Crater Glacier - Description

Description

True to its name, the glacier lies inside the north-facing crater left by the 1980 eruption of Mount St. Helens. A massive central lava dome emplaced from 1980 to 1987 occupies the center of the crater, and the glacier formed in the shape of a horseshoe around the dome, with two terminal moraines on the eastern and western sides. The elevation of the glacier is about 6,794 ft (2,071 m). Heavy winter snowfall, repeated snow avalanches, rockfalls, and sun-shading by the surrounding cliffs to the south, led to the exceptionally rapid growth of this glacier. Thus, the glacier composition is estimated to be six-tenths ice and four-tenths rock. In addition, the glacier is very thick, averaging about 328 feet (100 m) with a maximum thickness of around 656 feet (200 m); nearly as deep as Mount Rainier's Carbon Glacier. None of the ice is older than the year 1980, however, the volume of the new glacier is about the same as all the pre–1980 glaciers combined. The surface of the glacier looks dark and dirty in the summer due to the numerous rockfalls from the steep, unstable crater walls along with ash from eruptions, all of which helps to insulate and protect the growing glacier. The 2004-2008 volcanic activity has created a new dome, which has split the glacier almost completely in half on the south end of the glacier. In spite of the four-year lava dome building period, the glacier remains North America's youngest and fastest growing glacier. With the joining of the termini on the north end of Crater Glacier in May 2008, the body of ice completely encircles the lava dome. Meltwater from the glacier gives rise to Loowit Creek.

Pre-2004 eruption glacier caves of Crater Glacier

In 2000, glacier caves were discovered on the then-smooth glacier surface. Many of these glacier caves were big enough to explore, like the glacier caves on the summit of Mount Rainier. Most of the glacier caves were located near the 1980s lava dome, where hot steam and volcanic gas emissions from hidden fumaroles on the crater floor or lava dome melted holes in the young glacial ice. About 7,900 feet or 2.4 km of underground caves and passageways in the glacier were mapped and studied.

Other glaciers and new rock glaciers

Since 2004, new glaciers have formed on the crater wall above Crater Glacier feeding rock and ice to Crater Glacier below. In addition, there are two rock glaciers to the north of the eastern lobe of Crater Glacier and one north of the western lobe.