The Army Corps of Engineers' Short-Term Response to the Eruption of Mount St. Helens

Article excerpt

AT 8:32 ON THE MORNING of MAY 18, 1980, an earthquake of magnitude 5 on the Richter scale precipitated a massive landslide on Mount St. Helens's outwardly bulging north flank. The collapse of roughly 12 percent of the mountain, the largest landslide ever recorded, exposed gas-charged magma that had risen within the volcano. Instantaneously, billions of gallons of superheated groundwater, trapped inside the mountain, flashed into steam. Scientists later estimated the explosion at 24 megatons of energy--a blast five hundred times more powerful than the 20-kiloton atomic bomb that destroyed Hiroshima. The explosion ripped more than 1,200 feet off the top and center of Mount St. Helens, forming a huge crater over a mile in diameter. The onrushing avalanche debris displaced the water in Spirit Lake and raised the lake bed by 200 feet. Debris from the eruption covered 23 square miles of the North Fork Toutle River Valley to a depth of 150 feet. (1)

Approximately 3 billion cubic yards of material spewed out of the mountain. Some of the ejected material consisted of volcanic ash, which ascended 14 miles into the atmosphere over a 9-hour period. Other matter comprised mud and pyroclastic flows or surges that sped down the mountain at 100 miles an hour, pushing into the upper reaches of the North Fork and South Fork Toutle River drainages. These flows (averaging from 33 to 66 feet in depth) contained massive amounts of debris, rock, trees, water, and glacial ices in superheated condition. As the flows raced downstream, they filled in and leveled out the river beds, reducing channel capacity in the Cowlitz from 70,000 to 13,000 cubic feet per second (cfs). The mudflow deposited as much as 15 feet of sand, volcanic ash, and pumice in the river channels and 10 feet on the floodplain. The mudflow into the Columbia reduced the 40-foot-deep ship channel to 15 feet. The debris avalanche also created lakes in the Toutle River drainage, blocking them with eroded, unstable material. As these lakes retained rainwater or snowmelt, the danger of breaching and downstream flooding increased. Flying over the devastated area shortly after the eruption, President Jimmy Carter mused, "I've never seen anything like it.... The moon looks like a golf course compared to what's up there." (2)

A deep-draft vessel was grounded in the Columbia River ship channel off the mouth of the Cowlitz River, and thirty-one other vessels were trapped in the Portland and Kalama harbors. Another fifty ships enroute to the area had to stand off or be diverted to other West Coast ports. It was a navigation emergency and a potential economic disaster for the ports, communities, and industries that depended on the ship channel. The lower Cowlitz drainage faced a flood-control problem from the mudflows. For 21 miles of the Cowlitz River, downstream from the Toutle to the Columbia, infill had eliminated natural channel capacities. Forty-five thousand people had been left without flood protection. (3)

The eruption was a major natural disaster. Fifty-seven people were killed and 150 square miles of valuable forest were turned into wasteland. The avalanche of mud and debris sent into the Toutle, Cowlitz, and Columbia rivers disrupted navigation on the Columbia and threatened to cause long-term navigation and flooding problems. The U.S. Army Corps of Engineers, the federal agency immediately responsible for dealing with the disaster, faced a difficult and uncertain situation. Could the Corps, a government agency that was considered highly bureaucratic and technically conservative in its engineering philosophy, respond with appropriate technical solutions to the immediate and long-term water problems caused by this unprecedented natural disaster?

The Corps' responsibility for responding to the Mount St. Helens emergency stemmed from its congressionally authorized mission. Since 1824, the Corps had been charged with improving the nation's rivers and harbors for navigation. …