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Mount St. Helens' Aftermath
Source: ENN, Date: , 2010
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.
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.
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.
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
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.
(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.
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