Publications

The conductivitites of selected gneiss (two) and amphibolite (one) core samples have been measured under conditions of elevated temperature and pressure with a needle‐probe. Water‐saturated thermal conductivity measurements spanning temperatures from 25 to 300°C and hydrostatic pressures of 0.1 and 34 MPa confirm the general decrease in conductivity with increasing temperature but...

Numerical simulations of multiphase fluid and heat transport through a porous medium define combinations of rock properties and boundary conditions which lead to geyser‐like periodic discharge. Within the rather narrow range of conditions that allow geyser‐like behavior, eruption frequency and discharge are highly sensitive to the intrinsic permeabilities of the geyser conduit and the...

Inverting P- and S-wave polarities and P:SH amplitude ratios using linear programming methods suggests that about 20% of earthquakes at The Geysers geothermal area have significantly non-double-couple focal mechanisms, with explosive volumetric components as large as 33% of the seismic moment. This conclusion contrasts with those of earlier studies, which interpreted data in terms of...

Volcaniclastic units cored at depths of about 87, 164, 178, 226, and 246 m below sea level and carbonate units located between depths of 27 and 53 m below sea level in the Hilo drill core were found to be deposited at or near sea level. Four of these units are hydroclastic deposits, formed when subaerially erupted Mauna Loa lava flows entered the ocean and fragmented to produce quenched...

Geophysical, geological, and seismicity data are combined to develop a transpressional strain model for the southern Washington Cascades region. We use this model to explain oblique fold and fault systems, transverse faults, and a linear seismic zone just west of Mt. Rainier known as the western Rainier zone. We also attempt to explain a concentration of earthquakes that connects the...

The Alaska Volcano Observatory (AVO), a cooperative program of the U.S. Geological Survey, the Geophysical Institute of the University of Alaska, Fairbanks, and the Alaska Division of Geological and Geophysical Surveys, has maintained a program of seismic monitoring at potentially active volcanoes in the Cook Inlet region since 1988. The principal objectives of this program include the...

Three-dimensional seismic travel-time tomography of The Geysers geothermal area, in the coast ranges of northern California, shows a strong (−9%) anomaly in VP/VS, the ratio of the compressional and shear wave speeds, that is not evident in VP alone and corresponds closely to the most intensively exploited part of the geothermal reservoir. This anomaly probably indicates low pore...

Comb-layered quartz is a type of unidirectional solidification texture found at the roofs of shallow silicic intrusions that are often associated spatially with Mo and W mineralisation. The texture consists of multiple layers of euhedral, prismatic quartz crystals (Type I) that have grown on subplanar aplite substrates. The layers are separated by porphyritic aplite containing equant...

No abstract available.

In this paper we describe a new thermal model for the initial cooling of pahoehoe lava flows. The accurate modeling of this initial cooling is important for understanding the formation of the distinctive surface textures on pahoehoe lava flows as well as being the first step in modeling such key pahoehoe emplacement processes as lava flow inflation and lava tube formation. This model is

Channel adjustments in the North Fork Toutle River and the Toutle River main stem were initiated by deposition of a 2.5km3 debris avalanche and associated lahars that accompanied the catastrophic eruption of Mount St. Helens, Washington on 18 May 1980. Channel widening was the dominant process. In combination, adjustments caused average boundary shear stress to decrease non-linearly with...

Extensive flows of the Columbia River Basalt (CRB) Group in Washington, Oregon, and Idaho are dominantly inflated compound pahoehoe sheet lavas. Early studies recognized that CRB lavas are compound pahoehoe flows, with textures suggesting low flow velocities, but it was thought that the great thickness and extent of the major flows required very rapid emplacement as turbulent floods of...