“The Future of Eruptions: Unveiling Yellowstone’s Next Volcanic Adventure”

When Yellowstone erupts again, which it undoubtedly will, it won’t matter if individuals reside in Bozeman, Montana or Cody, Wyoming — they’ll meet the same fate. However, recent seismological studies have precisely identified where the eruption will pierce the surface. For those wishing to be overwhelmed by magma rather than ash, the northeastern section of the park is the best location.

Hikers needn’t be concerned. A team from the United States Geological Survey (USGS), published last week in Nature Geoscience also assessed the proportion of rock within Yellowstone’s magma reservoirs that has actually melted. Their findings indicate that none of it is approaching levels where an eruption is likely.

Mount Saint Helens, prior to and following a lateral eruption that removed half the mountainside. Photo: USGS

Yellowstone magma near the surface

When Mount Saint Helens erupted in 1980, the majority of the mountain’s upper portion collapsed and cascaded down the slopes in a colossal avalanche. What remained was a caldera. This bowl-like indentation in the rock isn’t supplied by a slender vent like conventional volcanoes. In contrast, a substantial magma pool lies just below a thin layer of surface rock.

This is what resides beneath the ground at Yellowstone National Park. However, unlike Mount Saint Helens, the Yellowstone caldera possesses not just one magma reservoir, but four.

The Yellowstone caldera boasts a lengthy history. It has erupted at least thrice prior, the most recent occurrence being 70,000 years ago. Earlier eruptions have left the northeast comparatively untouched, but that will alter with the arrival of the next eruption.

To pinpoint magma, the USGS team utilized a network of stations measuring the conductivity of materials deep within the Earth. This technique, known as magnetotellurics, takes advantage of the property that solid rock exhibits high resistance to electric currents. As soon as rock begins to melt, however, electric currents can flow through it. Thus, magma is indicated on the magnetotellurics readings as areas of elevated subterranean conductivity.

These magma hotspots are not truly underground pools akin to aquifers but instead a honeycomb structure of solid and molten rock. Provided the melting percentage remains below 40%, the various pockets within the honeycomb cannot accumulate sufficient pressure to force their way to the surface. The highest melting fraction discovered in the recent study is only 18%, and it is unlikely to see significant increase over the next several decades.

Magnetotelluric stations like this one in Antarctica were established all over Yellowstone. Photo: Kerry Key/Columbia University

Where the magma lies deeper

An illustration of the Yellowstone magma system in the northeast. Photo: Yellowstone Volcano Observatory

Although the USGS has identified regions of melted rhyolite rock beneath all of Yellowstone, conduits of magma link the northeastern rhyolite melt pockets to deeper reserves of molten basalt. Rhyolite magma produces distinctive volcanic ash, but basalt is the actual force behind eruptions due to its fluidity. This property allows it to transfer heat from deep within the Earth, propelling molten rhyolite to the upper layers.

Currently, the amount of magma beneath Yellowstone exceeds that of any previous eruptions. It remains uncertain how much of that will still be present when the caldera eventually erupts.