Effects of the eruptions of Mount St. Helens on physical, chemical, and biological characteristics of surface water, ground water, and precipitation in the Western United States

Abstract

This report is a review of literature pertaining to the 1980 eruptions of Mount St. Helens, and to the subsequent effects of those eruptions on physical, chemical, and biological characteristics of surface water, ground water, and precipitation in the Pacific Northwest, Montana, and Colorado. Scores of studies dealing with the eruption and changes in water quality have been published; however, the data and information are contained in numerous U.S. Government and State government publications, proceedings of symposia, and a myriad of scientific journals. The salient published findings and conclusions on eruptionrelated, water-quality topics are compiled and categorized here to illustrate the scope of previous investigations. Conclusions, other than those reported by the authors listed in the Selected References, are not presented. This report contains quantitative information and descriptions of changes in the physical, chemical, and biological characteristics of water quality caused by the volcanic activity of Mount St. Helens during 1980. Lakes that received only ashfall experienced fewer effects than lakes that were within the blast zone. Phenomena occurring in new lakes created by the eruption are unique, and in some cases, had never been observed or documented prior to 1980. Different lakes are described, using a casestudy approach that includes sufficient background information on each lake to put the effects of the eruption in perspective. The changes attributable to the volcanic blast, mudfiows, and ashfall varied dramatically from one lake to another depending on the location of the lake under the ash plume, the distance of the lake from Mount St. Helens, and other physical circumstances. Similarly, the effects on rivers and streams varied in magnitude from barely perceptible changes to profound alterations that virtually created new drainage systems. Limited literature exists about the effects of the eruption on ground water. Changes in ground-water levels and chemistry are principally associated with the most heavily effected river systems those which lay in the path of mudflows generated by the volcanic eruption. Potentially toxic chemical compounds, such as phenols, were identified by researchers in several investigations. Ground-water levels in parts of the Cowlitz River system appear to have been raised above historical levels. Few studies were done about the effects of the eruption on precipitation. Observations from investigations in Colorado and Oregon suggest that physicochemical changes, such as altered specific conductance and pH of rainwater samples, were not long-lived.