<P> The semiarid climate of Wyoming still manages to support about a dozen small glaciers within Grand Teton National Park, which all show evidence of retreat over the past 50 years . Schoolroom Glacier is located slightly southwest of Grand Teton is one of the more easily reached glaciers in the park and it is expected to disappear by 2025 . Research between 1950 and 1999 demonstrated that the glaciers in Bridger - Teton National Forest and Shoshone National Forest in the Wind River Range shrank by over a third of their size during that period . Photographs indicate that the glaciers today are only half the size as when first photographed in the late 1890s . Research also indicates that the glacial retreat was proportionately greater in the 1990s than in any other decade over the last 100 years . Gannett Glacier on the northeast slope of Gannett Peak is the largest single glacier in the Rocky Mountains south of Canada . It has reportedly lost over 50% of its volume since 1920, with almost half of that loss occurring since 1980 . Glaciologists believe the remaining glaciers in Wyoming will disappear by the middle of the 21st century if the current climate patterns continue . </P> <P> In the Canadian Rockies, glaciers are generally larger and more widespread than to the south in the Rocky Mountains . One of the more accessible in the Canadian Rockies is the Athabasca Glacier, which is an outlet glacier of the 325 km (125 sq mi) Columbia Icefield . The Athabasca Glacier has retreated 1,500 m (4,900 ft) since the late 19th century . Its rate of retreat has increased since 1980, following a period of slow retreat from 1950 to 1980 . The Peyto Glacier in Alberta covers an area of about 12 km (4.6 sq mi), and retreated rapidly during the first half of the 20th century, stabilized by 1966, and resumed shrinking in 1976 . The Illecillewaet Glacier in British Columbia's Glacier National Park (Canada), part of the Selkirk Mountains (west of the Rockies) has retreated 2 km (1.2 mi) since first photographed in 1887 . </P> <P> In Garibaldi Provincial Park in Southwestern British Columbia over 505 km (195 sq mi), or 26%, of the park, was covered by glacier ice at the beginning of the 18th century . Ice cover decreased to 297 km (115 sq mi) by 1987--1988 and to 245 km (95 sq mi) by 2005, 50% of the 1850 area . The 50 km (19 sq mi) loss in the last 20 years coincides with negative mass balance in the region . During this period all nine glaciers examined have retreated significantly . </P> <P> There are thousands of glaciers in Alaska but only few have been named . The Columbia Glacier near Valdez in Prince William Sound has retreated 15 km (9.3 mi) in the last 25 years . Its calved icebergs partially caused the Exxon Valdez oil spill, when the tanker changed course to avoid the ice tips . The Valdez Glacier is in the same area, and though it does not calve, has also retreated significantly . "A 2005 aerial survey of Alaskan coastal glaciers identified more than a dozen glaciers, many former tidewater and calving glaciers, including Grand Plateau, Alsek, Bear, and Excelsior Glaciers that are rapidly retreating . Of 2,000 glaciers observed, 99% are retreating ." Icy Bay in Alaska is fed by three large glaciers--Guyot, Yahtse, and Tyndall Glaciers--all of which have experienced a loss in length and thickness and, consequently, a loss in area . Tyndall Glacier became separated from the retreating Guyot Glacier in the 1960s and has retreated 24 km (15 mi) since, averaging more than 500 m (1,600 ft) per year . </P>

4 different types of precipitation that are key for glacier survival