Reply #43: Some random crap about volcano stuff and things...

[Cessna Invesco Palin]

Some info for those who don't know...

Yellowstone national park sits above what is known in geology as a "hotspot." A hotspot can be best thought of as a stationary upwelling of heat from deep within the earth that persists over many millions of years. The hotspot stays in the same place, and the plates, which are thin (usually less than 60km) move above the hotspot. Imagine moving a piece of paper around beneath a stationary pen and you get the basic idea - the hotspot (the pen) stays in one place - the plates (paper) move. Thus, the Yellowstone hotspot appears to have moved over the western united states, though it is actually the western united states that has moved over the hotspot.

Hawaii is the result of just such a hot spot, though the hawaiian hotspot is under thin ocean crust and is thus able to assert itself on the surface more easily, in the form of relatively non-destructive basalt shield volcanoes. You can follow the path of the Pacific plate over the Hawaii hotspot if you get a map and look at the chain of hawaiian islands and underwater seamounts (Emperor Seamounts) that stretch over almost 1/3 the width of the pacific plate.
The Hawaii hotspot asserts itself as volcanoes, because the crust above the hotspot is thin. It's more difficult for Yellowstone to assert itself because it's got many kilometers of the North American plate on top of it, but when it *does* assert itself... well, you wouldn't want to be in the neighborhood.

Now, that said, the short-term behavior of hot spots is not well understood. We can look at the chain of Emperor seamounts and Hawaiian islands, or Yellowstone's path across North America to gain a general understanding of how they function over millions of years, but the day-to-day and year-to-year fluctuations of hotspots are relatively unstudied. Geologic time is loooooooooooooong, and we really have no idea how many times something like the current Yellowstone weirdness has happened in the past hundred, thousand, ten thousand, or million years.

On calderas...
A caldera is best thought of as a supervolcano that has blown itself up in one massive, explosive eruption. (Calderas are not necessarily associated with hot spots. If you're in California, you can find a good example of a caldera in the seismically/volcanically active Owens Valley area along 395- it's called the Long Valley caldera.)

A caldera eruption is one of the most catastrophic natural events imaginable - think of quite a few square kilometers of earth being more-or-less pulverized and sent skyward. It has been theorized that caldera eruptions have been responsible for large-scale extinction events. Until the asteroid theory gained popularity, it was commonly thought that the cretaceous extinction was the result of an enormous caldera eruption or a (arguably) related phenomenon known as a flood basalt flow. Flood basalts are just about as scary as caldera eruptions - Imagine 300,000 square miles being covered with basalt hundreds of meters thick in something like two months. (I suppose the time might be shorter or longer, and any geologists out there are free to argue with me on this point and tell me I'm wrong. you're probably right.) There's one of these in the western US that stretches from the Columbia river all the way to northern California. But I'm getting off topic...

So, while the current situation in yellowstone is somewhat odd, it's nothing to be too worried about, as long as the ground beneath your feet isn't burning you. I don't think a caldera eruption is the sort of thing that happens without more significant warning signs.

-y