My Authors
Read all threads
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:
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
Missing some Tweet in this thread? You can try to force a refresh.

Enjoying this thread?

Keep Current with Paul Byrne

Profile picture

Stay in touch and get notified when new unrolls are available from this author!

Read all threads

This Thread may be Removed Anytime!

Twitter may remove this content at anytime, convert it as a PDF, save and print for later use!

Try unrolling a thread yourself!

how to unroll video

1) Follow Thread Reader App on Twitter so you can easily mention us!

2) Go to a Twitter thread (series of Tweets by the same owner) and mention us with a keyword "unroll" @threadreaderapp unroll

You can practice here first or read more on our help page!

Follow Us on Twitter!

Did Thread Reader help you today?

Support us! We are indie developers!

This site is made by just two indie developers on a laptop doing marketing, support and development! Read more about the story.

Become a Premium Member ($3.00/month or $30.00/year) and get exclusive features!

Become Premium

Too expensive? Make a small donation by buying us coffee ($5) or help with server cost ($10)

Donate via Paypal Become our Patreon

Thank you for your support!