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Science After the Volcano Blew

Research near Mount St. Helens proceeded despite bureaucratic hurdles, limited funding and an extremely hazardous environment

Douglas Larson

2010-07LarsonF1.jpgClick to Enlarge ImageOn May 20, 1980, two days after the catastrophic eruption of Mount St. Helens, U.S. Geological Survey (USGS) scientists landed in a helicopter near the volcano’s base, a short distance from what should have been the south shore of Spirit Lake. The lake, just 8 kilometers north-northeast of the volcano, was the largest of dozens of subalpine lakes battered by the eruption. Unable to see much that resembled a lake, the scientists suspected that Spirit Lake had either boiled away or was buried by avalanche debris. Further investigation revealed that the lake had survived, but it looked more like land than water because thousands of logs, tons of volcanic ash and other rubble blanketed its surface.

2010-07LarsonF2.jpgClick to Enlarge ImageVolcanic activity and mudflows from Mount St. Helens created Spirit Lake roughly 3,000 years ago. But the 1980 eruption nearly blasted it to extinction. A debris avalanche, triggered by the eruption, slammed into the lake like an enormous tidal wave, sweeping water out of the lake basin northward and up the steep slopes of nearby Mount Margaret. Some water may have spilled over Margaret’s summit—about 800 meters above the lake’s surface. Most of the lake water rushed back down, stripping slopes of trees, rock and soil—down to bedrock—and washing all that was dislodged into the lake. Debris pushed the lake’s surface elevation 60 meters higher than its pre-eruption level of 975 meters, greatly altering its morphometry and blocking its natural outlet, the North Fork Toutle River. Previously kept in hydrological balance by that outlet, the lake had become locked in a hydrologically unstable basin by a debris dam 150 to 180 meters thick.

Within hours of the eruption, pyroclastic flows, mudflows, heavy tephra fall and high-temperature geothermal waters poured into Spirit Lake, altering its waters. An initial survey described the lake as hypereutrophic, or oversupplied with nutrients; thoroughly anoxic; blackish in appearance; highly concentrated with metals and organic compounds; and containing extraordinarily prolific bacteria that reached densities thought to be unprecedented in natural aquatic systems. Phytoplankton, zooplankton and macroinvertebrates were almost nonexistent, with most taxa thought to be eliminated. Lacking oxygen, fish and other aquatic vertebrates perished. Considering these conditions, scientists predicted that the lake would take 20 years to recover, perhaps longer.

2010-07LarsonF3.jpgClick to Enlarge ImageI have spent the past 30 years observing the post-eruption response and recovery of Spirit Lake, first as a limnologist for the Portland District of the U.S. Army Corps of Engineers, and later, occasionally, as an independent researcher. Despite early predictions, the lake had made a remarkable recovery by 1986, which I reported in this magazine (see “The Recovery of Spirit Lake,” American Scientist, March–April 1993). In that article, I alluded to the unusual field-science experiences and challenges involved with working in a devastated landscape near the base of a still-active volcano. Over the past three decades, I have come to better appreciate the scale of those challenges and additional, human-made obstacles. Both took a toll on a once-in-a-lifetime scientific opportunity to study the microbial and chemical transformations—as well as the restoration—of a lake impacted so severely by a volcano. Needed research was accomplished. But more could and should have occurred. My hope is that by sharing a deeper explanation of my experiences, others will learn from the failures and the successes at Spirit Lake.

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