As a resident of Jackson Hole, this makes me a little nervous. (Scroll down the window in "Activity Update".)

They closed part of Norris Geyser Basin last month, because of increased activity and temperatures.

The Yellowstone Caldera blows once every 600,000 years or so. It's been 630,000 since the last one. I don't know what the standard deviation is, so we might be overdue, or it could be good for tens of thousands of years more, but when it does, it will be the largest natural disaster in human history, dwarfing events like Mt. St. Helens, Krakatoa, Pinatubo by orders of magnitude.

It may not kill that many people directly (perhaps just a few hundred thousand), because the region is sparsely populated, relative to the rest of the country, but it would probably wipe out Gardiner and Boseman, Montana, and perhaps some towns in eastern Idaho. It will be, literally, a sound heard round the world. The ash would probably wipe out crops in the US for at least a year or so, and it could even kick off a new glacial advance if it cuts off the sunlight for a few years.

It would certainly be a distraction from the War on Terror. Also a good reason to make a little more effort in establishing extraterrestrial homes. We may be able to deflect killer asteroids, but it will be a long time, if ever, before we have the technology to circumvent an event like that.

Anyway, have a nice day.
[Update at 8:52 PM PDT]

Glenn points out a similar (though more local) threat that's probably even more imminent.

Indeed, talk about making all other problems pale in significance.

Okay, I'll say it: If it does go in the near future, the Islamists will of course say it's Allah's punishment against the West - never mind that the loss of crops and damage to the world economy will hurt Muslims too.

Having spent twenty years in and around the thermal areas of Yellowstone, there's nothing new here. The Norris Back Basin has few boardwalks, with most of its trails right on the ground. Being an acidic area, there's considerable leeching going on underneath, and acidic areas are notorious for their instability. Norris is also known for steam explosions, too, the self-destruction of Porkchop Geyser and Graceful Geyser being prime examples. So on the whole, these reports have about as much relation to an immanent eruption of the caldera as the current European heatwave has to global warming-- none, but it helps sell "news."

I was once on a backcountry hike into an acidic area. The lightest person was bringing up the rear, and she was the one who broke through the crust. I broke through on a solo hike once, and it's a cheap thrill, especially when you are ten miles from help. Fortunately, in both cases were dry holes, so I've been spared having to deal with any scaldings.

Norris is also well outside the caldera boundary, and it's hydrothermal system is part of a fault system runing due north to Mammoth.

The real danger in Yellowstone is from a lava flow from the northeast resurgent dome near LeHardy Rapids, one which results in blockage of the river. The Lake only needs to rise about 20 meters to start spilling southward into the Snake River. Then things get fun because Montana would want the water back, and there would be political pressure to breach a natural dam in a national park to restore the status quo ante.

Barbara, if it does go in the near future (and I should say that this post was written at least partly with tongue firmly in cheek, because it really is unlikely), what the Muslims say will be the least of our problems...

The geology of supervolcanoes makes global climatology look like well developed science. We have no good way of knowing if Yellowstone will blow tomorrow, or after we've colonized other star systems. But we can make predictions about the effects. And, from what I know, Rand, you needn't be much more worried living in Jackson Hole than about anywhere else. The siesmic wave alone would level Salt Lake City. The heat front and fallout would turn the entire Front Range into one giant flash flood.

Raoul, you're quite right. This sort of activity is common in caldera areas. I was around Yellowstone last month (shortly after the closing), and there's a bit of new activity further north as well. A crack a few hundred yards long opened up over the winter and was killing trees. Norris is a very active basis. So lots of things happen there. BTW, there were also two steam explosions around Roaring Mountain about six to ten miles north of Norris basis. Both are at least centuries old.

I found your remarks about Yellowstone Lake to be interesting. Since the resurgent dome under the LeHardy rapids, which are a couple of miles down the Yellowstone river from the mouth of the Yellowstone lake, is rising at a pretty good rate, such flooding seems likely to occur sooner or later though probably not in our lifetimes.

Most people think lava is the major danger with volcanoes.  Actually, it's the pyroclastic flows (aka glowing clouds), superheated magma/debris clouds rushing along the ground at 150 km/hour, that are usually the greatest risk.  It's pyroclastic flows that molded the bodies of the people of Pompeii, and that killed all 30,000 inhabitants (less 1) of the Caribbean town of Saint-Pierre in 1902 in less than 5 minutes.

In this regard it's worth taking a look at a measure of the violence of several volcanic eruptions in terms of volumes of matter ejected:

Mt. St. Helens  (1980)  2.7 cu. km. (0.5 new magma)
Krakatoa  (1883)  18 cu. km.
Tambora  (1815)  50-100 cu. km.
Mt. Mazama (Crater Lake)  (6,600 BP)  70 cu. km.
Yellowstone caldera  (2,000,000 BP)  3,000 cu. km.

As Encyclopaedia Britannica (my source for these figures) put it with regard to the last of these:  "Civilizations have never been tested by a cataclysm on the scale of the eruption at Yellowstone about 2,000,000 years ago; that eruption involved nearly 3,000 cubic kilometres of explosively boiling magma" — i.e., pyroclastic flows.

Fascinating. I'm curious about the 'blowing' which is it - 2,000,000 years ago or 600,000 years ago.

A word of note - with Mars cruising at its closest gravitational pull on the earth on Agust 27, 2003 in 60,000 years and the new moon occuring at the same time, not to mention a minimum of 7 oppositions and 6 conjunctions in the galaxy - I'm betting there will be a little pulling somewhere on the globe. I vote for earthquake.