GLACIER BAY NATIONAL PARK AND PRESERVE

national park and preserve in southeastern Alaska, U.S., on the Gulf of Alaska. It was proclaimed a national monument in 1925, established as a national park and preserve in 1980, and designated a World Heritage site in 1992. The park covers an area of 5,040 square miles (13,053 square km) and includes Glacier Bay itself, the northern, southern, and western slopes of Mount Fairweather (15,300 feet [4,663 metres]), and the U.S. portion of the Alsek River. Adjoining the park to the north is Tatshenshini-Alsek Wilderness Provincial Park in British Columbia, Canada. Among the most notable features of the park are great tidewater glaciers. As recently as 200 years ago almost all of Glacier Bay, a fjord, was covered by the Grand Pacific Glacier; this glacier was more than 4,000 feet (1,200 metres) thick and some 20 miles (32 km) wide. Since then the ice has been retreating, and Glacier Bay, now 65 miles (105 km) long, has taken its present form. As the original glacier diminished in size, it left 20 separate glaciers, of which 12 are tidewater glaciers that calve into the bay. In the process of calving, blocks of ice up to 200 feet (61 metres) high break loose and fall into the water with tremendous force. The Johns Hopkins Glacier, for example, cannot be approached any nearer than about 2 miles (3 km) by sea because of the volume of the ice blocks that break loose from its cliffs. Most visitors to the park come by cruise ship and thus view the glaciers from the water. The park has a dramatic range of plant life, in particular of vegetation returning to a landscape long covered by ice, and an unusual variety of wildlife. Glacial moraines have mosses and lichens growing on them, lush coastal rainforest includes huge Sitka spruce and western hemlock, and alpine tundra occurs above elevations of 2,500 feet (760 metres). Wildlife includes wolves, brown and black bears, mountain goats, deer, moose, eagles, trumpeter swans, seals, and endangered humpback whales. The park's headquarters are at Gustavus, near the mouth of the bay. Mountain glaciers In this discussion the term mountain glaciers includes all perennial ice masses other than the Antarctic and Greenland ice sheets. These ice masses are not necessarily associated with mountains. Sometimes the term small glaciers is used, but only in a relative sense: a glacier 10,000 square kilometres (4,000 square miles) in surface area would not be called small in many parts of the world. Classification of mountain glaciers Mountain glaciers are generally confined to a more or less marked path directing their movement. The shape of the channel and the degree to which the glacier fills it determine the type of glacier. Valley glaciers are a classic type; they flow at least in part down a valley and are longer than they are wide. Cirque glaciers, short and wide, are confined to cirques, or amphitheatres, cut in the mountain landscape. Other types include transection glaciers or ice fields, which fill systems of valleys, and glaciers in special situations, such as summit glaciers, hanging glaciers, ice aprons, crater glaciers, and regenerated or reconstituted glaciers. Glaciers that spread out at the foot of mountain ranges are called piedmont glaciers. Outlet glaciers are valley glaciers that originate in ice sheets, ice caps, and ice fields. Because of the complex shapes of mountain landscapes and the resulting variety of situations in which glaciers can develop, it is difficult to draw clear distinctions among the various types of glaciers. Mountain glaciers also are classified as polar, subpolar, or temperate and their surfaces by the occurrence of dry-snow, percolation, saturation, and superimposed-ice zones, as for ice sheets.