Mount St. Helens' Aftermath

A volcano erupts and the world seems to end. What happens afterwards? May 18 marks the 30th anniversary of the eruption of Mount St. Helens in Washington state and scientists to this day use what's being learned there to challenge established thinking about how landscapes evolve and rebound.

Mount St. Helens is an active volcano located in Skamania County, Washington, in the Pacific Northwest region of the United States. It is 96 miles south of Seattle and 50 miles northeast of Portland, Oregon. Mount St. Helens takes its English name from the British diplomat Lord St Helens, who made a survey of the area in the late 18th century.

The volcano is located in the Cascade Range and is part of the Cascade Volcanic Arc, a segment of the Pacific Ring of Fire that includes over 160 active volcanoes.

Mount St. Helens is most famous for its catastrophic eruption on May 18, 1980, which was the deadliest and most economically destructive volcanic event in the history of the United States. Fifty seven people were killed; 250 homes, 47 bridges, 15 miles of railways, and 185 miles of highway were destroyed. The eruption caused a massive debris avalanche, reducing the elevation of the mountain's summit from 9,677 feet to 8,365 feet and replacing it with a 1 mile wide horseshoe shaped crater.

So a volcano can be massively destructive. But there is another side to consider.

Ecological succession, a fundamental concept in ecology, refers to a more or less predictable and orderly change in the composition or structure of an ecological community. Succession may be initiated either by formation of new, unoccupied habitat (e.g., a lava flow or a severe landslide) or by some form of disturbance (e.g. fire or logging) of an existing community. Succession that begins in areas where no soil is initially present is called primary succession, whereas succession that begins in areas where soil is already present is called secondary succession.

The relationship between vegetation and environment can be initially random then, over time, environmental effects such as moisture and soil conditions began to play more of a role. Such "deterministic" processes, as opposed to happenstance, are just now being observed at Mount St. Helens and are the subject of papers in early 2010 and late last year in the Journal of Vegetation Science. It is how nature assembles its communities and ecology as it starts to transform the landscape.

One study by University if Washington (UW) professor Roger del Moral, found that distance is important in determining which species arrive on a site. Development is governed by a functional clock, not by the calendar. Thus, of two sites that are similar except being at different elevations, the higher elevation site will be colder and develop more slowly than the lower, warmer, site.

Hinckley (also of UW) and his students have studied how different species, stand compositions and ages affected the recovery of trees that were covered with ash. While young trees recovered in as little as two seasons, old growth silver firs underwent extensive decline, die back and mortality. Silver firs have stiff needles and rigid branches that held onto the ash, reducing the amount of sunlight that reaches their needles and making them less vigorous.

Snow and erosion patterns have also shaped recovery in the blast zone. For example, many very small, but surprisingly old, mountain hemlock and silver fir trees were covered in snow when the eruption occurred. Those trees survived and today they form stands over 30 feet tall with many of the trees producing seed for the last several years.

The initial ash from Mount St. Helens was lethal to many insects. It stripped away the waterproofing layer, insects lost moisture and quickly died. "It was like sandpapering an insect to death,"John Edwards of UW says. But as the ash became less gritty, predatory beetles, ballooning spiders and other bugs began to arrive. It was calculated that 1,500 insect species were carried by winds into the blast zone from the surrounding forest and farmlands.

For further information: http://uwnews.org/article.asp?articleid=57570