Present Mount Shasta, California, area hydrologic characteristics were documented to compare future changes due to land use or volcanic activity. Lower flanks of Mount Shasta consist of broad aprons of pyroclastic-flow, debris flow, and fluvial deposits, with incised channels on upper parts of the mountain. Data include glacial areas and volumes, streamflow, sediment concentrations, temperature, and water chemistry of groundwater and springs. Many springs issue from fractures in lava and lava tubes around Mount Shasta and serve as sources of water for nearby towns. Groundwater levels fluctuate as much as 27 ft. Water sampled from wells meets U.S. Environmental Protection Agency drinking water standards. Streamflow is affected by snowfield and glacial melt and precipitation, with some streams showing diurnal variations related to daily air temperature changes. Only four streams have sufficient streamflow to travel more than about 6 mi from the summit; differences in low flows are attributed to groundwater stored in materials that compose the mountain and alluvial fans and the rain shadow effect on precipitation in northwest areas of the mountain. Most streamflow is ephemeral and percolates into channel beds on alluvial fans. (USGS)
