Publications

Single crystals of Gd3Ga5O12 have been strained under confining pressure (1 5 GPa) at temperatures below 950°C. No evidence for macroscopic plasticity was found, but transmission electron microscopy revealed dislocation generation at crack tips. Deformation mechanisms are different from those operating in the high-temperature regime: extending stacking faults in {110} planes and the 〈010...

No abstract available.

For ground ice to exist on Mars, two conditions have to be met. One is the presence of permafrost; the second is the availability of water. Because the mean temperature of Mars’surface is − 80 C., permafrost 1–3 km thick occurs over the entire planet. Remote-sensing measurements suggest that water presently exists in the atmosphere and in the polar caps; frost has been observed at the...

No abstract available.

A one-dimensional sediment-transport computer model was used to study the effects of an outburst of Spirit Lake on the Columbia River. According to the model, flood sediment discharge to the Columbia from the Cowlitz would form a blockage to a height of 44 feet above the current streambed of the Columbia River, corresponding to a new streambed elevation of -3 feet, that would impound the...

Rapid shoreline regression and transgression along the western Gulf of Maine between 13,000 and 9000 years B.P. are inferred to have produced a nearshore marine environment low in biologic productivity. Paleo-Indians living near the coast of the Gulf were probably forced to rely on nonmarine resources landward of the late-glacial marine limit. Thus, Paleo-Indian sites of the time period...

Seismic-refraction profiles recorded north of Mammoth Lakes, California, using earthquake sources from the January 1983 swarm complement earlier explosion refraction profiles and provide velocity information from deeper in the crust in the area of the Long Valley caldera. Eight earthquakes from a depth range of 4.9 to 8.0 km confirm the observation of basement rocks with seismic...

A highly detailed record of both the direction and intensity of the Earth's magnetic field as it reverses has been obtained from a Miocene volcanic sequence. The transitional field is low in intensity and is typically non-axisymmetric. Geomagnetic impulses corresponding to astonishingly high rates of change of the field sometimes occur, suggesting that liquid velocity within the Earth's...

The new International Geomagnetic Reference Field (IGRF) model of the main geomagnetic field for 1980 is based heavily on measurements from the MAGSAT satellite survey. Assessment of the accuracy of the new model, as a description of the main field near the Earth's surface, is important because the accuracy of models derived from satellite data can be adversely affected by the magnetic...

Dunes that are morphologically of linear type, many of which are probably of longitudinal type in a morphodynamic sense, are common in modern deserts, but their deposits are rarely identified in aeolian sandstones. One reason for non-recognition of such dunes is that they can migrate laterally when they are not exactly parallel to the long-term sand-transport direction, thereby...

The crustal and upper mantle compressional-wave velocity structure across the southwestern Arabian Shield has been investigated by a 1000-km-long seismic refraction profile. The profile begins in Mesozoic cover rocks near Riyadh on the Arabian Platform, trends southwesterly across three major Precambrian tectonic provinces, traverses Cenozoic rocks of the coastal plain near Jizan, and...

No abstract available.