Supervolcanoes

[neufer]

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<<Lake Toba is a lake and supervolcano, 100 kilometres long and 30 kilometres wide, and 505 metres at its deepest point. Located in the middle of the northern part of the Indonesian island of Sumatra with a surface elevation of about 900 metres it is the largest volcanic lake in the world. In addition, it is the site of a supervolcanic eruption that occurred about 74,000 years ago, a massive climate-changing event. The eruption is believed to have had a VEI intensity of 8. This eruption, believed to have been the largest anywhere on Earth in the last 25 million years, may have had catastrophic consequences globally.

Some anthropologists and archeologists believe that it killed most humans then alive, creating a population bottleneck in Central Eastern Africa and India that affected the genetic inheritance of all humans today.>>

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<<A supervolcano or super volcanic eruption is a volcanic eruption which is substantially larger than any volcano in historic times (generally accepted to be greater than 1,000 cubic kilometers or 240 cubic miles). Supervolcanoes can occur when magma in the Earth rises into the crust from a hotspot but is unable to break through the crust. Pressure builds in a large and growing magma pool until the crust is unable to contain the pressure. They can also form at convergent plate boundaries (for example, Toba). Supervolcanoes are relatively new to science. Although there are only a handful of supervolcanoes, super volcanic eruptions typically cover huge areas with lava and volcanic ash and cause a long-lasting change to weather (such as the triggering of a small ice age) sufficient to threaten the extinction of species.>>

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The last full-scale eruption of the Yellowstone Supervolcano, the Lava Creek eruption which happened nearly 640,000 years ago, ejected approximately 240 cubic miles (1000 cubic kilometres) of rock and dust into the sky.


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. The upward movement of the Yellowstone caldera floor—almost 3 inches (7 centimeters) each year for the past three years—is more than three times greater than ever observed since such measurements began in 1923.The U.S. Geological Survey, University of Utah and National Park Service scientists with the Yellowstone Volcano Observatory maintain that they "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."

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[bystander]

This is not the Yellowstone Caldera, but the Long Valley Caldera in California.
http://www.youtube.com/watch?v=1Vn6kxfD3Ek

[neufer]

This is not the Yellowstone Caldera, but the Long Valley Caldera in California.

Thanks for the correction, bystander.

Whether it is earth quakes, super volcanoes, ice ages, or the imminent loss of the magnetosphere
I'm beginning to think that natural disasters are more likely to come from beneath our feet than from outer space.

(Not that man won't beat mother Nature, at least, on the scale of centuries.)

[bystander]

Yellowstone Has Bulged as Magma Pocket Swells
National Geographic News | Brian Handwerk | 2011 Jan 19

Some places saw the ground rise by ten inches, experts report.

Steam rises from Castle Geyser in Yellowstone National Park. [i](Photograph by Mark Thiessen, National Geographic)[/i]

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Yellowstone National Park's supervolcano just took a deep "breath," causing miles of ground to rise dramatically, scientists report.

The simmering volcano has produced major eruptions—each a thousand times more powerful than Mount St. Helens's 1980 eruption—three times in the past 2.1 million years. Yellowstone's caldera, which covers a 25- by 37-mile (40- by 60-kilometer) swath of Wyoming, is an ancient crater formed after the last big blast, some 640,000 years ago.

(See "When Yellowstone Explodes" in National Geographic magazine.)

Since then, about 30 smaller eruptions—including one as recent as 70,000 years ago—have filled the caldera with lava and ash, producing the relatively flat landscape we see today.

But beginning in 2004, scientists saw the ground above the caldera rise upward at rates as high as 2.8 inches (7 centimeters) a year. (Related: "Yellowstone Is Rising on Swollen 'Supervolcano.'")

The rate slowed between 2007 and 2010 to a centimeter a year or less. Still, since the start of the swelling, ground levels over the volcano have been raised by as much as 10 inches (25 centimeters) in places.

"It's an extraordinary uplift, because it covers such a large area and the rates are so high," said the University of Utah's Bob Smith, a longtime expert in Yellowstone's volcanism.

Scientists think a swelling magma reservoir four to six miles (seven to ten kilometers) below the surface is driving the uplift. Fortunately, the surge doesn't seem to herald an imminent catastrophe, Smith said. (Related: "Under Yellowstone, Magma Pocket 20 Percent Larger Than Thought.")

"At the beginning we were concerned it could be leading up to an eruption," said Smith, who co-authored a paper on the surge published in the December 3, 2010, edition of Geophysical Research Letters.

"But once we saw [the magma] was at a depth of ten kilometers, we weren't so concerned. If it had been at depths of two or three kilometers [one or two miles], we'd have been a lot more concerned."

Studies of the surge, he added, may offer valuable clues about what's going on in the volcano's subterranean plumbing, which may eventually help scientists predict when Yellowstone's next volcanic "burp" will break out. ...