THE INFLUENCE OF REDOUBT VOLCANO EMISSIONS ON SNOW CHEMISTRY

Measurements of air and snow constituents in the vicinity of Redoubt V olcano were made during the summer of 1990 following its major eruptiv e cycle. Plumes from the degassing volcano were found to have an avera ge SO2/HCl molar ratio of 6.43 based on two observations. Snow samples were collected up to 100 km from the volcano and chemically character ized. Snow samples which contained ash deposits generally had elevated pH and conductivities and enhanced loadings of Cl-, SO42-, Ca, Na, an d Mg. This result is believed to be due to hydrolysis of silicate mine rals and was confirmed in laboratory studies using crushed Redoubt roc k samples and prepared aqueous solutions. Snow samples collected at th e higher elevation sites contained higher concentrations of all consti tuents due to less melt water percolation through the snowpack. Some o f the snow samples which contained no visible ash appear to have been influenced by the Redoubt gas emissions. These samples have decreased pH and enhanced Cl- and SO42- concentrations. In these samples the mol ar ratio of SO42-/Cl- is smaller than the SO2/HCl ratios observed in t he plume, suggesting that deposition of HCl occurs more rapidly than S O2 removal and/or oxidation.