Newberry Volcano, Oregon: New Data Supports Conceptual Hydrologic Model

Abstract

Previously unreleased thermal and hydrologic data from three core holes located at Newberry Volcano, Oregon (GNC-2, GNC-4, GNC-5) are presented and used to refine the current conceptual hydrologic model for the volcano. Conductive thermal gradients exhibited by these core holes are respectively 6.9° F/100 ft, 4.9° F/100ft, and 6.8°F/100 ft. The temperature/depth relationships in these three core holes are compared with relevant geophysical and hydrologic information in support of a hydrogeologic model that incorporates the following major components: 1) A vadoze zone (rain curtain) that extends to greater depths at locations more distal to the summit caldera, but which is relatively limited in extent on the western flank of the volcano. 2) The existence of shallow convective systems within the caldera proper which occur over a range of elevations coincident with elevation at which flank core holes begin to exhibit conductive thermal regimes. 3) The observation that equilibrium temperature gradients generally decrease with radial distance from the center of the volcano, and that caldera thermal profiles are unique compared with those for flank wells. 4) The utilization of regional groundwater gradients to explain the occurrence of artesian flow in GNC-3. %) A maximum recorded temperature in GNC-2 of 332°F which supports the existence of a major geothermal system at Newberry Volcano. All the above aspects support a hydrogeologic model in which lateral outflow of the water available as recharge exits form the summit caldera and/or ring fractures to flanks and beyond. In addition, water acquisition and appropriation are other elements of geothermal exploration and development which have logistical and physical constraints. During core hole drilling at Newberry, approximately twelve percent of operational expense has been water related.