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JOURNAL OF GEOPHYSICAL RESEARCH, VOL. 108, NO. B12, 2557, doi:10.1029/2003JB002565, 2003

Groundwater flow, heat transport, and water table position within volcanic edifices: Implications for volcanic processes in the Cascade Range

Shaul Hurwitz

U.S. Geological Survey, Menlo Park, California, USA

Kenneth L. Kipp

U.S. Geological Survey, Denver, Colorado, USA

Steven E. Ingebritsen

U.S. Geological Survey, Menlo Park, California, USA

Mark E. Reid

U.S. Geological Survey, Menlo Park, California, USA

Abstract

The position of the water table within a volcanic edifice has significant implications for volcano hazards, geothermal energy, and epithermal mineralization. We have modified the HYDROTHERM numerical simulator to allow for a free-surface (water table) upper boundary condition and a wide range of recharge rates, heat input rates, and thermodynamic conditions representative of continental volcano-hydrothermal systems. An extensive set of simulations was performed on a hypothetical stratovolcano system with unconfined groundwater flow. Simulation results suggest that the permeability structure of the volcanic edifice and underlying material is the dominant control on water table elevation and the distribution of pressures, temperatures, and fluid phases at depth. When permeabilities are isotropic, water table elevation decreases with increasing heat flux and increases with increasing recharge, but when permeabilities are anisotropic, these effects can be much less pronounced. Several conditions facilitate the ascent of a hydrothermal plume into a volcanic edifice: a sufficient source of heat and magmatic volatiles at depth, strong buoyancy forces, and a relatively weak topography-driven flow system. Further, the plume must be connected to a deep heat source through a pathway with a time-averaged effective permeability ≥1 × 10⁻¹⁶ m², which may be maintained by frequent seismicity. Topography-driven flow may be retarded by low permeability in the edifice and/or the lack of precipitation recharge; in the latter case, the water table may be relatively deep. Simulation results were compared with observations from the Quaternary stratovolcanoes along the Cascade Range of the western United States to infer hydrothermal processes within the edifices. Extensive ice caps on many Cascade Range stratovolcanoes may restrict recharge on the summits and uppermost flanks. Both the simulation results and limited observational data allow for the possibility that the water table beneath the stratovolcanoes is relatively deep.

Received 1 May 2003; accepted 27 August 2003; published 11 December 2003.

Index Terms: 1829 Hydrology: Groundwater hydrology; 3210 Mathematical Geophysics: Modeling; 3230 Mathematical Geophysics: Numerical solutions; 8424 Volcanology: Hydrothermal systems (8135); 9350 Information Related to Geographic Region: North America.

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Citation: Hurwitz, S., K. L. Kipp, S. E. Ingebritsen, and M. E. Reid (2003), Groundwater flow, heat transport, and water table position within volcanic edifices: Implications for volcanic processes in the Cascade Range, J. Geophys. Res., 108(B12), 2557, doi:10.1029/2003JB002565.

This paper is not subject to U.S. copyright. Published in 2003 by the American Geophysical Union.