| The cataclysmic eruption of Mount St. Helens May 18, 1980, altered the physical, chemical, and biological characteristics of numerous Washington lakes. As would be expected, those lakes closest to the volcano were the ones affected most by the eruption. Spirit Lake can now be considered a completely different lake because of its higher altitude, larger area, shallower depth, and changed hydrology, biology, and water chemistry. Water-quality changes were observed only in the lakes situated in the blast zone of the volcano. The changes included increases in most chemical constituents and reductions in transparency. Productivity levels in these lakes, as estimated by chlorophyll a concentrations, probably increased. No chemical or biological changes were observed in lakes that received only ash fall. -- Dion and Embrey, 1981 |
