GLACIERS AND GLACIATION I. Topics n Intro n Glaciers and the Hydrologic cycle n Types n Movement n Glacial landforms –Glacial erosion –Glacial sedimentation

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  • GLACIERSAND GLACIATIONI

  • TopicsIntro Glaciers and the Hydrologic cycleTypesMovementGlacial landformsGlacial erosionGlacial sedimentationGlacial lakesGlaciations and global climate

  • GLACIERA large body of moving ice Formed on landRecrystallization of snowTypes:Alpine (valley) glaciersContinental glaciers

  • Winter Sea Ice- Beaufort Sea

  • Sea Ice- Bering Sea

  • Timble Glacier, Alaska

  • Valley Glaciers in Denali National ParkCourtesy USGS

  • Hydrologic Cycle - 2% of water is Ice

  • What if the glaciers melt?

  • Glaciers-Where they are Develop where all of annual snow doesnt melt away in summerPolar regionsHeavy winter snowfallHigh elevations85% in Antarctica10% in Greenland

  • Types of GlaciersValley glacierContinental Glaciers:Ice sheets (big)Ice cap (small)

  • Greenland Ice Sheet:contours indicate elevation of ice sheet above sea level

    Fig. 12.5

  • Ross Ice Shelf, Antartica

  • Formation and Growth of GlaciersMetamorphism of SnowGlacial BudgetsZone of accumulation Zone of wastageSnow line- divides the zonesNegative budget- Receding glacierPositive budget- Advancing glacierTerminus- movement reflects budget

  • GLACIERSWastage of glaciers (shrinkage)Meltingmore melting at lower elevationsEvaporationCalving into Icebergswhere a glacier flows onto a sea

  • Movement of GlaciersValley GlaciersGravity driving forceSliding along its base -basal slidingInternal flowage- plastic flowRigid zoneCrevasses may form hereIce sheetsMove downward & outward from central high

  • Glacial ErosionUnder glacierAbrasion & pluckingBedrock polished & striatedRock flour washes out of glacierPolishing and roundingSheep RocksStriations- scratches & grooves on rockAbove glacierFrost wedging takes placeErosion by glaciers steepens slopes

  • Erosional Landscapes Associated with Alpine GlaciationGlacial valleysU-shaped valleysHanging valleysTruncated spursTriangular facetsRock -basin lakes (tarns)Rounded knobs- rouche moutonnees

  • Erosional Landscapes Associated with Alpine GlaciationCirque- at head of valley glacierRock stepsRock basin lakesHornArete- sharp ridge

  • Erosional Landscapes Associated with Continental GlaciationGrooved and striated bedrockGrooves may be channelsRounded hills & mountains

  • Glacial DepositionTillUnsorted debrisErraticMoraine- body of tillLateral MoraineMedial Moraine- where tributaries joinEnd moraine-Terminal Recessional

  • Erratic-Alberta, Canada

  • Other Glacial Landforms Drumlins- Elongated hills of glacial tillPoint down-glacierEskersSinuous ridges of stratified till Form in tunnels under the ice sheetSome times 100km long or more

  • Glacial DepositionOutwashStream-deposited sedimentsortedBraided streams typicalEskerKettleGlacial lakes

  • Glacial LakesPluvial Lakes-Due to wetter climateExamples: Lake Bonneville, Death ValleyLake Bonneville flood into Snake River CanyonProglacial LakesIn front of the glacial sheetIce dammed lakesExamples: Great Lakes, Lake Missoula

  • Lake Bonneville- 14,000 yrs ago- Utah

  • Lake Bonneville FloodThe lake was up to 1000 feet deepA ridge on the north side gave wayPeak flow 33 million cubic feet/second33 MCF would fill in a tanker train 165 miles longA raft would move at 75 mph on a wave 300 ft highFlood left behind giant ripples

  • Glacial agesNorthern Europe & North America heavily glaciatedPeak of glaciation 18,000 years agoEnded about 10,000We are still in the cold part of the climate cycleEpisodic climate changesAt peak glaciation Average global temperature only 5 degrees colder

  • Effects of Past Glaciation Glacial agesDirect effects in North AmericaScoured much of CanadaCut Great LakesDeposited till & flattened MidwestExtensive alpine glaciation in mountains

  • Effects of Glacial AgesIndirect effectsPluvial lakesLowering of sea level FiordCrustal reboundEvidence for older glaciationTilliteLate Paleozoic glaciationEvidence for a supercontinentPrecambrian glaciation

  • Causes for glaciationAstronomical (Milankovitch cycles)Eccentricity of orbit (100,000 yr cycle)Wobble of rotation axis (41,000 yr cycle)Precession of equinox (23,000 yr cycle)Variations in solar radiationAtmospheric changesCO2 (Greenhouse)Volcanic ashTectonic causesContinents near the polesOceanic circulation patterns