Glaciers are thick masses of ice that form from accumulated snowfall and flow downhill under their own weight. There are four main types of glaciers: valley glaciers, piedmont glaciers, ice caps, and ice sheets. Glaciers erode and transport sediment, forming characteristic landforms such as cirques, horns, and moraines through processes like plucking, abrasion, and scouring. As glaciers advance and retreat in response to climate changes, they leave behind deposits of till and stratified drift that create landforms like kettle lakes, outwash plains, and loess deposits. Evidence such as glacial erosion features, pluvial lakes, changing sea levels, and crustal re
21. Depositional Landscapes
Glacial drift = all sediment
deposited by glaciers
Two types of drift:
a) Till = sediment deposited
directly by glaciers (unsorted)
22. Two types of drift:
b) Stratified drift = sediments
deposited by glacial meltwater
- sorted by size
23. Landforms composed of till
1) Erratic
- boulders that differ from
underlying bedrock
- source area is outside region
where they’re found
24. Landforms composed of till
2) Moraine – ridge of till
Several types:
a) Lateral moraine – found only w/
valley glaciers
- parallels sides of valley
28. Types of Moraines
d) Recessional moraines
- end moraines created as a
receding glacier occasionally
stabilized
29. Types of Moraines
e) Terminal moraine
- outermost end moraine that
marks limit of glacial advance
30. Types of Moraines
f) Ground moraine
- associated w/ receding glaciers
- forms behind end moraines
- acts to level the land
31. Landforms composed of
stratified drift
Deposited by glacier’s melt water
- flows through moraines & picks
up sediment
- braided stream channels
common
32. Landforms composed of
stratified drift
1) Outwash plains
- broad ramp-like surface built in
front of end moraines
- associated w/ ice sheets
(called “valley trains” w/valley
glaciers)
33. Landforms composed of
stratified drift
2) Kettle/kettle lakes
- large blocks of stagnant ice
buried in sediment
- ice melts
- creates a depression
35. Loess
- associated with meltwater
drainages from glaciation
- thickest near drainages and
thins away from valleys
36. Movement of a glacier
Two methods:
1) Plastic flow = internal flow
- occurs in ice below 50 meters
- occurs fastest in center of glacier
(less friction)
37. Zone of Fracture
Upper 50 meters of
glacier
- brittle
- breaks into cracks
called “crevasses”
38. Movement of a glacier
2) Basal slip
Melt water at base of glacier
- entire ice mass slips over
surface
39. Glacial Budgets
Zone of Accumulation = area
where snow accumulates & ice
forms
Zone of Wastage = net loss as
glacier advances into warmer
climates (lower elevations)
40. Zone of Wastage
Loss of snow & ice is called
ablation
Ablation is due to:
- melting
- calving
42. Glacial Budgets
1) Advancing glacier – more
accumulation than ablation
- glacial front advances
- snowline drops in elevation
43. Glacial Budgets
2) Retreating glacier
- ablation exceeds accumulation
- snowline rises in elevation
- caused by warming trend or
decrease in snowfall
44. Glacial Budgets
3) Stationary Budget
- accumulation equals ablation
- total area of glacier is not
changing
NOTE: Ice is always moving
downhill!
45. Evidence for past glacial
periods (“Ice Ages”)
Periodically, northern Europe & N.
America covered by great ice
sheets
Last one melted from Canada
<10,000 years ago
46. Evidence for past glacial
periods (“Ice Ages”)
1) Glacial erosion
Ice sheets: polished bedrock in
northern regions, striations,
recessional moraines
Ex: Central Park, New York City
47. Evidence for past glacial
periods (“Ice Ages”)
Valley glaciers:
- Yosemite National Park
- Yellowstone National Park
49. Evidence for past glacial
periods (“Ice Ages”)
2) Pluvial lakes
- form during cooler times w/
moderate rainfall
- occurred at lower latitudes where
ice did not advance
50. Pluvial lakes
Most evident in Basin & Range
region in western U.S.
Ex: Lake Manley, Death Valley
Ex: Lake Bonneville, Utah
(Great Salt Lake is a remnant)
51. Evidence for past glacial
periods (“Ice Ages”)
3) Decreasing sea level
Water is locked onto land by ice
Estimated maximum 100 meters
lower than present sea level
53. Evidence for past glacial
periods (“Ice Ages”)
4) Crustal Rebound
Land readjusts upward after ice
sheets melt
Hudson Bay region has uplifted
300 meters since end of last ice
age
55. Evidence for past glacial
periods (“Ice Ages”)
5) Lake Missoula
Ice dam blocked melt water
- formed huge lake that flooded
western Montana
(half the size of Lake Michigan)
57. Lake Missoula
Melting weakened ice dam
- lake emptied in 1-2 days
- discharge ~ 386 million cfs
(Amazon discharge = 6 million
cfs)
58. Lake Missoula
Evidence:
a) channeled scablands in western
Oregon & southern Idaho
b) giant ripples of coarse gravel
30’ high, 300’ apart, 2 miles long
