Yellowstone Caldera

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Yellowstone Caldera

The northeastern part of Yellowstone Caldera, with the Yellowstone River flowing through Hayden Valley and the caldera rim in the distance
Elevation 10,308 feet (3,142 m) at Mount Sheridan
Location Wyoming, U.S.
Range Rocky Mountains
Coordinates 44°24′N, 110°42′W
Topo map USGS Yellowstone National Park
Type Caldera
Age of rock 70,000 – 2.1 million years
Last eruption 640,000 years ago
Easiest route hike/auto/bus

The Yellowstone Caldera is the volcanic caldera in Yellowstone National Park in the United States. It is located in the northwest corner of Wyoming, measuring about 55 kilometers (34 mi) by 72 kilometers (45 mi). The caldera was discovered based on geological field work conducted by Bob Christiansen of the United States Geological Survey in the 1960s and 1970s. After a BBC television science program coined the term supervolcano in 2000, it has often been referred to as the "Yellowstone supervolcano."

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[edit] Volcanism

Yellowstone, like the Hawaiian Islands, is believed to lie on top of one of the planet's few dozen hotspots where light, hot, molten mantle rock rises towards the surface. 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 caldera's 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.

Yellowstone sits on top of three overlapping calderas. (USGS)
Yellowstone sits on top of three overlapping calderas. (USGS)

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 three eruptions happened 2.1 million years ago, 1.3 million years ago, and 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 13,800 years ago left a 5 kilometer diameter crater at Mary Bay on the edge of Yellowstone Lake (located in the center of the caldera).[1] 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. Craters of the Moon National Monument in Idaho is the result of volcanic activity between 11,000 and 2,000 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 the top of the chamber, the result is a very large gas explosion.

[edit] Volcanic hazard

A full-scale eruption of the Yellowstone caldera could result in millions of deaths locally. The last full-scale eruption, the so-called Lava Creek eruption, ejected approximately 240 cubic miles of rock and dust into the sky and is believed to have almost driven the young human race to extinction, over 600,000 years ago.[2]

Geologists are closely monitoring the rise and fall of the Yellowstone Plateau, which averages +/- 0.6 inches (about 1.5 cm) yearly, as an indication of changes in magma chamber pressure.[3][4] Explosions of this magnitude "happen about every 600,000 years at Yellowstone," says Chuck Wicks of the U.S. Geological Survey, who has studied the possibilities in separate work. "And it's been about 620,000 years since the last super explosive eruption there."[5] The U.S. Geological Survey, University of Utah and National Park Service scientists with the Yellowstone Volcano Observatory "see no evidence that another such cataclysmic eruption will occur at Yellowstone in the foreseeable future. Recurrence intervals of these events are neither regular nor predictable."[6].

[edit] Hydrothermal explosion hazard

Studies and analysis may indicate that the greater hazard comes from hydrothermal activity which occurs independently of volcanic activity. Over 20 large craters have been produced in the past 14,000 years since the glaciers retreated from Yellowstone, resulting in such features as Mary Bay, Turbid Lake and Indian Pond.

Lisa Morgan, a USGS researcher, explored this threat in a 2003 report, and again in a 2008 report revealed further that an earthquake may have displaced more than 77 million cubic feet (2,200,000 m³) of water in Yellowstone Lake, creating huge waves that essentially unsealed a capped geothermal system leading into the hydrothermal explosion that formed Mary Bay.[7][8]

Other research shows that earthquakes from great distances do reach and have effects upon the activities at Yellowstone, such as the 1992 7.3 magnitude Landers earthquake in California’s Mojave Desert that triggered a swarm of quakes from more than 800 miles (1,300 km) away and the Denali fault earthquake 2,000 miles (3,200 km) away in Alaska that altered the activity of many geysers and hotsprings for several months afterwards.[9]

The head of the Yellowstone Volcano Observatory, Jake Lowenstern, has proposed major upgrades and extended monitoring since the federal government classified Yellowstone as a “high-threat” system.[10]

[edit] Origin

Path of the Yellowstone hot spot over the past 15 million years
Path of the Yellowstone hot spot over the past 15 million years

The source of the Yellowstone hotspot is controversial. Some geoscientists theorize that the Yellowstone hotspot is the effect of an interaction between local conditions in the lithosphere and upper mantle convection.[11][12] Others prefer a deep mantle origin (mantle plume).[13] Part of the controversy is due to the relatively sudden appearance of the hotspot in the geologic record. Additionally, the Columbia Basalt flows appeared at the same approximate time, causing speculation about their origin.[14]

[edit] See also

  • Supervolcano, a two-part docudrama about a hypothetical eruption of the Yellowstone caldera
  • When Yellowstone Erupts, a documentary about the hypothetical after-effects of the Yellowstone caldera eruption, and warning signs that scientists are looking for.
  • Long Valley Caldera, Valles Caldera, La Garita Caldera, and Bruneau-Jarbidge - examples of other calderas close to but not related to Yellowstone.
  • End Day, an apocalyptic docu-drama with five scenarios, the fourth being the eruption of the Yellowstone supervolcano.

[edit] Further reading

  • Breining, Greg, Super Volcano: The Ticking Time Bomb beneath Yellowstone National Park (St. Paul, MN: Voyageur Press, 2007). A popularized scientific look at the Yellowstone area's geological past and potential future. ISBN 978-0-7603-2925-2
  • Vazquez, J.A., and Reid, M.R., 2002, Time scales of magma storage and differentiation of voluminous rhyolites at Yellowstone caldera, Wyoming: Contributions to Mineralogy & Petrology, v. 144, p. 274-285
  • Iceland hotspot and Iceland plume describes aspects of volcanic processes
  • Sutherland, Wayne, and Sutherland, Judy, Yellowstone Farewell (SPUR RIDGE, 2003). A novel looking at an eruption in the Yellowstone Caldera written by a practicing Wyoming geologist. Contains a wealth of technical details on the geology of western Wyoming.

[edit] References

  1. ^ Introduction to hydrothermal (steam) explosions in Yellowstone
  2. ^ Jones, Bruce. "Volcanoes helped create Yellowstone", The Topeka Capital-Journal, BNET, 2004-10-4. Retrieved on 2008-02-21. 
  3. ^ John Timmer (2007-11-08). Yellowstone recharges. arstechnica.com. Retrieved on 2007-11-08.
  4. ^ Smith, Robert B.; Wu-Lung Chang, Lee Siegel. "Yellowstone rising: Volcano inflating with molten rock at record rate", Press release, University of Utah Public Relations, EurekAlert! (American Association for the Advancement of Science), 2007-11-08. Retrieved on 2007-11-09. 
  5. ^ Super Volcano Will Challenge Civilization LiveScience.com
  6. ^ pubs.usgs.gov
  7. ^ Frequently asked questions about findings at Yellowstone Lake
  8. ^ Tsunami linked to Yellowstone crater
  9. ^ Quake in Alaska changed Yellowstone geysers
  10. ^ Yellowstone is being monitored
  11. ^ Foulger, Gillian (2006-02-08). Yellowstone. Retrieved on 2008-02-10.
  12. ^ www.gsajournals.org)
  13. ^ See list of off-line references in mantleplumes.org/CRB.html
  14. ^ www.mantleplumes.org/CRBSubduction

[edit] External links