At 8:32 am Pacific time, May 18, 1980, it happened.
#MountStHelens exploded, producing the largest landslide ever recorded, sending a tower of rock and ash 19 km into the stratosphere, and killing 57.
I've added the Empire State Building to this image for scale.
A thread:
#MountStHelens exploded, producing the largest landslide ever recorded, sending a tower of rock and ash 19 km into the stratosphere, and killing 57.
I've added the Empire State Building to this image for scale.
A thread:
A shallow earthquake caused the entire northern flank of the volcano to slide. The reduced pressure allowed a huge "cryptodome" of hot, pressurised magma inside the volcano to explode—creating a lateral blast that flattened trees for tens of kilometres.
The eruption blasted fragments of volcanic rock and glass, powered by superheated gases, into a huge column (a Plinian eruption) that reached 19 km into the atmosphere; ash blanketed towns 400 km, and some even landed in the Great Plains, 1,500 km away.
The Plinian eruption also included numerous pyroclastic flows—very hot, very fast clouds of ash, lava fragments, and gas—that flowed down the damaged volcano's flanks. The lateral blast itself produced a pyroclastic flow that, briefly, might have gone supersonic.
The superheated gases and lava melted snow on the upper flanks, driving surges of water mixed with rock debris down the volcano as "lahars". These destructive mudflows wreaked even more damage—see the "mudline" in this photo on the tree trunks (with scientist for scale).
All told, this eruption was (and remains) the most destructive volcanic event in U.S. history. Fifty-seven people were killed, hundreds of square kilometres of land was damaged, and the volcano's height was reduced by 390 m (and 13% of its volume).
The shape of the volcano was irrevocably changed, although eruptive activity has continued at Mount Saint Helens since (albeit at much lower levels). But the May 1980 eruption taught us some very valuable lessons—and told us just how destructive volcanoes like this one can be.
This was how the volcano looked when I visited the nearby Johnston Ridge Observatory in 2017. It was humbling to see such a devastated landscape, and mountain. But harder still to image what that eruption was like.
#MountStHelens #MSH40
#MountStHelens #MSH40
