WORK OF GLACIER:
A thick moving mass of ice under the influence of gravity on earth is called a Glacier. The snowfall becomes a glacier after being dumped and compacted. The frequent snowfall in a region causes glaciations. The underlying layer of snow is compressed by the newly fallen snow. The compressed layer of the old snow is compacted by the pressure exerted by the upper newly formed layer of snowfall. Glaciers form in places where more snow accumulates each year than melts away. They are found chiefly in high latitudes as in the Arctic region, or at high elevations as on the Himalayan Mountains above the snow-line. The “snowline” is the lower limit of accumulating snow. Bellow the snowline the snow melts in summer. The elevation of the snowlines varies considerably. In Polar Regions, it may be at sea level, whereas in areas near the equator, the snowline may occur at 6000 meters. In the Himalayas, the snowline lies at altitudes varying between 4200 to 5700 meters.
Types of Glaciers:
Glaciers are categorized into two groups. One is Unconstrained Glaciers and the second is the Constrained Glacier.
Unconstrained Glaciers: The morphology and flow pattern of this type of glaciers is independent of the underlying topographic features.
Constrained Glaciers: In this type of glaciers the underlying topographic features determines the flow and morphological features of the glacier.
Types of Unconstrained Glaciers:
(1). Ice Sheets:
An extensive area of the earth is covered by ice covering the regions of Greenland and Antarctica. This type of glacier is known as Ice Sheets. Two such glaciers that exist today are Greenland and Antarctic ice sheets. The ice sheet of Greenland coverers an area of about 1.7 million sq. km and the thickness of the Greenland ice sheet is about 1500 meter/1.5 km. These types of glaciers are included in the unconstrained glaciers because they are not influenced by the topographic features of the bedrock or the underlying earth surface.
The ice caps are another type of unconstrained glaciers. The area covered by the Icecaps is not as large as that of an ice sheet. An ice cap is a miniature of the ice sheet. It generally covers less than 50,000 square kilometers (19,305 square miles). Ice caps are formed generally in the Polar and the Sub-polar regions. There are smaller than the continental ice sheets.
(3). Ice Streams:
Another type of unconstrained glaciers is the ice stream. A region of fast-moving ice masses through channels surrounded by the ice sheet is known as an ice stream. It is a type of glacier, a body of ice that moves under its own weight. They can move upwards of 1,000 meters a year and can be up to 50 kilometers in width, and hundreds of kilometers in length.
Types of Constrained Glaciers:
(1). Valley Glaciers:
The accumulation of the snowfall and its compaction in the crest of high mountains, and their movement through rivers and streams along the valleys are known as Valley Glaciers.
(2). Ice Fields:
An ice field is similar to an ice cap, but ice fields are not included in the category of unconstrained glaciers, because they move under the influence of the underlying topographic features and landscape. This is the reason, and the ice field is included in the constrained glaciers.
(3). Transection Glaciers:
It is a system of valley glaciers. Transection glaciers have web-like shapes, which flows in different directions often in a web-like/ radiating pattern. Transection glacier networks develop where bedrock valleys are deeply dissected, allowing ice to overflow the cols between adjacent valleys.
(4). Piedmont Glaciers:
With the altitude of a hilly region, a number of valley glaciers combine with one another to form a single, thick, and wide ice sheet. The thickness of the ice layer increases with the rise in altitude. At the bottom of the hill, the piedmont glacier divides into many valley glaciers. The divided low-lying glaciers type are known as the valley glaciers, while near the peaks, the consolidated form is known as “piedmont glacier”. Malaspina Glacier in Alaska is one of the most famous examples of this type of glacier.
(5). Tide Water Glaciers:
They are included in the valley glaciers. As the name implies, they flow far enough to reach out into the sea. In some locations, tidewater glaciers provide breeding habitats for seals. These glaciers cause the calving of numerous small icebergs, which can pose obstacles in the way of shipping. Although they are not as huge as the Antarctic icebergs are.
(6). Hanging Glaciers:
When the valley glaciers get thinner and retreated, as well as the above central glacier surface is also shrunken, the tributary glaciers are left isolated in the low lying valley. These separated parts of the glaciers are known as the hanging glaciers. In case of the melting, and disappearance of the entire glacier system, the emptied high valleys are, then, known as the “hanging valleys”.
(8). Cirque Glaciers:
These are the bowl-like glaciers near or within a mountainous region. The snowfall is accumulated in the depressed bowl-shaped region of the mountain. The ice from the adjoining steep hills slips in the form of avalanches and accumulates in the bowl. The ice accumulates in the form of a concave crater, raised from the sides and deepened in the center.
(9). Ice Aprone:
This type of glacier is very common in New Zealand and the Alp Mountains. Their width is greater than its length. Avalanches slip slides down from the nearby steep mountainsides and get accumulated in the bottom of the mountainsides.
(10). Rock Glaciers:
As the name implies, a rock glacier is a mixture of ice and rocks, gravels, and debris. The snowfall enters into the spaces of the rocks and binds them as a result of dumping and compaction. The shape and movement of these glaciers is similar to those of the regular glaciers, however, their ice may be confined to the core of the glacier and spaces between rocks. Rock glaciers are the result of creeping down of the frozen ground. The same composition can be observed in avalanches and landslides.
(11). Ice Shelves:
Ice shelves are very common to be found in the Antarctic region. They are formed when the ice sheets extend above the seawater and cover its surface. Their thickness may range from a few hundred meters to 1.5 km above the sea surface. Due to the continuous extremely low temperature in the Antarctic region, some of the ice shelves have been persisting for several hundred years. The span of the ice sheet may extend to several hundred square miles.