Lecture 9: Glaciers and Glacial Landforms · Glacial Sedimentation Direct deposition by melting ice deposits unsorted material termed moraine Outwash plain contains sorted and bedded

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 LandformsAlpine Landforms

HornHornAreteAreteCirqueCirque

Alpine LandformAlpine Landform

CrevassesCrevasses

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