Glaciers are made of large amounts of fallen snow that has compressed into large, thickened ice masses or rivers. Glaciers can expand, contract and move very slowly forward due to their enormous weight. Most glaciers are found near the poles, but there are some located on every continent except for Australia. The largest glaciers are huge ice sheets found in Greenland and Antarctica. Both would cause significant rises in sea level if they were to melt.
How do glaciers form?
Glaciers form over many years and occur where snow remains in one location for a long time. This allows the snow to form into ice, which is the first step in the creation of a glacier. Glaciers generally form in areas where the temperature is cool during the summer and there are regions of high snowfall. Glaciers form in a region where the levels of snow and ice that accumulate over winter are more than the amount that melts or is blown away by the wind during warmer months. As the snow and ice compacts and thicken the heavy weight causes the ice to move. The snow and ice melts and refreezes causing layers of granular ice called firn. The firn is compacted by the weight of the accumulating snow and ice on top of it. The firn becomes denser as years pass and it is compacted further. The snow grains turn into ice crystals making the firn harder and denser. Layers of compacted firn become blue glacier ice.
Glaciers are unique in that they are not stationery but actually move, grow and shrink. Glaciers flow outwards and downwards depending on their location and the type of glacier. Valley glaciers will flow down a valley moved by gravity and the weight of compacted snow and ice. They don’t flow outwards unless there is a break in the valley wall. Continental glaciers, also called ice sheets, flow both outwards and downwards from a central location. Glaciers can also shrink in size if the temperature, evaporation and wind erosion are higher than the amount of snow accumulated.