Glacial Geomorphology How do glaciers and meltwater shape

Glacial Geomorphology • How do glaciers and meltwater shape landforms? • Most processes covered by ice, so glacial terrain exposed by melting http: //upload. wikimedia. org/wikipedia/commons/5/5 c/Perito_Moreno_Gla cier_Patagonia_Argentina_Luca_Galuzzi_2005. JPG

Alpine Glaciers 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 Tongas National Forest, Alaska

Continental Glaciers • Continental 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 bases

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

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 rock • However rocks held firmly in basal ice are often hard enough to cut the underlying bedrock Chattermarks http: //chattermarks. ncascades. org/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. • 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 valleys • Converted to U-shape by plucking of lateral channel walls ("ice-abraded shoulders"). Fast: 10, 000 years • Different lithologies exposed in valley result in paternoster lakes

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

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

Horn Cirques Aircraft Engine Frost Wedging Accumulation Arête Ablation ice-rock plug w/ imbricate thrusting Equilibrium Line Col Accumulation Crevasses Icefall Skipped 381 left - 382 left lateral moraines

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

Glacial or Periglacial Erosion of Finger Lakes

Glacial Erosion – Roche Moutonée

Glacial Erosion – Roche Moutonée Yosemite NP, Calif

Huge Glacial Erratic Glacial Deposits: Drift r d d e i f i t a r st t c a t n co 1. Unsorted and Unstratified Drift: Till dropped Ice from ice melting Stationary & Retreat: End Moraine at Terminus 2. Sorted and Stratified Drift: Outwash 3. Ice-contact stratified drift http: //www. geomorphology. org. uk/pages/education/alevel/coldenvirons/Lesson%2015. htm

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 deposition • Formed close to the ice • Large range of sizes, chaotic sedimentary structures. slump features. faults, till inclusions http: //www. dcnr. state. pa. us/topogeo/photogallery/icecontact. aspx

http: //www. geol. umd. edu/%7 Ejmerck/nature/landscapes/images/outwash 21962. s. jpg Stratified Drift - Outwash fines are source of Loess: fines lift by wind and re-deposited elsewhere • Alluvium deposited by meltwater not in close proximity to melting ice. • Better sorted than ICSD Skipped Prest Classification p 384 -385 right

Landforms of Till: Drumlins • • • Elliptical Hills, blunt on the upglacier side Form under the ice Many theories to explain their origins 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 subglacial ice contact zone. • 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.

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 lake Missoula/Spokane floods -Breaching of moraine dams or floating of ice dams. -Typically cyclic -Massive geomorphic work

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

Next time: New Jersey Glaciation