Upload
nuru
View
467
Download
0
Embed Size (px)
DESCRIPTION
Glacial Processes and Landforms. Glacial Processes and Landforms. Glaciers’ ability to erode soil and rock, transport sediment, and deposit sediment influenced more than 50 million square kilometers of land surface geomorphically during the last glacial period. Rivers of Ice. Figure 17.1. - PowerPoint PPT Presentation
Citation preview
Glacial Processes and Glacial Processes and LandformsLandforms
Glacial Processes and Glacial Processes and LandformsLandforms
Glaciers’ ability to erode soil and rock, Glaciers’ ability to erode soil and rock, transport sediment, and deposit sediment transport sediment, and deposit sediment influenced more than 50 million square influenced more than 50 million square kilometers of land surface geomorphically kilometers of land surface geomorphically during the last glacial periodduring the last glacial period
Rivers of IceRivers of Ice
Figure 17.1
VatnajVatnajöökull kull Ice CapIce Cap
Figure 17.5
Patagonian Ice FieldPatagonian Ice Field
Figure 17.5
Greenland’s East CoastGreenland’s East Coast
Figure 17.6
Glacial Processes:Glacial Processes:Growth of GlaciersGrowth of Glaciers
Formation of Glacial IceFormation of Glacial Ice Begins as Begins as snowsnow (density = 50 to 300 kg/m3)(density = 50 to 300 kg/m3)
that can then be modified to icethat can then be modified to ice Neve Neve – snow that has been reduced via partial – snow that has been reduced via partial
meltingmelting and and sublimationsublimation (ablation; (ablation; density = density = >500 kg/m3>500 kg/m3))
FirnFirn – Neve that survives seasonal ablation; – Neve that survives seasonal ablation; may be compacted under later accumulations may be compacted under later accumulations into glacial ice – may take decades or centuriesinto glacial ice – may take decades or centuries
Glacial ice Glacial ice (density = +/- 850 kg/m3)(density = +/- 850 kg/m3) Density of fresh water is +/- 1000 kg/m3Density of fresh water is +/- 1000 kg/m3
Glacier MovementGlacier Movement Not a glacier until it movesNot a glacier until it moves
When snow and ice > +/-20m When snow and ice > +/-20m thickness, ice mass too heavy to thickness, ice mass too heavy to keep rigid shapekeep rigid shape
Begins to flow via plastic deformationBegins to flow via plastic deformation
Glacier Flow RatesGlacier Flow Rates Movement not uniformMovement not uniform
Center and top portions move fasterCenter and top portions move faster
Sides and bottom move slower due Sides and bottom move slower due to frictional drag against valley floor to frictional drag against valley floor and walls.and walls.
Glacier FlowGlacier FlowOverhead view of an alpine valley glacier
showing the relative speed of ice movement
Physical Geography.net
Glacier FlowGlacier Flow
Physical Geography.net
Long cross-section view of an alpine valley glaciershowing the relative speed of ice movement
Glacier FlowGlacier Flow Accumulation in broad, erosional basinAccumulation in broad, erosional basin
Constricted down valley by convergence of Constricted down valley by convergence of narrowing – ice flow compression in narrowing – ice flow compression in central section of the glaciercentral section of the glacier
Flow lines spread out at terminus as ice is Flow lines spread out at terminus as ice is no longer constricted by valley walls. no longer constricted by valley walls. Snout/LobeSnout/Lobe - - swollen tongue of ice at terminus swollen tongue of ice at terminus
due to rapid advancedue to rapid advance
Terminus of Alpine Terminus of Alpine Glaciation Glaciation
Snout/LobeSnout/Lobe - - swollen tongue of ice at swollen tongue of ice at terminus due to rapid advanceterminus due to rapid advance
Merged glaciersMerged glaciers – two or more – can – two or more – can be quite largebe quite large
Glacier FlowGlacier Flow
Physical Geography.net
Typical flow pattern in alpine glacier
Temperate vs.Temperate vs.Cold Climate GlaciersCold Climate Glaciers
Temperate GlaciersTemperate Glaciers Pressure meltingPressure melting may occur despite sub- may occur despite sub-
freezing T’sfreezing T’s May lead to May lead to basal sliding basal sliding May lead to liquified soils beneath glacier May lead to liquified soils beneath glacier Reduced friction = easier, faster Reduced friction = easier, faster
movement (typ. <1m/day but may surge movement (typ. <1m/day but may surge 50 m/day)50 m/day)
Temperate vs.Temperate vs.Cold Climate GlaciersCold Climate Glaciers
Cold Climate GlaciersCold Climate Glaciers
move very slowly - no basal sliding move very slowly - no basal sliding
Movement mainly due to internal Movement mainly due to internal slippage of the ice over the ground slippage of the ice over the ground
Glacier Mass BalanceGlacier Mass BalanceTwo main components:Two main components: AccumulationAccumulation of snow vs. of snow vs. ablationablation of ice of ice
The The Zone of AccumulationZone of Accumulation - upper reaches of - upper reaches of glacierglacier
yearly yearly additionsadditions of snow exceed losses of snow exceed losses (from melting, evaporation, and sublimation)(from melting, evaporation, and sublimation)
Glacier surface covered by snow throughout Glacier surface covered by snow throughout the year in this zone. the year in this zone.
Glacier Mass BalanceGlacier Mass BalanceTwo main components: Two main components: AccumulationAccumulation vs. vs. ablationablation
The The Zone of AblationZone of Ablation - below the zone of - below the zone of accumulationaccumulation
losses of snow and ice from melting, evaporation, losses of snow and ice from melting, evaporation, and sublimation are greater than the additionsand sublimation are greater than the additions
Firn Limit/snow lineFirn Limit/snow line separates these two separates these two zoneszones
Glacier Mass BalanceGlacier Mass Balance
Lag time possible (up to decades) between Lag time possible (up to decades) between accumulation surplus and actual glacial advanceaccumulation surplus and actual glacial advance
Physical Geography.net
Glacier Mass BalanceGlacier Mass Balance
Figure 17.7
Glacier Mass BalanceGlacier Mass Balance
Can experience rapid forward Can experience rapid forward surge (10 (10 to 20 m/day - greater with basal sliding) to 20 m/day - greater with basal sliding) – related to past large snow inputs.– related to past large snow inputs.
Lag time possible (up to decades) Lag time possible (up to decades) between accumulation surplus and between accumulation surplus and actual glacial advanceactual glacial advance
Glacial Ice LossGlacial Ice Loss Due to two processes:Due to two processes:
AblationAblation MeltingMelting EvaporationEvaporation SublimationSublimation
CalvingCalving Occurs when glacier terminus reaches Occurs when glacier terminus reaches
large body of water.large body of water. Portions of the glacier ice break off into Portions of the glacier ice break off into
the water body.the water body. Origin of many icebergs - calving of the Origin of many icebergs - calving of the
Greenland and Antarctic ice Greenland and Antarctic ice sheets/glaciers. sheets/glaciers.
Glacial Ice LossGlacial Ice Loss Gangotri glacier - HimalayasGangotri glacier - Himalayas
Physical Geography.net
Glacial Ice LossGlacial Ice Loss Most glaciers had advanced significantly from the Most glaciers had advanced significantly from the
Middle Ages until around the year 1800, when Middle Ages until around the year 1800, when global temperatures were cooler than present and global temperatures were cooler than present and the northern continents experienced the the northern continents experienced the Little Ice Little Ice Age.Age.
Most glaciers are in retreat due to global warming Most glaciers are in retreat due to global warming of last 1-2 centuries as earth recovered from the of last 1-2 centuries as earth recovered from the Little Ice Age.Little Ice Age.
Mass balances of these glaciers are negative Mass balances of these glaciers are negative because of less snow accumulation or higher because of less snow accumulation or higher ablationablation
Glacial Erosional Glacial Erosional ProcessesProcesses
Two major Two major erosional processes occur processes occur at the base of a glacier:at the base of a glacier:
ScouringScouring
PluckingPlucking
ScouringScouring Rock and sediment, incorporated into Rock and sediment, incorporated into
the moving glacial ice by partial the moving glacial ice by partial melting and refreezing, erodes the melting and refreezing, erodes the bedrock by abrasion.bedrock by abrasion.
Scouring creates a variety of featuresScouring creates a variety of features StriationsStriations Glacial polishGlacial polish Glacial flour/rock flourGlacial flour/rock flour Glacial milkGlacial milk
PluckingPlucking Plucking - Plucking - particle detachment by particle detachment by
moving glacial ice:moving glacial ice: basal ice freezes in rock surface cracks;basal ice freezes in rock surface cracks;
ice pulled and plucked out, detaching rock/soil;ice pulled and plucked out, detaching rock/soil;
greatest on the lee-side (down flow side) of rock greatest on the lee-side (down flow side) of rock mounds, called mounds, called Roche moutonneeRoche moutonnee – longitudinal – longitudinal asymmetry due to asymmetry due to abrasionabrasion on stoss side, on stoss side, pluckingplucking on lee side; on lee side;
Ice extends and spreads apart as it flows over Ice extends and spreads apart as it flows over rock mounds, causing rock mounds, causing crevassescrevasses. .
Glacial Erosional Glacial Erosional ProcessesProcesses
http://www.nature.nps.gov/geology/education/education_graphics.cfm
abrasion
Glacial PolishGlacial Polish
Figure 17.9
Glacial MovementGlacial Movementand Crevassesand Crevasses
Figure 17.8
CrevassesCrevasses
Figure 17.8
CrevassesCrevasses
Figure 17.8
CrevassesCrevasses
CrevassesCrevasses
Glacial LandformsGlacial LandformsTwo types:Two types:
Erosional Erosional
DepositionalDepositional
Erosional Alpine Erosional Alpine LandformsLandforms Merging Glaciers Merging Glaciers – can be quite large– can be quite large
Erosional Alpine Erosional Alpine LandformsLandforms
Erosion exerted on bottoms and sides of alpine valleys - Erosion exerted on bottoms and sides of alpine valleys - guide the flow of glaciersguide the flow of glaciers
TalusTalus – ang. debris-freeze-thaw shattering of bedrock – ang. debris-freeze-thaw shattering of bedrock Talus SlopesTalus Slopes accumulate along valley walls/on glacier accumulate along valley walls/on glacier Bottom and sides of glaciated valley widen and Bottom and sides of glaciated valley widen and
deepen over timedeepen over time Cross-sectional shape changes over time (U-shaped)Cross-sectional shape changes over time (U-shaped) Hanging valleysHanging valleys - small adjoining feeder valleys enter - small adjoining feeder valleys enter
a large valley at some elevation above trunk valley a large valley at some elevation above trunk valley floorfloor May be due to greater erosion by larger, trunk glacierMay be due to greater erosion by larger, trunk glacier May be due to more ice having passed through trunk valleyMay be due to more ice having passed through trunk valley May have spectacular waterfallsMay have spectacular waterfalls
Cliff Caudle, P.G.Environmental Specialist 4
Talus SlopeTalus Slope
Hanging Hanging ValleysValleys
At left: Milford Sound, At left: Milford Sound, South Island, New ZealandSouth Island, New Zealand
Above: Bird Woman Falls, Above: Bird Woman Falls, Glacier National ParkGlacier National Park
Alpine Glacial LandscapeAlpine Glacial Landscape
Figure 17.10
Postglacial LandscapePostglacial Landscape
Figure 17.10
Alpine Erosional FeaturesAlpine Erosional Features
Figure 17.11
Norwegian FjordNorwegian Fjord
Figure 17.12
Glacial DepositionGlacial Deposition
Two major Two major erosional processes add processes add sediment to a glacier:sediment to a glacier:
Abrasion and PluckingAbrasion and Plucking
Mass WastingMass Wasting
Glacial Depositional Glacial Depositional LandformsLandforms
Glacial drift Glacial drift - All glacial deposits including till and outwash - All glacial deposits including till and outwash
TillTill- Heterogeneous, unstratified- Heterogeneous, unstratified- boulders to clay-size- boulders to clay-size
MorainesMorainesDepositional landforms composed of tillDepositional landforms composed of till- End- End- Lateral- Lateral- Medial- Medial
Glacial Depositional Glacial Depositional LandformsLandforms
End MorainesEnd MorainesTerminal moraine Terminal moraine - farthest advance of a - farthest advance of a glacier.glacier.Recessional moraineRecessional moraine – mark halts in – mark halts in retreat of glacierretreat of glacier
Alpine GlacialAlpine GlacialDepositional LandformsDepositional Landforms
End Moraines/terminal morainesEnd Moraines/terminal moraines
Alpine Depositional Alpine Depositional FeaturesFeatures
Figure 17.13
End End MorainesMoraines
End Moraines off End Moraines off the end of Sperry the end of Sperry Glacier, Glacier Glacier, Glacier National ParkNational Park
Alpine GlacialAlpine GlacialDepositional LandformsDepositional Landforms
MorainesMorainesLateral moraineLateral moraine – narrow belt of debris from – narrow belt of debris from
valley side slopes valley side slopes Medial moraine Medial moraine – merging of two lateral – merging of two lateral
morainesmoraines
Alpine GlacialAlpine GlacialDepositional LandformsDepositional Landforms
Lateral and Medial MorainesLateral and Medial Moraines
Glacial Depositional Glacial Depositional LandformsLandforms
Till plainTill plain - large, relatively flat plain of till that forms - large, relatively flat plain of till that forms when detached ice sheet melts in place when detached ice sheet melts in place
ErraticsErratics - Sometimes the sediments in a till plain - Sometimes the sediments in a till plain can contain large boulders. If these boulders are can contain large boulders. If these boulders are transported a great distance from their place of transported a great distance from their place of origin, they are called erraticsorigin, they are called erratics
DrumlinsDrumlins - large, ovoid hills of till shaped by the re- - large, ovoid hills of till shaped by the re-advance of a glacier over previously deposited advance of a glacier over previously deposited ground moraine.ground moraine.
Continental Glaciation Continental Glaciation Erosional LandformsErosional Landforms
-Widespread -Widespread abrasion and gougingabrasion and gouging-Widespread glacial polish and striations-Widespread glacial polish and striations-Huge U-shaped valleys from previously -Huge U-shaped valleys from previously
V-shaped stream valleysV-shaped stream valleys-Large basins scooped out, many with -Large basins scooped out, many with
large lakes in them today (i.e., Great large lakes in them today (i.e., Great Lakes) Lakes)
Glacial ErosionGlacial Erosion
http://www.nature.nps.gov/geology/education/education_graphics.cfm
Glacial FlowGlacial Flow WhalebackWhaleback
Glacial PolishGlacial Polish
Figure 17.9
Continental Glacial Continental Glacial Depositional LandformsDepositional Landforms
Till plainTill plain - large, relatively flat plain of till that - large, relatively flat plain of till that forms when detached ice sheet melts in place forms when detached ice sheet melts in place
ErraticsErratics - Sometimes the sediments in a till plain - Sometimes the sediments in a till plain can contain large boulders. If these boulders are can contain large boulders. If these boulders are transported a great distance from their place of transported a great distance from their place of origin, they are called erraticsorigin, they are called erratics
DrumlinsDrumlins - large, ovoid hills of till shaped by the - large, ovoid hills of till shaped by the re-advance of a glacier over previously re-advance of a glacier over previously deposited ground moraine.deposited ground moraine.
Continental Continental Glacier Glacier Depositional Depositional
FeaturesFeatures
Figure 17.15
Till Till PlainsPlains
Left: Northwest Territories, Lac Left: Northwest Territories, Lac de Gras, Canada – Geological de Gras, Canada – Geological Survey of Canada. Note Survey of Canada. Note Erratics.Erratics.
Above: Till Plain, Region Above: Till Plain, Region Unknown, from University of Unknown, from University of California – Santa Barbara California – Santa Barbara Photo Collection. Note Braided Photo Collection. Note Braided Meltwater Channels.Meltwater Channels.
http://www.nature.nps.gov/geology/education/education_graphics.cfm
Drumlin SwarmDrumlin Swarm
Figure 17.17
Glacial Depositional Glacial Depositional LandformsLandforms
DrumlinsDrumlins
Glacial Depositional Glacial Depositional LandformsLandforms
ErraticsErratics
Glacial Depositional Glacial Depositional LandformsLandforms
Glacial driftGlacial driftAll sediments that are carried and deposited by All sediments that are carried and deposited by
glaciersglaciers
Most debris added to a glacier arrives at the snout Most debris added to a glacier arrives at the snout either through either through - continual forward flow of glacial ice, deposited - continual forward flow of glacial ice, deposited as till, oras till, or
- through - through meltwatermeltwater, as , as glaciofluvial depositsglaciofluvial deposits. .
Glacial Depositional Glacial Depositional LandformsLandforms
Glaciofluvial depositsGlaciofluvial deposits - stratified and less well sorted.- stratified and less well sorted.
Outwash depositsOutwash deposits- deposited where there are a great - deposited where there are a great number of meltwater streams number of meltwater streams depositing material ahead of the glacier. depositing material ahead of the glacier.
Glacial Depositional Glacial Depositional LandformsLandforms
Glaciofluvial LandformsGlaciofluvial LandformsKameKame - conical-shaped pile of sand - conical-shaped pile of sand and gravel formed where sediment-and gravel formed where sediment-rich water flows into a crevasse or rich water flows into a crevasse or depression in the icedepression in the ice EskerEsker – sand and gravel deposited – sand and gravel deposited by meltwater flowing under glacierby meltwater flowing under glacierKettles Kettles - -
Glacial Depositional Glacial Depositional LandformsLandforms
Glaciofluvial deposits/Outwash depositsGlaciofluvial deposits/Outwash deposits
Glacial Depositional Glacial Depositional LandformsLandforms
Glaciofluvial Landforms: KameGlaciofluvial Landforms: Kame
Glacial Depositional Glacial Depositional LandformsLandforms
Glaciofluvial Landforms: EskerGlaciofluvial Landforms: Esker
Glacial Depositional Glacial Depositional LandformsLandforms
Glaciofluvial Landforms: KettlesGlaciofluvial Landforms: Kettles