Ask a Californian about Mammoth Mountain, and they’ll probably bring up packed ski lifts and powdery slopes; about 3 million people visit the 11,053-foot volcano and the surrounding region every year. What they may not know is that carbon dioxide gas periodically seeps out from the mountain and nearby sites. These fumes kill trees and even took the lives of three ski patrollers in 2006.
Since the emissions were discovered in 1989, geologists have been monitoring and studying the carbon dioxide vents. Now Dawson et al. have found new evidence that suggests Mammoth Mountain harbors vast reserves of carbon dioxide in its rocky interior—enough for the mountain to emit 500 tons of gas per day for the next 28 to 1100 years.
Mammoth Mountain consists of 25 overlapping volcanic domes formed by a series of eruptions that lasted from 100,000 to 50,000 years ago. To this day, it still shows signs of volcanic activity, including gas emissions and swarms of small earthquakes.
Since 1982, scientists have monitored earthquakes at Mammoth Mountain with a permanent seismometer network. To gather more detail on the carbon dioxide emissions, the U.S. Geological Survey temporarily set up 11 more stations that collected data on the mountain from November 2011 to October 2013.
Here the team used both the temporary and permanent seismometers to track waves of energy generated by earthquakes called P and S waves as they traveled through Mammoth Mountain. P waves and S waves travel at different speeds through different materials, such as solid rock, liquid, or gas, which means they can provide researchers with important clues about the structure of Earth below the surface. In fact, scientists used seismic waves to determine that Earth has a solid inner core.
Similarly, Dawson’s team tracked P and S waves through Mammoth Mountain to build a better picture of the volcano’s inner structure. By tracking wave location and speed, the researchers were able to determine the location of carbon dioxide reservoirs within the mountain.
The team pinpointed pockets of fluid that may represent gas, water, or molten rock up to 5 kilometers below the mountain’s surface. Using computer models, the researchers calculated that the rock there harbors between 4.6 × 109 and 1.9 × 1011 kilograms of carbon dioxide in flattened spherical pores. The gas travels up from these pores through fractures and fault lines before it’s released at the surface of the volcano. (Journal of Geophysical Research: Solid Earth, doi:10.1002/2015JB012537, 2016)
—Sarah Stanley, Freelance Writer
Citation: Stanley, S. (2016), Massive carbon dioxide stores beneath Mammoth Mountain, Eos, 97, doi:10.1029/2016EO044319. Published on 2 February 2016.