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UO GEOL 102 - Glaciers and their Features, Ice Ages

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GEOL 102 1st Edition Lecture 8 Outline of Last Lecture I. Types of GlaciersII. Making GlaciersIII. Glacial MovementOutline of Current Lecture I. Relationship Between Slope and Thickness for Glacial DynamicsII. Glacial BudgetIII. Glacial Erosion and LandformsIV. Ice AgesV. Consequences of GlaciationCurrent LectureI. Relationship Between Slope and Thickness for Glacial DynamicsWith no slope, you need lots of icy accumulation, so a glacier can’t be no slope and thinStress at base of glaciers tends to increase when slopes are steep and ice is thickGlacial DynamicsMovement driven by gravitySloping surface (valley glacier)Gravitational spreadingFlat surfacePressure builds with thicknessThese notes represent a detailed interpretation of the professor’s lecture. GradeBuddy is best used as a supplement to your own notes, not as a substitute.II. Glacial BudgetZone of ablation: Loss of ice near base of the glacier Sublimation Melting: meltwater pools accumulate and travel under the glacier to form small streams underneathCalving: avalanchesZone of accumulation: where a glacier is gaining mass, the upper portion, winter snow doesn’t meltThe equilibrium line separates the two zonesBalancing BudgetNegative: ablation exceeds accumulation, glacier retreatsPositive: accumulation exceeds ablation, glacier advancesSteady: accumulation and ablation are equal, there is no size changeIII. Glacial Erosion and LandformsDepositional LandformsGlaciers are like conveyer belts with sedimentMoraines: glacial deposits (till)Lateral: what a glacier is picking up on valley wallsMedial: when two glaciers meet and the lateral moraines combineEnd: when the glacier terminatesRecessional: deposits made by a receding glacierMechanismsGlacial abrasion: sediment at baseStriations polishReveals flow directionGlacial quarryingPlucking blocks of rocksChattermarks Erosional LandformsCirques: bowl-shaped depressionsArete: ridge between cirquesHorn: series of meeting arêtesU-shaped valleysHanging valleysIV. Ice AgeProlonged period of cold temperaturesHundreds of millions of years apartExtensive glaciationHow do we know?Tillites: glacial depositsCurrent Ice Age: PleistoceneSince 65 million years ago there’s been a gradual cooling ~10*CIA began 2-3 myaGlacial deposits widespreadSea ice near poles Ice sheets grew from polesMountain glaciationIce Ages have occurred 4-5 times in Earth’s historyThey persist for millions of yearsThere is no cyclicityWhat do IAs have in common?Sizable amount of land mass at or near polesLand surfaces with high elevationNearby oceans to provide moistureOcean circulationDriven by plate tectonicsAdditional factorsCO2BioactivityVolcanic activityWeathering of rocksFluctuations within Ice AgesCycles of glacier advance and retreatTerrestrial records: 4-5 episodes in last 0.5 million years- limited by preservation depositsMarine records: 25-30 cycles over 3 million yearsDetermined using isotopes in planktonic shells deposited on seafloorStrong periodicityGlaciations: 60k-100k yearsInterglacials: 10k yearsToo rapid for platesInsolation (solar radiation exposure)Varies with orbital eccentricity, tilt of Earth’s axis, and wobbleV. Consequences of GlaciationSea level changeThree times more ice 15,000 years agoSea level was lower by 80-100mIce-dam break floodsGlacial Lake MissoulaGlacially induced subsidenceIce loading causes lithosphere to


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