A supereruption at Yellowstone National Park is extremely unlikely. However, a new computer modeling system in use at the US Geological Survey (USGS) shows that it could coat cities as far away as Los Angeles, New York and Miami in Ash.

A supereruption is the largest class of volcanic eruption. Such an event involves the release of more than 240 cubic miles of material being ejected. The volcano at Yellowstone National Park is fed by an enormous reservoir of hot and molten rock. There have been three large eruptions of the volcano in the last 2.1 million years, with the most recent occurring 640,000 years ago. There have also been smaller eruptions and non-explosive lava flows as recently as 70,000 years ago.

While there is no indication that the volcano at Yellowstone is nearing any sort of large volcanic event, researchers at the USGS have used a hypothetical Yellowstone super eruption as a case study to test their new ASH3D model. The model incorporates data on wind patterns to determine the thickness of ash fall.

The study, published in the in the journal Geochemistry, Geophysics, Geosystems, published by American Geophysical Union provides the first qualitative estimates of the distribution and thickness of ash across the US from a Yellowstone supereruption.

Cities close to Yellowstone could be blanketed in several feet of ash. Cities in the midwest could see several inches while cities on both coasts would see less than an inch, but would still have some accumulation.

While a small eruption produces an ash spread that forms a fan shape when seen from above, the researchers believe that a Yellowstone eruption would spread like an umbrella cloud. Deposits of ash in an umbrella formation look more like a bulls eye, with a heavy deposit in the center and lessening deposits in all directions.

“In essence, the eruption makes its own winds that can overcome the prevailing westerlies, which normally dominate weather patterns in the United States. “This helps explain the distribution from large Yellowstone eruptions of the past, where considerable amounts of ash reached the west coast,” said Larry Mastin, a geologist at the USGS Cascades Volcano Observatory in Vancouver, Washington, and the lead author of the new paper in a statement.

Even small amounts of volcanic ash can lead to serious health problems such as respiratory issues. It can also cause power failures by shorting out electrical transformers, damage buildings, block sewer and water lines, make roads slippery and disrupt livestock and crop production.