national park and preserve in southeastern Alaska, U.S., on the Gulf of Alaska (Alaska, Gulf of). 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 (Fairweather, Mount) (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.