Geology Vocab 3

Glaciers

pleistocene

the epoch of the Cenozoic Era during which glaciers covered much of the Northern Hemisphere

alpine glacier

a glacier confined by valley topography

continental glacier

a massive ice sheet covering large areas of a continent

unconfined by topography

cordilleran ice sheet

ice sheet confined to the region west of the Rocky Mountains during the Pleistocene Epoch

esker

a sinuous ridge representing a sediment filled subglacial tunnel

usually associated with continental ice

cirque

a subcircular, steep-walled valley at the “headwaters” of an alpine glacier

milankovitch cycle

combined astronomical variations in Earth’s orbital characteristics thought to result in cooling of climate and glaciation

arete

sharp ridge separating two glacial valleys

horn

conical peak that was glaciated on multiple sides

drift

generic term for glacial sediment of any type

till

unsorted, unstratified sediment deposited directly by glacial ice

outwash

sand and gravel sorted and stratified by glacial meltwater

moraine

sediment (usually till) marking the boundaries of a glacier

includes terminal, medial, lateral, and ground

plucking

form of glacial erosion

freezing of fractured bedrock to base of glacier, subsequent removal and incorporation into base of ice

abrasion

rasping at base of glacier by plucked bedrock fragments

ablation

melting or wasting of global ice

downhill

direction that ice within a glacier always moves

recession/advance

refers to the movement of the terminus of a glacier, independent of direction of ice movement

roche mountonnee

rock drumlin

glacially sculpted bedrock mound

streamlined in direction of ice movement; down-ice side steep, up-ice side gently sloped, polished.

drift drumlin

mound of till deposited by moving ice

streamlined in direction of ice movement

steep on up-ice side

viscosity

measure of the ease with which a substance flows

ice has a high viscosity relative to water

loess

wind-deposited silt

in PNW, loess is derived from glacial deposits

missoula floods

catastrophic outburst flood resulting from the failure of a huge ice dam on Clark’s Fork near Missoula, Montana

touchet beds

graded beds of sand-silt representing as many as 70 floods from Lake Missoula

found in SE Washington