Chapter 19 Flashcards
Glacier Formation
- snow compressed to granular form
- more compression= granules coalesce into neve/firn
- further compression leads to glacial ice
Glacial flow/movement
glacial “flow” is the orderly sliding of ice molecules
- ice under extreme pressure deforms instead of slipping
- meltwater contributes surface for glaciers to slide on
- flow in response to overlying weight
erosion of glaciers (BASICS)
volume and speed determine success of glacial erosion
erosive power of moving ice> that of water
glacial plucking
picking up of rock material through refreezing of meltwater
glacial abrasion
bedrock worn down by rock debris collected by the glacier
transportation by glaciers
can move large rock pieces; typically move glacial flour; most rock material transported along the base of the ice
- remaining glacial ice is free of rock debris
- melt streams: role of flowing water on moving ice
moulins
cracks in ice in which streams run
deposition by glaciers
glaciers move lithospheric material from one region to another in a vastly different form
drift
material moved by glaciers
till
rock debris deposited by moving ice
glacial erratics
large boulders that are different from surrounding local bedrock
deposition by meltwater
large portion of debris carried by glaciers deposited or redeposited by meltwater; subglacial streams from glaciers carry sedimentary material
deposition by ice sheets
irregular, uneven surface of deposition (till plain)
Moraines
land consisting primarily of till; material left behind a moving glacier
terminal moraine
marks outermost limit of glacial advance
recessional moraine
positions where ice front is stabilized
ground moraine
large quantities of till laid down under a glacier instead of from its edge, kettles
continental ice sheets
exist in nonmountainous areas (Antarctica and Greenland); outlet glaciers
highland icefields
ice sheets that submerge most underlying topography; valley and piedmont glaciers
alpine glaciers
develop individually instead of as part of an ice field; cirque glaciers
continental ice sheets: WHAT ARE THEY MADE OF
- composed of gravel, sand, and silt since meltwater is incapable of moving larger materials
- outwash plains, valley trains, eskers, kames, and lakes are very common
- stratified drift
development of ice sheets
- Pleistocene ice sheets originated in midlatitudes and subpolar regions
- ice flowed outward from the center of accumulation
- ice sheets ebbed and flowed with changing climate
Pleistocene Glaciation (2.5 mya)
- last ice age
- refrigeration of high latitude and high elevation areas
- 1/3 of total land covered in ice
causes of Pleistocene glaciations
- cold vs warm climate for glaciation
- role of Milankovitch cycles
- variation in solar output
- variation in CO2
- changes in continental positions
- atmospheric circulations
mountain glaciers development
usually formed in sheltered depressions near heads of stream valleys
mountain glaciers basic landform
basic landform in glaciated mountains is cirque
marks the location where an alpine glacier originated
erosion by mountain glaciers (they do erode)
- quarried fragments from the cirque are carried away when ice flows out of the cirque
- cirque ice melts (the depression that holds water is a tarn)
- several cirques cut back into interfluve and result in the spine of rock (arete)
erosion in the valleys
- some glaciers never leave cirques
- principle erosive work is to deepen, steepen, and widen valley
- U-shaped glacial troughs
primary mechanism of deposition by mountain glaciers
- continental ice sheets are more responsible for deposition than mountain glaciers
- primary deposition mechanism: moraines (lateral and medial)
the Periglacial environment
- periglacial: on the perimeter of glaciation
- permafrost presence
- extends to great depths, patterned ground, proglacial lakes
