On May 18th 1980 Mount St Helens (an active stratovolcano of the Cascades located in the North West US), erupted explosively following a magnitude 5.1 earthquake. The quake triggered a devastating landslide which swept away the volcano’s northern flank – in what is the largest debris avalanche recorded on Earth to date. Removal of a section of the edifice depressurised the volcano’s magmatic system triggering powerful lateral eruptions, which removed the top 300 m of the volcano.
In total, 57 people lost their lives, 250 homes were destroyed and the local infrastructure, including bridges, highways and railways, were badly damaged. Prior to the eruption, the flanks Mount St Helens and its surrounding areas were covered in a dense forest. Following the lateral blasts, all trees within a 10 km radius of the volcano were obliterated, while those further afield were badly scorched.
Andy Smedley, an atmospheric scientist, visited Mount St Helens recently, as part of a road trip around Washington and Oregon states.
“What I can tell you is that the scale is still fairly awe-inspiring, as is the devastation still evident on the ground,” he says of his visit to this extraordinary mountain. “The image in question was taken from the Johnston Ridge, which is named after David Alexander Johnston,” goes on to say Andy.
At the time of the eruption, Johnston was a volcanologist with the United States Geological Survey, in charge of volcanic-gas studies and spent long hours working on the flanks of the volcano. On the morning of the eruption he was one of the first geologists on the mountain. Observing the volcano from what he though was a safe distance (10 km from the vent), upon a ridge know at the time as Coldwater II, Johnston was one of the first to report the eruption: “Vancouver, Vancouver! This is it!” He was swept away by the lateral blast shortly after.
Alongside his USGS colleagues, Johnston was pivotal in ensuring the area around Mount St Helens remained closed to the public after unrest at the volcano was detected in early 1980. The data Johnston collected in the run-up to the devastating blast was crucial to unravelling the processes which governed the eruption.
Coldwater II has since been renamed to Johnston Ridge in memory of the dedicated geologist. There is also a visitor centre, with the same name, from which Andy took this impressive photo of Mount St. Helens.
“The peak is about 6 miles away from the camera and there’s very little vegetation that’s returned in the intervening 36 years [since the eruption],” describes Andy “you get some sense of the size of the eruption from the debris flows down the front flanks of the mountain, but it’s also worth pointing out the new lava dome building and Crater Glacier, one of the youngest glaciers on Earth, both within the 1980 crater.”
“Though it can’t be seen in the image, another thing that struck me was the extent of the blast – it can still be clearly seen by the ranks of toppled tree trunks pointing away from Mount St Helens that surround the nearby hills and extend for some miles on the drive up.”
As volcanic eruptions go, Mount St Helen’s wasn’t particularly large (VEI 5), but Andy thinks it’s relative proximity to centres of population in Washington State and Oregon made it stand out in the public’s consciousness.
“It’s not often that the contiguous USA experiences such a full on eruption (I think the nearby Lassen Peak was the last in 1915), and to have it right there on people’s doorsteps, with the ash column eventually blowing across several states, seemed to make its mark.”
By Laura Roberts, EGU Communications Officer
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