Glacial 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 melting glacial terrain exposed by melting cier_Patagonia_Argentina_Luca_Galuzzi_2005.JPG

Alpine Glaciers Tongas National Forest, Alaska Valley glaciers get most of sediment loads from mass wasting and intense weathering of adjacent slopes Rock debris of lateral and medial moraines stays high up

Continental Glaciers Continental ice sheets cannot gain much sediment from mass wasting - little is exposedContinental ice sheets cannot gain much sediment from mass wasting - little is exposed Polar ice sheets are mostly devoid of sediment except windblown dust from lower latitudes, except near their basesPolar ice sheets are mostly devoid of sediment except windblown dust from lower latitudes, except near their bases

Processes and Bedforms Glaciers have no competence limit - all grain sizes "from clay to giant boulders" are carried regardless of flow rateGlaciers have no competence limit - all grain sizes "from clay to giant boulders" are carried regardless of flow rate Huge Glacial Erratic End Moraine

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

Crushing and Fracture The weight of kilometers of ice is insufficient to crush most rockThe weight of kilometers of ice is insufficient to crush most rock However rocks held firmly in basal ice are often hard enough to cut the underlying bedrockHowever rocks held firmly in basal ice are often hard enough to cut the underlying bedrock Chattermarks

Plucking 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 Glaciers Water flowing in subglacial channels can erode the bedrock or sediment beneath the ice.Water flowing in subglacial channels can erode the bedrock or sediment beneath the ice. Erosion of subglacial sediment …is claimed to be the source of almost all of the outwash ….Erosion of subglacial sediment …is claimed to be the source of almost all of the outwash ….

Erosional and Residual Landforms Glacial troughs in former stream valleysGlacial troughs in former stream valleys Converted to U-shape by plucking of lateral channel walls ("ice-abraded shoulders"). Fast: 10,000 yearsConverted to U-shape by plucking of lateral channel walls ("ice-abraded shoulders"). Fast: 10,000 years Different lithologies exposed in valley result in paternoster lakesDifferent lithologies exposed in valley result in paternoster lakes

A rock sill and/or end moraine blocks lower end of troughA rock sill and/or end moraine blocks lower end of trough Trough (Proglacial) Lakes

Hanging Troughs (Hanging Valleys) Another type of waterfall

U-Shaped Valley in Tracy Wilderness, Southeastern Alaska

Seawater Flooded U-Shaped Valleys: Fiords =Fjords When glaciers melt, sea-level rises

Cirques Frost Wedging Accumulation Ablation ice-rock plug w/ imbricate thrusting w/ imbricate thrusting Equilibrium Line Crevasses Arête Accumulation lateral moraines ColHorn Aircraft Engine Skipped 381 left left Icefall

Tarn

Icefalls and Ogives Ogives - Arcuate bands or waves, with their apices pointing down-glacier, that develop in an icefall. Alternating light and dark bands are called band ogives. Each pair of bands, or one wave and trough, is believed to represent a year’s movement through the icefall.Ogives - Arcuate bands or waves, with their apices pointing down-glacier, that develop in an icefall. Alternating light and dark bands are called band ogives. Each pair of bands, or one wave and trough, is believed to represent a year’s movement through the icefall. Ogives on Svinafellsjökull, southern Iceland. Photo J. Alean, 2001.

Glacial or Periglacial Erosion of Finger Lakes

Glacial Erosion – Roche Moutonée

Yosemite NP, Calif

Stationary & Retreat: End Moraine at Terminus Glacial Deposits: Drift 1. Unsorted and Unstratified Drift: Till dropped from ice melting Huge Glacial Erratic 2. Sorted and Stratified Drift: Outwash 3. Ice-contact stratified drift Ice-contact stratified drift

Till – dropped by melting ice unsorted unstratified Boulders to fine silts

Ice Contact Stratified Drift - ICSD Ice-contact stratified drift - drift modified by meltwater during or after depositionIce-contact stratified drift - drift modified by meltwater during or after deposition Formed close to the iceFormed close to the ice Large range of sizes, chaotic sedimentary structures. slump features. faults, till inclusionsLarge range of sizes, chaotic sedimentary structures. slump features. faults, till inclusions

Stratified Drift - Outwash Alluvium deposited by meltwater not in close proximity to melting ice.Alluvium deposited by meltwater not in close proximity to melting ice. Better sorted than ICSDBetter sorted than ICSD Skipped Prest Classification p right Outwash fines are source of Loess: fines lift by wind and re-deposited elsewhere

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

An Origin of Drumlins Theory Glacier retreats, leaving behind a terminal moraine. Later it advances again, and meltwater reshapes the moraine into a drumlin.

Landforms of ICSD: Kames and Kettles Commonly found together in the sub- glacial ice contact zone.Commonly found together in the sub- glacial ice contact zone. Kettles are lakes form in ablation zone when isolated chunks of melting ice are buried in glacial drift deposited from meltwater.Kettles are lakes form in ablation zone when isolated chunks of melting ice are buried in glacial drift deposited from meltwater. A stratification of the drift forms a Kame; during higher melting, larger particles are suspended and deposited near the ice; at lower discharge, more fines are deposited.A stratification of the drift forms a Kame; during higher melting, larger particles are suspended and deposited near the ice; at lower discharge, more fines are deposited..

Moulin Kames Moulin Kame

Moulin Kames

Kame Terrace Interaction between valley wall and glacier wall. Example: Blackfoot River Valley Kame terrace

Melted Ice sheet yields “ground moraine” Kame and kettle topography

Landforms of ICSD-Eskers Deposits in subglacial ice tunnels

Outwash: Clark Fork of the Yellowstone

Isostacy

Lowered Sea-level - Landbridge

Outburst Floods (Jökulhlaup) Sudden drainage of a glacial lakeSudden drainage of a glacial lake -Breaching of moraine dams or floating of ice dams. -Typically cyclic -Massive geomorphic work Missoula/Spokane floods

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

Pluvial Lakes - excess rain near continental glaciers Closed basins –Bonneville –Lahontan

Lake Bonneville Salt Flats

Proglacial Lakes Proglacial Lake at Sheridan Glacier, near Cordova, Alaska Lakes dammed by moraine or ridge in front of melting glacier

Next time: New Jersey Glaciation