The scariest thing I've ever read

In 1815, Mount Tambora, on the island of Sumbawa, Indonesia, erupted in the largest and most powerful display ever witnessed by mankind. The eruption itself and associated tidal waves killed 88,000 people.

If we reduce all the ash from Tambora to dense rock equivalents and include all ash flow tuffs that formed at the same time, we come up with about 36 cubic miles of rock. Quite a bit compared with the destructive U.S. eruptions of Mount St. Helens in 1980 that produced about 1/4 cubic mile.

Wow. Except, that's not the scary part. Geologists have been studying a geologically active region that has in the past underwent events of unimaginable power, dwarfing even Tambora. That place is called Yellowstone.

The volume of volcanic rock produced by the first Yellowstone caldera eruption was about 600 cubic miles—about 17 times more than Tambora, and 2,400 times as much as Mount St. Helen's, an almost incomprehensible figure. One more statistic: Ash from Tambora drifted downwind more than 800 miles; Yellowstone ash is found in Ventura, California to the west and the Iowa to the east.

Yellowstone was created by three separate volcanic geologic events. The last may have removed the southern portions of the Washburn mountain range.

Read that last sentence again.

Here's a simple analogy:

Imagine a bottle of carbonated water lying in the sun. Pick it up, shake it vigorously, maybe tap the cap...boom, it blows off. Instantly the pressure in the bottle drops, the dissolved carbon dioxide exsolves into bubbles and an expanding mass of bubbles and water jets into the sky. In a few seconds, the event is over. Wipe off your face and check the bottle; some of the water remains, but most of the gas is gone. This simple scenario is a scaled-down analogy of what happened 600,000 years ago in Yellowstone when the volatile-rich upper part of the magma chamber vented and erupted the Lava Creek Tuff.

And a simplified reconstruction of the real thing:

Nearer the vents, fiery clouds of dense ash, fluidized by the expanding gas, boiled over crater rims and rushed across the countryside at speeds over one hundred miles per hour, vaporizing forests, animals, birds, and streams into varicolored puffs of steam. Gaping ring fractures extended downward into the magma chamber providing conduits for continuing foaming ash flows.

More and more vapor-driven ash poured from the ring fractures, creating a crescendo of fury. As the magma chamber emptied, large sections of the foundering magma chamber roof collapsed along the ring fractures, triggering a chain reaction that produced a caldera 45 miles long and 28 miles wide.

Yellowstone is three separate but overlapping caldera, and the area is still extremely active in the geological sense. So a reoccurance isn't necessarily imminent, but at some point, it will happen.

Victims of the Mt. St. Helen's eruption were found with their lungs, sinuses and mouths full of ash. We've already seen how relatively minor that eruption was. Here's what you'll experience if you happen to be too close to the action.

Hot ash flows are fascinating. Driven by expanding gas, they are really clouds of hot glass shards and pumice plus expanding gas whose turbulence keeps everything flowing like water.

Not that you'd experience it for more than a fraction of a second. Merciful, that.

So there you have it, the scariest thing I've ever read, and I meant that literally. The full text is here: Yellowstone Calderas, and I have Transterrestrial Musings to thank for the nightmares.

Posted by Ted at May 20, 2005 05:54 AM
Category: SciTech