Yellowstone Caldera
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The Yellowstone Caldera, also known as the Yellowstone supervolcano, is a volcanically active region in Yellowstone National Park. It measures 55 kilometers by 72 kilometers. The caldera was discovered with difficulty due to its size, as geologists were "looking on the wrong scale". This was done by field work by Bob Christiansen of the USGS in the 1960's and 1970's.
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Volcanism
Image:Yellowstone Caldera map2.jpg
Yellowstone is on top of one of the planet's few dozen hotspots where light hot molten mantle rock rises towards the surface. Hawaii is believed to lie over a similar hotspot, explaining its solitary position in the Pacific. The Yellowstone hotspot 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 hotspot. The oldest identified caldera remnant is straddling the border near McDermitt, Nevada-Oregon. The calderas' apparent motion to the east-northeast forms the Snake River Plain. However, what is actually happening is the result of the North American plate moving west-southwest over the stationary hotspot deep underneath.
Currently, volcanic activity is 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, up to 2,500 times the size of the 1980 Mount St. Helens eruption. The most recent such eruption produced the Lava Creek Tuff 640,000 years ago and spread a layer of volcanic ash over most of the North American continent. Smaller steam explosions 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). Additionally, non-explosive eruptions of lava flows have occurred in and near the caldera since the last major eruption; the most recent of these was about 70,000 years ago.
The volcanic 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.
Image:Welded tuff at Golden Gate in Yellowstone-750px.JPG
Volcanic hazard
A full-scale eruption of the Yellowstone caldera could result in millions of deaths locally and catastrophic climatic effects globally, but there is little indication that such an eruption is imminent. However, the system is not yet completely understood, and the study of Yellowstone is ongoing. Geologists are closely monitoring the rise and fall of the Yellowstone Plateau, which averages 1.5 cm yearly, 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 will not 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.
Origin
The source of the Yellowstone Hot Spot is not without controversy. Many geologists believe that the Yellowstone Hot Spot source is an upper mantle convection current [1], others prefer a deep mantle origin and still others prefer a meteor impact. Part of the controversy is due to the rather sudden appearance of the hot spot in the geologic record. Additionally, the Columbia Basalt flows appear at the same approximate point in time, causing speculation about their origin.[2]
See also
- Supervolcano, a two-part docudrama about a hypothetical eruption of the Yellowstone caldera