Post on 03-Feb-2022
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Applied GeomorphologyApplied Geomorphology
Lecture 9: Glaciers and Glacial Lecture 9: Glaciers and Glacial LandformsLandforms
Types of GlaciersTypes of Glaciers
Valley (Alpine): rivers of ice that flow Valley (Alpine): rivers of ice that flow through valleys to lower elevationsthrough valleys to lower elevationsContinental: large ice masses that cover Continental: large ice masses that cover significant portions of continents and are a significant portions of continents and are a mile or more thickmile or more thickCurrently only 2 continental glaciers exist: Currently only 2 continental glaciers exist: the Greenland and Antarctic ice sheetsthe Greenland and Antarctic ice sheets
Alpine GlacierAlpine Glacier
Alpine glaciers often Alpine glaciers often display lateral and display lateral and medial morainesmedial moraines
Lateral moraine
Medial moraine
Continental GlacierContinental Glacier
Thick ice masses actually Thick ice masses actually depress the lithosphere depress the lithosphere below sea levelbelow sea level
Glacial IceGlacial Ice
Accumulates where snowfall in Accumulates where snowfall in winter exceeds melting in winter exceeds melting in summersummerWhen snow is greater than When snow is greater than several meters thick it is several meters thick it is compressed into a more compressed into a more compact form termed firncompact form termed firnWhen the snow/When the snow/firnfirn layer is > layer is > 30m thick the material is 30m thick the material is compacted into pure icecompacted into pure ice
Glacial IceGlacial Ice
Glacial ice will Glacial ice will recrystallizerecrystallize under the pressure of under the pressure of the overlying snow/the overlying snow/firnfirn to form a polygonal to form a polygonal texture (similar to granoblastic metamorphic texture (similar to granoblastic metamorphic rocks)rocks)
Glacial BudgetGlacial Budget
Accumulation zone: the Accumulation zone: the ““rechargerecharge”” area of the glacier area of the glacier marked by fresh snowfallmarked by fresh snowfallAblation zone: zone of melting or sublimation where the Ablation zone: zone of melting or sublimation where the glacier is losing massglacier is losing mass
Glacial MovementGlacial Movement
Plastic flow: under the influence of gravity Plastic flow: under the influence of gravity glacial ice will undergo plastic flow as glacial ice will undergo plastic flow as much as several meters per yearmuch as several meters per yearBasal slip: under sufficient pressure the Basal slip: under sufficient pressure the basal ice in a glacier will melt allowing the basal ice in a glacier will melt allowing the entire glacier to undergo basal slip up to a entire glacier to undergo basal slip up to a kilometer per yearkilometer per year
Basal MeltingBasal Melting
Remember that HRemember that H22O is an unusual O is an unusual compound in that its solid phase is less compound in that its solid phase is less dense than its liquid phasedense than its liquid phase
Temperature
Pressure
1
2
0 100
Gas
Liquid
Solid
Alpine Glacial LandformsAlpine Glacial Landforms
UU--shaped valleys are very characteristic of shaped valleys are very characteristic of alpine glaciationalpine glaciation
Alpine GlaciationAlpine Glaciation
After glacier has retreated several After glacier has retreated several distinctive landforms are left:distinctive landforms are left:
AreteAreteSeratedSerated ridgeridgeCirqueCirqueHornHornWaterfallWaterfall
Glacial SedimentationGlacial Sedimentation
Direct deposition by melting ice deposits Direct deposition by melting ice deposits unsorted material termed moraineunsorted material termed moraineOutwash plain contains sorted and bedded Outwash plain contains sorted and bedded alluvial fans but the material is extremely alluvial fans but the material is extremely immature (angular, many immature (angular, many lithiclithic and and feldspar grains)feldspar grains)Lake sediments termed glacial Lake sediments termed glacial varvesvarves form form in numerous lakes in outwash plainin numerous lakes in outwash plain
Glacial Glacial SedimentsSediments
Glaciers Glaciers have an have an unlimited unlimited carrying carrying capacitycapacity
Continental GlaciationContinental Glaciation
Landforms are Landforms are produced by the produced by the motion of a thick ice motion of a thick ice sheetsheet
DrumlinsDrumlinsEskersEskersKettle LakesKettle LakesVarvesVarvesTillTill
Continental Glaciation Landform Continental Glaciation Landform FeaturesFeatures
Polished and striated Polished and striated bedrockbedrockRoche Roche moutoneemoutonee
Ice ShelvesIce Shelves
Large portions of Large portions of continental glaciers continental glaciers that are floating in that are floating in the oceansthe oceans
IsostasyIsostasy
Floating ice is Floating ice is buoyed up by a buoyed up by a force equal to the force equal to the weight of the weight of the displaced fluiddisplaced fluid
Pleistocene GlaciationPleistocene Glaciation
Wisconsin glacial Wisconsin glacial maximum: 18,000 maximum: 18,000 years agoyears ago
Astronomical EffectsAstronomical Effects
EarthEarth’’s Elliptical orbits Elliptical orbitEarthEarth’’s s ““eccentricityeccentricity””: the variation of apogee : the variation of apogee positionpositionThe above combine to give an approximate The above combine to give an approximate 25,000 year cycle of glaciation favorable 25,000 year cycle of glaciation favorable conditionsconditionsRemember that a continent must still be at a Remember that a continent must still be at a high latitude before continental glaciation is high latitude before continental glaciation is possiblepossible