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