Document: AND-3-35-7

Radiocarbon studies of plant leaves and tree rings from Mammoth Mountain, CA: A long-term record of magmatic CO₂ release.

COOK, A.C.* ¹, L.J.HAINSWORTH ², M.L.SOREY ³, W.C.EVANS ³ and J.R.SOUTHON ¹

Lawrence Livermore National Laboratory, Livermore, CA 94551 ¹
Emory and Henry College, Emory, VA 24327 ²
U.S. Geological Survey, Menlo Park, CA 94025 ³

Abstract:
Beginning in 1990, extensive tree mortality was observed at seven locations on the flanks of Mammoth Mountain, California. The species independent nature of the tree death was unprecedented and hinted at a cause other than the typical drought stress or pest infestation. In 1994, the cause of these tree kills was linked to the diffuse release of CO₂ from beneath Mammoth Mountain. We evaluated the ¹⁴C signature in the annual rings of trees and other surrounding vegetation with two main purposes: (1) to track changes in the magnitude of magmatic CO₂ emission over time, and (2) to determine the onset of magmatic CO₂ emission at numerous sites on Mammoth Mountain. The relative quantity of magmatic CO₂ being released at a specific location is inferred from the extent of ¹⁴C deficiency in the plant material from areas of high flux relative to that being produced on other parts of the mountain where CO₂ concentrations are ambient. This inference is possible due to the absence of ¹⁴C in magmatic CO₂ as opposed to that of atmospheric CO₂ which is on the order of 110 per _ml. The onset of CO₂ emission at the different areas of tree kill was determined to be in 1990, closely following the seismic events of 1989. At Horseshoe Lake, CO₂ emission was found to have peaked in 1991 and to have subsequently declined by a factor of two through 1998. The tree-ring data also show that emissions of magmatic carbon from cold springs below the tree-kill areas occurred well before 1989. Trees located on the margins of the kill areas or otherwise away from zones of maximum gas discharge were found to be better integrators of magmatic CO₂ emission than those located in the center of tree kills. In the interest of human safety on both large (volcanic hazard) and small scales (asphyxia hazard), changes in CO₂ flux over time must be understood.

Keywords: Mammoth Mountain, CO₂ emission, radiocarbon, tree rings

This abstract is being presented at: 2:45 PM in session:
Oral Session #66: Large Scale Climate Change.