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Posts Tagged ‘mantle plume’

Yellowstone Supervolcano 2.5 Times Previous Estimates

Posted by feww on December 11, 2013

Supervolcano’s  magma chamber contains up to 600km³ molten rock: Report

The supervolcano that lies beneath Yellowstone National Park (YNP) is about 2.5 times larger than was previously thought, and contains up to 600km³ molten rock, according to a new scientific report.

“We’ve been working there for a long time, and we’ve always thought it would be bigger,  but this finding is astounding,” said University of Utah geophysicist Prof Bob Smith.

The findings are reportedly being presented at the American Geophysical Union Fall Meeting in San Francisco.

In 2009, a related University of Utah study used gravity measurements to show the banana-shaped magma chamber of hot and molten rock a few miles beneath Yellowstone is 20 percent larger than previously believed, so a future cataclysmic eruption could be even larger than thought.

Seismic imaging was used by University of Utah scientists to construct this picture of the Yellowstone hotspot plume of hot and molten rock that feeds the shallower magma chamber (not shown) beneath YNP, outlined in green at the surface, or top of the illustration. The Yellowstone caldera, or giant volcanic crater, is outlined in red. State boundaries are shown in black. The park, caldera and state boundaries also are projected to the bottom of the picture to better illustrate the plume’s tilt. Researchers believe “blobs” of hot rock float off the top of the plume, then rise to recharge the magma chamber located 3.7 miles to 10 miles beneath the surface at Yellowstone. The illustration also shows a region of warm rock extending southwest from near the top of the plume. It represents the eastern Snake River Plain, where the Yellowstone hotspot triggered numerous cataclysmic caldera eruptions before the plume started feeding Yellowstone 2.05 million years ago. The image shows the plume an angle of 60 degrees and extends 150 miles west-northwest to a point at least 410 miles under the Montana-Idaho border–as far as seismic imaging could “see.”Photo Credit: University of Utah

The last major eruption at Yellowstone, which occurred about 640,000 years ago, ejected ash and volcanic matter  across the whole of North America, affecting the global climate.

A cross section of the plume of hot and molten rock that tops out about 50 miles beneath YNP and tilts downward to the northwest to a depth of at least 410 miles. The plume is mostly hot rock with about 1 to 2 percent molten rock. Researches believe “blobs” of hot rock slowly detach from the top of the plume and rise upward to recharge the magma chamber that lies from 3.7 to 10 miles beneath Yellowstone. The chamber is also mostly hot rock, but with a sponge-like structure containing about 8 to 15 percent molten rock.  Photo Credit: University of Utah

cisternCistern Spring and Steamboat Geyser are linked underground. During a major eruption of Steamboat, the water in Cistern Spring’s pool drains. Normally, Cistern is a beautiful blue pool from which water continually overflows. It is quite creative, depositing as much as 1/2 inch (12mm) of grayish sinter each year. By comparison, Old Faithful Geyser and many other thermal features may build at the rate of only 1/2 to 1 inch (12 – 25mm) per century. Cistern Spring’s influence expands throughout the lodgepole pine forest below. This forest has been slowly flooded with silica rich water since 1965. The pioneering lodgepole pine forest at Norris is in constant flux, retreating here and in other areas of increasing heat while advancing in places of diminished thermal activity.  Source: National Park Service/Yellowstone.

“Geoelectric” image of the Yellowstone Hotspot

In their latest attempt, the research team at University of Utah used a network of seismometers that strategically surrounded the YNP to map the colossal magma chamber.

The latest imaging showed a colossal magma chamber about 90 km, 30km wide and extending up to 15km deep.

Several researchers have doubted the existence of a mantle plume feeding Yellowstone, arguing instead that the area’s volcanic and hydrothermal features are fed by convection – the boiling-like rising of hot rock and sinking of cooler rock – from relatively shallow depths of only 185 miles to 250 miles.

Electrical conductivity image of YNP volcanic plumeThis image April 11, 2011 image, based on variations in electrical conductivity of underground rock, shows the volcanic plume of partly molten rock that feeds the Yellowstone supervolcano. Yellow and red indicate higher conductivity, green and blue indicate lower conductivity. Made by University of Utah geophysicists and computer scientists, this is the first large-scale “geoelectric” image of the Yellowstone hotspot. The geoelectric image can “see” only 200 miles deep. Photo Credit: The University of Utah

The Yellowstone Hotspot at a Glance

The new study says nothing about the chances of another cataclysmic caldera (giant crater) eruption at Yellowstone, which has produced three such catastrophes in the past 2 million years.

Almost 17 million years ago, the plume of hot and partly molten rock known as the Yellowstone hotspot first erupted near what is now the Oregon-Idaho-Nevada border. As North America drifted slowly southwest over the hotspot, there were more than 140 gargantuan caldera eruptions – the largest kind of eruption known on Earth – along a northeast-trending path that is now Idaho’s Snake River Plain.

The hotspot finally reached Yellowstone about 2 million years ago, yielding three huge caldera eruptions about 2 million, 1.3 million and 642,000 years ago. Two of the eruptions blanketed half of North America with volcanic ash, producing 2,500 times and 1,000 times more ash, respectively, than the 1980 eruption of Mount St. Helens in Washington state. Smaller eruptions occurred at Yellowstone in between the big blasts and as recently as 70,000 years ago.

Seismic and ground-deformation studies previously showed the top of the rising volcanic plume flattens out like a 300-mile-wide pancake 50 miles beneath Yellowstone. There, giant blobs of hot and partly molten rock break off the top of the plume and slowly rise to feed the magma chamber – a spongy, banana-shaped body of molten and partly molten rock located about 4 miles to 10 miles beneath the ground at Yellowstone.

Yellowstone  straddles three states: Wyoming, Montana and Idaho.

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