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Jul 22, 2014 10:22 AM by Stephen Bowers

Yellowstone's Magma Reservoir Larger Than Earlier Thought

Yellowstone has produced some of the most violent volcanic eruptions in Earth's history. It is classified as a supervolcano, one of three in the United States and only six known in the world. The others are the Long Valley Caldera in California, which last violently erupted 760,000 years ago, and the Valles Caldera in northern New Mexico, which last erupted more than 1.2 million years ago.

Yellowstone's last eruption, about 640,000 years ago, is estimated to have spewed as much as 8,000 times as much ash and lava as the Mount Saint Helens eruption in Washington nearly 30 years ago, resulting in an abrupt climate change that spanned the globe. Previous eruptions are thought to have occurred 1.3 million years ago and 2.1 million years ago.

A new report from the website EarthSky, based on research published in science journal Geophysical Research Letters in May, says the magma reservoir beneath Yellowstone is two-and-a-half times larger than previously thought. 

Seismic sensors put in place around Yellowstone Caldera in the past decade have helped scientists fine tune their research. Studying the seismic waves from over 4,000 earthquakes around Yellowstone helped the researchers to determine the size of Yellowstone's magma reservoir. It was found to be about 56 miles long and 3 to 11 miles deep. 

The reservoir sits atop a hotspot in the Earth's mantle and collects molten rock, or magma, on its ascent to the Earth's surface. Based on current information Yellowstone's magma reservoir is thought to be the largest in the world.

The report from EarthSky also says that the magma reservoir contains only 5 to 15% melt, which is much lower than earlier estimates. The report credits information from the USGS and says magma typically does not erupt with melt contents of less than 50%.

Scientists believe the supervolcanoes of the western U.S. formed due to tectonic plates that carry western North America trying to rift apart and separate. 

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