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St. Helens Anniversary Spotlights Surprising Rebound

Stefan Lovgren
for National Geographic News
May 13, 2005
 
When Mount St. Helens erupted 25 years ago, the north face of the
volcano collapsed in a massive rock-debris avalanche. The landslide and
the accompanying flow of searing gases instantly obliterated the
surrounding landscape in southwestern Washington State on May 18, 1980.

(Recent eruptions have been markedly less cataclysmic—see recent photo.)

In 1980, after flying in by helicopter, Virginia Dale was among the first ecologists to see the devastation up front.

"It appeared to be totally lifeless," said Dale, who works at the Oak Ridge National Laboratory in Tennessee. "Everything was gray. There was nothing there."

Or so it seemed.

On closer inspection Dale found pockets of survival, often something as small as a piece of root close to the surface. When she came back in summer, she saw that a few herbs known as lupines had begun to spring to life. "The fact that anything could do that was just phenomenal," she said.

In fact, scientists are stunned at the area's recovery. In the 25 years since the eruption, Dale has counted more than 150 species of wildflowers, shrubs, and trees that have returned to the debris deposit she has been studying.

To Dale and other scientists, Mount St. Helens has been a unique natural laboratory in which to test models of ecological recovery after a natural disaster.

The ecological recovery turned out to be different than the models had predicted. "The patterns of impact and destruction were not as anticipated, and survival and establishment [of new plants and animals in affected areas] have also been different than theory would have predicted," Dale said.

Dale, who received National Geographic Society funding for her research, is the co-editor of a new book, Ecological Responses to the 1980 Eruptions of Mount St. Helens. The book documents the research of dozens of scientists studying Mount St. Helen's comeback. She is also the co-author of an article on the St. Helens that appears this week in the academic journal Science.

Breaking the Rules

Mount St. Helens erupted with 500 times the force of the Hiroshima atomic blast. The accompanying landslide was the largest in recorded history. Forests, meadows, streams, and lakes were turned into ash-gray wastelands.

"But it wasn't just one event," Dale said. "You had pyroclastic flow"—a mix of hot gas and ash that speeds down a volcano's slope—"debris avalanche, and heavy ash deposits. And each of these events had a different pattern of survival and then recovery."

Traditional thinking on ecological succession—the pattern by which life-forms come back over time—held that first, certain species would recover, and then others would, along a particular order. For instance, grasses might appear, followed by rabbits and other animals that eat grasses.

But the reality at Mount St. Helens has proved far more complex. Ecological succession has proceeded at different speeds in different areas. Succession proved to be highly unpredictable.

"Chance factors, such as what time of day or year the eruption occurs, can strongly influence survival and the course of succession," Dale said.

For example, the eruption occurred in May, when some of the mountain was still covered in snow. The snow proved to have a strong influence on plant survival. Also, many of the salmon that inhabit local rivers were out to sea when the volcano erupted—as they are every May.

Natural Laboratory

Many other animals also did better than expected.

Twelve of the 15 amphibian species found in the Cascade mountains survived in many locations. Today amphibians thrive even in areas where no amphibians survived the eruption. Not long after the blast, frog, toad, salamander, and newt species traveled several miles of inhospitable ground and moved into the affected habitats.

The recovery of Spirit Lake was especially impressive. Located on the northern side of Mount St. Helens, the lake had been displaced by an enormous avalanche of rock and superhot gases, and covered with floating trees that had been ripped from the surrounding forest.

But instead of taking decades to recover, Spirit Lake underwent a complex set of biological, chemical, and physical changes. Within about six years the lake looked almost undisturbed.

Frederick Swanson is a geologist with the U.S. Department of Agriculture's Forest Service in Corvallis, Oregon. He studied how the physical landscape around St. Helens functioned as a stage on which ecological processes played out.

"We found that there was a succession of geological processes," Swanson said.

"Just as we think of ecological succession—where some plants come into a bare area and prepare the site for the occupancy by other plants and animals—so too in the geophysical world did we find a succession of processes paving the way for each other," he said.

For example, in some areas falling debris removed the top layer of the land, liberating buried plant parts. "We usually think of erosion as bad, but in this particular set of circumstances it actually helped the ecological recovery," Swanson said.

The scientists agree that Mount St. Helens, with its easy accessibility and close proximity to research institutions, has been the perfect laboratory.

"It has been an incredible place to study and learn because of the great diversity of things that happened. And we could come in and observe them immediately after they happened and in some cases as they occurred," Swanson said. "Our understanding of volcanic processes [among other things] has been greatly enhanced."

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