Stanford study finds drought changes carbon dioxide emissions on Mammoth Mountain – Can it be reduced?
New article in Geophysical Research Letter
Seasonal and multi-year changes in CO2 Degassing in Mammoth Mountain is explained by error correction driven by solid earth
abstract
Changes in CO2 Emissions from volcanoes can be evidence of volcanic instability. We use the multi-year time series of CO2 fluxes were collected at the Horseshoe Lake Tree Kill site on Mammoth Mountain, CA, to understand the processes that cause flux variations from this system. The seasonal variations are systematically lowest during the winter months and peak during the summer. Continuous 20% CO reduction2 The outflow occurred in the spring of 2017, coinciding with the arrival of the area due to drought and earthquake clusters in the Long Valley Caldera. We used continuous GNSS measurements to calculate seasonal strains and stresses over the Mammoth Mountain area, and also resolved the resulting stresses for the Mammoth Mountain Fault, which appear to facilitate favorable conditions for gas transport to the surface. Normal stress variation consistent with seasonal and multi-year changes in CO2 flux, suggesting that fault valuation by solid-earth processes can alter surface gas flows.
Pure language summary
Changes in the rate of volcanic emissions could be a precursor to impending eruptions. New methodologies allow us to measure these changes continuously and in near real time. With this information, new and unexpected signals were observed in Mammoth Mountain, California, such as seasonal declines and volcanic CO flows.2 emissions. It is necessary to understand the processes that produce these seasonal changes in order to distinguish them from signs of volcanism. This work investigates several potential mechanisms for these seasonal changes and concludes that they can be explained by the seasonal curvature of the solid earth upon changes in water and ice loads, as well as subsurface pressure due to water infiltration. This curvature of the solid earth can be measured with GNSS, allowing us to filter these effects from CO2 flow time series, as well as highlighting the ways in which volcanic systems can “breathe” over the course of a year with changing hydrological conditions.
Press Release
The snow cover changes the way California volcanoes breathe
STANFORD UNIVERSITY
Thirty years ago, on the slopes of a volcano in the Sierra Nevada range of California, trees began to die en masse, suffocating their roots by carbon dioxide seeping up from the depths of the mountain after a minor earthquake.
The wave of dead trees on Mammoth Mountain, located in one of the nation’s largest active volcanic systems, prompted scientists to begin monitoring the volcano’s emissions more closely.
Now, researchers led by a Stanford University geologist George Hilley made a surprising discovery in a long-standing record: The rise and fall and flux of carbon dioxide emissions from Mammoth Mountain are strongly linked to the weight of snow and ice atop the Sierra Nevada, and the amount of water infiltration. down from the ground into the volcano’s water pipes.
“This really shows how solid Earth is associated with climate and things going on at the surface,” said Hilley, a professor of geosciences at Stanford. School of Earth, Energy & Environmental Sciences (Stanford Earth). “Drought could change the way volcanoes breathe.”
The study, published March 9 in Geophysical research lettercame in the middle of a dry winter that left ice in California below average at this time of year, with less than a week left in the state’s rainy season and no major snowstorms in the forecast.
At the end of this century, state officials guess Snow and ice in the Sierra Nevada will be 48 to 65% less than the historic April 1 average. “Changes in Earth’s hydrology due to climate change could actually have an impact,” said Hilley. to something like the pacing of gases emitted by volcanic systems.
Horseshoe Lake
Hilley and co-authors analyzed carbon dioxide emissions measurements taken every 30 minutes for six years from Horseshoe Lake, the best-studied tree-killing site on Mammoth Mountain. The mountain rises along the southwestern rim of Caldera Long Valleya crater formed by a supervolcanic eruption 760,000 years ago.
The results showed that the amount of carbon dioxide seeping up from the ground dropped by 20% consistently throughout spring 2017. This drop coincided with the arrival of the region due to intense drought and the accumulation of carbon dioxide. the Sierra Nevada’s largest ice cover in decade.
Research is built on search by USGS volcanologist Jennifer Lewicki found that carbon dioxide emissions in the tree-killing area of Horseshoe Lake vary seasonally and over many years for reasons unrelated to the brewing eruption.
Looking for explanations for these variations, Lewicki and Hilley – with co-authors Curtis Baden of Stanford – developed mathematical models to test rational mechanisms. For example, snowmelt and rain can wash away permeable carbon dioxide from the ground. But their calculations show that the Mammoth Mountains receive too little rainfall to account for the low CO levels in the spring.2 levels observed in 2017.
The most likely explanation for the seasonal variation in Mammoth Mountain’s carbon dioxide emissions involves a fissure, or fault, underground, which to the trained eye is evident in the vegetation type and topography of the landscape. Changes in stress distribution over the entire mountain range appear to open and close the fault like a valveor as small gaps between old floorboards that can bend under the shifting weight.
Using GPS data and snow depth measurements, the authors found that compression forces on the fault between 2014 and 2020 typically peak in winter when snow and ice accumulates across the Sierra Nevada and subsides during the winter. summer months without snow. Carbon dioxide emissions dropped during a period when the weight of snow and mountain water curved the Earth’s crust, squeezing rocks on either side of the Mammoth Mountain fault.
One limitation of the study is that it does not provide a physically-based model of the fault’s motion and how gas flows through it. “We are using stress changes as a proxy to open and close a conduit,” says Hilley. “An interesting study would be to run a three-dimensional model of gas transport through a duct that you can actually open and close, and then run that model over and over to see if its predictions match. quantitatively with the carbon dioxide measurements we’re taking.”
Predict future eruptions
Ability to distinguish between CO2 Climate-driven fluctuations driven by those caused by an impending eruption would allow for better hazard forecasting, based in part on signs that rising magma is causing earthquakes, distortions the surface of the earth or conduct air upwards. “The association of all three is often a clue that an eruption may be imminent,” says Hilley.
For decades, ground deformation and seismicity around some of the United States’ active volcanoes have been continuously monitored using GPS and satellites, and scientists can view the data. close to real time. But they take a more murky view of volcanic gases. “Previously, at most volcanoes, scientists had to go into the volcanic region before eruptions, or even between eruptions, and collect this gas for later analysis. It’s really Indiana Jones stuff,” Hilley said.
Difficulty in capturing volcanic gases has resulted in limited documentation, sometimes with only one snapshot of volcanic degassing in any given year, which makes detecting changes potentially difficult. It is difficult to warn of an eruption – or to understand patterns related to Earth’s climate system.
New research provides a glimpse into the insights that have come as scientists gain access to more volcanic emission data, thanks in part to the development of less expensive and more durable instruments. than.
“The hope is that in the next few years we can have a record of what gas is doing in real time,” says Hilley. “When you look at the details, you can see there are seasonal fluctuations that probably have nothing to do with the actual state of the volcano.”
Baden is a graduate student in geosciences at Stanford Earth.
JOURNEYS
Geophysical research letter
DOI
RESEARCH METHODS
Data analysis / statistics
RESEARCH SUBJECTS
Do not apply
ARTICLE TITLE
Seasonal and multi-year changes in CO2 degassing at Mammoth Mountain explained by fault valuation caused by solid soils
ARTICLE PUBLICATION DATE
March 9, 2022
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