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Recipes for Volcanoes

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augustine-eruption-2006.jpg

Mount Augustine erupts, 27 March 2006

US Geological Survey photo by Cyrus Read (CC-2.0)
You don't believe me that this scenery
Could be a cold blooded killer
It's gonna blow, volcano


—PUSA, "Volcano"

Volcanoes are cool—just ask any kid. Lots of kids want to build a working volcano for a science project, and the Web has lots of places with instructions. You'd think that at least one of these kids would grow up and keep building better and better volcanoes, but it doesn't seem to happen. Still, there are signs of progress in this important endeavor.

Volcanoes for Kids

But first things first. If you or your child wants to make a volcanic science project, see About.com Chemistry Guide Anne Helmenstine's set of easy chemical volcanoes.

These are not dangerous things, these models. They're mostly powered by the fizzing of baking soda mixed with vinegar. No heat is involved, no melting, no explosions—and no meaningful resemblance to real volcanism. Little wonder that kids soon move on to the kitchen for their educational kicks.

Kitchen Volcanoes

The kitchen has some useful analogs for understanding volcanoes. Popping the cork of a champagne bottle is a good approximation for what happens in the throat of a volcano—the release of pressure on the wine makes the dissolved carbon dioxide come out in bubbles. The bubbles grow faster than they can pop, and in the crowded neck of the bottle you can get quite a gusher.

Another analogy is a soufflé. What makes a soufflé rise is a careful mix of ingredients subjected to intense heat. The bubbles in the soufflé, unlike those in the champagne, are made of steam and a good deal of air, which comes from the beaten egg whites. If the conditions are right in the oven, the eggs cook firm enough to hold the expanding air and steam in the bubbles, and the result is something crusty and fluffy, much lighter than its plain ingredients.

Volcanic lava can go both ways. As it rises from its deep magma chamber, lava grows fizzy as its dissolved gases (carbon dioxide and sulfur gases and steam) come out of solution at the lower surface pressure. Often the result is a champagne-like eruption.

If the bubbles expand faster than the lava around them can stretch, the lava tears apart into tiny pieces and a really explosive eruption begins. Nothing like that goes on in the average kitchen! Not mine, anyway.

But there are two ways that volcanic eruptions act like a soufflé. One is when an erupting cloud rises out of the volcano into the atmosphere. There the intensely hot cloud of lava and gas begins to mix with air, just as we fold air into the soufflé with the egg whites. That added air expands with the heat until the cloud becomes buoyant, lighter than the air around it. Then it rises under its own power. That is how the largest eruptions, like that of Pinatubo in 1991, can inject ash and gas well into the stratosphere.

A similar soufflé effect can happen even when lava just froths out of the volcano and rolls down its side. I don't mean the well-behaved flows that you can visit in Hawaii. More typically, you get a racing red-hot avalanche, a roiling mass of lava bits and scalding gases that may be the most fearsome spectacle in nature. (That happened at Mount St. Helens in the spring of 1980.)

These mix with air as they go along, too, and they too expand into boiling clouds of ash and rock. They can even grow light enough to launch into the air and start rising, many kilometers from their origin. But unlike a soufflé, they always fall. Often they fuse into rock deposits called ignimbrite, one of my favorite scientific-Latin words that means "fire rain stone."

Bigger Volcanoes?

Maybe it's just as well that kids can't make realistic volcanoes. Nobody can, unless you count spectacles like the artificial volcano in the Mirage Hotel in Las Vegas. Even the best-funded artists in the world, Hollywood moviemakers, had to use digital fakes in the most recent volcano blockbusters. Maybe some day, an ambitious group of pyromaniacs like Survival Research Laboratories will get the recipe right. If they do, stand back!

But actually, a few geologic chefs have worked on this dish; the English mathematician Andy Woods is one. Much volcano behavior can be modeled with basic physics, and he has boiled down the data into an interesting numerical stew. Woods summarized this work in detail in the November 1995 Reviews of Geophysics. He has since wandered off into other problems involving the dynamics of mixed fluids. That's what being a mathematician is like.

Another is Michael Manga, an American geophysicist who is more of an experimentalist. See his neat stuff in the lab page for his models of magma.

Volcanologists in England have begun constructing realistic-looking volcano models for public education (and to celebrate notable occasions). The University of East Anglia mounted a firework volcano in 2013 to celebrate its 50th anniversary. The London Natural History Museum's London Volcano (June 2014) is a 3-meter replica of La Soufriere.

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