Publications

The isotopic compositions of Pb and Sr in Pleistocene basalt, high-silica rhyolite, and andesitic inclusions in rhyolite of the Coso volcanic field indicate that these rocks were derived from different levels of compositionally zoned magmatic systems. The 2 earliest rhyolites probably were tapped from short-lived silicic reservoirs, in contrast to the other 36 rhyolite domes and lava...

An explosive eruption of Mount St. Helens on 19 March 1982 had substantial impact beyond the vent because hot eruption products interacted with a thick snowpack. A blast of hot pumice, dome rocks, and gas dislodged crater-wall snow that avalanched through the crater and down the north flank. Snow in the crater swiftly melted to form a transient lake, from which a destructive flood and...

Diverse and abundant late Miocene to Pleistocene silicoflagellates at DSDP Site 504 can be correlated by tropical biostratigraphic zones and relative paleotemperature values to eastern tropical Pacific reference site DSDP 503A farther to the west. Early Pliocene assemblages, which were poorly known until now, are present and can be correlated locally between DSDP Holes 504, 503A, and 495...

No abstract available.

New investigations of the geology of Crater Lake National Park necessitate a reinterpretation of the eruptive history of Mount Mazama and of the formation of Crater Lake caldera. Mount Mazama consisted of a glaciated complex of overlapping shields and stratovolcanoes, each of which was probably active for a comparatively short interval. All the Mazama magmas apparently evolved within...

The bulging sector of the north slope of Mount St. Helens collapsed on 18 May 1980, triggered by an earthquake, thereby creating a tremendous mass movement. This movement in turn initiated volcanic eruptions resulting in the formation of an avalanche of debris. Limit equilibrium analysis of the slope suggests that failure was due to several culminating factors, including progressive...

The bimodal Pleistocene part of the Coso volcanic field has erupted rhyolite and basalt at constant long-term rates during the past ∼0.5 m.y. Both basalt and high-silica rhyolite were erupted in several independent, geologically brief episodes. The interval between eruptions of rhyolite was proportional to the volume of the preceding eruption. Basaltic eruptions appear to have followed a...

Diverse lower Miocene to Pleistocene silicoflagellate assemblages occur at Deep Sea Drilling Project Site 495, but many samples are dominated by one or two taxa. Low-latitude zonation can be applied throughout. Cool-indicating Distephanus speculum s. ampl. is only abundant in the upper Miocene; however, relative paleotemperature values (Ts) suggest temperature extremes in the lower...

Loihi seamount is the southeasternmost active volcano in the Hawaiian-Emperor volcanic chain. The seamount is considered representative of the early phase of Hawaiian volcanism because of its youth, small size, and location near the melting anomaly. Seventeen dredge stations recovered transitional basalt, alkalic basalt, and basanite, in addition to the expected tholeiitic basalt. Four...

The Mammoth Lakes area in east-central California has experienced unusual seismicity and ground deformation since 1978, highlighted by four M>6 earthquakes in May 1980 and by the discovery soon thereafter of a broad uplift within Long Valley caldera. Recurrent seismic swarms during June 1980-May 1982 raised concern over the possibility of renewed volcanic activity in the foreseeable...

In the central and southern Cascade Range, plate convergence is oblique, and Quaternary volcanism produces mostly basalt and mafic andesite; large andesite-dacite composite volcanoes and silicic dome fields occur in restricted areas of long-lived igneous activity. To the north, plate convergence is normal, producing widely spaced centers in which mafic lavas are minor. Most Cascade...

No abstract available.