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The Yellowstone Caldera, also known as the Yellowstone
supervolcano, is a highly geologically active region in Yellowstone National Park. It measures 55 kilometers by
72 kilometers.
Its volcanic activity is currently exhibited only via numerous geothermal vents scattered throughout the region, including the famous Old Faithful Geyser, but within the past two million years it has
undergone three extremely large explosive eruptions. The most recent such eruption occurred 640,000 years ago, and spread a layer
of volcanic ash over most of the North American continent. Smaller explosive eruptions,
similar to the 1980 Mount St. Helens
eruption, occur every 20,000 years or so; an explosion 13,000 years ago left a 5 kilometer diameter crater at Mary Bay, on the edge of Yellowstone
Lake (located in the center of the caldera). As a result of all this activity small earthquakes are common; in 2002 about 2,300 earthquakes were recorded in Yellowstone park. Most of these were
too small to be felt by humans.
These eruptions, as well as the continuing geothermal activity, are a result of a large chamber of magma located below the caldera's surface. The magma in this chamber contains gases that are kept dissolved
only by the immense pressure that the magma is under. If the pressure is released to a sufficient degree by some geological
shift, then some of the gases bubble out and cause the magma to expand. This can cause a runaway reaction. If the expansion
results in further relief of pressure, for example by blowing crust material off of the top of the chamber, the result is a very
large gas explosion.
Welded tuff at Golden Gate was created by one eruption of the Yellowstone Caldera
A full-scale eruption of the Yellowstone supervolcano could result in millions of deaths locally and catastrophic climactic
effects globally. Fortunately there is little indication that such an eruption is imminent in the near future, although study of
Yellowstone is ongoing and the system is not yet completely understood. Geologists are closely monitoring the rise and fall of
the Yellowstone
Plateau, which averages 1.5 cm per year, as an indication of changes in magma chamber pressure.
Occasionally proposals are suggested for ways to safely relieve the buildup of dissolved gas in the Yellowstone magma chamber,
usually involving drilling holes or using explosives to release small amounts of pressure in a controlled manner. However, none
of these ideas are likely to have a noticeable impact. The magma beneath Yellowstone is not very mobile so release of dissolved
gases from any given point is not going to do much to the chamber as a whole, and in any event the scale of the problem is far
too large for current engineering capabilities to handle.
Apparently Yellowstone is riding on one of the planet's few dozen hot spots,
where light hot molten mantle rock rises towards the surface. Hawaii and Iceland lie over similar hot spots.
The Yellowstone hot spot has a long history. Over the past 17 million years or so successive eruptions have flooded lava over
wide stretches of Washington, Oregon, California, Nevada, and Idaho, forming a string of comparatively flat calderas linked like
beads, as the North American plate moves across the stationary hot
spot. The calderas' apparent motion to the east-northeast forms the Snake River Plain. However,
what is actually happening is the result of the west-southwest motion of the North American plate with respect to the stationary
hot spot deep underneath.
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