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The Recovery of Mount St. Helens
| Article
# : |
20373 |
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Section : |
NATURAL SCIENCE
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| Issue
Date : |
6 / 1992 |
2,019 Words |
| Author
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Virginia H. Dale
Virginia H. Dale is a research ecologist with the
Environmental Sciences Division of the Oak Ridge National
Laboratory, Oak Ridge, Tennessee. |
Twelve years ago, on May 18, 1980, Washington State's Mount St. Helens erupted for the first time since 1921. Its explosion caused the north side of the mountain to collapse into the north fork of the Toutle River Valley and released gases, ash, and tephra (airborne material) skyward. Only a small area was covered by pyroclastic materials, but more than 500 square kilometers (193 square miles) of forest were literally blown down by the force of the explosion. The heat of the blast scorched many additional square miles of forest. The heat also melted much of the mountain's glaciers, and this water swept debris into flows of mud down the river valleys. All told, the event devastated more than 600 square kilometers (230 square miles) of forested and clear-cut land in the southern Cascade Mountains.
Although much damage occurred, the large area of land cleared of vegetation now serves as a natural laboratory for botanists and ecologists to study the natural process of plant recovery. Such studies enable scientists to formulate improved prescription for reclamation of areas cleared by human activities.
Disturbance type affected plant survival and recovery
The massive area affected by the eruption created logistical problems in coordinating the many scientific studies and collating the data that could allow comparison of the recovery between areas that experienced different disturbances. Researchers set up a system of permanent plots that could be monitored over many decades. The idea was to establish a sample design whereby the few, small plants appearing during the first years of recolonization could be observed and also the large trees that are expected to grow over future decades would be recorded. A system of circular plots (each 7.9 meters--26 feet--in radius) was set up at 50-meter (164-foot) intervals on linear transects in each of the major kinds of disturbance zones. Scientists studying vegetation reestablishment over the entire devastation zone used this sample design to facilitate comparison of recovery patterns.
The type of volcanic disturbance greatly influenced both the survival and recovery pattern of the vegetation. No plants survived on the 0.25 square kilometer (0.10 square mile) pyroclastic flow, where the area was first buried by the debris slide from the north side of the mountain and was then covered by a mixture of hot gases and pumice. The few plants or animals now found there were brought in by the wind and established themselves on the newly created substrate. However, the most abundant plant species in
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