17 August, 2011

Geological Words that Sound Vaguely Naughty: Nuée Ardente

I'm sorry, I really am, but a nuée ardente isn't some amazingly sensual French dance along the same lines of the tango. If it's any comfort, though, it is hot. Really hot. Like, almost 2,000 degrees F.

The thing about French is it makes everything sound beautiful and elegant. Like this: nuée ardente. Glowing cloud. Doesn't that sound lovely? We like glowing clouds. They're pretty. And it almost sounds like some metaphor for a sexual delight, along the lines of le petite mort, which is such wonderful euphemism for an orgasm. Just remember, though, the French are the same people who can call you a shithead and make it sound sophisticated. So when they speak of glowing clouds, you might want to suspect they're not talking about something altogether pleasant.

It's really not.

Mount Pelée's nuée ardente
I found this out as a tender young age, whilst reading a book entitled Ripley's Believe it or Not: Great Disasters. This is the perfect book for children. It's got blood and gore and destruction aplenty. And it had an essay on the 1902 eruption of Mount Pelée, in which the term nuée ardente was used. I remember the accompanying illustration was of Louis-Auguste Cyparis staring out at the flattened city of Saint-Pierre from the bars of his prison cell. Who says crime doesn't pay? Saved his life, because if he hadn't been in that protected space, he would've been fried. As it was, he merely got baked.

So what was this nuée ardente that sounds so lovely, and yet is so deadly? The modern scientific term for it is pyroclastic flow. That's good Greek, that, very evocative: fire broken in pieces. The "fire" is superheated gasses, which can attain temperatures of nearly 2,000 degrees F. The "broken in pieces" are chunks of pumice and rocks (sometimes even boulders), combined with ash. Mix it all up, and you have a recipe for painful death if you're in its path, and pure horrifying awesome if you're not. This is one of the most dramatic, dangerous things a volcano does.

View of Ridge at Spirit Lake. Note baldness. Photo by Moi.

I remember watching a television program on volcanoes back in the 90s, in which they showed the eruption of Mount Pinatubo. There were farmers in a field, and this pyroclastic flow came rushing down the mountain with its roiling, boiling gray clouds of doom, and the poor buggers were trying to run away. I'm sorry, but unless you run for a ridge or try to get into some protected spot like, oh, say, an underground dungeon, you're out of luck: those flows travel at speeds of around 60-150 miles per hour. Some sources claim they can go even faster, but that's irrelevant when you're considering whether you can outrun one. And even if you somehow manage to see the thing coming and get to the other side of a ridge before it reaches you, you may still be royally screwed. If it's a pyroclastic surge rather than flow, it might see the ridge as more of an inconvenience than a barrier. You're really better off staying out of range of any possible pyroclastic anythings to begin with.

Pyroclastic Flow at Night, Soufrière Hills. See link for more.

Here we see the reason why the French went with the term "glowing cloud" rather than "fire broken in pieces." This is a pyroclastic flow at night. It looks rather like a cloud that glows. Hell of an amazing light show, for those who can watch from a safe distance. Geology can be beautiful and terrible all at once. The Earth is so remarkably powerful, and few things illustrate that power so well as a pyroclastic flow.

They make for some amazing rocks, too, but we'll wait to discuss those until I have some drool-worthy photos from the field. For now, just savor the term nuée ardente for a bit, and maybe work up a suitably gorgeous yet dangerous-looking dance to go with it.

Tip o' the shot glass to Elli Goeke, who mentioned that lovely phrase and got me thinking about it.

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