February 21, 1997
A lush volcanic island in Indonesia provides clues about Mount St. Helens’ recovery from its moon-like state
On August 27, 1883, the volcano Krakatau in the Dutch East Indies erupted with the force of more than 10,000 Hiroshima-type hydrogen bombs, killing an estimated 30,000 people and leaving a wide swath of devastation. The recovery from that volcanic upheaval is providing scientists with glimpses of the renewal that can be expected after more recent eruptions, in particular that of Mount St. Helens in 1980.
Today, the islands surrounding the blasted volcano, in what is now Indonesia, are rich tropical rain forests abundant with vegetation and wildlife, and seemingly an eternity away from the moon-like slopes of Mount St. Helens. Will the area surrounding the Washington volcano recover its majestic forests of Douglas fir and western hemlock within a similar period of time? Definitely, says University of Washington zoologist John Edwards, who recently returned from Krakatau.
As one example of recovery he cites French researchers’ discovery of a proliferation of ballooning spiders on Krakatau only three months after the explosion. On Mount St. Helen’s, there was also a profusion of spiders in the first few weeks after the eruption. Indeed, says Edwards, a lean, bearded New Zealander who was co-leader of a National Geographic Society-financed expedition to Indonesia last fall, “we can clearly see some strong parallels between Krakatau and St. Helens.”
The Krakatau eruption was one of history’s true cataclysms. Located in the Sunda Strait between the islands of Java and Sumatra, the volcano created an explosion that was heard 2,500 miles away in central Australia. The tsunami (or marine pressure wave) generated was a wall of water seven stories high that destroyed more than 160 towns and villages. The airwaves from the blast made four journeys around the globe, and a great belt of ash encircled the Earth. Two-thirds, or about 25 square miles, of Krakatau Island (now named Rakata) disappeared, and one entire side of the volcano was torn away and dumped into the sea.
In 1930, 47 years after the eruption, a new island with its own smoking volcano suddenly appeared in the waters surrounding the battered Krakatau. This was called Anak Krakatau — or child of the volcano. Over the years this second volcano has been erupting and gradually enlarging the island. Indeed, says Edwards, during his visit, the ash from the “child” volcano “made all of us look like chimney sweeps.”
A celebrated entomologist as well as a developmental neuroscientist, Edwards made a decade-long, detailed study of Mount St. Helens’ recovery, beginning just three weeks after the eruption. Of all the contrasts between the Washington volcano and Krakatau, the most puzzling to him is that the volcanic ash from the 1893 eruption appears to be harmless to insect life.
In contrast, the initial ash from the Mount St. Helens upheaval was lethal to the insects in its path. It settled on the hard, waxy shell, and then acted like sandpaper, stripping away the waterproofing layer. The insects lost moisture, and quickly died. “It was just like sandpapering an insect to death,” says Edwards.
On Rakata and its three adjoining islands, there was an abundance of grasshoppers, butterflies and a “marvelous big bee” despite the fine, almost black, basaltic ash that covers the islands. “They were jumping and flying around in all this tephra (volcanic material) seemingly unaffected by it,” says Edwards. “The fact that the insects seemed to be moderately indifferent to the ash was my biggest surprise.”
Why the difference between the sites of the Washington and the Indonesian eruptions? The researcher’s hypothesis is that the ash thrown up in the first days of an eruption is sharp and highly abrasive pumice — basically powdered glass. But in the later stages, the ash has far more mineral content and is less “pointy and abrasive.” The first ash from Krakatau, he says, was almost certainly much more like the ash found shortly after the Mount St. Helens explosion. Even the first, sharp tephra is quickly rendered less lethal, as it gets “matted” by rain, and covered with detritus. So that by the spring of 1981, Edwards found insects living on the pumice surface around Mount St. Helens.
The pumice on Rakata, particularly on the slopes of the blasted volcan, is still deep. “I would rather climb Mount Rainier any day than slog my way up the 2,000 meters (1 1/4 miles) to the top of the volcano,” says Edwards. “It’s very loosely embedded.”
The pumice is bound by the roots of an abundance of plants. To the untrained eye, the entire island looks like a mature tropical forest, with fruit-laden fig trees, deep- buttressed trees with draped creepers, and about 300 species of flowering plants.
Within a century, says Edwards, Mount St. Helens similarly will present the appearance of an undisturbed, subalpine wilderness. Already, he says, the mountain is being revegetated. As with Krakatau, recovery is dependent upon plants establishing a reasonably stable surface. Occasionally, rainfall and erosion will sweep away the vegetation clinging to the pumice substratum, and the cycle of growth will begin once again. “But gradually, as we saw at Krakatau, the landscape stabilizes, more and more plants grow, and they stabilize the surface and hold back the water. Then it feeds on itself, and revegetation continues.”
The parallels between the two volcanoes might seem to be affected by their different geography, one on an island, the other inland. But Edwards insists that Mount St. Helens is also an island, as is every volcano in the Cascade chain. “It is an island of its species. The insects and plants that live on the upper slopes cannot live in the lower elevations, so the volcano might just as well be in the ocean.”
The recovery of Mount St. Helens will come through natural, cyclical regeneration, says Edwards. Although eruptions are viewed as cataclysmic events, they have happened many times before, and “to plants and insects around the ring of fire, it’s just one more eruption to cope with.”
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Edwards is at (206) 543-8829 or hardsnow@u.washington.edu
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