Glacial Modification of Terrain

Question 1

Glacier

Answer 1

Moving mass of ice
Types:
1) Mountain glacier
2) Continental ice sheet

Question 2

Mountain Glacier

Answer 2

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

Question 3

Continental Ice Sheets

Answer 3

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

Question 4

Extent of Pleistocene Glaciation

Answer 4

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

Question 5

Pleistocene Glaciation

Answer 5

1) Dominant environment = cooling of high latitude + high elevation areas –> icy
2) BUT not universally icy
3) alternating glacial + interglacial periods

Question 6

Indirect effects of glaciation

Answer 6

1) Periglacial zone = outermost extent of ice advance (never touched by glacial ice)
2) erosion + deposition –> solifluction of frozen subsoil

Question 7

Sea Level changes in Pleistocene

Answer 7

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)

Question 8

Crustal Depression in Pleistocene

Answer 8

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

Question 9

Pluvial Effects in Pleistocene

Answer 9

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

Question 10

Glacial formation depends on which two factors

Answer 10

1) accumulation (addition of ice via snow)
2) ablation (wastage of ice via sublimation + melting)

Question 11

Layers of Glacier

Answer 11

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

Question 12

Glacial Formation

Answer 12

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)

Question 13

Glacial Movement

Answer 13

Generally –> partial melting aids in movement bc meltwater acts as a lubricant
Type Types of movement
1) Plastic Flow
2) Basal Slip

Question 14

Plastic Flow of Ice

Answer 14

1) If ice is over 165 feet thick, the ice mass does not move uniformly
2) oozes outward from around edge of icesheet

Question 15

Basal Slip

Answer 15

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

Question 16

Rate of Movement of Glaciers

Answer 16

1) VERY SLOWLY, few centimeters per day
2) Erratic, pulsating movement
3) Ice at surface moves fastest

Question 17

Glacial flow vs Advance

Answer 17

1) Ice flowing forward in both cases
2) Advance = More accumulation than ablation
3) Retreat = Less accumulation than ablation

Question 18

Glacial flour

Answer 18

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

Question 19

Glacial Plucking

Answer 19

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

Question 20

Subglacial Meltwater Erosion

Answer 20

1) Meltwater streams beneath glaciers
2) move rock + smooth grooves + channels in bedrock below glacier

Question 21

Glacial Abrasion

Answer 21

1) Less significant erosive force
2) wears down bedrock by rock debris being dragged along
3) minor features = POLISHES surfaces + striations

Question 22

Meltwater Streams (on surface)

Answer 22

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

Question 23

Glacial Deposition

Answer 23

1) Drift = all materials moved by glaciers
2) Two Types: Direct, secondary deposition

Question 24

Direct Glacial Deposition

Answer 24

Direct: Rock debris deposited by moving ice is called till (angular - hasn’t been shaped by moving water, it just sat on ice)

Question 25

Secondary Deposition by Meltwater

Answer 25

1) meltwater streams (has many peculiarities like distinct day/night volume difference, peak flows in midsummer, etc.)
2) Most debris carried by glaciers is deposited by meltwater
3) mostly involves debris that was originally reposited by ice AND THEN picked up and redeposited by meltwater well beyond outer margin of ice (glaciofluvial deposition)

Question 26

Till, sorted or unsorted

Answer 26

1) Unsorted - drops unsorted (mixed pile of sizes) of sediment
2) COMPARED TO fluvial processes –> competence + capacity causes it to drop large then medium then small

Question 27

Kettles and drumlins

Answer 27

Kettle = ice that falls off glacier, goes into soil, melts, creating mini depressions
Drumlin = mini hill of till, one rough side one smooth side (smooth side - direction glacier moving in)

Question 28

Continental Ice Sheets

Answer 28

MUCH MUCH larger than glaciers

Question 29

Ice Sheet Erosion

Answer 29

1) Ice Sheet erosion = creates gently undulating surface
2) Create valleys (troughs)

Question 30

Roche Moutonnee

Answer 30

1) Hills sheared off + rounded by moving ice
2) two sides: stoss + lee side
3) stoss side = smooth + where ice went over
4) lee side = faces opposite ice direction SO shaped by plucking = very angled
5) high pressure as glacier goes onto hill BUT on other side it’s low pressure so some of glacier melts –> goes into ground –> Frost wedging, creating boulders WHICH are plucked away

Question 31

Ice Sheet Erosion makes

Answer 31

Roche Moutonnee

Question 32

Ice Sheet Deposition makes

Answer 32

Moraines

Question 33

Moraines

Answer 33

1) glacier-deposited landform made mostly or entirely of till
2) longer than wide
3) Types of moraines: terminal, recessional, ground

Question 34

Terminal vs Recessional vs Ground moraine

Answer 34

1) Terminal = ridge of till that marks maximum advance of glacier
2) Recessional = behind terminal, marks position where ice front was temporarily stable
3) ground = formed by deposition of lots of till in middle of glacier
for terminal + recessional = till at edge

Question 35

Glacial Troughs

Answer 35

1) Alpine glacier moving down mountain = more corrosive erosive than stream
2) Creates a U-cross section + relatively straight since ice doesn’t meander like water
Not all glacial troughs/valleys U-shaped, resistance of bedrock + exfoliation also play role

Question 36

Hanging Glacial Troughs

Answer 36

1) Valley formed by glacial activity that sits above main valley floor
2) smaller tributary glaciers feed into main glacier creating shallower troughs, which “hang” above main valley
3) height difference often creates waterfalls as streams go from hanging valley to main

Question 37

Depositional Landform associated with mountain glacier

Answer 37

Moraines

Question 38

Lateral Moraines

Answer 38

1) largest depositional feature made by mountain glaciation
2) well-defined ridges of till along sides of valley glaciers

Question 39

Medial Moraine

Answer 39

1) Occurs when tributary glacier joins main valley glacier
2) their lateral moraines unit –> creating a combined medial moraine