Climate Change Has Significantly Altered the Way This California Volcano 'Breathes'

Thirty years ago, trees began to die on the sides of a volcano in California's Sierra Nevada range, choked at their roots by carbon dioxide seeping out from the mountain's bowels following a series of minor earthquakes.

Scientists began intensively monitoring the volcano's emissions after a wave of tree fatalities on Mammoth Mountain, part of one of the nation's greatest active volcanic systems.

On-Going Research

Now, a team of academics led by Stanford University geologist George Hilley has discovered something unexpected in the long-running record:

The quantity of water that percolates down into the volcano's plumbing and the weight of snow and ice atop the Sierra Nevada are important factors in the ebb and flow of carbon dioxide emissions from Mammoth Mountain.

According to Hilley, a professor of geological sciences at Stanford's School of Earth, Energy & Environmental Sciences, "this truly highlights how the solid Earth is related to climate and what goes on at the surface" (Stanford Earth).

Droughts have the potential to alter the way volcanoes breathe. The study, published in Geophysical Research Letters, comes amid a dry winter that has left California's snowpack considerably below the average for this time of year, with less than a week left in the state's rainy season and no large snowstorms predicted.

State experts forecast that the Sierra Nevada snowpack will drop by 48 to 65 percent by the century, compared to the historical April 1 average.

Essential Correlation

According to Hilley, climate change-related changes in Earth's hydrology might influence things like the rate at which gases are emitted from volcanic systems.

Hilley and coauthors investigated carbon dioxide emissions data collected every 30 minutes for six years from Horseshoe Lake, Mammoth Mountain's best-studied tree death location. The mountain stands along the southwest rim of Long Valley Caldera, and a crater was created 760,000 years ago by a supervolcano eruption.

During the spring of 2017, the quantity of carbon dioxide seeping up from the Earth was consistently reduced by 20%, according to the findings. The downshift corresponds with the region's recovery from a severe drought and the accumulation of the largest snowfall in decades in the Sierra Nevada.

Using Previous Works

The research relies on previous work by USGS volcanologist Jennifer Lewicki, who discovered that carbon dioxide emissions in the Horseshoe Lake tree-kill region fluctuated seasonally and overtime for reasons unrelated to a looming eruption.

To find an explanation for these differences, Lewicki and Hilley created mathematical models with Stanford collaborator Curtis Baden to test various possible pathways.

Snowmelt and rainfall, for example, can wash away carbon dioxide that would otherwise leak out of the Earth. However, their calculations suggest that Mammoth Mountain receives much too little precipitation to explain the low CO2 levels reported in the spring of 2017.

The most likely cause of the seasonal variations in Mammoth Mountain's carbon dioxide emissions is an underground fissure, or fault, visible in the landscape's flora patterns and topography to a trained eye.

Changes in the load distribution throughout the mountain range appear to open and shut the fault like a valve or the tiny spaces between old floorboards that flex under changing weight.

Analyzing Data

Using GPS data and snow depth measurements, the authors discovered that compressive strain on the fault peaked in the winter as snowpack built throughout the Sierra Nevada and decreased during snow-free summer months between 2014 and 2020.

When the weight of snow and water in the mountains strained the Earth's crust, pressing the rocks on either side of the Mammoth Mountain fault together, carbon dioxide emissions decreased.

One of the study's limitations is that it lacks a physics-based model of the fault's movement and how gas flows through it.

Comparing Different Changes

The capacity to discern between CO2 changes caused by climate change and those caused by an approaching eruption would improve hazard forecasting, which is based in part on indicators that rising magma is causing earthquakes, deforming the ground surface, or causing gases to rise.

"When all three things are aligned, it's usually a sign that an eruption is likely to happen," Hilley added.

Ground deformation and seismicity surrounding several of America's active volcanoes have been regularly monitored for decades using GPS and satellites, and scientists can see the data in near real-time.

Challenges

Due to the difficulties of collecting volcanic gases, records are limited. Some years have just a single picture of a volcano's degassing, making it impossible to spot changes that may signal an eruption - or to comprehend patterns connected to Earth's climate system.

According to the new study, scientists will be able to access more volcanic emission data in the future, owing to the development of less expensive and more robust sensors.

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