CO2 Emissions in Yellowstone, USA, and Solfatara Volcano, Italy: Use of Eddy Covariance and Mass Flux Modeling
Open Access
- Author:
- Werner, Cynthia Anne
- Graduate Program:
- Geosciences
- Degree:
- Doctor of Philosophy
- Document Type:
- Dissertation
- Date of Defense:
- April 22, 2002
- Committee Members:
- Melissa Deines, Committee Member
Susan Louise Brantley, Committee Chair/Co-Chair
Kenneth James Davis, Committee Member
David H Eggler, Committee Member
John Corry Wyngaard, Committee Member - Keywords:
- Yellowstone
carbon dioxide
Solfatara
volcanic degassing
diffuse fluxes
eddy covariance - Abstract:
- ABSTRACT Carbon dioxide emissions are monitored in volcanic and hydrothermal areas to understand volcanic processes, to assess hazards in active regions, and to improve estimates of global volcanic and hydrothermal degassing. Over the last twenty years, significant advances have been made in linking surface emissions of CO2, SO2, and other acid gases to volcanic processes at depth. This advancement has been accompanied by improvements in methods to measure and monitor emissions in volcanic regions. Despite these improvements, no tested method exists for obtaining large-scale (km2) estimates of CO2 degassing. In this work, eddy covariance, a micrometeorological technique, was tested for the first time in volcanic and hydrothermal terrain to measure CO2 fluxes over large land areas (km2). An eddy covariance (EC) station was deployed at Yellowstone National Park during August 1999 to determine if EC fluxes were consistent with surface flux measurements using the accumulation chamber technique in volcanic regions. A second deployment of EC at Solfatara Crater, Italy, June 8-25, 2001 assessed if EC could continuously measure CO2 fluxes for volcanic hazards monitoring at this site. Both regions had slopes less than 15 %, but displayed significant variations in CO2 and heat flux upwind of the EC tower. At Yellowstone, fluxes measured using EC varied over three orders of magnitude (from ~100 to 10,000 g CO2 m-2 d-1) and were consistent with fluxes measured using the chamber technique within a factor of 2. At Solfatara, EC measurements of CO2 fluxes were made continuously for three weeks at six locations. Turbulent (EC) fluxes were calculated in 30-minute averages and varied between 950 and 4460 g CO2 m-2 d-1 depending on location within Solfatara. Comparing turbulent fluxes with chamber measurements of surface fluxes using footprint models yielded an average difference of 0 ± 4 %, indicating EC measurements were representative of surface fluxes at this hydrothermal site. Reliable EC measurements (i.e., measurements with sufficient and stationary turbulence) were obtained primary during daytime hours (08:00 and 20:00 local time). EC fluxes measured closest to the degassing pools within Solfatara were the highest measured during the campaign (4392-4459 g CO2 m-2 d-1). Because EC fluxes include the contribution from degassing pools, where chamber fluxes do not, the difference between the EC measurements and estimates using chamber fluxes yielded emission rates between 12 to 27 t CO2 d-1 for the degassing pools in Solfatara. For comparison, emissions for these features was previously estimated at 84 t CO2 d-1 following a seismic crisis in 1984 when the area experienced 3 meters of uplift. Daily average EC fluxes varied by ± 50 % with changes in atmospheric pressure, indicating volcanic emissions would have to exceed this for in order to predict volcanic hazard. First-order models of magma emplacement or eruption suggest emissions could exceed this rate for events similar to those observed in the past. In conclusion, eddy covariance was found to provide reliable estimates of surface fluxes both at Solfatara, and Yellowstone, thereby providing a new technique for monitoring significantly larger areas than previous methods. Monitoring larger areas provides new insight to the temporal variability and spatial distribution of degassing in volcanic regions, and thus provides a new and useful technique for monitoring volcanic hazard. CO2 emissions were estimated for the Yellowstone volcanic / hydrothermal system using ground-based measurements and through modeling of the volcanic system. The estimates of degassing of Yellowstone were within an order of magnitude of one another, and indicate that Yellowstone likely emits 3.7 ± 1.3 x 1011 mol CO2 y-1. This estimate is significant in that it represents up to 16 % of the global emission rate estimated for volcanic plumes, and up to 7 % of global emissions from volcanic and hydrothermal environments estimated at 6-7 x 1012 mol CO2 y-1, suggesting that more measurements are needed in hydrothermal regions to estimate global volcanic and hydrothermal emissions more accurately.