The great masses of ice that cover the planet's poles and the highlands of the world's great mountain ranges are called glaciers, although they are of two different types.
Glaciers are the remains of the great ice cover that extended over a good part of the Earth's high latitudes during the last quaternary glaciations. They have a great importance as erosive agents of the first order and constitute a great reserve of fresh water of the planet.
Formation and structure of glaciers
Glaciers form when snow falls on the bottoms and slopes of the valleys, in high mountain areas. The thicknesses can reach great proportions, if the snow lost in the thaws is less than the one that accumulates during the snowfall. Its compact mass is produced because each snowfall compresses the previously fallen snows. If the heat fails to fuse the ice, it increases in thickness and begins to move towards the bottom of the valley.
The density of snow increases with depth. At the base of the glacier the highest density is produced due to the weight of the ice that it has to support. But this ice from the base of the glacier flows as if it were liquid. The center of the glacier moves faster than the lateral masses, so there are breaks, tensions and stretches that manifest in huge and deep cracks in the upper layers.
The glacier is moving and tearing out the outgoing rocks it finds in its path. These rock fragments are called Morrenas. In the final area of the glacier, where the thaw occurs, small hills are formed whose set is called the terminal Morrena.
While the glacier continues to maintain snow feed in the upper part, the sliding down the valley is maintained. Finally, the glacier melts or falls apart forming streams.
There are occasions when several glaciers flow through a valley at the foot of a mountainous system, at their junction they usually form an extensive glacier wider than long; These glaciers are called Piedemonte.
Polar ice caps and continental ice sheet
When a glacier covers plateaus and high-latitude islands, it is called the Polar Cap. Alpine glaciers are usually born from these polar ice caps, which descend through the valleys, even reaching the sea.
When the glacier is so extensive and ancient that it covers the surface of a continent, it is called the continental ice sheet. They usually flow slowly outwards and reach the oceans, where they fragment into different sizes during the summer forming the icebergs.
Normally, the term is used to describe the ice masses that cover Antarctica and Greenland, as well as those that covered most of the northern hemisphere during the Pleistocene ice age, in the Quaternary period.
A large glacier mantle, with more than 1.8 million square kilometers of surface and exceeding 2,700 meters of maximum thickness, covers almost the entire surface of Greenland. The rock only emerges near the coast, where the glacier fragments into ice tongues reminiscent of valley glaciers. From the place where these languages reach the sea, pieces of ice of various sizes are broken during the summer and form icebergs.
A similar type of glacier covers the entire Antarctic, with an area of 13 million square kilometers
|Surface waters: Lagos|