Geologic setting of Merrill Lake and evaluation of volcanic hazards in the Kalama River valley near Mount St. Helens, Washington

Volcanic rocks and unconsolidated geologic deposits in the upper Kalama River valley were studied in order to determine the kind of catastrophic geologic events that might accompany a future eruption of Mount St. Helens. The chief purpose of the study was to appraise the potential geologic hazards at the site of a hydroelectric project under consideration by the Cowlitz County Public Utility District. It is concluded that if future eruptions of Mount St. Helens are like those of the recent geologic past, the principal hazards near the project site probably will be from nuees ardentes, mudflows, floods, and lava flows. If the volcano should erupt after the hydroelectric facility is constructed, it is recommended that the reservoir be emptied as quickly as possible, and that persons be evacuated from the valley floors adjacent to the volcano.