ES Ch 7 Glaciers, Deserts, & Wind

ice age

period of time when much of Earth's land is covered in glaciers

glacier

thick ice mass that moves slowly over the land surface

snowline

lowest elevation in particular area that remains covered in snow all year

valley glacier

ice masses that slowly advance down valleys that were originally occupied by streams

ice sheets

enormous ice masses that flow in all directions from one or more centers & cover everything but the highest land

plastic flow

under high pressure, normally brittle ice begins to change shape causing it to flow

basal slip

liquid water & mud at bottom of glacier reduce friction between glacier & ground, causing entire ice mass to slip & slide downhill

zone of fracture

brittle layer that rides on flowing ice below

crevasses

gaping cracks in the brittle surface ice of a glacier

zone of accumulation

glaciers gain when snow accumulates & becomes ice at head of glacier

zone of wastage

area of glacier below snowline where it loses mass of ice as snow melts

calving

when large pieces of ice break off at foot of glacier

iceberg

pieces of ice that break off into the ocean

plucking

occurs when rocks & sediment from bedrock become embedded in ice as glacier flows past them

abrasion

occurs as glacial ice & its load of rock slide over bedrock

glacial trough

U shaped valley created by glacier

hanging valley

higher valleys off the main trough produced by smaller side glaciers

cirque

bowl-shaped depression at head of glacial valley that is surrounded on three sides by steep rock walls

arete

snaking, sharp-edged ridges

horns

sharp pyramid-like peaks

till

material deposited directly by glacier as it melts & drops load of debris

stratified drift

rock debris laid down by glacial meltwater

erratics

rocks transported by glacier & which differ from underlying bedrock

moraine

layers or ridges of till left when glacier melt

lateral moraine

ridges that form along sides of glacial valleys from rock fragments that fall from valley walls along edge of glacier

medial moraine

formed when two valley glaciers join to form single ice stream

end moraine

ridge formed by deposits of debris when ice melts at the end of glacier

ground moraine

form when glaciers begin to recede

terminal end moraine

farthest end moraine in glaciers retreat

outwash plain

wide gently-sloping apron of rock debris formed when streams of fast-moving meltwater emerge from bases of glacier

kettle

form when blocks of stagnant ice become buried in drift & eventually melt leaving pits in glacial rock material

drumlin

elongated parallel hills made of till

esker

narrow winding ridges composed of sand & gravel that were deposited by streams once flowing in tunnels beneath glaciers

washes/arroyos

dry channels

alluvial fans

fan-shaped deposit of sediment formed when stream's slope is abruptly reduced

playa

dry, flat lake bed

playa lake

flat area on floor of undrained desert basin that fills & becomes lake after heavy rain

deflation

occurs when wind lifts & removes loose particles such as clay & silt

saltation

when coarser particles roll or skip along surface

blowouts

shallow depressions in land as result of deflation

desert pavement

stony surface layer made of coarse pebbles & cobbles that are too large to be moved by wind

abrasion

occurs when windblown sand cuts & polishes exposed rock surfaces

loess

windblown silt that has built up forming a thick deposit

sand dunes

deposits of sand in mounds or ridges when wind encounters an obstruction