History
In the months after the eruption, the crater floor of St. Helens remained hot and unstable, with five minor volcanic eruptions, and lava dome construction between May and October 1980. After the eruptions ceased in the winter of 1980, the crater floor cooled down enough for snow and ice accumulation. Beginning with snowfall in the winter of 1980-1981, the glacier began to grow very rapidly in the shadow of the crater. The glacier thickened at a rate of as high as 50 ft (15 m) per year and advanced northward as much as 135 ft (41 m) a year. This glacier growth was discovered by scientists working in the crater about seven to nine years later. However, the existence of the glacier was not publicized until 1999. By 2004, Crater Glacier covered about 0.36 square mile (0.93 km2), about 20% of the glacier area in the pre-1980 glaciers, and there was a western and eastern lobe flowing around the 1980s dome. Due to the gas emissions on the crater floor, there were glacier caves (ice caves) in the once smooth glacial ice, and several of them had been explored by the late 1990s. With the volcanic activity starting in 2004, the glacier lobes were pushed aside and higher by the growth of new volcanic domes. The surface of the glacier, once mostly uncrevassed, turned into a chaotic jumble of icefalls heavily criss-crossed with crevasses and seracs due to movement of the crater floor and lava dome growth. The new domes created since 2004 have almost split the Crater Glacier into two separate glaciers and melted 10% in volume of the glacier's ice. Cold rock on the edge of the glacier insulated the glacier ice from the 1,300 °F (700 °C) lava spewing out of the lava dome, easing concerns of a catastrophic lahar caused by glacier melting.
The thickness of the glacier continues to increase at a slower rate of 15 ft (5 m) per year. Despite the 2004-2008 volcanic activity, the termini of the glacier continue to advance at 3 ft (1 m) per day. By late-May 2008, the two arms of the glacier merged north of the lava dome.
Read more about this topic: Crater Glacier
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