The subterranean volcanic processes beneath Yellowstone National Park in the United States have recently demonstrated a notable shift in activity.

Recent scholarly investigations indicate that the magma reservoirs, which are integral to the supervolcano’s explosive episodes, appear to be migrating northeastward, away from their previous locations within the Yellowstone Caldera. This emerging region may potentially represent the epicenter of imminent volcanic activity, according to a research team spearheaded by seismologist Ninfa Bennington of the United States Geological Survey.

“Based on the substantial volume of rhyolitic melt storage situated beneath the northeastern sector of the Yellowstone Caldera, alongside its direct link to a lower-crustal heat reservoir, we posit that the focal point of forthcoming rhyolitic volcanism has indeed transitioned to the northeastern quadrant of the Caldera,” the authors elucidate in their publication.

In stark contrast, the rhyolitic volcanic activity observed over the last 160,000 years has been predominantly distributed across the majority of the Yellowstone Caldera, conspicuously excluding this particular northeastern segment.

Characterized as one of the most colossal supervolcanoes globally, Yellowstone constitutes a vast, multi-faceted, and dynamic geological expanse that is both awe-inspiring and perilously hazardous. During the past two million years, it has experienced three significant caldera-forming eruptions—the cataclysmic events that result when subterranean magma chambers vacate and subsequently collapse.

These cataclysmic eruptions have been interspersed with less monumental, yet still substantial, volcanic events.

The caldera-forming eruptions draw from reservoirs of rhyolitic melt, a silica-rich magma analogous to granite. This magma is characterized by its stickiness and high viscosity, and it is believed to be harbored in vast quantities beneath the Yellowstone region.

Previous research had presumed these rhyolitic reservoirs were undergirded by deeper basaltic magma reservoirs, which possess a significantly lower silica composition yet contain substantial iron and magnesium. This basaltic magma, notable for its reduced viscosity and higher density, provides a contrasting electrical conductivity profile compared to rhyolitic magma.

This distinction has equipped Bennington and her colleagues with the necessary tools to delve into the magmatic compositions beneath the Yellowstone Plateau.

One effective approach to scrutinizing subterranean activity involves observing surface variances in the planet’s magnetic and electric fields, a method known as magnetotellurics, which is acutely sensitive to the presence of subsurface melts.

Employing a comprehensive magnetotelluric survey covering the Yellowstone Caldera, Bennington’s team analyzed the resultant data to model the distribution of melt reservoirs concealed beneath the surface.

Their findings unveiled the existence of at least seven distinct regions with elevated magma content, some interlinking, located at depths between 4 and 47 kilometers (2.5 to 30 miles) beneath the surface, extending down to the crust-mantle boundary.

Of particular interest were the substantial melt reservoirs situated in the northeastern sector. Here, considerable accumulations of basaltic magma in the lower crust serve to heat and sustain rhyolitic magma chambers in the upper crust. These rhyolitic magma chambers are estimated to harbor a melt storage volume ranging from 388 to 489 cubic kilometers—an order of magnitude greater than the corresponding storage volumes in the southern, western, and northern regions where previous eruptive activity has occurred.

This volume is noteworthy and bears comparison to the melt volumes associated with prior caldera-forming eruptions at Yellowstone.

The researchers further noted that rhyolitic caldera-forming eruptions were punctuated by smaller-scale basaltic eruptions within the caldera. However, the specific mechanics governing these eruption types remain inadequately understood. Their research suggests that for basaltic magma to ascend, the underlying rhyolitic magma chambers must first relinquish their thermal energy and cool completely.

Determining the precise timelines and modalities of potential future eruptions will necessitate additional analytical endeavors.

This body of research has been published in Nature.