Volcanic activity beneath Yellowstone’s vast caldera may be on the move: ScienceAlert

Volcanic activity apparently continues to bubble beneath Yellowstone National Park in the USA.

New research shows that the magma reservoirs that fuel the supervolcano’s wild eruptions appear to be shifting to the northeast of the Yellowstone caldera. According to a team led by US Geological Survey seismologist Ninfa Bennington, this region could be the new site of future volcanic activity.

“Based on the volume of rhyolitic melt storage beneath the northeastern Yellowstone caldera and the region’s direct connection to a heat source in the lower crust, we suspect that the location of future rhyolitic volcanism has shifted to the northeastern Yellowstone caldera,” write them in their report paper.

“In contrast, post-caldera rhyolitic volcanism has occurred throughout most of the Yellowstone caldera over the past 160,000 years, with the exception of this northeastern region.”

Yellowstone is one of the largest supervolcanoes in the world; a vast, complex, dynamic region of the Earth’s crust that is both spectacularly beautiful and extremely dangerous.

In the last 2 million years, Yellowstone National Park has experienced three huge caldera-forming eruptions – those that form cauldron-like pools on the Earth’s surface when an underground magma chamber empties and collapses into the hollowed-out cavity. These large eruptions were punctuated by smaller eruptions.

The caldera-forming eruptions in Yellowstone originate from reservoirs of rhyolitic melt. This is siliceous magma, the volcanic equivalent of granite, sticky, viscous and slow, and is thought to have been deposited in vast quantities beneath the Yellowstone region.

Previous studies assumed that the rhyolite reservoirs were supported by deeper reservoirs of basaltic magma – molten material that is much lower in silica than rhyolite but abundant in iron and magnesium. It is also significantly less viscous than rhyolite, but also denser, and the way it conducts electricity is different from rhyolite.

This latter difference in properties gave Bennington and her colleagues the tools they needed to study the contents of the magmatic reservoir beneath the Yellowstone Plateau.

One way to monitor activity beneath Earth’s surface is to measure surface fluctuations in the planet’s magnetic and electric fields. This is known as magnetotellurics and is particularly sensitive to the presence of melts beneath the surface.

Bennington and her colleagues conducted a large-scale magnetotelluric survey of the Yellowstone caldera and used the resulting data to model the distribution of melt reservoirs lurking within.

Their results showed that at depths between 4 and 47 kilometers (2.5 to 30 miles) underground – to the crust-mantle boundary – there are at least seven different regions of high magma content, some of which flow into others.

The most interesting smelter was in the northeast. There, vast reservoirs of basaltic magma in the lower crust heat and sustain chambers of rhyolitic magma in the upper crust. These chambers of rhyolitic magma contain an estimated melt storage volume of about 388 to 489 cubic kilometers – almost an order of magnitude larger than melt storage zones to the south, west and north, where previous eruptions have occurred.

The researchers note that this volume is also comparable to the melt volume of previous caldera-forming eruptions in Yellowstone.

The rhyolitic caldera-forming eruptions, the researchers note, were interspersed with smaller, basaltic eruptions within the caldera. However, it is unclear exactly how these types of eruptions work. The team’s research suggests that the rhyolitic magma chambers must cool completely before the basaltic magma can intrude.

When exactly and how these future outbreaks will occur requires further analysis, according to researchers.

The research was published in Nature.