Three‐year decline of magmatic CO 2 emissions from soils of a Mammoth Mountain Tree Kill: Horseshoe Lake, CA, 1995–1997

We used the closed chamber method to measure soil CO 2 efflux over a three‐year period at the Horseshoe Lake tree kill (HLTK)—the largest tree kill on Mammoth Mountain in central eastern California. Efflux contour maps show a significant decline in the areas and rates of CO 2 emission from 1995 to 1997. The emission rate fell from 350 t d −1 (metric tons per day) in 1995 to 130 t d −1 in 1997. The trend suggests a return to background soil CO 2 efflux levels by early to mid 1999 and may reflect exhaustion of CO 2 in a deep reservoir of accumulated gas and/or mechanical closure or sealing of fault conduits transmitting gas to the surface. However, emissions rose to 220 t d −1 on 23 September 1997 at the onset of a degassing event that lasted until 5 December 1997. Recent reservoir recharge and/or extension‐enhanced gas flow may have caused the degassing event.