Yellowstone supervolcano holds more magma than we thought, new study finds

New research conducted by an international team of researchers suggests that there's more magma under Yellowstone than was previously thought.

The discovery adds critical data to current models, which could lead to improved predictions for the next large eruption.

The tomographic imaging method revealed the "melt"

The goal of the study, led by geologist Ross Maguire of the University of Illinois Urbana-Champaign, was to estimate how much magma was present in Yellowstone's supervolcano. The team also wanted to determine how this magma was distributed underground.

They were specifically looking for melt (magma in liquid form)- which is frequently used to predict eruptions.

While it's usually challenging to see deep underground, the researchers used a recently developed tomographic imaging method to examine seismic wave recordings between 2000 and 2018. They then applied a technique called full waveform inversion to better understand the bouncing and reflecting vibrations.

They discovered that the magma reservoir beneath Yellowstone has a partial melt fraction of between 16 and 20 percent, compared with earlier models indicating 10 percent or less. This was determined by looking at how the speed of the detected waves fluctuated at different depths.

More magma is at shallower depths

According to earlier estimates, a melt volume of between 35 and 50 percent is needed to start an eruption. Still, many other variables at work make it difficult to forecast when these events will occur. According to the experts, even the latest scanning techniques can still miss some areas of liquid magma.

However, while the melt fraction estimated in the latest study is substantially lower than this, the researchers argued that "the presence of small subset volumes of the concentrated silicic melt cannot be ruled out."

Additionally, the new study found that the slowest speeds were between 3 and 8 kilometers (approximately 2 and 5 miles) below the surface. This suggests that the liquid melt is most concentrated at these shallow depths in the Earth's crust.

Still, R. Maguire and colleagues highlighted, "Although our results indicate that Yellowstone's magma reservoir contains substantial melt at depths that fueled prior eruptions, our study does not confirm the presence of an eruptible body or imply a future eruption."

One piece of the puzzle

Although it's only one piece of the puzzle, the newly described melt-rich zone is an "important indicator" of where Yellowstone is in its eruptive cycle, according to the researchers. As more information becomes available and eruptions occur, prediction models are continually improved.

In the past 2.1 million years, Yellowstone has seen three catastrophic eruptions. While it is uncertain when the next one will occur, having a better understanding of the caldera's geology will always be beneficial.

The study was published in Science.

Abstract:

What controls how and when a volcano will erupt? Despite some notable successes (1, 2), forecasting volcanic eruptions remains a challenge—not least because there is no way to directly see what is happening beneath volcanoes. Instead, indirect methods are used to glimpse conditions below the surface. An obvious but key requirement for an eruption is the presence of magma (molten rock, consisting of variable proportions of liquid, solid crystals, and volatiles). This magma also needs to be distributed so that it can mobilize and erupt as a coherent body. Therefore, a key issue for eruption hazard assessment is to ascertain how much magma is below the surface and where. On page 1001 of this issue, Maguire et al. (3) modeled seismic data to image melt (the liquid part of magma) beneath the Yellowstone Caldera. They conclude that more melt is present than had been recognized, and it is located at shallow depths in the crust.