Mercury anomalies in soils in geothermal areas form as a result of vapor transport. Comparison of the Hg distribution in Long Valley, measured in 1975 and again in 1982, indicates that a new Hg anomaly formed in the Inyo crater zone in the intervening period. Two models can explain this new anomaly: (1) geothermal water has reached shallow levels as a result of increased permeability created by seismic activity, or (2) addition of a CO2-rich, magnetic vapor to the geothermal system at depth caused vapor exsolution in zones where it did not occur before. If the Hg anomaly in the Inyo crater zone is related to the addition of magmatic vapors, the site of the new anomaly may overlie young, intruding magma.

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