Chemical Changes of Lakes Within the Mount St. Helens Blast Zone
ROBERT C. WISSMAR 1,
ALLEN H. DEVOL 1,
AHMAD E. NEVISSI 1, and
JAMES R. SEDELL 2
1 Fisheries Research Institute, University of Washington, Seattle 98195
2 Forestry Science Laboratory, 3200 Southwest Jefferson Way, Corvallis, Oregon 97331
Differences in the dissolved chemistry of lakes devastated by the 18 May 1980 eruption of Mount St. Helens are attributable to location relative to the lateral blast trajectory of the eruption and to the emplacement of mineral deposits. Elemental enrichment ratios of pre- and posteruption measurements for Spirit Lake and comparisons of the chemical concentrations and elemental ratios for lakes inside and outside the blast zone reflect the influences of the dissolution of magmatic and lithic deposits. The pH changes were minor because of buffering by carbonic acid and reactions involving mineral alteration, dissolved organics, and biological processes.
Submitted on April 20, 1981
Revised on August 24, 1981
