Help me track down a geology fact from a John McPhee book?
October 9, 2020 12:21 PM   Subscribe

I'm pretty sure I once followed a link (maybe from the blue?) once many, many years ago to a page about a fantastical geological phenomenon involving shards or spikes of stone being fired out of the ground, without warning, fast enough to break the sound barrier. It sounded preposterous, but I found out about John McPhee's books on geology from the citations, so I'm pretty sure it's true. Now, I can't find a single citation. Unfortunately, it's not in Basin and Range, which I found cheap at a used book store, and I thought maybe asking here for a citation (or even the name of the phenomenon!) would be faster than reading the other 3 books. Does anyone know what I'm talking about?
posted by paul_smatatoes to Science & Nature (9 answers total) 5 users marked this as a favorite
I have no idea, but you might try reddit dot com for this one: specifically r/science or r/geology. That site has a bad rep for misbehavior—which is sometimes well deserved—but I've found it to be pretty helpful for the truly bizarre, and the question you're asking is decidedly that.
posted by ivanthenotsoterrible at 1:12 PM on October 9, 2020

Hmm. I have my copy of Annals of the Former World in my lap, and I skimmed the index ("exploding rock" is in there but not what you're remembering) so if you think of something, a region or name, let me know.
posted by BlackLeotardFront at 1:37 PM on October 9, 2020

Kimberlite pipes?
"...a kimberlite eruption could launch rocks from the mantle at over 250 kilometers an hour!"
posted by thatwhichfalls at 1:41 PM on October 9, 2020 [4 favorites]

I have it! Transcribing...
posted by BlackLeotardFront at 1:45 PM on October 9, 2020 [1 favorite]

"The source of a diamond is a kimberlite pipe, a form of diatreme — a relatively small hole bored through the crust of the earth by an expanding combination of carbon dioxide and water which rises from within the earth's mantle and moves so fast driving magma to the surface that it breaks into the atmosphere at supersonic speeds. Such events have occurred at random through the history of the earth, and a kimberlite pipe could explode in any number of places next year. Rising so rapidly and from so deep a source, a kimberlite pipe brings up exotic materials the like of which could never appear in the shallow slow explosion of a Mt. St. Helens or the flows of Kilauea. Among the materials are diamonds."

This is in the first 10 pages of book 2, "In Suspect Terrain."
posted by BlackLeotardFront at 1:49 PM on October 9, 2020 [15 favorites]

I came at this from another angle and looked into natural phenomena that're supersonic. They're very uncommon at a macro-scale and none involved natural rock explosion.

Also, what's supersonic varies massively with temperature and pressure and air density, so defining this as supersonic may not be the 700-800mph we're familiar with. But whatever: if there's such a thing as a natural nuclear reactor, there could just be some supersonic magma squirting, and that would be amazing to see from a safe distance.
posted by Sunburnt at 2:44 PM on October 9, 2020

From Wikipedia:
Volcanic pipes or volcanic conduits are subterranean geological structures formed by the violent, supersonic eruption of deep-origin volcanoes.
posted by sjswitzer at 6:38 PM on October 9, 2020

Geologist here! Two possible suspects from your description, I would say.

As above, kimberlites are one, though I would argue "occured at random" isn't quite true if we're being nitpicky. Still, they are definitely violent, carrot-shaped eruptions that ripped up rock from *deep, deep* in the crust.

The fun one I like is shatter cones! They're very rare, since they only form in bedrock under a meteorite impact big enough to really leave a good sized crater.

I will also note that John McPhee was a writer, not a geologist persay, and they're from 1981-1994 so, eh, "truth" is as biased as any popularized science writing tends to be. Geology has modernized as most do since then as we move into the digital age - new technology has changed our science just as much as any other discipline you can think of!
posted by aggyface at 7:04 PM on October 9, 2020 [4 favorites]

I would also look into just, like, normal volcanic eruptions as well. Lava can shoot thousands of feet into the air. Mount Etna erupted in 1999 to over 2km (6562 feet) and Vesuvius is believed to have reached over 3km (9843ft) in 1779. Considering how heavy lava is, it must be moving at at least near supersonic when leaving the vent, but I don't know what math to use here to try to figure an exact speed. Any takers? (Lava has an avg density of 3100kg/m^3 and a viscosity of 100-1000 Pa*s(if that helps))
posted by sexyrobot at 9:24 PM on October 9, 2020 [1 favorite]

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