Glaciers
Glaciers
V. Glacial Erosion
A.Mechanisms
1. Glacial Quarrying
Masses of (fractured) bedrock are
lifted from the bed and
incorporated into the ice
Melt water penetrates the cracks
 frost wedging
2. Glacial Abrasion
Sediment carried along at the
base of a glacier scrapes along
the underlying bed
Fine sediment  polishes
bedrock  glacial flour,
streams have milky grayish
color
Bedrock  striations
V. Glacial Erosion
A. Mechanisms
1.Glacial Quarrying
Masses of (fractured) bedrock
are lifted from the bed and
incorporated into the ice
Melt water penetrates the
cracks  frost wedging
Ice freezes to the rock and as the glacier flows
down slope boulders are plucked free and
incorporated into the ice.
V. Glacial Erosion
B. Landforms
1. Cirques
Horseshoe shaped basin at or
above snow line
Lack of sunlight & accumulation
of wind-blown snow  growth
of persistent snowfields
Frost wedging will erode basin
High snow accumulation
produces cirque glacier
V. Glacial Erosion
B. Landforms
2. Arête (French for “fishbone”)
Two cirques on opposite sides erode
backwards
A sharp ridge of rock
3. Col: Continued headward erosion
of cirques. A pass through an
arête
4. Horn: Three or more cirques
erode back to form a steep peak
V. Glacial Erosion
B. Landforms
2. Arête (French for “fishbone”)
Two cirques on opposite sides erode
backwards
Sharp ridge of rock
3. Col: Continued headward erosion
of cirques
A pass through an arête
4. Horn: Three or more cirques
erode back to form a steep peak
V. Glacial Erosion
B. Landforms
5. U-shaped Valley
As glaciers advance down
river valleys they carve
them into U-shaped valleys.
Contrast to V-shaped valley
formed by lateral stream
erosion.
V. Glacial Erosion
B. Landforms
5. U-shaped Valley
As glaciers advance down river valleys they carve V-shaped valley into U-shaped
valleys
V. Glacial Erosion
B. Landforms
6. Hanging Valley
Formed by tributary glaciers that feed
a larger glacier
Glacier does not down-cut as quickly
After the ice melts, a “hanging” valley
is perched above the main valley
V. Glacial Erosion
B. Landforms
7. Fjord
When ocean water floods into a Ushaped valley after glacial retreat
7. Fjord
When ocean water floods into a U-shaped valley after glacial retreat
VI. Glacial Deposits
A. Moraine
Landform at the margin of
a glacier
Accumulation of till
1. Terminal Moraine:
marks furthest advance
of the ice
2. Recessional Moraine:
up-glacier from and
usually parallel to the
terminal moraine, marks
a stationary point
VI. Glacial Deposits
A. Moraine
Landform at the margin of a glacier consisting of glacial till
1. Terminal Moraine: marks furthest advance of the ice
VI. Glacial Deposits
A. Moraine
VI. Glacial Deposits
A. Moraine
Landform at the margin of a
glacier
Accumulation of till
3. Lateral Moraine: at the
side of a glacier
4. Medial Moraine: when
two glaciers merge,
there’s a moraine
between them
VI. Glacial Deposits
B. Outwash
Material below a glacier
Deposited by melt water not the
glacier itself
Transported by braided streams
VI. Glacial Deposits
VI. Glacial Deposits
VI. Glacial Deposits
Pacific Northwest: >12,000 yrs BP