Yellowstone supervolcano contains twice as much melted rock as thought

James Dinneen is a writer.

The amount of melted rock under the caldera is double what was thought. The threshold that suggests an eruption at Yellowstone is more likely isn't met by the increase in estimate.

One of the largest volcanos in the world is located in Wyoming. In the past 2.1 million years, there have been three catastrophic eruptions that blanketed North America in ash and a number of smaller eruptions. Researchers watch for any changes that could indicate an eruption.

There are two huge reservoirs beneath the caldera, one close to the mantle and the other a few kilometres below the surface. The reservoirs were once thought of as big tanks of magma, but now have a complex "crystal mush" of melted rock and crystals. The composition of this mush is a factor in the volcano's likelihood of eruption.

Because seismic waves move more slowly through areas with more melted rock, Maguire and his colleagues were able to analyse data from the past two decades to estimate the proportion of melted rock.

Past analyses used a simple model that treated the waves as linear rays, but their analysis used supercomputers to model the waves in three dimensions.

Depending on the shape of spaces between solid crystals, the estimate of the amount of melted rock is 16 to 20 per cent. The previous estimate of the amount of melted rock in the reservoir was 900.

The proportion of melted rock is still below the threshold needed for an eruption. He says that Yellowstone can spend a lot of time with melt.

According to a commentary written by the University of California, Davis, there could be enough for a small eruption if the melted rock is distributed the right way.

Cooper says that it is a big improvement in our ability to understand what is underneath the mountain.

The journal's title is "science."