glaciers. v. glacial erosion a.mechanisms 1.glacial quarrying masses of (fractured) bedrock are...
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Glaciers
Glaciers
V. Glacial Erosion
A.Mechanisms
1. Glacial QuarryingMasses of (fractured) bedrock are
lifted from the bed and incorporated into the ice
Melt water penetrates the cracks frost wedging
2. Glacial AbrasionSediment 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 QuarryingMasses 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 ValleyAs 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 ValleyAs glaciers advance down river valleys they carve V-shaped valley into U-shaped
valleys
V. Glacial Erosion
B. Landforms
6. Hanging ValleyFormed 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. FjordWhen ocean water floods into a U-
shaped valley after glacial retreat
7. FjordWhen 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. MoraineLandform 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