10,000 feet thick in some areas, and the weight of this glacier is so heavy that much of the region has
been depressed below sea level. Smaller glaciers that occur at higher elevations are called alpine or
valley glaciers. Another way of classifying glaciers is in terms of their internal temperature. In
temperate glaciers, the ice within the glacier is near its melting point. Polar glaciers, in contrast,
always maintain temperatures far below melting.
B. The majority of the earth’s glaciers are located near the poles, though glaciers exist on all
continents, including Africa and Oceania. The reason glaciers are generally formed in high alpine
regions is that they require cold temperature throughout the year, in these areas where there is
little opportunity for summer ablation (loss of mass), snow changes to compacted firm and then
crystallized ice. During periods in which melting and evaporation exceed the amount of snowfall,
glaciers will retreat rather than progress. While glaciers rely heavily on snowfall, other climatic
conditions including freezing rain, avalanches and wind, contribute to their growth. One year of below
average precipitation can stunt the growth of a glacier tremendously. With the rare 7 exception of
surging glaciers, a common glacier flows about 10 inches per day in the summer and 5 inches per day
in the winter. The fastest glacial surge on record occurred in 1953, when the Kutiah Glacier in
Pakistan grew more than 12 kilometers in three months.
C. The weight and pressure of ice accumulation causes glacier movement. Glaciers move out
from under themselves, via plastic deformation and basal slippage. First, the internal flow of ice
crystals begins to spread outward and downward from the thickened snow pack also known as the
zone of accumulation. Next, the ice along the ground surface begins to slip in the same direction.
Seasonal thawing at the base of the glacier helps to facilitate this slippage. The middle of a glacier
moves faster than the sides and bottom because there is no rock to cause friction. The upper part of a
glacier rides on the ice below. As a glacier moves it carves out a U-shaped valley to a riverbed, but
with much steeper walls and flatter bottom.
D. Besides the extraordinary rivers of ice, glacial erosion creates other unique physical features
in the landscape such as horns, fjords, hanging valleys, and cirques. Most of these landforms
do not become visible until after glaciers have receded. Many are created by moraines, which
occur at the sides and front of a glacier. Moraines are formed when material is picked up along the
way and deposited in a new location. When many alpine glaciers occur on the same mountain, these
moraines can create a horn. The matter horn, in the Swiss Alps is one of the most famous horns.
Fjords, which are very common in Norway, are coastal valleys that fill with ocean water during a
glacial retreat. Hanging valleys occur when two or more glacial valleys intersect at varying elevations.
It is common for waterfalls to connect the higher and lower hanging valleys, such as in
Yosemite National Park. A cirque is a large bowl-shaped valley that forms at the front of a glacier.
Cirques often have a lip on their down slope that is deep enough to hold small lakes when the ice
melts away.
E. Glacier movement and shape shifting typically occur over hundreds of years. While presently
about 10% of the earth land is covered with glaciers, it is believed that during the last Ice Age glaciers
covered approximately 32% of the earth’s surface. In the past century, most glaciers have been
retreating rather flowing forward. It is unknown whether this glacial activity is due to human impact
or natural causes, but by studying glacier movement, and comparing climate and agricultural
profiles over hundreds of years, glaciologists can begin to understand environmental issues such as
global warming.
Choose the most suitable heading for each paragraph
I. Glacial continents
V. Glaciers through the years
II. Formation and growth of Glaciers
VI. Types of Glaciers
III. Glacial Movement
VII. Glacial Effects on Landscape
IV. Glaciers in the last Ice Age
VIII. Glaciers in National Parks
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