Muir Glacier, a glacier of southeastern Alaska in Glacier Bay National Park and Preserve. It was named after John Muir, who discovered it in 1879. The glacier is more than 10 miles (16 km) long and lies on the southern slopes of the St. Elias Mountains. Its lower end, on Glacier Bay, is about 80 miles (130 km) west-northwest of Juneau. Here ice cliffs nearly two miles (3 km) wide rise some 265 feet (80 m) above the water which undermines them until huge chunks break off. The glacier's edge has been receding since the 1800's, forming Muir Inlet.
Muir Glacier is one of the most active glaciers in Alaska. Parts of it move as much as 30 feet (9 m) a day, although the main trunk averages only 7 feet (2 m) a day. An earthquake in 1899 speeded the downhill ice flow and increased the amount lost to the sea.