Interdisciplinary Study of Magmatic Carbon Dioxide at Mammoth Mountain, California

A unique opportunity for studying carbon exchange between the deep earth and the surface exists at Mammoth Mountain in eastern California, where mantle-derived carbon dioxide has leaked through soils, springs, and fumaroles for decades, if not centuries. An estimated 3.5 × 10E9 kg of CO2 has escaped in the past 20 years. A long-term program of geochemical monitoring of gas at numerous sites reveals a consistent chemical and isotopic signature indicative of a large, well-mixed, CO2-rich gas reservoir residing within a few kilometers of the surface. Leakage of CO2 increases when the low-permeability seal capping the gas reservoir fails due to critical build-up of fluid-pressure, magma intrusion, and/or tectonic earthquakes. The high CO2 efflux at Mammoth Mountain has caused human fatalities, ecosystem disturbance, acidification of local water supplies, and raises the specter of CO2-rich gas explosions. The USGS Volcano Hazards Program recently launched an integrated geochemical, geophysical, hydrologic, and biologic research project aimed at holistic understanding of the origin, transport, and impact of magmatic carbon dioxide, with Mammoth Mountain as a natural, outdoor laboratory. Key elements of the project include: (I) Lithosphere Studies: Experimental investigation of deep, CO2-rich degassing of basaltic magmas, spatial-temporal analysis of fluid-driven earthquakes, and modeling of dynamic permeability provide insight into the origin and transport of CO2-rich fluids. (II) Hydrosphere/Atmosphere Studies: Tracking the concentration and geochemistry of surface exhalations through fumarole and spring sampling, soil efflux measurements, and 14C depletion in tree cores provide characteristics of the shallow gas reservoir and a time-series record of total CO2 efflux. (III) Biosphere Studies: Field-based studies and greenhouse experiments investigate the effect of elevated CO2 on biogeochemical cycles, soil nutrient levels, and changes in vegetation and microbial communities. We expect discipline-specific results from (I, II) to advance our understanding of the dynamics of restless volcanoes and deep crustal magma systems, and from (II, III) to help predict ecosystem stress induced by global climate change, CO2 sequestration, and enhanced geothermal production. Ultimately, results from (III) may circle back into advances in (I) whereby past episodes of magma intrusion and volcanic gas release are recognized by ecosystem disturbance, independent of traditional monitoring data.