Glacial Geomorphology How do glaciers and meltwater shape landforms?How do glaciers and meltwater...

Glacial GeomorphologyGlacial Geomorphology

• How do glaciers and meltwater shape landforms?How do glaciers and meltwater shape landforms?• Most processes covered by ice, soMost processes covered by ice, so

glacial terrain exposed by meltingglacial terrain exposed by melting

http://upload.wikimedia.org/wikipedia/commons/5/5c/Perito_Moreno_Glacier_Patagonia_Argentina_Luca_Galuzzi_2005.JPG

Alpine GlaciersAlpine Glaciers

Tongas National Forest, Alaska

Valley glaciers get most of sediment loads fromValley glaciers get most of sediment loads frommass wasting and intense weathering of adjacent slopesmass wasting and intense weathering of adjacent slopesRock debris of lateral and medial moraines stays high upRock debris of lateral and medial moraines stays high up

Continental GlaciersContinental Glaciers

• Continental ice sheets cannot gain much sediment from mass wasting - Continental ice sheets cannot gain much sediment from mass wasting - little is exposedlittle is exposed

• Polar ice sheets are mostly devoid of sediment except windblown dust Polar ice sheets are mostly devoid of sediment except windblown dust fromfrom lower latitudes, lower latitudes, exceptexcept near their bases near their bases

Processes and BedformsProcesses and Bedforms

• Glaciers have no competence limit - all Glaciers have no competence limit - all grain sizes "from clay to giant boulders" grain sizes "from clay to giant boulders" are carried regardless of flow rateare carried regardless of flow rate

Huge Glacial ErraticHuge Glacial Erratic

End Moraine

Glaciotectonism

Ice pushed ridges of [wet sediment] become stacked as imbricate thrust sheets

Crushing and FractureCrushing and Fracture

• The weight of kilometers of ice is The weight of kilometers of ice is insufficient to crush most rockinsufficient to crush most rock

• However rocks held firmly in basal ice are However rocks held firmly in basal ice are often hard enough to cut the underlying often hard enough to cut the underlying bedrockbedrock

http://chattermarks.ncascades.org/chattermarks/

Chattermarks

Plucking and AbrasionPlucking and Abrasion

• Lee-side rock fragments get incorporated into regelation ice and are carried away. They become sharp tools that can abrade the upglacier (stoss Gr. "push") side

The tools concentrate the force of the glacier's weight on a small area

Fluvial Erosion Beneath GlaciersFluvial Erosion Beneath Glaciers

• Water flowing in subglacial channels can Water flowing in subglacial channels can erode the bedrock or sediment beneath erode the bedrock or sediment beneath the ice.the ice.

• Erosion of subglacial sediment …is Erosion of subglacial sediment …is claimed to be the source of almost all of claimed to be the source of almost all of the outwash ….the outwash ….

Erosional and Residual LandformsErosional and Residual Landforms

• Glacial troughs in former stream valleysGlacial troughs in former stream valleys

• Converted to U-shape by plucking of Converted to U-shape by plucking of lateral channel walls ("ice-abraded lateral channel walls ("ice-abraded shoulders"). Fast: 10,000 yearsshoulders"). Fast: 10,000 years

• Different lithologies exposed in valley Different lithologies exposed in valley result in paternoster lakesresult in paternoster lakes

• A rock sill and/or end moraine blocks lower A rock sill and/or end moraine blocks lower end of troughend of trough

Trough (Proglacial) LakesTrough (Proglacial) Lakes

Hanging Troughs (Hanging Valleys)Hanging Troughs (Hanging Valleys)

Another type of waterfallAnother type of waterfall

U-ShapedU-Shaped Valley in Tracy Wilderness, Southeastern AlaskaValley in Tracy Wilderness, Southeastern Alaska

Seawater Flooded U-ShapedSeawater Flooded U-Shaped Valleys: Fiords =FjordsValleys: Fiords =Fjords

When glaciers melt, sea-level risesWhen glaciers melt, sea-level rises

CirquesCirquesFrost WedgingFrost Wedging

AccumulationAccumulation

AblationAblation

ice-rock plugice-rock plug w/ imbricate thrustingw/ imbricate thrusting

Equilibrium LineEquilibrium Line

CrevassesCrevasses

ArêteArête

AccumulationAccumulation

lateral moraineslateral moraines

ColCol

HornHorn

Aircraft EngineAircraft Engine

Skipped 381 left - 382 left

IcefallIcefall

TarnTarn

Icefalls and OgivesIcefalls and Ogives

• Ogives - Ogives - Arcuate bands or waves, with Arcuate bands or waves, with their apices pointing down-glacier, that their apices pointing down-glacier, that develop in an icefall. Alternating light and develop in an icefall. Alternating light and dark bands are called band ogives. Each dark bands are called band ogives. Each pair of bands, or one wave and trough, is pair of bands, or one wave and trough, is believed to represent a year’s movement believed to represent a year’s movement through the icefall. through the icefall.

Ogives on Svinafellsjökull, southern Iceland. Photo J. Alean, 2001.

Glacial or Periglacial Erosion of Finger LakesGlacial or Periglacial Erosion of Finger Lakes

Glacial Erosion – Roche MoutonéeGlacial Erosion – Roche Moutonée

Glacial Erosion – Roche MoutonéeGlacial Erosion – Roche Moutonée

Yosemite NP, Calif

Stationary & Retreat: End Moraine at TerminusStationary & Retreat: End Moraine at Terminus

Glacial Deposits: DriftGlacial Deposits: Drift

1. Unsorted and Unstratified Drift: 1. Unsorted and Unstratified Drift: TillTill dropped from ice melting dropped from ice melting

Huge Glacial Erratic

2. Sorted and Stratified Drift: 2. Sorted and Stratified Drift: OutwashOutwash

3. Ice-contact stratified drift3. Ice-contact stratified drift

http://www.geomorphology.org.uk/pages/education/alevel/coldenvirons/Lesson%2015.htm

Ice-co

ntact str

atified drift

Ice-co

ntact str

atified drift

Till – dropped by melting ice unsorted unstratifiedTill – dropped by melting ice unsorted unstratifiedBoulders to fine siltsBoulders to fine silts

Ice Contact Stratified Drift - Ice Contact Stratified Drift - ICSDICSD

• Ice-contact stratified drift - drift modified by Ice-contact stratified drift - drift modified by meltwater during or after depositionmeltwater during or after deposition

• Formed close to the iceFormed close to the ice

• Large range of sizes, chaotic sedimentary Large range of sizes, chaotic sedimentary structures. slump features. faults, till structures. slump features. faults, till inclusionsinclusions

http://www.dcnr.state.pa.us/topogeo/photogallery/icecontact.aspx

Stratified Drift - OutwashStratified Drift - Outwash

• Alluvium deposited by meltwater not in Alluvium deposited by meltwater not in close proximity to melting ice.close proximity to melting ice.

• Better sorted than ICSDBetter sorted than ICSD

Skipped Prest Classification p384-385 right

http://www.geol.umd.edu/%7Ejmerck/nature/landscapes/images/outwash21962.s.jpg

Outwash fines are source of Loess: fines lift by wind and re-deposited elsewhere

Landforms of Till: DrumlinsLandforms of Till: Drumlins

• Elliptical Hills, blunt on the upglacier sideElliptical Hills, blunt on the upglacier side

• Form under the iceForm under the ice

• Many theories to explain their originsMany theories to explain their origins

e.g. former drift moved by glacial return: e.g. former drift moved by glacial return: shaped by subglacial meltwater floodsshaped by subglacial meltwater floods

An Origin of Drumlins TheoryAn Origin of Drumlins Theory

Glacier retreats, leaving behinda terminal moraine. Later it

advances again, and meltwater reshapes the moraine into a

drumlin.

Landforms of ICSD: Kames and KettlesLandforms of ICSD: Kames and Kettles• Commonly found together in the sub-glacial ice Commonly found together in the sub-glacial ice

contact zone.contact zone.

• Kettles are lakes form in ablation zone when Kettles are lakes form in ablation zone when isolated chunks of melting ice are buried in isolated chunks of melting ice are buried in glacial drift deposited from meltwater.glacial drift deposited from meltwater.

• A stratification of the drift forms a Kame; during A stratification of the drift forms a Kame; during higher melting, larger particles are suspended higher melting, larger particles are suspended and deposited near the ice; at lower discharge, and deposited near the ice; at lower discharge, more fines are deposited. more fines are deposited.

• .

Moulin KamesMoulin Kames

Moulin Kame

Moulin KamesMoulin Kames

Kame TerraceKame Terrace

• Interaction between valley wall and glacier wall.

• Example: Blackfoot River Valley

Kame terrace

Melted Ice sheet yieldsMelted Ice sheet yields“ground moraine”“ground moraine”

Kame and kettle topography

Landforms of ICSD-EskersLandforms of ICSD-Eskers

• Deposits in subglacial ice tunnels

Outwash: Clark Fork of the YellowstoneOutwash: Clark Fork of the Yellowstone

IsostacyIsostacy

Lowered Sea-level - LandbridgeLowered Sea-level - Landbridge

Outburst Floods (JOutburst Floods (Jöökulhlaup)kulhlaup)

• Sudden drainage Sudden drainage of a glacial lakeof a glacial lake-Breaching of moraine -Breaching of moraine dams or floating of ice dams or floating of ice dams.dams.

-Typically cyclic-Typically cyclic

-Massive geomorphic -Massive geomorphic workwork

Missoula/Spokane floodsMissoula/Spokane floods

We studied these giant ripples earlier in our consideration of Froude numbers

Pluvial Lakes - Pluvial Lakes - excess rain near excess rain near

continental glacierscontinental glaciers• Closed basins

– Bonneville– Lahontan

Lake Bonneville Salt FlatsLake Bonneville Salt Flats

Proglacial LakesProglacial Lakes

Proglacial Lake at Sheridan Glacier, near Cordova, Alaska

Lakes dammed by moraine or ridge in front of melting glacier

Next time: New Jersey GlaciationNext time: New Jersey Glaciation