The Day a Mountain Lost Its Top: Mount St. Helens 1980

A mountain loses about 400 metres of its summit in minutes. The largest landslide in recorded history. A blast that flattens 230 square miles of forest. Ash that turns Spokane dark. A scientist's last radio call. This is Mount St. Helens. Here's how it happened.

Start with a mountain. Mount St. Helens, in the Cascade Range of Washington State, in the northwestern United States. In early 1980 it is a snow-capped cone, 2,950 metres, or 9,677 feet, tall. Its last activity was in the 1850s. On the sixteenth of March 1980, small earthquakes begin under it. On the twenty-seventh, a blast of steam opens a crater in the summit. It is the first eruption in the lower forty-eight states since Lassen Peak in California finished erupting in 1921. Scientists rush in. In early spring, the mountain has just one seismograph. It is about to get a lot more attention. Then, in April, geologists notice something strange. The north side of the mountain is moving.

Here is what is happening. Magma, molten rock, is pushing up into the mountain, and the north flank is swelling like a balloon. In late April and May the bulge is growing by about a metre and a half a day. Some measurements say closer to two. By the seventeenth of May, the north side has moved outward about 135 metres. That is 450 feet. The geologists see the danger. If that bulge slides away, it could uncork the magma inside. What they cannot say is when, or how big. On the thirtieth of April, the governor of Washington orders a red zone around the mountain. Breaking it can cost five hundred dollars, or six months in jail. Not everyone is willing to go. One man, in particular, has lived here for decades. He is not going anywhere.

Harry Randall Truman is eighty-three. He has run the Mount St. Helens Lodge, on the shore of Spirit Lake, for fifty-two years. He lives there with sixteen cats. Officials ask him to leave. He refuses. He is reported to have said that you could not pull him out with a mule team. He also told reporters he had no idea whether the mountain would blow. Schoolchildren write to him, and he writes back, and sends them an envelope of volcanic ash. On the seventeenth of May, one last attempt to persuade him fails. Six miles north of the summit, another man is on duty. David Johnston is thirty, a volcanologist with the U.S. Geological Survey. He is at an observation post called Coldwater Two, covering a shift for a colleague. He knows the risk. He is reported to have compared the mountain to a dynamite keg with the fuse lit. But the post is miles from the summit, and is believed to be safe. It is Saturday night, the seventeenth of May. The next morning, at 8:32, the north side of the mountain lets go.

At 8:32 on Sunday morning, a magnitude 5.1 earthquake shakes the mountain. Within fifteen to twenty seconds, the bulge and the summit slide away. It is the largest landslide in recorded history. About two and a half cubic kilometres of rock, enough to fill a million Olympic swimming pools. It races down the valley of the North Fork Toutle River for up to twenty-three kilometres. With the weight gone, the gas-charged magma inside is suddenly free. A lateral blast, a sideways explosion, bursts out of the north side. Its speed is uncertain. The Geological Survey says at least 480 kilometres an hour. Some studies put its peak far higher. It flattens forest across 600 square kilometres, 230 square miles. David Johnston is believed to be watching the bulge when it collapses. His last radio call is recorded by an amateur radio operator. Vancouver! Vancouver! This is it! The message never reaches the Survey's office in Vancouver, Washington. His body is never found. Behind him, the radio operator Gerry Martin reports that the cloud will get him too. Then his transmissions stop. On Spirit Lake, the landslide throws up a wave about 180 metres high. Harry Truman's lodge lies under some 46 metres of debris. In minutes, the mountain has lost about 400 metres, 1,300 feet, of its height. And above it, a column of ash is climbing.

The column of ash climbs more than twenty-four kilometres, fifteen miles, in less than fifteen minutes. The main phase of the eruption lasts nine hours. Winds carry the ash east, at about sixty miles an hour. In all, about 540 million tons of ash fall across more than 57,000 square kilometres. In Spokane, 400 kilometres away, the day turns completely dark. By the next morning, ash is found on cars as far away as Edmonton, in Alberta. Visible ash reaches more than 1,500 kilometres east. The cloud circles the Earth in fifteen days. Whole towns spend the next week learning that volcanic ash is not like snow. It does not melt. But on the mountain itself, there is a second disaster. The mountain is wrapped in snow and glacier ice. And the eruption has just melted a lot of it.

Meltwater mixes with ash and debris, and becomes lahars: volcanic mudflows. They pour down the valleys. The largest, on the North Fork Toutle, reaches its maximum size about midnight, on the Cowlitz River, 80 kilometres downstream. In all, 220 kilometres of river channel are affected. The mud damages 27 bridges and nearly 200 homes. It reaches the Columbia River, and cuts the shipping channel from forty feet deep to fourteen. Thirty-one ships are stranded. Fifty-seven people are killed. Some counts differ by a few, depending on how deaths are defined. Among them are David Johnston, the volcanologist. The photographers Reid Blackburn and Robert Landsburg. Landsburg, in his last moments, protected his film with his body. And Harry Truman, who would not leave. The mountain falls quiet. The forest is flat, grey, and still. It looks like nothing could ever live here again. That turns out to be only partly true.

Under the grey ground, something survived. Seeds. Spores. Fungi. And pocket gophers, in their burrows beneath the debris. As early as the summer of 1980, fireweed starts to appear. On the Pumice Plain, where hot flows left sterile ground, the pioneer is a small purple wildflower, the prairie lupine. Lupines make their own nitrogen, and their roots create small pockets of soil where other plants can start. The gophers help, too. By tunnelling, survivors mix volcanic ash with older soil, which gives roots and seeds a better start. Northern pocket gophers take about twelve years to reach the Pumice Plain, because they move mostly by digging. Lakes recover within about six years. Ecologists call the leftover life biological legacies. Today, Mount St. Helens is called the most-studied volcano in the world. Scientists have been watching the mountain for what comes back, and they still are. But the mountain's other legacy is in the way we now watch volcanoes.

In 1980, there is no Cascades Volcano Observatory. Scientists work from a Forest Service building in Vancouver, Washington. They collect gas samples by hand, and measure sulphur dioxide from an aeroplane. Two years to the day later, the eighteenth of May 1982, the Vancouver office is named the David A. Johnston Cascades Volcano Observatory. That same year, Congress creates the Mount St. Helens National Volcanic Monument. Today, networks watch Mount St. Helens, Mount Rainier, Mount Hood, the Three Sisters, Newberry Volcano and Crater Lake, with instruments precise to the centimetre. The Survey's lesson is simple: a volcano needs good monitoring before it erupts. It has worked. The Survey's forecasts of the dome-building eruptions that followed often came hours to weeks ahead. And on a ridge named for him, the Johnston Ridge Observatory has stood since 1997, facing the crater. That is the next story, a bigger one, and not in America. Krakatoa, 1883, heard thousands of kilometres away. But first, remember how this one began. A mountain loses about 400 metres of its summit in minutes.