# Mt. Saint Helens volcano **URL:** \ **Category:** Factual Questions\ **Created:** [November 9, 2002, 4:51am UTC](https://boards.straightdope.com/t/mt-saint-helens-volcano/135987 "2002-11-09T04:51:28Z")\ **Posts on this page:** 13\ **Page:** 1
**Author:** ![Fuel](https://avatars.discourse-cdn.com/v4/letter/f/df705f/32.png) [@Fuel](https://boards.straightdope.com/u/Fuel)\ **Post date:** [November 9, 2002, 4:51am UTC](https://boards.straightdope.com/t/mt-saint-helens-volcano/135987/1 "2002-11-09T04:51:28Z")
i was watching a documentary about disasters. it mentioned that the soot or dust from the volcano blew down the side of the mountain at 700 mph! is this possible? for dust to almost break the sound barrier??? they also said that the explosion was equivalent to 30 million tons of TNT… this also sounds far out. just curious about this. thanks. ---
**Author:** ![Fuel](https://avatars.discourse-cdn.com/v4/letter/f/df705f/32.png) [@Fuel](https://boards.straightdope.com/u/Fuel)\ **Post date:** [November 9, 2002, 4:55am UTC](https://boards.straightdope.com/t/mt-saint-helens-volcano/135987/2 "2002-11-09T04:55:15Z")
i just realized this was kind of a dumb question, i mean the explosion could make that soot go 700 mph, but i would think it would only go 700 for a split second then slow down. i don’t know. :o ---
**Author:** ![Fear\_Itself](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/fear_itself/32/19637_2.png) [@Fear\_Itself](https://boards.straightdope.com/u/Fear_Itself)\ **Post date:** [November 9, 2002, 5:22am UTC](https://boards.straightdope.com/t/mt-saint-helens-volcano/135987/3 "2002-11-09T05:22:23Z")
[This site](http://volcano.und.edu/vwdocs/msh/ov/ovd/ovdbd.html) confirms that the blast wave was moving at 670mph, and maintained enough force to uproot trees as far away as six miles. ---
**Author:** ![Squink](https://avatars.discourse-cdn.com/v4/letter/s/b5e925/32.png) [@Squink](https://boards.straightdope.com/u/Squink)\ **Post date:** [November 9, 2002, 5:27am UTC](https://boards.straightdope.com/t/mt-saint-helens-volcano/135987/4 "2002-11-09T05:27:13Z")
Not a dumb question at all. The 700 mph figure for Mount St. Helens seems to be for the initial lateral explosion, not the subsequent pyroclastic flows. Those only get up to ~450 mph. > [@](#): > > Landslide… The next event, not predicted by scientists, was a huge lateral blast. As the mountain side slid down the semi solid magma that caused the bulge was exposed. Magma is a combination of liquid rock and pressurized gas. As long as it’s contained it remains stable. But once exposed it behaves much like a partially frozen can of soda that is vigorously shaken and then opened. Being sort of solid it’s more difficult for the gas to escape. So it doesn’t just fizz, it explodes. Sizzling hot gas and rock came blasting out the side of the mountain at speeds up to 700 mph, quickly overtaking the landslide. [Lateral explosion](http://www.outthereliving.com/worldbike/wbike029.html) [Pyroclastic flows](http://www.google.com/search?hl=en&lr=&ie=ISO-8859-1&safe=off&as_qdr=all&q=+%22pyroclastic+flow%22) ---
**Author:** ![Tapioca\_Dextrin](https://avatars.discourse-cdn.com/v4/letter/t/3d9bf3/32.png) [@Tapioca\_Dextrin](https://boards.straightdope.com/u/Tapioca_Dextrin)\ **Post date:** [November 9, 2002, 12:37pm UTC](https://boards.straightdope.com/t/mt-saint-helens-volcano/135987/5 "2002-11-09T12:37:41Z")
If you want some figures on the eruption, the [USGS](http://vulcan.wr.usgs.gov/Volcanoes/MSH/May18/summary_may18_eruption.html) (United States Geological Survey) is the place to go - they say 24 megatons of energy released - and this was a **tiny** eruption compared to some ---
**Author:** ![Yossarian](https://avatars.discourse-cdn.com/v4/letter/y/9de0a6/32.png) [@Yossarian](https://boards.straightdope.com/u/Yossarian)\ **Post date:** [November 9, 2002, 1:59pm UTC](https://boards.straightdope.com/t/mt-saint-helens-volcano/135987/6 "2002-11-09T13:59:18Z")
[Volcano World’s](http://volcano.und.nodak.edu/vw.html) entry on [Mt. St. Helens.](http://volcano.und.nodak.edu/vwdocs/msh/) ---
**Author:** ![Duckster](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/duckster/32/1244_2.png) [@Duckster](https://boards.straightdope.com/u/Duckster)\ **Post date:** [November 9, 2002, 6:40pm UTC](https://boards.straightdope.com/t/mt-saint-helens-volcano/135987/7 "2002-11-09T18:40:46Z")
[nitpick] Ah, it’s Mount St. Helens. (Don’t spell out St.) [/nitpick] Mount St. Helens was named for British diplomat Alleyne Fitzherbert (1753-1839), whose title was Baron St. Helens. The mountain was named by Commander George Vancouver and the officers of H.M.S.Discovery while they were surveying the northern Pacific coast from 1792 to 1794. ---
**Author:** ![TVGuy](https://avatars.discourse-cdn.com/v4/letter/t/82dd89/32.png) [@TVGuy](https://boards.straightdope.com/u/TVGuy)\ **Post date:** [November 9, 2002, 10:16pm UTC](https://boards.straightdope.com/t/mt-saint-helens-volcano/135987/8 "2002-11-09T22:16:08Z")
Harry Truman’s Spirit Lake Lodge (and Harry along with it) was wiped of the face of the planet then in, what, about 20 seconds after the blast? I wonder what goes through your mind when you suddenly realize you’re in the last 20 seconds of your life… Here’s a recent [ride](http://www.mistered.com/bikestuff5.html) that I took into the Mountain’s back yard, FWIW. ---
**Author:** ![Moirai](https://avatars.discourse-cdn.com/v4/letter/m/96bed5/32.png) [@Moirai](https://boards.straightdope.com/u/Moirai)\ **Post date:** [November 9, 2002, 10:39pm UTC](https://boards.straightdope.com/t/mt-saint-helens-volcano/135987/9 "2002-11-09T22:39:40Z")
Check out the National Georgaphic website archives for some really cool info about the eruption and it’s aftermath. They did an extensive story on it just this year. ---
**Author:** ![Squink](https://avatars.discourse-cdn.com/v4/letter/s/b5e925/32.png) [@Squink](https://boards.straightdope.com/u/Squink)\ **Post date:** [November 9, 2002, 11:33pm UTC](https://boards.straightdope.com/t/mt-saint-helens-volcano/135987/10 "2002-11-09T23:33:55Z")
> [@](#): > > \*Originally posted by TVGuy \* > \*\*Here’s a recent [ride](http://www.mistered.com/bikestuff5.html) that I took into the Mountain’s back yard, FWIW. \*\* 🆒 [Here’s](http://www.educeth.ch/stromboli/perm/msh/c00-en.html) a recent virtual climb of Mount St. Helens, from a great vulcanology site; Stromboli online ---
**Author:** ![bbeaty](https://avatars.discourse-cdn.com/v4/letter/b/c0e974/32.png) [@bbeaty](https://boards.straightdope.com/u/bbeaty)\ **Post date:** [November 10, 2002, 5:53am UTC](https://boards.straightdope.com/t/mt-saint-helens-volcano/135987/11 "2002-11-10T05:53:51Z")
A big glob of dirt and gas can be driven faster than the speed of sound. Remember, relative to itself, and object isn’t moving! “Speed of sound” usually is measured relative to the still air, and if the air is moving, then the “speed of sound” concept isn’t so simple. If a big blob of gas was moving through the atmosphere at faster than 720mph, you’d get shock waves coming from the region where the two bodies of gas were in contact. Ever see a photo of a supersonic jet figher with glowing exhaust coming out of it’s engines? Or close-ups of the space shuttle main engines during liftoff? That gas exceeds 720mph (otherwise the aircraft couldn’t fly faster than the speed of sound.) Those glowing v-shaped thingies in the exhaust stream are standing-wave shock waves. If the exhaust was moving slower than 720mph or so, those glowing shapes wouldn’t be there. I remember a story about one volcano which probably was exceeding the speed of sound. There were reports of weird shadowy circles coming out of the peak of Mt. Etna during an eruption decades ago. They were probably shock waves made visible by condensation, by “flash clouds” in the shock wave. ---
**Author:** ![RM\_Mentock](https://avatars.discourse-cdn.com/v4/letter/r/e274bd/32.png) [@RM\_Mentock](https://boards.straightdope.com/u/RM_Mentock)\ **Post date:** [November 10, 2002, 12:32pm UTC](https://boards.straightdope.com/t/mt-saint-helens-volcano/135987/12 "2002-11-10T12:32:23Z")
> [@](#): > > \*Originally posted by EJsGirl \* > \*\*Check out the National Georgaphic website archives for some really cool info about the eruption and it’s aftermath. They did an extensive story on it just this year. \*\* Eh, I just used their search feature to search for “mount st. helens” and it returned “0 items found in our interactive features, news stories, and updates.” Wait a minute…nope, same result for “Mount St. Helens” Do you have some links? Do you remember the photos of a person watching the mountain from very far away, and as it erupted they fell down? Just imagine what they were thinking. ---
**Author:** ![lieu](https://avatars.discourse-cdn.com/v4/letter/l/c2a13f/32.png) [@lieu](https://boards.straightdope.com/u/lieu)\ **Post date:** [November 10, 2002, 4:33pm UTC](https://boards.straightdope.com/t/mt-saint-helens-volcano/135987/13 "2002-11-10T16:33:40Z")
I’ve seen the sequence you mentioned. They were climbing a sister volcano, Ranier or Hood perhaps, and witnessed the entire event from a like elevation. Their climbing axes even began to hum from all the static electricity generated by the blast cloud. The gal in the forefront of the pictures fell over just from the overwhelming magnitude of the experience and not from a physical force. Understandable. Lucky bastards.