Untitled Document
Mount St. Helens volcano
erupted in Washington state 24 years ago this week, on On May 18, 1980. A series
of earthquakes preceded the eruption, triggering a collapse of the north side
of the mountain into a massive landslide. This avalanche coincided with a huge
explosion that destroyed over 700 square kilometers (270 square miles) of forest
in a few seconds, and sent a billowing cloud of ash and smoke 24,000 meters
(80,000 feet) into the atmosphere.
Because the eruption occurred
in an easily accessible region, Mount St. Helens has provided unprecedented
opportunities for researchers to collect scientific observations of the geology
of an active volcano and document the regional ecological impact and recovery
from an eruption.
On an earlier Space Station
expedition, astronauts observed and captured this detailed image of the volcano’s
summit caldera, the somewhat bowl-shaped depression left by the eruption. In
the center of the crater sits a lava dome that is 876 feet above the crater
floor and is about 3,500 feet in diameter. The dome began to form after the
1980 eruption, but there have been no dome building eruptions for more than
a decade.
Afternoon lighting accents
the flow features in the volcanic and debris flows and the steep valleys eroded
into the loosely consolidated material near the summit. The upper slopes of
the 1980 blast zone begin at the gray colored region that extends north (upper
left) from the summit of the volcano. The volcanic mud and debris from the eruption
choked all of the drainages in the region.
The deeply incised valley
to the left (west) is the uppermost reach of the South Fork of the Toutle River.
Devastating mudslides buried the original Toutle River Valley to an average
depth of 150 feet, but in places up to 600 feet. Even today, heavy precipitation
can send unconsolidated volcanic debris downstream.
A special dam was constructed
on the North Fork of the Toutle River to catch the sediments from moving further
downstream. Levees and dredging also help stem further mudslides. The dark green
area south of the blast zone is the thickly forested region of the Gifford Pinchot
National Forest.
This astronaut photograph
was taken Oct. 25, 2002 with a Kodak DCS760 digital camera equipped with an
800 mm lens.
Credit: NASA/ISS/Earth
Observations Laboratory, Johnson Space Center
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