Justastone’sthrownorthof Mount St. Helens, the oddly hummocky terrain is covered with a patch- work of vegetation and small
ponds. Sediment-rich rivers thread
through and meander across floodplains
once hidden beneath lush, tall forests.
Although harshly pruned in the recent
past, the region’s tree of life is beginning
to sprout with vigor.
It has been nearly 30 years since the
largest volcanic eruption ever observed
in the lower 48 states pulverized the top
of Mount St. Helens into a roiling cloud
of rock and ash. A 550-square-kilometer
swath of the Pacific Northwest — an area
about three times the size of the District
of Columbia — was almost immediately
transformed from vibrant ecosystem to
denuded wasteland.
In the decades since, the region has
been a natural laboratory for studying the
processes that bring life back in the aftermath of devastation. Ecological recovery
has proceeded more quickly than many
scientists thought possible, but has nev-
ertheless been a slow and halting affair.
Ecologists have been especially struck
by how important the time and season of
the eruption — a roughly nine-hour episode that began a little after 8: 32 a.m. on
May 18, 1980 — has influenced the mountain’s ecological rebound. The severely
winnowed mix of flora and fauna living
in the shadow of the peak today has been
largely determined by what survived that
mid-spring morning, ecologists note. The
region’s ecosystems may not resemble
those in place before the eruption for a
couple of centuries.
A cataclysm commences
When most people think of a volcanic eruption, they think of a mountain
blowing its top. But on that spring morning, Mount St. Helens —the youngest
and most active major volcano in the
Cascades — blew its side. It was not a
simple eruption but a concatenation of
ruinous events that utterly transformed
the landscape.
The peak itself was profoundly changed.
Mount St. Helens had been 2,950 meters
( 9,677 feet) tall, snowcapped and beautifully symmetric — so much so that the
dormant volcano was often called America’s Mount Fuji, a reference to Japan’s
tallest and most revered peak. That all
changed when the eruption trimmed about
400 meters off the summit of Mount St.
Helens and left a 1.5-kilometer–wide,
amphitheater-shaped crater.
The peak’s former symmetry stemmed
from its geological youth, says Michael
A. Clynne, a geologist with the U.S. Geological Survey in Menlo Park, Calif. Most
material in the volcano’s facade had
erupted during the last 3,900 years, so the
forces of erosion hadn’t had much time to
sculpt the flanks of the peak.
“Mount St. Helens is the baby volcano
of the Cascades,” says Scott F. Burns, a
geologist at Portland State University
in Oregon.
Like many youngsters, the mountain has frequent and erratic outbursts.
Dozens of eruptions have occurred in
distinct clusters over the past 45,000
MAjor/USGS
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