image (533 Kb)
On May 18,
1980, the Mount St. Helens volcano erupted. A series of earthquakes
preceded the eruption and triggered a collapse of the north side
of the mountain into a massive landslide. This avalanche coincided
with a huge explosion that destroyed more than 700 square kilometers
(270 square miles) of forest in a few seconds, and sent a billowing
cloud of ash and smoke approximately 24 kilometers (15 miles) into
the atmosphere. Because the eruption occurred in an easily accessible
region of the United States, Mount St. Helens has provided unprecedented
opportunities for U.S. researchers to collect scientific observations
of the geology of an active volcano and document the regional ecological
impact and recovery from an eruption.
During an International
Space Station expedition, astronauts observed and captured this
detailed image of the volcano's summit caldera. In the center of
the crater sits a lava dome that is 267 meters (876 feet) above
the crater floor and is about 1,067 meters (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.
The upper slopes
of the 1980 blast zone begin at the gray-colored region that extends
north 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 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 46 meters (150
feet), but in places up to 183 meters (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.
was provided by the Earth Sciences and Image Analysis Laboratory
at Johnson Space Center. The International
Space Station Program supports the laboratory to help astronauts
take pictures of Earth that will be of the greatest value to scientists
and the public, and to make those images freely available on the
Internet. Additional images taken by astronauts and cosmonauts can
be viewed at the NASA/JSC Gateway
to Astronaut Photography of Earth.