105_14-glaciers_part_2 - Budget of a Glacier Zone Zone of...

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Unformatted text preview: Budget of a Glacier Zone Zone of Accumulation – Where snow and ice accumulate Accumulation balances ablation; stationary terminus. BUDGET BALANCED Zone Zone of Ablation – Where snow and ice are lost Melting Melting Sublimation Sublimation Calving Calving Accumulation exceeds ablation; terminus advances. POSITIVE BUDGET Ablation exceeds accumulation; terminus recedes. NEGATIVE BUDGET Budget of a Glacier South South Cascade Glacier, Washington 1957 1980 Glacial Flow Valley Valley glaciers flow downhill under the influence of gravity Rates Rates vary from a few mm/day to 15 m/day Velocity Velocity also varies within the glacier itself – Center of valley moves faster than sides – Surface of ice moves faster than base Lost Lost 7.5 meters in 23 years = Negative glacial budget, Receding terminus. Glacial Flow Pipe Pipe moves downglacier = basal sliding – basal entire body of ice moves over the underlying rock Pipe Pipe is bent Glacial Flow Rigid Rigid zone is brittle, and ice breaks under extensional stresses. Forms crevasses crevasses = plastic flow – plastic movement within the glacier. Ice is deformable, or ‘plastic’ Plastic flow occurs along bottom of glacier. Upper portion is a rigid zone. 1 Movement of ice sheets Glacial Erosion Glacial Glacial plucking – Glacier freezes to bedrock and removes it Glacial Glacial abrasion Move Move down in elevation and outward from a central point in the sheet towards the edges – Rock fragments scrape and polish bedrock Glacial Erosion Glacial Glacial abrasion – Rock fragments scrape and polish bedrock Glacial Erosion Glacial Glacial abrasion forms: – Rock flour – powder of very fine grained particles – Striations – grooves or scratches in underlying bedrock Glacial Glacial Quarrying – Chunks of rocks lifted out of bedrock Striations, Blue Mounts, Minnesota Striations, Lake Superior, Ontario 2 Erosional Erosional Features of Alpine Glaciation • Glacial valleys ∪ shaped Striations, South Africa U-shaped glacial valley Erosional Features of Alpine Glaciation Hanging valley Main glacial channel is larger and deeper than its tributaries. After glaciers retreat, this main channel valley is generally bounded by large cliffs. Hanging valleys typically have large waterfalls where tributary valleys enter. Erosional Features of Alpine Glaciation Roche Moutonée Elongated, rounded mass of rock which was more resistant to glacial erosion than the surrounding rock 3 Erosional Features of Alpine Glaciation Erosional Features of Alpine Glaciation Tarn Tarn A lake within a cirque Cirque Cirque Steep sided, halfhalfbowl recess carved into a mountain at the head of a glacier Erosional Features of Alpine Glaciation Horn sharp peak that remains at the intersection of three or more cirques 4 Matterhorn, Switzerland Erosional Features of Alpine Glaciation Arête sharp ridges separating adjacent glacial valleys Erosional Features of Alpine Glaciation Erosional Features of Ice Sheets • • • More rounded topography Roche moutonées Striated bedrock • Fjords ∪ shaped valleys which have flooded Glacial Deposition Glacial Glacial Till: unsorted, angular sediments deposited as a result of glacial erosion Till 5 ...
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