While the presence of glaciers in polar regions - wherein 99 percent of the glacial ice on the planet is stored in form of ice sheets, is quite prominent, these masses of ice are also found in tropics - wherein they are restricted to tall mountains.
How Are Glaciers Classified?
While some sources categorize glaciers into different types on the basis of their morphology, others prefer categorizing them on the basis of their behavior and thermal characteristics. In a broad sense though, glaciers are classified into two categories on the basis of where they are found - 'alpine glaciers' and 'continental glaciers'.
At times, these glaciers are grouped into 'constrained glaciers' and 'unconstrained glaciers' on the basis of whether the ice flow is constrained by the underlying topographical features. Each of these categories are further divided into different types such as ice caps, ice domes, ice field, cirque glaciers, etc.
Different Types of Glaciers
Basically, the formation of glaciers can be attributed to accumulation of snow and ice at a particular place - over the course of time, such that the pressure exerted upon this mass of ice makes it move along the surface slope. If the slope is steep, even 50 ft of snow and ice mass may start moving down as a result of its overall weight.
Even though this phenomenon is most often seen in polar areas wherein the climate is extremely cold and conducive for freezing and thawing, the presence of such conducive environment can also trigger formation of glaciers on mountains in the tropics. The presence of glaciers on the African continent backs this fact very well.
Continental glaciers - aka ice sheets, are the largest of the glacial bodies on the planet, as they cover more than 20,000 square miles of surface area. Ice sheets on the planet are found in Antarctica and Greenland.
At times, buildup of ice causes these ice sheets to extend over the sea, wherein they start floating. These floating ice sheets - with their size ranging between a few hundred to several thousands meters in terms of thickness, are referred to as ice shelves.
Yet another popular glacier type happens to be the tidewater glaciers which are known to eventually terminate into the sea. As these glaciers begin floating on the sea surface, they give in to the pressure that they are subject to and start collapsing in form on huge chunks of ice which eventually float in the sea in form of ice bergs.
The Hubbard Glacier in Alaska is considered to be the largest tidewater glacier in the world. While the surface of ice sheets is cold owing to freezing surroundings, its base tends to be relatively warm as a result of geothermal heating.
In some cases, geothermal heating causes the ice in a particular region of the ice sheet melt faster than the ice in the surroundings, as a result of which the melted part starts moving rapidly - faster than the surrounding ice. This moving part of the ice sheet is referred to as the ice stream.
Even though it is a part of the ice sheet, ice stream is considered to be a type of glacier in glaciology. Lambert Glacier, Bailey Ice Stream, Helheim Glacier, etc. are some examples of ice streams in Antarctica and Greenland.
Alpine glaciers - also referred to as mountain glaciers, are glaciers which form on mountains at a considerable elevation as a result of accumulation of snow and ice that this part of the mountain is subjected to.
This type of glaciers are found on almost all the mountains of the world with considerable - right from Himalayas in Asia to the Rocky mountain range in North America. Such glaciers are known to span across several peaks in a mountain range and cover several thousand miles. If a glacier covers the entire mountain top, it is referred to as an ice cap.
While ice caps are similar to ice sheets, the two are differentiated on the basis of their size. Unlike ice sheets - which span over an area of 20,000 square miles or more, ice caps are typically characterized by a spread of less than 20,000 square miles. These glaciers are more often known to form in highland areas of in polar and sub-polar regions.
While ice caps are not constrained by underlying topography, ice fields - which are quite similar to ice caps, are constrained by underlying topography. Similarly, a mountain glacier which is formed all along the length of a mountain valley is often referred to as a valley glacier.
There are instances wherein the glacier doesn't cover the entire mountain top, nor does it come down the valley; but instead is formed at the cirque i.e. a roughly steep-walled, bowl-shaped depressions in a mountain. This type of glaciers are referred to as the cirque glaciers. The Lower Curtis Glacier in the North Cascades is a good example of this type.
Other than this classification of glaciers, which was based on their morphological features, there exists yet another classification wherein their thermal characteristics are taken into consideration.
Glaciers are categorized into 'temperate glaciers' - which are at their melting point all year round, 'polar glaciers' which are below the freezing point throughout the year and 'sub-polar glaciers' - which demonstrate the traits of temperate as well as polar glaciers.