Glacial Modification of Terrain Flashcards
Glacier
Moving mass of ice
Types:
1) Mountain glacier
2) Continental ice sheet
Mountain Glacier
1) Accumulation of ice in unconfined sheet covering hundred-thousands square kilometers
2) Icefield = large unconfined sheet in highlands
3) Valley glaciers - when icesheet overflows + goes down valley very long + “tongues” of ice down mountain valleys
4) Piedmont = valley glacier escapes onto flat land
Continental Ice Sheets
1) Form in nonmountainous areas
2) much larger –> significant agents of glaciation –> only 2 left today in Antarctica + Greenland
3) Thinner at outskirts + thickest ice sheets in middle
4) outlet glaciers - thinner parts –> break off (calving) and ice floats in ocean as icebergs
5) ice shelf = glacier projecting over sea
Extent of Pleistocene Glaciation
1) at max = ice covered 1/3 land area of Earth
2) Most ice = North America
3) Europe = half covered with ice
4) Canada = mostly covered with ice except for small sections called Driftless area
5) Major mtn ranges underwent glaciation
Pleistocene Glaciation
1) Dominant environment = cooling of high latitude + high elevation areas –> icy
2) BUT not universally icy
3) alternating glacial + interglacial periods
Indirect effects of glaciation
1) Periglacial zone = outermost extent of ice advance (never touched by glacial ice)
2) erosion + deposition –> solifluction of frozen subsoil
Sea Level changes in Pleistocene
1) Less water in oceans (more trapped in glaciers)
2) Glacial advance - drop in sea levels
3) Glacial retreat - increase in sea levels
at peak sea level was 120 meters lower than today (allowed for Bering Strait bridge)
Crustal Depression in Pleistocene
1) Weight of accumulated ice –> portions of Earth’s crust sank ~1300 feet
2) Isostatic adjustment = crust slowly rebounded after ice melted BUT not complete, even today parts of crust rising by 4 in per decade
Pluvial Effects in Pleistocene
1) Increase in moisture caused by increased meltwater runoff, precip, decreased evaporation
2) resulted in creation of lakes where none existed i.e. Pleistocene lakes like Great Salt Lake
Glacial formation depends on which two factors
1) accumulation (addition of ice via snow)
2) ablation (wastage of ice via sublimation + melting)
Layers of Glacier
1) Upper portion = accumulation zone –> amount of new snow exceeds amount lost by melting
2) lower portion = ablation zone = amount of new ice less than amount lost
3) theoretical equilibrium line between two layers
Glacial Formation
1) Snow –> granular snow (density doubles)
2) more compression –. granules packed more closely + become neve/firn (half density water)
3) further compression –> becomes glacier ice (90% density of water)
Glacial Movement
Generally –> partial melting aids in movement bc meltwater acts as a lubricant
Type Types of movement
1) Plastic Flow
2) Basal Slip
Plastic Flow of Ice
1) If ice is over 165 feet thick, the ice mass does not move uniformly
2) oozes outward from around edge of icesheet
Basal Slip
1) Entire mass AS ONE slides over bed bc of lubricating film of water
2) Molds itself to shape of terrain it’s going over
Rate of Movement of Glaciers
1) VERY SLOWLY, few centimeters per day
2) Erratic, pulsating movement
3) Ice at surface moves fastest
Glacial flow vs Advance
1) Ice flowing forward in both cases
2) Advance = More accumulation than ablation
3) Retreat = Less accumulation than ablation
Glacial flour
1) Glacier load = heterogenous collection of particles of all sizes
2) majority of load in lower portions of glacier
3) mtn glaciers = have some load on top from rockfalls
Glacial Plucking
1) Most significant erosive work
2) Rock fragments beneath ice grasped by freezing meltwater
3) frost wedging loosens rock
4) Rock plucked out + dragged along
5) ROUGHENS SURFACE
Subglacial Meltwater Erosion
1) Meltwater streams beneath glaciers
2) move rock + smooth grooves + channels in bedrock below glacier
Glacial Abrasion
1) Less significant erosive force
2) wears down bedrock by rock debris being dragged along
3) minor features = POLISHES surfaces + striations
Meltwater Streams (on surface)
1) Warmer months = meltwater streams on surface of moving ice
2) streams hit crack/crevasse/moulin (steep drainage shaft) + plunge into glacier + joins meltwater streams at bottom = lubricates
3) plays role in moving rocks from surface into the middle/bottom of glacier
Glacial Deposition
1) Drift = all materials moved by glaciers
2) Two Types: Direct, secondary deposition
Direct Glacial Deposition
Direct: Rock debris deposited by moving ice is called till (angular - hasn’t been shaped by moving water, it just sat on ice)
