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 U- shaped 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

Pacific Northwest: >12,000 yrs BP