Let's learn How the glaciers form?
You know, a glacier is like a "river of ice", with incredible erosive capabilities -- but moves slowly over land, only a few centimeters a day.
A considerable amount of snow accumulation is necessary for glacial ice to form. Thus, glaciers can form only in regions where snow cover is permanent, that is at the poles (i.e., at high latitudes) and at high altitudes, where year-round temperatures remain low. Snow accumulates there from year to year. When the snowfall of the winter exceeds the loss of snow (due to temperature rise and subsequent melting) in the summer, a new layer of snow is added to the surface of the glacier.
Surface snow, actually known as "snowflakes" -- hexagonal crystals of frozen water readily precipitated from the atmosphere. As thick layers of snow accumulate, the deeply buried hexagonal snowflakes become more tightly packed together and take on rounded shapes. With enough time, the deeply buried, well-rounded grains become very densely packed, expelling most of the air trapped between the grains. "The granular snow grains are called firn and take approximately two years to form." The process of compaction from snow to glacial firn is called "firnification."
The thick, overlying snowpack exerts tremendous pressure onto the layers of buried firn, and these grains begin to melt a tiny bit without any increase in temperature. The firn and meltwater slowly recrystallize. When the ice mass grows thick enough (about 50 meters or more) the firn grains fuse into a huge mass of solid crystalline glacial ice. This transformation process may take several decades to hundreds of years because the rate of glacial ice formation is highly dependent upon the amount of snowfall and the annual range of temperature. (Really, you can compare the crystallization process of glacial ice as a type of metamorphic rock).
Finally, the weight of the glacier exerts so much pressure that the firn and snowmelt. The meltwater makes the bottom of the heavy glacier slicker and able to spread across the landscape under its own weight as well as pull of gravity.
