Hydrology of the Newberry Volcano caldera, Oregon

Precipitation in the Newberry Caldera is very nearly in balance with evaporation, evapotranspiration, and streamflow. Calcium, magnesium, and bicarbonate ions predominate in the more dilute ground and surface water. Thermal waters from springs and wells have concentrations of 900 milligrams per liter or more and are characterized by high concentrations of sodium and sulfate. Attempts to account for the origin of the hot springs on the basis of mixing relations and isotopic analyses were inconclusive; the springs may represent mixtures of thermal and nonthermal water which are altered by gases rising from sources beneath the caldera floor. Annual recharge to deep aquifers beneath the caldera is probably in the range 2,500 to 6,500 acre-feet. Observations in a Geological Survey drill hole suggest that part of the water may flow to aquifers at depths as much as 1,900 feet beneath the caldera floor. Potential recharge to a postulated geothermal reservoir probably is extremely small. (USGS)