I ground Found in arid climates A dry ephemeral stream bed 3 is caled a Wash Stream Discharge Geologists measure the amount of water that a stream carries by measuring its discharge Discharge The volume of water that passes through an imaginary cross section across a stream Expressed at some volume per time e g meters3second Discharge varies widely Amazon 200000 m3s largest discharge on Earth 15 of total runoff on Earth Congo 40000 m3s Mississippi 17000 m3s Stream gauging station In arid regions discharge decreases away from source In temperate regions discharge increases away from source Can also vary due to seasons or human activity Stream Velocit The average velocity of a stream is dif cult to measure because ow in streams is complex Friction along the sides and bottom of a stream channels slows the water s velocity The smaller the Wetted Perimeter assuming the cross sectional area is the same the faster the water can ow Streams with meanders will have the fastest velocity and deepest depth at the outer banks T halwegs of the meanders Crescent shaped Point Bars may form on the inner banks of meanders Width 39 12 In Straight semicircular channel cross sectional area 57 m2 Wide shallow channel crossvsectional area 57 m2 Deposition of point bar Erosion of cut bank Thalweg Curving channel Rotation of water as it slows complex down along margin interactions With underwater boulders and the stream banks cause Turbulent F low ie flow that is complex and not all in the same direction Eddy Turbulent ow Erosional Processes Stream ow does work is The energy imparted to stream ow is derived from gravity Streams do work by converting potential to kinetic energy Erosion is maximized during oods Large water volumes High water velocities Abundant sediment Running water eroded these Er channel walls in northern Arizona The kinetic energy of moving water can cause erosion in four main ways Scouring running water can remove loose fragments Breaking and Lifting running water can lift blocks out of a material Abrasion pure clean water has little erosive effect but sandladen water acts like sandpaper and grinds away the channel wall This is how potholes are carved Dissolution Running water can dissolve soluble minerals Transportation and Sediment Load Sediment Load The amount of sediment that a stream carries It consists of Dissolved Load ions oating in the water solution Suspended Load sediment silt amp clay that is suspended no settling within the stream Bed Load Larger particles that bounce or roll along the stream oor Moves by Saltation bouncing an rolling along the stream oor Normal bed load Dissolved Rolling ions Suspended load clay f Moves during ood Substrate Clast collides and bounces another into water Deposition When Streams Lose Their Loads Comgetence the maximum particle size that a stream can transport Depends on stream velocity Cagac 39 the total quantity of sediment that a stream can carry Depends on competence and discharge Rivers will deposit their sediment loads when their energy drops to the point that a certain particle size can no longer be transported This may seem counterintuitive but fastmoving streams deposit coarse sediment pebbles amp boulders and slowmoving streams deposit fine grained sediment fine sandmud Because the stream gradient or slope of the stream may change at times along a stream s path sediment tends to get sorted Basically any time a stream slows down it deposits some of its sediment Longitudinal Changes The character of a stream changes with ow distance Near the headwater source of the stream Gradient is steep Discharge is low Sediments are coarse Channels are straight and rocky Longitudinal Changes The character of a stream changes with ow distance Toward the mouth Gradient attens Higher discharges Smaller grain sizes typical Channels describe broad meander belts dinal Stream Pro le Lang ource Flow N Longitudinal profile 9 O Elevation Limit of drainage basin Plane of longitudinal profile Tributary Base Level There is a depth below which a stream cannot cut This is called the Base Level Present profile graded with respect to the lake Lake level local base level Sea lave ultimate base level Base levels can be local e g a lake but all streams have the ultimate base level of sea level a Rock ledge defines local base level Local base levels can Waterfall be removed over long periods of time Sea level Sltream Valleys and Canyons I If a stream downcuts faster than erosion of the channel walls it will form narrow riot M eg Zion If a stream downcuts W slowly erosion of the channel walls will form a VShaged Valley 6 g New river If a stream cuts through rocks of contrasting strengths sandstone vs shale it may form a valley with a stairstep shape 6 g Grand Canyon Joint Stream Terraces If base levels change or if discharge changes a stream can form multiple Terraces within an alluvium lled valley Waterfalls and Rapids Rapids form where water ows over boulders or where a stream s gradient increases Waterfalls form when a streams gradient becomes very steep possibly due to a resistant layer at its base Niagara Falls Waterfalls slowly change due to headward erosion A good example of this is Niagara Falls l Class V rapids gt afar Niagara Falls Lake Erie Niagara Gorge Lockport Dolostone Goat Island Niagara Escarpment Lake Ontario 21 Headward Erosion at Niagara Falls Geologists studied the headward erosion of Niagara Falls and determined that the fall is eroded back towards Lake Ontario by 1 in year Now it is about r 7 39 half that because some water is diverted for hydroelectric power In 60000 yrs the falls will erode all the way back to Lake b Erie Lockport Dolostone Plunge pool Joint Undercutting Environments with much topography consists of sand amp cobbles ArkoseSandstone Breccia Alluvial Fans Alluvial Fans form where a fastmoving mountain stream emerges from a canyon at the range front onto an open plain The water was once con ned to a narrow channel can now spread out Because of this its ow slows and it deposits its sediment load in a fan shape Common in arid Typically Rock T mes Braided Streams In some locations streams carry abundant coarse sediment during storms but cannot carry this sediment during normal ow During normal ow the sediment is deposited and the stream divides into numerous meandering channels forming a Braided Stream Because of the large amount of sediment that is deposited braided streams cannot cut deep channels loose sediment is weak Common to glaciallyfed streams A braided stream In Alaska Meanders Where rivers ow over relatively at land comprised of a relatively soft substrate natural variations in the substrate strength and the velocity of the water will cause the channel to begin to form curved segments called meanders Once the meander sweeps through 180 the meander neck may continue to be eroded by the cut bank Eventually the river s cut bank may erode through the meander neck leaving an abandoned meander called an Oxbow Lake ean gt illecE V out Flood Plains Levees 0 Ameandering stream occupies only a small portion of a greater ood gluin which is inundated during a large ood event Yazoo stream Floodplain l Bluff 0 Water spilling out from the edges of a river forms a natural levee Natural levee Point bar High water level 0 The levee can sometimes grow so high that the river bottom is higher than the ood plain deposits Ancient Channel Ancient oodplain I and pomt bar deposrts Stream bed C gravel Deltas 0 When rivers enter open water such as an ocean they divide into multiple channels called distrihwm es 0 Greek historians originally termed these deltas because the Nile river delta is roughly shaped like the Greek letter delta Deltas can have many shapes 39The Mississippiriver ddta Heleileuriver delfa Mediterranean Sea K Gulf of Mexico Midstream Bars Avulsion Why do distributaries form When a river enters standing water the water in the middle of the channel is moving fastest so it is carrying the most sediment Therefore the most deposition occurs in the middle of the main channel forming a Midstream Bar and choking off the river and forcing it to split into Distributaries Main Channel Eventually the midstream bar may grow so large it totally blocks the ow of the river I Natural levee gt4 t Midstream quot 39 V 7 quot39 bar Standing This causes Avulsion water whereby the river will quot get deeper and 39 eventually break the W at an upstream location Now the river will enter Distributal y the standing water at a Channel new location causing a new delta to form The Migrating Mississippi Delta Age Baton o 100 deposit years Amara R39 O Rouge km 4 400 bp present 1000 bp present 2500 bp 800 bp rw 4000 bp 2000 bp Re 7 5500 bp 3800 bp 7500 bp 5000 bp Gulf of Mexico AL GA 39 Avulsion has caused the Mississippi LA MS river delta to migrate through time TX Ma Engineers now help keep the river on Areg FL its present day track so that it still 300m flows through New Orleans GulfofMexiw 0 400 km Earth s Composition and Structure A Journey to the Center of the Earth Earth s Surface 0 Our experience with Earth is limited to its surface Yet Earth has a complicated interior 0 Earth is characterized by An internally generated magnetic eld TheBack Canyonofme Gumson co Solid and liquid layers A gaseous envelope A layered interior I The Solar System Human perceptions have changed Early history Planets as moving lights 16005 lSt telescopes saw hazy spheres Today A complex evolving system Structure History Space probes have photographed and analyzed planets Scientists have hypothesized likely origins of the solar system Mars Mercury Venus Earth and the Solar System What would solar system Visitors notice Magnetic eld Atmosphere Surface features Continents Oceans Polar ice caps Evidence of humanity Structures gtgt Dams gtgt Great Wall of China gtgt Cities gtgt Roads canals Electric lights The Celestial Neighborhood Interstellar space a Vacuum with a Virtual absence of matter The amount of matter greatly increases approaching the Sun The Sun ejects matter outward into space as the solar wind Solar wind Magnetically amp electrically charged particles Stream outward in all directions Consists of o Protons charge 0 Electrons charge Only a small percentage of the solar wind impinges upon Earth Five Key Characteristics About Earth s Structure 1 Earth has a dipole magnetic eld that de ects solar Wind and protects earth s surface from solar radiation 2 Earth has a strati ed atmosphere mainly composed of nitrogen N 2 and oxygen 02 3 Earth is made of a variety of minerals glasses melts uids and volatiles all left behind during birth of the solar system 4 The Earth has layers a thin silicate crust a thick iron amp magnesium silicate mantle and a thick metallic core 5 Physically the earth can be divided into a rigid outer lithosphere and a plastic ductile asthenosphere Earth s Magnetic Field Geodynamo The Earth s magnetic eld is produced by the geodynamo Flow in the liguid iron outer core creates a magnetic eld Magnetic eld region affected by force emanating from a magnet grows stronger as separating distance decreases attracts or repels magnetically charged or moving electrically charged objects compasses work because Earth is a large magnet Earth s Magnetic Field Magnetic eld Like a bar magnet Earth s magnetic eld is a dipole has both a N and S pole Solar Wind contains electromagnetic particles that are de ected by earth s eld These particles distort the shape of earth s magnetic eld in space Van Allen belts two belts in the inner magnetic eld Where high energy cosmic rays are trapped Protects us from solar radiation Solar wind Magnetosphere Magnetic eld lines Deflecth solar wind Northern amp Southern Lights Form bacauw f 113 gublagmagna c eld Aurorae Some ions escape Van Allen belts These ions are pulled to the magnetic poles The ions create light in the upper atmosphere Spectacular aurora follow solar ares Aurora borealis Northern lights Aurora australis Southern lights Earth s Atmosphere Distinct layers of gas surround the solid portion of the earth 0 Composition is uniform regardless of altitude o 78 N2 Nitrogen N2 0 21 OZ 7808 yo o All others l 0 Ar C02 CH4 H20 Ne co so2 0 Some other Planets have atmospheres too 0 None have N2 amp 02 as dominant gasses Other gases 097 0 Earth was oxygenfree until 25 Ga Earth s Atmosphere Less dense 0 Pressure decreases with increasrng altitude o Re ects of moleculesvolume o 0 0 Lower pressure less moleculesvolume o 0 Air pressure sea level 147 lbin2 1 bar 39 O O O O 0 Pressure is caused by the weight of 0 overlying material 1 39 0 Upper atmosphere has less material above it 390 o Gravi O 0 0 Pressure 1s lower 0 o 99 of atmosphere is below 50 km the rest is between 50 and 500 km lllIlWWMWAAA Denser a b o Earth s Atmosphere is divided into distinct layers based on altitude o Exosphere veg thin 500 km 0 Atmosphere merges with space Thermosphere gt90 km 0 O Mesosphere 5090 km 0 Stratosphere 1 1250 km 0 Tropopause 1 1112 km Troposphere 1011 km 0 O O Earth s Atmosphere Where space shuttles orbit Meteors burn up here Altitude km Stable air good for jets Tropopause Mixing layer All weather is limited to this layer Tropo Greek for turning 0 02 04 06 08 10 Pressure bars Earth s Atmosphere 0 Troposphere o A wellmixed layer dominated by convection of air masses 0 Convection o 0000 Method ofheat transfer in a uid 0 Think lava lamp Cold is more dense sinks Hot is less dense rises This process resulm in circular convection cells Also causes pressure gradients which create windl Also applies to the interior ofthe Earth Lhis guy likes cunvectiun 7 Earth s Components Earth s surface 30 land 7 0 water 0 unlike any other known planet Hydrosphere includes oceans lakes seas rivers amp groundwater Cryosphere glaciers snow and sea ice Mountains Earth s surface lS IlOt at it 8 Continental interiors plains Deep has topogranhx E 6 Continental shelf trenches Ignoring oceans Earth s E 4 iquot surface is dominated by two 3 3 Sealevel distinct elevations E 2 0 Most land is 02 km g 4 abovesealevel 5 6 V l WWW I o Mostofthesea ooris g 8 35kmbelowsealevel 10 quoth 60 so 100 of Earth s surface Earth s Components 0 Earth s elemental composition re ects mostly heavier elements not blown away by solar Wind during formation of the solar system 0 Most abundant elements 0 Fe O Si Mg 0 Most common minerals consis1 of silica SiOz mixed in varying proportions With other elements such as Fe Mg Al Ca K Na 0 m more silica less FeMg amp less dense o E g Granite o m less silica more F eMg amp more dense Bulk Ea omposition o E g Gabbro Basalt 0 Range Felsic Intermediate Ma c Ultrama c quotJ Earth Materials 0 Elements combine in a variety of Earth materials 7 Organic 1 J 7 Cmb l J 0 Most are residue from onceliving creatures 0 Include wood peat lignite coal and oil 0 Geologically rare decomposes in contact with oxygen Earth Materials Elements combine in a variety of Earth materials Minerals Inorganic crystalline solids Comprise rocks and hence most of the Earth 0 Most rocks on Earth are silicates based on Si and O Glasses Noncrystalline minerallike matter 0 Cool too quickly to form structure Rocks Aggregates of minerals There are many types 0 Igneous Cooled from a liquid melt Sedimentary Debris cemented from preexisting rock 0 Metamorphic Rock altered by pressure and temperature V quot sv39amp 7 Earth Materials Metals Solids made of metallic elements Melts Rocks that have been heated to a liquid 7 Magma 7 Molten rock beneath the surface 7 Lava 7 Molten rock at the surface Volatiles Materials that turn into gas at surface temps 7 H20 C02 CH4 and so2 7 Volatiles are released from volcanic eruption A Layered Earth 0 We live on the thin outer skin of Earth 0 Early perceptions aboutPEaIth s interior were wrong 7 Open cavems filled with magma water and air i 7 Furnaces and ames A 0 We now know that Earth is comprised of layers 7 The Crust 7 The Mantle 7 The Core Outer Core 39 Inner Core Some basic rul f physics give some clues me Mlmn I Paradlsz L052 Earth s Density Earth s Density gives us clues about its internal structure Density MassVolume Measures how much mass is in a given volume Expressed in units of massvolume e g gcm3 Ice oats Why Estimates of earth s mass and volume 5 give a whole earth density of 55 gcm3 139 quotNew instrument Typical rocks at the surface of the Earth have a density of 2025 gcm3 What does this require of the density of material in the Earth s interior Earth s Density Earth s shape as a clue to the internal structure of the Earth If density increased gradually and uniformly towards the center a significant portion ofEarth s mass would be near the outer edges s Then centrifugal force not centripetal would cause the planet to atten into a disk This has obviously not happened Earth s Layers Earth s shape as a clue to the layering of the earth If the Earth consisted of a thin solid shell over a thick liquid center then the surface would rise and fall with tides like the ocean This does not happen only the oceans rise and fall Low Tide High nae Iquot 39 New Mann Full Moon The Earth The Sun Thus the Crust does not oat over a liquid interior A Layered Earth Earthquake clues Earthquake energy transmitted as seismic waves that pass through Earth Seismic waves have been used to probe the interior Wave velocity changes with density Velocity changes give depth of layer changes 0 Changes with depth Pressure Temperature More on this in Chapter 10 and Interlude D Earth s Interior Layers The Earth and other planets have layered interiors Crust Continental Oceanic Mantle Upper Lower Core Outer Liquid Inner Solid Thinned Thickened Normal continental continental continental V 1 Lithosphere The Crust The outermost skin of Earth with variable thickness Thickest under mountain ranges 70 km 40 miles Thinnest under midocean ridges 3 km 2 miles The Mohorovicic discontinuity or Moho is the lower boundary Separates the crust from the upper mantle Discovered in 1909 by Andrija Mohorovicic Marked by a change in the velocity of seismic P waves Continental crust Oceanic crust Two Types of Crust Continental crust Underlies the continents Avg rock density about 27 gcm3 Avg thickness 3540 km Felsic composition Avg rock type Granite Oceanic crust Underlies the ocean basins Density about 30 gcm3 Avg thickness 710 km Ma c composition Continental crust Oceanic crust 0km 50 Avg rock type BasaltGabbro 100 150 Two Types of Crust Crustal density controls surface position Continental crust Less dense oats higher Oceanic crust More dense floats lower Continental crust Oceanic crust 0km Continental crust 5 o 100 a Granite Basalt 150 Crustal Composition 0 985 of the crust is comprised of just 8 elements 0 Oxygen is by far the most abundant element in the crust This re ects the importance of silicate SiOZbased minerals As a large atom oxygen occupies 93 of crustal volume 100 Element Symbol Percentage Percentage Percentage 90 by welght by volume by atoms 80 Oxygen O 466 938 605 70 Silicon Si 277 09 205 Aluminum Al 81 08 62 60 Iron Fe 5 05 19 Calcium Ca 36 1 19 50 Sodium Na 28 12 25 Potassium K 26 1 5 18 40 Magnesium M9 21 03 14 All others 15 001 33 30 I Percentage by weight 20 I Percentage39by volume 10 Percentage by atoms Fe Ca 0 i AI Na K Mg Oxygen Silicon Aluminum Iron Calcium Sodium Potassium Magnesium AllOthers Bulk Earth Composition Oxygen 30 Silicon Earth s Mantle m rock layer between the crust and the core 2885 km thick the mantle is 82 of Earth s volume Mantle composition ultrama c rock called peridotite Below 100150 km the rock is hot enough to ow It convects hot mantle rises cold mantle sinks Three subdivisions upper transitional and lower Upper mantle Transition zone Lower man le Liquid outer core The Core An ironrich sphere with a radius 0f3471 km 2 components with differing seismic wave beh avic i Outer core M 0 Liquid ironnickelsulfur 0 2255 km thick 0 Density 1012 gcm3 name I I Inner core T I T 0 Solid ironnickel alloy Radius of 1220 km 0 Density 13 gcm3 lnnercore solid metal a lay Flow in the outer core generates the magnetic 1e1d LithosphereAsthenosphere The Crust Mantle Core boundaries defined by composition but sometimes we want to divide the layers of the Earth by their behavior or physical properties Lithosphere The brittle portion of Earth s interior Behaves as a non owing rigid material The material that moves as tectonic plates Made of 2 components crust and upper mantle Asthenosphere The ductile portion of Earth s interior Continental crust Oceanic crust Shallower under oceanic lithosphere 0km Deeper under continental lithosphere Flows as a soft solid so 150
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