Geology Final Exam Study Guide

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  • Topic: Glacier, Glaciology, Water
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GSCI Final Exam Study Guide
Glaciers q 1-24 34%
Text book p 570-587
Ice as a Rock
- Mass of crystalline grains of the mineral ice
- Like sedimentary: formed from material in deposited layers, can accumulate a great
Thickness
- Igneous: formed by the freezing of a fluid
- Metamorphic: transformed by recrystallization under pressure
- Flows readily downhill like a viscous fluid because of structural weakness
- Glaciers: large masses of ice on land that show evidence of being in motion or of once
Having moved under the force of gravity
- Valley/Alpine Glaciers : Rivers of ice formed in cold heights of mountain ranges where snow accumulates and then move down slope in an existing stream valley or carving a new one. Usually occupies the complete width of the valley and may bury its floor under hundreds of meters of ice. - Iceberg Calving: masses of ice break off glaciers that terminate at ocean’s edge and form icebergs - Continental glacier: thick slow moving sheet of ice (ice sheet) that covers a large part of a continent or some other land mass. - Greenland, Antarctica, 10% of Earth’s land, 75% fresh water. - Ice shelves: thinner sheets of ice floating on the ocean and attached to the main glacier on land

How Glaciers Form
- Abundant winter snowfall that does not melt, slowly converted to ice, when thick enough it begins to flow - Snow line: elevation at which snow does not melt in the summer. Lower near poles - Unlikely to form in arid climates because of need for moisture, except Antarctica because nothing ever melts - Over time snow accumulates and compacts

- Snow (90% air)  granular ice (50%)  firn (20-30%)glacial ice (20% as bubbles)
- May only take a few years, 10 to 20 more likely
- Accumulation: amount of ice added to a glacier annually
- Ablation: total amount of ice a glacier loses annually
1. Melting - #1
2. Iceberg calving - #2
3. Sublimation – water directly from ice to water vapor in cold climates
4. Wind erosion
- Most ablation takes place at glacier’s leading edge (ice front)
- Glacial budget: difference between accumulation and ablation
How Glaciers Flow
- Plastic flow: ice crystals slip tiny distances relative to eachother because of gravity, this is amplified over time and enormous number of ice crystals to move the glacier via microscopic deformation - Basal slip: sliding of the glacier along the boundary between the ice and the ground - Louis Agassiz 1830 Swiss zoologist observed valley glacier movement with stakes over years. Center moves faster than sides or base, diagnostic of plastic flow - Surge: sudden period of fast movement by a valley glacier

- Crevasses: cracks caused by dragging of the basal ice
- Most likely to occur in places where glacial deformation is strong -Ice streams : large areas of rapid glacial flow
Glacial Landscapes
- movement of glaciers is responsible for geologic work done by ice of erosion transportation and sedimentation -Rock flour: fine silt and clay sized material eroded by glaciers - Striations: grooves caused on bedrock by glacier dragging other rocks across

- Show direction of ice movement, important for continental glaciers w/ no valleys - Cirque/Bowl: amphitheatre like valley formed at head of glacial valley from plucking and tearing of rocks at glacial origin - glacial horns: sharp mountaintops formed by meeting of cirques - arêtes: jagged crests along divide

- U-shaped valley: characteristic of glaciers, deepen stream bed or create new valley
- Wide and flat in contrast to V valleys created by streams - Hanging valley: tributary glacial valley not as deep as the main valley - fjords: u valleys flooded with sea water
- glacial drift: all material of glacial origin on land or under sea - glacial till: drift deposited directly by melting ice, poorly sorted - erratics: random large boulders differing from local rocks - outwash: drift that has been picked up and deposited by...
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