Publications

The surface of Gaspra can be divided into several facets separated by ridges. Superimposed on the facets and ridges are two populations of craters. Type 1 craters are crisply defined and constitute a production function of impact origin. Type 2 craters are mostly irregular shallow depressions and probably of various origins. Some of the type 2 craters may have formed by impact and be...

Inflated pahoehoe sheet flows have a distinctive horizontal upper surface, which can be several hundred meters across, and are bounded to steep monoclinal uplifts. The inflated sheet flows studied ranged from 1 to 5 m in thickness, but initially propagated as thin sheets of fluid pahoehoe lava, generally 20-30 cm thick. The morphology of the lava as flow advanced is described. Inflated...

Phenocrysts in porphyritic volcanic rocks may originate in a variety of ways in addition to nucleation and growth in the matrix in which they are found. Porphyritic rhyodacite lavas that underlie the eastern half of Mount Mazama, the High Cascade andesite/dacite volcano that contains Crater Lake caldera, contain evidence that bears on the general problem of phenocryst origin. Phenocrysts...

The Hat Creek fault is a major, young, north-striking, normal fault along the western boundary of extensional Basin and Range deformation in the Lessen region of northeastern California. Volcanic rocks of Quaternary and late Pliocene age are displaced a total of >500 m down to the west along west-facing, en echelon scarps now retreated to ∼35° slopes. Fresh, young scarps as much as 30 m...

Seismic profiling data indicate that the thickness of an accreted oceanic terrane of Paleocene and early Eocene age, which forms the basement of much of the forearc beneath western Oregon and Washington, varies by approximately a factor of 4 along the strike of the Cascadia subduction zone. Beneath the Oregon Coast Range, the accreted terrane is 25 to 35 kilometers thick, whereas...

Trace-element abundances were measured in situ by ion microprobe in five samples of hornblende and melt ranging from basaltic andesite to high-silica rhyolite. Except for one sample, for which quench overgrowth or disequilibrium is suspected, the abundance ratios show systematic inter-element and inter-sample variations, and probably approach true partition coefficients. Apparent...

A commercially-available lightning-detection system was temporarily deployed near Cook Inlet, Alaska in an attempt to remotely monitor volcanogenic lightning associated with eruptions of Redoubt Volcano. The system became operational on February 14, 1990; lightning was detected in 11 and located in 9 of the 13 subsequent eruptions. The lightning was generated by ash clouds rising from...

During the 1969-1974 Mauna Ulu eruption on Kilauea's upper east rift zone, lava tubes were observed to develop by four principal processes: (1) flat, rooted crusts grew across streams within confined channels; (2) overflows and spatter accreted to levees to build arched roofs across streams; (3) plates of solidified crust floating downstream coalesced to form a roof; and (4) pahoehoe...

Venusian canali, outflow channels, and associated volcanic deposits resemble fluvial landforms more than they resemble volcanic features on Earth and Mars. Some canali have meandering habits and features indicative of channel migration that are very similar to meandering river channels and flood plains on Earth, venusian outflow channels closely resemble water-carved outflow channels on...

We infer the composition of the crust beneath and on the flanks of the Kenya rift based on a comparison of the KRISP-90 crustal velocity structure with laboratory measurements of compressional-wave velocities of rock samples from Kenya. The rock samples studied, which are representative of the major lithologies exposed in Kenya, include volcanic tuffs and flows (primarily basalts and...

Many types of landslide movement are induced by large rainstorms, and empirical rainfall intensity/duration thresholds for initiating movement have been determined for various parts of the world. In this paper, I present a simple pressure diffusion model that provides a physically based hydrologic link between rainfall intensity/duration at the ground surface and destabilizing pore-water...

This paper describes a general method for determining the amount of earthquake-induced landsliding that occurs in a seismically active region over time; this determination can be used as a quantitative measure of the long-term hazard from seismically triggered landslides as well as a measure of the importance of this process to regional slope-erosion rates and landscape evolution. The...