Glaciers need extremely specialized climatic conditions. Most are found in areas with heavy snowfall in the winter and cold temperatures in the summer. These circumstances ensure that the snow accumulated throughout the winter does not melt during the summer. Such circumstances are common in polar and high-alpine locations.
A glacier forms when large quantities of snow fall into a relatively small area, causing it to get covered by ice. The weight of this ice then causes more snow to be absorbed into the growing body of ice. This process continues until all the available land is covered and no new snow can fall to replenish the existing ice. Glaciers can grow very large in just a few years if they receive enough snow. They tend to be much smaller over time if they are not receiving new snow.
The type of climate required for glaciers to form varies depending on the location of these frozen bodies of water. In general, they require cold winters and cool summers. But there are exceptions to this rule. For example, tropical glaciers have been observed in certain regions of South America and Asia. These bodies of ice accumulate each year as raindrops freeze after falling onto the ground surface.
The amount of precipitation, whether snowfall, freezing rain, avalanches, or wind-drifted snow, is critical to glacier life. Low temperatures, for example, are favorable for glacier formation in particularly dry portions of Antarctica, resulting in a desert on top of a ice sheet.
Glaciers form when water vapor from the atmosphere freezes into small crystals that accumulate on top of each other until they become large enough to fall as snow. As more and more snow falls, it compacts under its own weight and becomes an ice mass. Glaciers can be found in both the land and sea worlds. Land glaciers are formed where there is sufficient precipitation and no major rivers to prevent accumulation of snow. Marine glaciers are found in polar regions around the world where ocean waters are frozen in large bodies known as ice shelves. Ice shelves act like giant arms that reach out from the edge of the continent toward open water, preventing them from being flooded by land-based glaciers.
As glaciers melt, they lose their protective cover and become vulnerable to further erosion by wind and water. If enough heat is added to the melting ice, it will also begin to flow again, leading to a new glacial advance. Human activities such as burning fossil fuels and removing forest cover can increase the rate of glacier retreat; others factors including volcanic eruptions and earthquakes can have the same effect.
A glacier must meet three conditions: (1) a cold local environment (polar latitudes or high elevation); (2) abundance of snow; more snow must fall than melt; and (3) snow must not be removed by avalanches or wind. Glacier scientists use the term "calcite" to describe the mineral form of calcium carbonate that occurs in large crystals within glacial rocks. Calcite is very stable under pressure, so it can be used to date the age of the rock from which it was extracted.
Glaciers are known for their spectacular colors, ranging from white to red. The color depends on the type of sediment present in the water that melts to create the glacial ice. If much of the sediment is clay, then the water will be dark blue. If much of the sediment is sand, then the water will be light blue. If there is little or no sediment, then the water will be clear yellow or white.
In general, glaciers move down mountainsides at a rate of about 1 foot per year. However, some glaciers flow faster or slower depending on how much rain or snow falls on them. The shape of a glacier is also important; glaciers can be flat or rounded. Flat glaciers tend to cover larger areas of ground than rounded ones. When glaciers retreat away from the poles, they may leave behind bodies of ice called ice caps.