O. Chapter 14 - Chapter 14 Glaciers and Glaciation Glaciers...

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Unformatted text preview: Chapter 14 Glaciers and Glaciation Glaciers are also dynamic systems. They move, although very slowly . As dynamic systems, they continually adjust to changes (in temperature, snow supply, etc.). Defn: Glacier a mass of ice on land consisting of compacted and recrystallized snow that flows under its own weight. Not glaciers:- sea ice in the North Pole region- ice shelves adjacent to Antarctica- icebergs (even if they broke off glaciers)- mountain snowfields (even if persist for years) Extent of glaciers- about 1/10 of Earths land surface- continental glaciers are Antarctica and Greenland (most of land mass glaciated)- Mountain glaciers common in Rocky Mts., Andes, Alps, Himalayas.- Only continent without glaciers is Australia Impact on human culture- Little Ice Age climatic changes affected growing seasons and global temperatures- About 75% of all fresh water is frozen in glaciers- Glaciation has created spectacular scenery- Glaciers are capable of considerable erosional and depositional work. Hydrologic Cycle The source of water in glaciers (just as in rainfall) is the oceans. Glaciers are a reservoir in the hydrologic cycle where water is stored for long periods of time. Water is returned to the hydrologic cycle when: 1. glaciers at high latitude (Greenland, Antarctica, Canada) flow directly into the oceans and melt. 2. Glaciers flow into the ocean and calve icebergs, which melt. 3. At low latitudes, glaciers melt and add to the groundwater reservoir. 4. Glacial ice may sublimate . Go directly from solid to gas without a liquid state. Glacial Formation A net accumulation of snow and ice occurs when more snow falls than melts during the warmer seasons. Temperature and amount of snowfall are important factors in glacial formation. Temperature varies with latitude and elevation. More glaciers are found at higher latitudes and higher elevations. Remember that ice is a crystalline solid with characteristic physical properties a mineral! Therefore, glacial ice must be a type of rock just one that is easily deformed. Snow: 80% air-filled pore space and 20% solids. As snow compacts, partly thaws, and refreezes, it is converted to a granular type snow known as firn . As more snow accumulates, the firn is buried, further compacted, and recrystallized at glacial ice . Glacial ice: 90% solids. Glacial Movement (Remember Chapter 10 Deformation) Critical thickness of ice and snow 40m. Stress on ice at depth induces plastic flow deformation without fracturing. This is the primary mechanism for glacial movement Basal slip the glacier may also slide over the underlying surface. This type of movement is facilitated by water. If the glacier is solidly frozen to the surface, it only moves by plastic flow. Kinds of Glaciers 1. Valley Glacier (Also alpine or mountain glacier)- confined to a mountain valley- flows from higher to lower elevations- may form a network of glaciers in inter-connected valleys (just like stream tributaries)...
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O. Chapter 14 - Chapter 14 Glaciers and Glaciation Glaciers...

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