What are the different types of Glaciers?

If the finer details of Ahlmann’s classification of glaciers on morphological basis are neglected for the sake of simplicity, the glaciers may be classified into four broad categories: continental glaciers, ice caps, valley glaciers and piedmont glaciers.

Even though all cate­gories of glaciers are characterized by certain common characteristics, they do differ in their size, position and origin.

Continental glaciers:

In size these are the largest glaciers covering extensive areas. In the most extensive form a continuous mass of ice is known as ice sheet. Antarctica and Greenland have typical examples of such glaciers. About 80% of Greenland and 90% of Antarctica are covered by the snow-covered ice sheets.

These glaciers may form anywhere, with the least regard for topography, such as on plains, plateaus or mountains. From the central part of these glaciers, the movement of ice may be multidirectional.

Thus, continental glaciers are not elongated but flow outward in all directions from their source area. These glaciers cover millions of square kilometers and submerge eyen the higher portions of the land.

Since these glaciers cover large parts of the Antarctica continent, they are called continental glaciers. In fact, these glaciers are ice sheets which are very extensive spreading over surrounding lowlands and enveloping all landforms that they encounter.

The continental ice sheets or continental glaciers of Antarctica and Greenland together cover nearly ten percent of the land area of the globe.

The real extent of the Greenland ice- sheet alone is about 1,300,000 km². It is surrounded by mountains on all sides. In the central region of this ice sheet, its thickness is over 3000 meters.

As a result of the immense pressure, the rock floor has a saucer like surface. The higher peaks of the mountains projecting through the ice-sheet are called nunataks. Under the weight of ice large portions of Greenland and Antarctica have been depressed more than 2000m below sea level.

The Continental glacier of Antarctica is seven times larger than that of Greenland. It forms a plateau that is more than 4300 meters high.

In most places the ice sheets spread over the sea in the form of vast masses of floating shelf ice. The Ross Ice Shelf offers the typical example f of such a shelf ice.

Ice caps:

An ice cap is the covering of snow and ice on mountains from which alpine glaciers (valley glaciers) originate and move in different directions. Ice caps are roughly circular is shape and may form either on an individual mountain or on a mountain range. At present about 50,000 km² is the real extent of the ice caps.

Ice caps which are smaller in size are present on many highlands. These smaller masses of ice may be subdivided into islands ice-caps and plateau ice-caps. Novaya Zemlya and Spits Bergen offer examples of islands ice-caps.

In Iceland there are many plateau ice-caps known as jokull. These ice caps have gently rolling surface. From their margins the glaciers flow in the form of Valley tongues. An ice cap completely buries the underlying landscape. It is always associated with mountains.

Valley glaciers:

Valley glaciers are one of the most characteristic features of greater mountain ranges of the world. They rise in ice caps or single snowfields. Valley glaciers occupy mountain valleys.

These are also called alpine glaciers because such valley glaciers were first observed and studied in the Alps. These glaciers are of different sizes. Some are very long, while others are only a fraction of a kilometer in length.

Such glaciers are longer in the direction of flow than they are wide. This is so because they are confined by the rock walls of the valleys that are occupied by them.

Valley glaciers originate in cirques, deep armchair-shaped hollows which are situated at the valley heads. There are cer­tain small individual glaciers, which occupy the hanging valleys or cirques that are situated high on the side of a deeper valley.

These are called the hanging glaciers. The upper end of an alpine glacier lies in the zone of accumulation, while the lower end lies in the zone of ablation. The snout of the valley glacier is heavily laden with rock debris.

The size and length of a valley gla­cier depends on the snow catch-ment area, on the amount of precipitation and on the tempe­ratures recorded in the valley course.

Piedmont glacier:

Piedmont glaciers are formed when two or more valley glaciers combine on a plain at the base of a mountain. A piedmont glacier is formed and spreads freely over the adjacent lowlands.

The best known example of a piedmont glacier is the Malaspina glacier in Alaska which covers an area of a few hundred square kilometers.

At present piedmont glaciers are rare because the valley glaciers have shrunk inside their valleys in the mountain ranges of the temperate zone. However, during the Pleistocene ice age such glaciers were found in large number.