ch 10 glaciers and deserts

glacier: thick mass of ice that forms over land from the compaction and recrystallization of snow and shows evidence of past or present flow

glaciers

valley, or alpine glaciers

• thousands of small glaciers

• stream of ice that flows downvalley, slowly

• form in mountainous areas

landforms created from alley, or alpine glaciers

• glacial trough: narrow valleys are transformed as the glacier widens and deepens them, creating a U-shaped. normal valleys are v shaped

• hanging valley: main glaciers, also called trunk glaciers, cut their valleys deeper than do their smaller tributary glaciers. Thus, after the ice has receded, the valleys of tributary glaciers are left standing above the main glacial trough

• crique

• arte: sinuous, knife-edged ridges

• horn: pyramid-like peaks

• fiord: A steep-sided inlet of the sea formed when a glacial trough was partially submerged.

ice sheets or continental glaciers

• completely cover land with ice

• alternating glacial and interglacial periods

ice caps and piedmont glaciers

• completely cover land with ice

• smaller than ice sheets

types of glacial movements

• plastic flow - can be cracked

• basal slip - along the ground lubricated from melt water

zone of fracture

• uppermost 50 meters

• crevasses form in brittle ice

crevasses - common in upper parts of glaciers bc ice is subjected to tension. open where brittle parts of glacier is stretched and cracks as it moves over a steeper slope in its valley

zone of accumulation - area where glacier forms

zone of wastage - area where there is net loss due to melting

glacial erosion

• plucking: acquire sediment load by lifting rock blocks on sides and base

• abrasion: ice and sediment load slide over bedrock. striation (grooves) in bedrock are evidence

glacial deposits

glacial drift

• all sediments of glacial origin

• types of glacial drift:

  • till: material deposited by ice with wide variation of glast sizes

  • stratified drift: sediment deposited by meltwater

depositional features

• moraines: layers or ridges of till.

  • lateral

  • medial

  • end

  • ground

• outwash plain/valley train

• kettles

• drumlins

• eskers

• kames

ice age glaciers

• many in earth’s history

• most recent began 2-3 million years ago

• called the plestocene epock

• ice covered 30% of earth’s land area

effect of ice age glaciers

• animals/plants migration

• crust rebounding upwards

• worldwide change in sea level

  • more ice - lower sea level

  • less ice - higher sea level

• climate changes

glacial cycle knowledge is based on

• ice cores

• seafloor sediments

variations in earths orbit - milankovitch hypothesis

• shape (eccentricity) of earth’s orbit varies

• angle of earth’s axis (obliquity) changes

• axis wobbles (precession)

deserts

• place with a water deficiency

• distribution and causes of dry lands

  • global distribution of air pressure and winds

  • deep interiors of landmasses

  • high mountains

• many deserts created bc lack of rain, and regional topography, or if area is in a rain shadow

weathering

• not as effected in bc shortage of water and organic acids

• mechanical weathering forms unaltered rock and minerals

• some chemical weathering that does occur

  • clay forms

  • thin soil forms

role of water

• desert streams are ephemeral

  • flow only during perios of rainfall. dry most of the time

• desert rainfall

  • rain occurs as heavy showers sporadically. causes flash floods

• erosional work done by running water

names for desert streams

• wash

• arroyo

• wadi

• donga

• nullah

basin and range: evolution of desert landscape

• uplifted crustal blocks

• interior drainage into basins produces

  • alluvial fans and bajadas

  • playas and playa lakes

playa lakes - salty

• salt concentration goes up in lake, eventually salt deposits are vissible

wind erosion

• less effective than water bc less dense

• only moves small particles, but it can travel long distances

• deflation: lifting of loose material which produces

  • blowouts

  • desert pavement

• abrasion: sand paper rubbing

sand dunes

• mounds and ridgest formed from wind’s bed load. characteristics include

  • slip face: leeward slope of due

  • cross beds: sloping layers of sand in due

loess

desert hazards

• sand/dust storms