Horseshoe lake in Mammoth mountains area

Stanford Research Finds Drought Alters Mammoth Mountain’s Carbon Dioxide Emissions

New paper in Geophysical Research Letters

Seasonal and Multiyear Changes in CO2 Degassing at Mammoth Mountain Explained by Solid-Earth-Driven Fault Valving


Changes in CO2 emissions from volcanoes may evidence volcanic unrest. We use a multiyear time series of CO2 flux collected at the Horseshoe Lake Tree Kill area on Mammoth Mountain, CA, to understand processes that cause variations in flux from this system. Seasonal variations are systematically lowest during the winter months and reach maximum values during the summer season. A persistent ∼20% reduction in CO2 flux occurred during the Spring of 2017, coincident with the emergence of the area from drought and earthquake swarms in Long Valley Caldera. We used continuous GNSS measurements to calculate seasonal strains and stresses across the Mammoth Mountain area, and resolved resultant stresses onto the Mammoth Mountain Fault, which appears to facilitate gas transport to the surface. The normal stress changes are consistent with seasonal and multiyear changes in CO2 flux, suggesting that fault valving by solid earth processes can alter surface gas fluxes.

Plain Language Summary

Changes in the rates of volcanic gas emissions may be harbingers of impending eruptions. New methodologies allow us to measure these changes continuously and in near-real time. With this information, new and unexpected signals have been observed at Mammoth Mountain, California, such as the seasonal ebb and flow of volcanic CO2 emissions. Understanding the processes that produce these seasonal changes is required to distinguish them from the signs of volcanic unrest. This work investigates a number of potential mechanisms for these seasonal changes, and concludes that they can be explained by the seasonal flexing of the solid earth under changing water and ice loads, and subsurface pressurization due to infiltrating water. This flexing of the solid earth can be measured by GNSS, allowing us to filter these effects from the CO2 flux time series, as well as highlight the ways in which volcanic systems may “breathe” over the course of a year with changing hydrologic conditions.

Press Release

Snowpack changes how a California volcano ‘breathes

Peer-Reviewed Publication


Thirty years ago, on the flanks of a volcano in California’s Sierra Nevada range, trees began to die en masse, suffocated at their roots by carbon dioxide seeping up from the mountain’s depths after a swarm of small earthquakes.

The wave of tree deaths on Mammoth Mountain, which lies within one of the nation’s largest active volcanic systems, prompted scientists to start monitoring the volcano’s emissions more closely.

Now, researchers led by Stanford University geologist George Hilley have made a surprising discovery in the long-running record: The ebb and flow of carbon dioxide emissions from Mammoth Mountain are strongly linked to the weight of snow and ice atop the Sierra Nevada, and to the amount of water that percolates from ground level down into the volcano’s plumbing.

“This really shows how the solid Earth is coupled to climate and the things that go on at the surface,” said Hilley, professor of geological sciences in Stanford’s School of Earth, Energy & Environmental Sciences (Stanford Earth). “Droughts can change the way in which volcanoes breathe.”

The research, published March 9 in Geophysical Research Letters, comes amid a dry winter that has left California snowpack well below average for this time of year, with less than a week remaining in the state’s wet season and no major snowstorms in the forecast.

By the end of this century, state officials predict the Sierra Nevada snowpack will decline by 48 to 65 percent from the historical April 1 average. “Changes in Earth’s hydrology due to climate change could actually impact something like the tempo at which gases are emitted from volcanic systems,” Hilley said.

Horseshoe Lake

Hilley and coauthors analyzed measurements of carbon dioxide emissions taken every 30 minutes for six years from Horseshoe Lake, the best-studied tree kill area on Mammoth Mountain. The mountain rises along the southwest rim of Long Valley Caldera, a crater formed by a supervolcano eruption 760,000 years ago.

The results reveal a persistent 20 percent reduction in the amount of carbon dioxide seeping up from the ground during the spring of 2017. The downshift coincides with the region’s emergence from intense drought and the pileup of the biggest Sierra Nevada snowpack in decades.

The study builds upon research by USGS volcanologist Jennifer Lewicki showing that carbon dioxide emissions in the Horseshoe Lake tree-kill area changed seasonally and across multiple years for reasons unrelated to a brewing eruption.

Seeking an explanation for these variations, Lewicki and Hilley – with coauthor Curtis Baden of Stanford – developed mathematical models to test out plausible mechanisms. Snowmelt and rainfall can wash away carbon dioxide that might otherwise seep from the ground, for example. But their calculations show Mammoth Mountain receives far too little precipitation to account for the low springtime COlevels observed in 2017.

The most likely explanation for the seasonal changes in Mammoth Mountain’s carbon dioxide emissions has to do with an underground crack, or fault, which to a trained eye is evident in the vegetation patterns and topography of the landscape. Changes in the distribution of stress across the whole mountain range seem to open and close the fault like a valve, or like the tiny gaps between old floorboards that flex under shifting weight.

Using GPS data and snow depth measurements, the authors found compressive force on the fault between 2014 and 2020 generally peaked in winter as snowpack accumulated across the Sierra Nevada and eased during snow-free summer months. Carbon dioxide emission levels dipped during periods when the weight of snow and water in the mountains flexed Earth’s crust, squeezing together the rocks on either side of the Mammoth Mountain fault.

One limitation of the study is that it does not provide a physics-based model of the fault’s movement and how gas flows through it. “We’re using stress changes as proxies for the opening and closing of a conduit,” Hilley said. “An interesting study would run a three-dimensional model of gas transport through a conduit that you could actually open and close, and then run that model many times to see if its predictions quantitatively match the carbon dioxide measurements we’re making.”

Predicting future eruptions

The ability to distinguish between CO2 fluctuations driven by climate from those driven by an impending eruption will enable better hazard forecasts, which are based partly on signs that rising magma is triggering earthquakes, deforming the ground surface or ushering gases upward. “The alignment of all three of those is generally a clue that an eruption might be about to happen,” Hilley said.

For decades, ground deformation and seismicity around some of the United States’ active volcanoes have been monitored continuously using GPS and satellites, and scientists can view the data in close to real time. But they have a murkier view on volcanic gas. “In the past, at most volcanoes, scientists had to go into a volcanic area in advance of an eruption, or even between eruptions, and go collect this gas for later analysis. It’s real Indiana Jones-type stuff,” said Hilley.

The difficulty of collecting volcanic gases has resulted in limited records, sometimes with only a single snapshot of a volcano’s degassing in any given year, which makes it challenging to detect changes that may warn of an eruption – or to understand patterns linked to Earth’s climate system.

The new study offers a glimpse of insights to come as scientists gain access to more volcanic emission data, thanks in part to the development of less expensive and more durable instruments.

“The hope is, in the next couple years, we can have a record of what the gas is doing in near real time,” Hilley said. “When you look in detail, you can see there are seasonal fluctuations that probably have nothing to do with the actual volcanic state.”

Baden is a PhD student in geological sciences at Stanford Earth.


Geophysical Research Letters




Data/statistical analysis


Not applicable


Seasonal and multiyear changes in CO2 degassing at Mammoth Mountain explained by solid-earth-driven fault valving



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Ian Magness
March 30, 2022 2:20 am

Natural CO2 fluxes from the Earth and added seasonality? Whatever next? More research cash needed to eliminate those ideas.
It would be really interesting to know, on a global basis, just how large in volume terms CO2 emissions from tectonic-type activity really are and how they compare with the anthropogenic emissions that warmists get so worked up about. If we knew the answer you suspect that it would make man’s efforts look pretty trivial, especially as mankind lives on such a puny percentage of the Earth’s surface and indeed inside its volume.
If anyone knows of any research that has attempted (no doubt with heroic assumptions especially with regard to the oceans but even so) to define such natural emissions, and possibly to compare them to man’s, I would love to see it.

Reply to  Ian Magness
April 1, 2022 5:10 am

Human beings (like animals) came from THE EARTH. They are (complexity) modules that can be complicated but whose magma doesn’t give a damn!
WE ARE part of the Earth! Whether we call ourselves human, critters or trees, it’s the same!

There are therefore no ‘anthropic disasters’.

Bob Tisdale(@bobtisdale)
March 30, 2022 3:35 am

[sarc on] The grant application was originally to study teutonic emissions so they could get a paid-for vacation in northern Europe, but there was a typo (tectonic) and the researchers from California were stuck studying volcanoes in California. [sarc off]


Reply to  Bob Tisdale
March 30, 2022 5:08 am

Teutonic emissions? Sounds like yet another sauerkraut study.

Reply to  Bob Tisdale
March 30, 2022 5:08 am

I’d rather study gin-tonic CO2 emissions.

Bob Tisdale(@bobtisdale)
Reply to  Scissor
March 30, 2022 5:41 am

Scissor, how long ’till they come after carbonated beverages like gin-tonic because of CO2 emissions? Then again, I like flat Coca-Cola.


Reply to  Bob Tisdale
March 30, 2022 7:47 am


Ron Long
March 30, 2022 3:48 am

This is poorly constructed, but probably well-funded, pseudo research from Stanford Geology Department. The Long Valley Caldera is very active, undergoing inflation due to magma ascension, active de-gassing of a variety of volcanic gasses, seismic events associated with magma inflation, and heating up of hot springs. Stanford Geologists want us to believe that several cubic kilometers of rising magma are controlled by variable snowpack? Long Valley erupted 760,000 years ago to form a caldera is a misleading statement, in that it also erupted 600 years ago, and had minor eruptions as recent as in the 1800’s. It’s going to erupt again, when and how big are unknown, but it is tending toward lesser eruptions (lesser means nothing if you’re standing on it).

Wait a minute, a volcano is out-gassing CO2? Let’s tax these pesky volcanos into political-correctness.

Disclaimer: I greatly enjoyed field excursions with famous Stanford Geologist Marco Einaudi, back before Dishonest and Delusional became required to get research funding, so I have nothing generally against Stanford.

A good reference is “Volcanic Hazards of the Long Valley Caldera” by Nathanial Brewer.

Curious George(@moudryj)
Reply to  Ron Long
March 30, 2022 7:42 am

The Horseshoe Lake Tree Kill area is named after trees killed since 1990 when CO2 began to seep from below. It was a popular area and the Forest Service had to close a huge parking lot. The event was probably triggered by an earthquake, not by weather.

Clyde Spencer
Reply to  Ron Long
March 30, 2022 1:06 pm

I remember attending lectures from Einaudi back in the days when I regularly attended the Peninsula Geological Society meetings at Stanford. Wasn’t he an economic geologist? I once had the opportunity to meet Dallas Peck, whom I was sitting next to, not long after the eruption of Mount St. Helens.

About 25 years ago I decided to see if I could detect heating from an ascending magma in the caldera. I merged Landsat thermal imagery with a visible and NIR band. I found no evidence of widespread heating, but I did discover a number of undocumented hot springs in the area. Actually, that image was used by ASPRS as a splash screen for their website for a number of years. It was quite colorful.

Peta of Newark
March 30, 2022 4:12 am

Quote:“….earthquake swarms in Long Valley Caldera. We used…blah blah ….Mammoth Mountain area, and …blah blah …. which appears to facilitate gas transport to the surface.

Lord help us, how dim can some people be – haven’t they just discovered (re-invented) fracking?

Thank Fugg. This Earth needs volcanoes, earthquakes and mountain building else it will become the New Planet Mars – notable for its especial lack of greenery.
Exploded watermelons more like.

The use of CO2 flux-meters is nice.
Now then boys & girls, take those intruments out onto some (what now passes for) farmland and see what you get….

Beware of descending pennies when you get there – those pennies are really rather big and some rather Beautiful Theories may get broken.

March 30, 2022 4:22 am

“seasonal ebb and flow of volcanic CO2 emissions.”

Volcanic emissions and the seasons? Really?

I think a large whisky is called for. How else can you believe such tripe?

Reply to  fretslider
March 30, 2022 5:13 am

Please drink responsibly. Don’t spill it.

Reply to  fretslider
March 30, 2022 7:19 am

Yep, that is the claim.
Seasonal CO2 variation, with no connection to plants.


Clyde Spencer
Reply to  whiten
March 30, 2022 1:09 pm

What they are reporting is the opposite of the typical seasonal draw-down resulting from photosynthesis.

Reply to  Clyde Spencer
March 30, 2022 2:00 pm

The point you making clyde???

Clyde Spencer
Reply to  whiten
March 30, 2022 5:55 pm

The CO2 is never without a “connection” to plants. What is important is that the CO2 flux is large enough that the net result apparently overwhelms the photosynthesis.

March 30, 2022 5:58 am

What were the CO2 emissions from the grant study itself, including trips, parties, and beverages?

March 30, 2022 6:48 am

“When you look in detail, you can see there are seasonal fluctuations that probably have nothing to do with the actual volcanic state.”
Poor Ph.D. student about to be turfed because he didn’t say there was clearly a need for more money to study the connection.

March 30, 2022 8:12 am

But their calculations show Mammoth Mountain receives far too little precipitation to account for the low springtime CO2 levels observed in 2017.
Just wondering. Did they take into account that CO² goes down naturally in spring, due to plants coming back to life and taking in CO²?

Andy Pattullo
March 30, 2022 9:08 am

By the end of this century, state officials predict the Sierra Nevada snowpack will decline by 48 to 65 percent from the historical April 1 average.

Or it may increase by a similar amount, or it might be just like before. They carefully hid the fact they have no copulating idea.

Reply to  Andy Pattullo
March 31, 2022 2:02 am

How many of us will still be around in 2100 to check the prediction? I certainly won’t.

michael hart
March 30, 2022 9:45 am

No free link to the full paper, but I’d like to see how long their data set is.

Of course, I can understand vulcanologists wishing to climb aboard the global-warming funding train.

Clyde Spencer
March 30, 2022 12:54 pm

Thirty years ago, on the flanks of a volcano in California’s Sierra Nevada range, trees began to die en masse, suffocated at their roots by carbon dioxide seeping up from the mountain’s depths after a swarm of small earthquakes.

This is the explanation I have most often read. However, I have to question how accurate “suffocated” is. CO2 is basically ‘food’ for plants, taken in by the needles of the trees. I suspect that the real problem is that the partial pressure of CO2 becomes so high that the trees can’t respire through the roots, as they commonly do. Perhaps there is a change in the pH of the soil when it is thawed and the CO2 dissolves into the water, creating carbonic acid.

I’d appreciate the opinion of someone who knows more about plants than I do.

April 1, 2022 5:05 am

Namely that ALL the gases in our atmosphere come out of the magma. The combustion of the incandescent ferric mass provides 86% of oxygen to the water of the seas & oceans.
Carbon dioxide has been part of these emissions like all other gases for BILLIONS of years and is diffusing into the atmosphere!! AND WE ARE NOT DEEEEEEAD!! (because since ALWAYS ALL gases are recycled).
The death of trees during seepage of faults is due to the presence of other gases, because carbon dioxide is necessary for the structure of plants (see in greenhouses the addition of carbon dioxide).

If gases were not recycled, life on Earth would not even have appeared!

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