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Plumbing of Yellowstone supervolcano larger than first thought

   |  Posted Dec 14th, 2009 @ 11:35am



 

YELLOWSTONE NATIONAL PARK, WYO. -- New studies of the plumbing that feeds the Yellowstone supervolcano in Wyoming's Yellowstone National Park shows the plume and the magma chamber under the volcano are larger than first thought and contradicts claims that only shallow hot rock exists.

University of Utah research professor of geophysics Robert Smith led four separate studies that verify a plume of hot and molten rock at least 410 miles deep that rises at an angle from the northwest.

The studies also indicate the banana-shaped magma chamber a few miles beneath Yellowstone is 20 percent larger than previously thought- meaning a cataclysmic eruption could be even larger.

"We have a clear image, using seismic waves from earthquakes, showing a mantle plume that extends from beneath Yellowstone,'' Smith says.

Seismic imaging was used by University of Utah scientists to construct this picture of the Yellowstone hotspot plume. Click to enlarge

Some 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.

But the series of studies show the plume angles downward 150 miles to the west-northwest of Yellowstone and reaches a depth of at least 410 miles. That puts the plume below the town of Wisdom, Mont.

Smith says "it wouldn't surprise me" if the plume extends even deeper, perhaps originating from the core-mantle boundary some 1,800 miles deep.

In fact, a preliminary study by other researchers suggests Yellowstone's plume goes deeper than 410 miles, ballooning below that depth into a wider zone of hot rock that extends at least 620 miles deep.

The notion that a deep plume feeds Yellowstone got more support from a study published this month indicating that the Hawaiian hotspot - which created the Hawaiian Islands - is fed by a plume that extends downward at least 930 miles, tilting southeast.

The study estimates the plume is mostly hot rock, with one to two percent molten rock in sponge-like voids within the hot rock. Smith also points out the plume isn't vertical, but has three components:

  • The 45-mile-wide plume that rises through Earth's upper mantle from at least 410 miles beneath the surface. The plume angles upward to the east-southeast until it reaches the colder rock of the North American crustal plate, and flattens out like a 300-mile-wide pancake about 50 miles beneath Yellowstone. The plume includes several wider "blobs" at depths of 355 miles, 310 miles and 265 miles.

  • A little-understood zone, between 50 miles and 10 miles deep, in which blobs of hot and partly molten rock break off of the flattened top of the plume and slowly rise to feed the magma reservoir directly beneath Yellowstone National Park.

  • A magma reservoir 3.7 miles to 10 miles beneath the Yellowstone caldera. The reservoir is mostly sponge-like hot rock with spaces filled with molten rock.

Researchers previously believed the magma chamber measured roughly six to 15 miles from southeast to northwest, and 20 or 25 miles from southwest to northeast, but new measurements indicate the reservoir extends at least another 13 miles outside the caldera's northeast boundary, Smith says.

The Yellowstone caldera, like other calderas on Earth, huffs upward and puffs downward repeatedly over the ages, usually without erupting. Since 2004, the caldera floor has risen 3 inches per year, suggesting recharge of the magma body beneath it.

The studies, funded by the National Science Foundation, appear in the latest issue of the Journal of Volcanology and Geothermal Research.


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