What types of glaciers are there?
The Larsen Ice Shelf in Antarctica, March 21, 1998. Taken at the beginning of the antarctic winter, the ice shelf is clearly visible. Notice that sea ice is forming over the ocean to the right the ice shelf.
—NSIDC AVHRR stretched thermal-band Image, March 21, 1998.
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.
Kalstenius Ice Field, located on Ellesmere Island, Canada, shows vast stretches of ice. The icefield produces multiple outlet glaciers that flow into a larger valley glacier. The glacier in this photograph is three miles wide.
—Royal Canadian Air Force photograph/NSIDC
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. Check out some of the remotely sensed satellite images scientists used to monitor the ice shelf breakup.
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 are channelized glaciers that flow more rapidly than the surrounding body of ice. For instance, the Antarctic ice sheet has many ice streams flowing outward.
In this undated photograph, Variegated Glacier winds through the Saint Elias Mountains in Alaska, terminating near Yakutat Bay. An ice field is visible in the upper left hand corner of the photograph.
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.
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.
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.
The massive lobe of Malaspina Glacier is clearly visible in this photograph taken from a Space Shuttle flight in 1989. Agassiz Glacier is to the left of Malaspina Glacier, and towards the top of the photograph Seward Ice Field is just visible.
–Photograph courtesy of SPACE.com and NASA.
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 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.
Lamplugh Glacier, in Glacier Bay, Alaska, shows the snout of a typical tidewater glacier. Because the surface of the ice is heavily crevassed and jagged, small bits of ice have broken off, seen here floating in the water.
—AGS collection, 1941/NSIDC
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.
As the name implies, these are valley glaciers that flow far enough to reach out into the sea. Tidewater glaciers are responsible for calving numerous small icebergs, which although not as imposing as Antarctic icebergs, can still pose problems for shipping lanes.