Yellowstone hotspot

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File:Yellowstone Caldera.svg
Schematic of the hotspot and the Yellowstone Caldera
Past locations of the hotspot in millions of years

The Yellowstone hotspot, also referred to as the Snake River Plain-Yellowstone hotspot, is a volcanic hotspot responsible for large scale volcanism in Oregon, Nevada, Idaho, and Wyoming, United States. It created the eastern Snake River Plain through a succession of caldera forming eruptions. The resulting calderas include the Island Park Caldera, the Henry's Fork Caldera, and the Bruneau-Jarbidge caldera. The hotspot currently lies under the Yellowstone Caldera.[1] The hotspot's most recent supereruption, known as the Lava Creek eruption, took place 640,000 years ago and created the Lava Creek Tuff and the Yellowstone Caldera.

Snake River Plain

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The eastern Snake River Plain is a topographic depression that cuts across Basin and Range Mountain structures, more or less parallel to North American plate motion. Beneath more recent basalts are rhyolite lavas and ignimbrites that erupted as the lithosphere passed over the hotspot. Younger volcanoes that erupted after passing over the hotspot covered the plain with young basalt lava flows in places, including Craters of the Moon National Monument.

The central Snake River plain is similar to the eastern plain, but differs by having thick sections of interbedded lacustrine (lake) and fluvial (stream) sediments, including the Hagerman Fossil Beds.

Nevada–Oregon calderas

Although the McDermitt volcanic field on the Nevada–Oregon border is frequently shown as the site of the initial impingement of the Yellowstone Hotspot, new geochronology and mapping demonstrates that the area affected by this mid-Miocene volcanism is significantly larger than previously appreciated.[2] Three silicic calderas have been newly identified in northwest Nevada, west of the McDermitt volcanic field as well as the Virgin Valley Caldera.[3] These calderas, along with the Virgin Valley Caldera and McDermitt Caldera, are interpreted to have formed during a short interval 16.5–15.5 million years ago, in the waning stage of the Steens flood basalt volcanism.[4] The northwest Nevada calderas have diameters ranging from 15–26 km and deposited high temperature rhyolite ignimbrites over approximately 5000 km2.

The Bruneau-Jarbidge caldera erupted between ten and twelve million years ago, spreading a thick blanket of ash in the Bruneau-Jarbidge event and forming a wide caldera. Animals were suffocated and burned in pyroclastic flows within a hundred miles of the event, and died of slow suffocation and starvation much farther away, notably at Ashfall Fossil Beds, located 1000 miles downwind in northeastern Nebraska, where a foot of ash was deposited. There, two hundred fossilized rhinoceros and many other animals were preserved in two meters of volcanic ash. By its characteristic chemical fingerprint and the distinctive size and shape of its crystals and glass shards, the volcano stands out among dozens of prominent ashfall horizons laid down in the Cretaceous, Paleogene, and Neogene periods of central North America. The event responsible for this fall of volcanic ash was identified as Bruneau-Jarbidge. Prevailing westerlies deposited distal ashfall over a vast area of the Great Plains.

Volcanic fields

Twin Falls and Picabo volcanic fields

Twin Falls volcanic field and Picabo volcanic field were active about 10 million years ago. The Picabo Caldera was notable for producing the Arbon Valley Tuff 10.2 million years ago.

Heise volcanic field

The Heise volcanic field of eastern Idaho produced explosive caldera-forming eruptions which began 6.6 million years ago and lasted for more than 2 million years, sequentially producing four large-volume rhyolitic eruptions. The first three caldera-forming rhyolites — Blacktail Tuff, Walcott Tuff and Conant Creek Tuff — totaled at least 2250 km3 of erupted magma. The final, extremely voluminous, caldera-forming eruption — the Kilgore Tuff — which erupted 1800 km3 of ash, occurred 4.5 million years ago.[5][6][7][8][9]

Yellowstone Plateau

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File:Yellowstone Caldera map2.JPG
Yellowstone sits on top of four overlapping calderas.

The Yellowstone Plateau volcanic field is composed of four adjacent calderas. West Thumb Lake is itself formed by a smaller caldera[10] which erupted 174,000 years ago.[11] The Henry's Fork Caldera in Idaho was formed in an eruption of more than 280 km3 1.3 million years ago, and is the source of the Mesa Falls Tuff.[12] The Henry's Fork Caldera is nested inside of the Island Park Caldera and the calderas share a rim on the western side. The earlier Island Park Caldera is much larger and more oval and extends well into Yellowstone Park. Although much smaller than the Island Park Caldera, the Henry's Fork Caldera is still sizeable at 18 miles (29 km) long and 23 miles (37 km) wide and its curved rim is plainly visible from many locations in the Island Park area.

Of the many calderas formed by the Yellowstone Hotspot, including the later Yellowstone Caldera, the Henry's Fork Caldera is the only one that is currently clearly visible. The Henrys Fork of the Snake River flows through the Henry's Fork Caldera and drops out at Upper and Lower Mesa Falls. The caldera is bounded by the Ashton Hill on the south, Big Bend Ridge and Bishop Mountain on the west, by Thurburn Ridge on the North and by Black Mountain and the Madison Plateau on the east. The Henry's Fork caldera is in an area called Island Park. Harriman State Park is situated in the caldera.

The Island Park Caldera is older and much larger than the Henry's Fork Caldera with approximate dimensions of 58 miles (93 km) by 40 miles (64 km). It is the source of the Huckleberry Ridge Tuff that is found from southern California to the Mississippi River near St. Louis. This supereruption occurred 2.1 million years BP and produced 2500 km3 of ash. The Island Park Caldera is sometimes referred to as the First Phase Yellowstone Caldera or the Huckleberry Ridge Caldera. The youngest of the hotspot calderas, the Yellowstone Caldera, formed 640,000 years ago and is about 34 miles (55 km) by 45 miles (72 km) wide. Non-explosive eruptions of lava and less-violent explosive eruptions have occurred in and near the Yellowstone Caldera since the last supereruption.

The most recent lava flow occurred about 70,000 years ago, while the largest violent eruption excavated the West Thumb of Lake Yellowstone around 150,000 years ago. Smaller steam explosions occur as well - an explosion 13,800 years ago left a 5 kilometer diameter crater at Mary Bay on the edge of Yellowstone Lake. Both Heise and Yellowstone produced a series of normal caldera-forming magmas and a series of light post-caldera magmas. The final stage of volcanism at Heise was marked by light magma eruptions. If Heise is any indication, this could mean that the Yellowstone Caldera has entered its final act, but the volcano could exit with a climactic fourth caldera event analogous to the fourth and final caldera-forming light magma of Heise (the Kilgore Tuff). The appearance of light magmas indicates that the uppermost portion of the continental crust has been consumed, exhausting the melting potential of the crust above the mantle plume. In this case Yellowstone could be expiring.[citation needed] It could be another 1-2 million years before a new supervolcano is born to the northeast, and the Yellowstone Plateau volcanic field joins the ranks of its deceased ancestors in the Snake River Plain.

The Yellowstone hotspot is one of the few volcanic hotspots underlying North America; others include the Anahim and Raton hotspots.

Eruptive history

File:Yellowstone earthquakes history.svg
Number of earthquakes in Yellowstone National Park region (1973 – 2014)[13]
File:Yellowstone volcano - ash beds.jpg
Map of recent Yellowstone eruption fields, in comparison with a recent Long Valley Caldera eruption and Mount St. Helens.

Notes

See also

References

  1. Yellowstone Caldera, Wyoming, USGS
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  10. West Thumb Lake is not to be confused with West Thumb Geyser Basin. The caldera created West Thumb Lake, and the underlying Yellowstone hotspot keeps West Thumb Geyser Basin active. See Fig. 22. See also File:Yellowstone Caldera map2.JPG.
  11. Please refer to File:Yellowstone Caldera map2.JPG.
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  14. http://imnh.isu.edu/digitalatlas/geo/greatrft/greatrft.htm
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  33. SummitPost.org, Southeast Oregon Basin and Range
  34. USGS, Andesitic and basaltic rocks on Steens Mountain
  35. GeoScienceWorld, Genesis of flood basalts and Basin and Range volcanic rocks from Steens Mountain to the Malheur River Gorge, Oregon
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Map references

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Further reading

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External links

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