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2010-05-06 02:40:03
glaciers dehon geology

Terms and questions regarding glaciers
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  1. Define a glacier.
    A glacier is a natural body of ice formed by the accumulation, compaction and recrystallization of snow that is thick enough to flow.
  2. Why is a glacier considered to be a geologic system?
    Glacial ice is really a type of metamorphic rock that begins as sediment (aggregate of mineral particles, or snow) and is then metamorphosed by compaction and recrystallization into glacial ice.
  3. What happens in the zone of accumulation?
    snow is transformed into glacial ice through compaction and recrystallization
  4. What happens in the zone of ablation?
    ice leaves the system by melting, calving, and evaporating
  5. What is the boundary between the zone of accumulation and ablation called?
    snow line
  6. Define calving.
    shedding of large blocks of ice from a glacier edge, usually into a body of water
  7. What are the two main types of glaciers?
    Valley and continental glaciers
  8. A valley glacier that emerges from the mountain front and spreads out as a large love at the foot of the mountain is commonly called what?
    piedmont glacier
  9. Define the condition of extending flow.
    Velocities of ice flow in the zone of accumulation increase progressively from the head to the snow line. Here, the ice is under tension and is constantly pulling away from upvalley ice.
  10. Define the condition of compressing flow.
    Below the snow line, velocities progressively decrease, therefore, upvalley ice is continually pushing against downvalley ice
  11. How fast do glaciers flow?
    The flow of glacial ice is not constant but varies significantly with time and place.
  12. The flow of glacial ice is constant. T or F?
  13. An extremely rapid flow of glacial ice, with velocities more than 100 times normal, is referred to as a -?
    glacial surge
  14. What are the three purposed causes of glacial surge?
    • basal slip
    • sudden slippages along the bases of glaciers
    • sudden addition of mass to the glacier
  15. What are crevasses?
    large cracks opened by fracturing of a brittle upper layer of ice as the underlying ice continues to flow
  16. Glacial plucking is the-
    lifting out and removal of fragments of bedrock by the moving ice
  17. Describe the process of Abrasion
    The angular blocks plucked and quarried by the moving ice freeze firmly into the glacier; thus firmly gripped, they are ground against the bedrock over which the glacier moves. The fragments become abraded and worn down as they grind against the bedrock surface. As a result, glacial boulders usually develop flat surfaces that are deeply scratched.
  18. What are two evidences of abrasion?
    roches moutonees and glacial striations
  19. Name valley glacier's distinctive landforms. (6)
    U-shaped valleys, cirques, hanging valleys, horns, moraines, and outwash plains
  20. How do lateral moraines form?
    As ice moves, it picks up rock and debris along its margins from abrasion, forming a marginal zone of dirty ice. The mass movement of rock debris from the valley walls above the glacier contributes to the rock debris along the ice margin. Below the snowline, the melting of the dirty ice concentrates the debris into a linear band along the side of the glacier
  21. Where a tributary glacier joins the main stream, the two adjacent lateral moraines merge to form a -?
    medial moraine
  22. _____ are scoped out parts of a mountain.
  23. Where there two or more cirques they sculpt the mountain crest into a sharp peak called a ____.
  24. The ridge along two cirques are called ____.
  25. The tributaries that lead into the main glacier are on the same level but with then glacier retreats the floor of the tributaries are higher than floor of the U-shaped valley. This area is known as what?
    hanging valleys
  26. Name the types of landforms continental glaciers produce. (6)
    Moraines, drumlins, eskers, kettles, lake sediment, and outwash plains.
  27. In rugged terrain, especially in areas close to the margins, the direction of ice movement of continental glaciers is greatly influenced by mountains ranges, and the ice moves through mountain passes in large streams of ____.
    outlet glaciers
  28. Streams of meltwater flow in tunnels within and beneath the ice and carry a large bed load, which is ultimately deposited to form a long, sinuous ridge known as an -?
  29. Till and outwash plain sediment, can be reshaped by subsequent advances of ice to produce streamlined hills called _____. They usually resemble a raindrop.
  30. Why are varves in a series of alternating light and dark layer
    The coarse, light-colored material accumulates during spring and summer runoff. During the winter, when the lake is frozen over, o new sediment enters the lake, and the fine mud settles out of suspension to form the thin, dark layers.
  31. How do kettles form?
    Ice blocks, left behind by the retreating glacier front, can be partly or completely buried in the outwash plain or in moraines. Where an isolated block of debris-covered ice melts a depression is left.
  32. What are erratics?
    Erratics are large boulders transported by glaciers and then dropped far from their pointed of origin.
  33. What were the major effects of the ice age? (9)
    • glacial erosion and deposition over large parts of the continents that modified river systems
    • creation of millions of lakes
    • changes in sea level
    • pluvial lakes developed far from ice margins
    • isostatic adjustments of the crust
    • abnormal winds
    • impact on the oceans
    • catastrophic flooding
    • modifications of biologic communities
  34. Milankovitch climate cycles are caused by periodic changes with time in Earth's orbital elements, including ...?
    orbital eccentricity, obliquity or tilit of the spin axis, precession or wobble of the spin axis