8.+What+is+a+glacier?

Glaciers Glaciers are large masses of snow, recrystallized ice and rock debris that accumulate in great quantities and begin to flow outwards and downwards under the pressure of their own weight.Glaciers form when yearly snowfall in a region far exceeds the amount of snow and ice that melts in a given summer. In this way, massive quantities of material accumulate in relatively small periods of geologic time. Glacier Types Ice Sheets Found only in Antarctica and Greenland, ice sheets are enormous continental masses of glacial ice and snow expanding over 50,000 square kilometers. The ice sheet on Antarctica is over 4200 meters thick in some areas, covering nearly all of the land features except the Transantarctic Mountains, which protrude above the ice. Another example is the Greenland ice sheet. Ice Shelves Ice shelves occur when ice sheets extend over the sea, and float on the water. In thickness they range from a few hundred meters to over 1000 meters. Ice shelves surround most of the Antarctic continent. Retreating ice shelves may provide indications of climate change. For example, the Larsen Ice Shelf has been retreating since the spring of 1998. Ice Caps

Ice caps are miniature ice sheets, covering less than 50,000 square kilometers. They form primarily in polar and sub-polar regions that are relatively flat and high in elevation. To really see the difference between an ice cap and an ice sheet, compare Iceland and Greenland on a globe or world map. The much smaller mass of ice on Iceland is an ice cap.

Ice Streams Ice Streams are channelized glaciers that flow more rapidly then the surrounding body of ice, for instance, the antarctic ice sheet has many ice streams flowing outward. Ice Fields Ice fields are similar to ice caps, except that their flow is influenced by the underlying topography, and they are typically smaller than ice caps. Mountian Glaciers These glaciers develop in high mountainous regions, often flowing out of icefields that span several peaks or even a mountain range. The largest mountain glaciers are found in Arctic Canada, Alaska, the Andes in South America, the Himalayas in Asia, and on Antarctica. Valley Glaciers Commonly originating from mountain glaciers or ice fields, these glaciers spill down valleys, looking much like giant tongues. Valley glaciers may be very long, often flowing down beyond the snow line, sometimes reaching sea level. Peidmont Glaciers Piedmont glaciers occur when steep valley glaciers spill into relatively flat plains, where they spread out into bulb-like lobes. The Malaspina Glacier in Alaska is one of the most famous examples of this type of glacier, and is the largest piedmont glacier in the world. Spilling out of the Seward Ice Field, Malaspina Glacier covers over 5,000 square kilometers as it spreads across the coastal plain. Cirque Glaciers Cirque Glaciers are named for the bowl-like hollows they occupy, which are called cirques. Typically, they are found high on mountainsides and tend to be wide rather than long. Hanging Glaciers

Also called ice aprons, these glaciers cling to steep mountainsides. Like cirque glaciers, they are wider than they are long. Hanging glaciers are common in the Alps, where they often cause avalanches due to the steep inclines they occupy. BY Pawn127