glacier - 1 Glaciers Glaciers are permanent bodies of...

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1 Glaciers Glaciers are permanent bodies of ice (recrystallized snow) which flow downslope by the action of gravity, and which are maintained over long periods of time by very low temperatures that prevent this ice from undergoing substantial melting. I- Types of glaciated terrain: 1- Alpine areas: These are mountainous areas where snow and ice are preserved by the low temperatures resulting from the high elevations. 2- Continental areas: Are large areas of land covered by glaciers because they lie close to the poles. II- Distribution of Glaciers: Glaciers cover ~ 10% of the land surface. However, during ice ages, approximately 30% of the land area was covered by glaciers. 85% of glaciers occur in Antarctica, and 10% in Greenland. III- Types of glaciers: 1- Valley glaciers (Alpine): Are glaciers flowing in valleys that occur in high altitudes. 2- Ice sheets (Continental): Are the largest types of glaciers occurring close to the poles and constituting 95% of the total ice on the earth's surface. 3- Ice Caps: Are dome-shaped bodies of ice occurring in polar areas, and which are much smaller than ice sheets. Glaciers could also be classified as advancing or receding depending on the amount of ice accumulated and that lost by melting. IV- Formation of a glacier: From snow to ice: névé firn ice through compaction and loss of trapped air (Fig. 1). Role of gravity Wasting of a glacier: Melting of glacial ice or its evaporation is known as "ablation", and results in the recession of the glacier. If the glacier flows down to a body of water, it is also wasted with its ice breaking up to form icebergs that float on water. Advancing and receding glaciers V- Definitions: Zone of accumulation: Is the area where snow is constantly accumulating (close to the head of the glacier) with no or very little melting (Fig. 2).
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