Publications

Uranium-series disequilibria in whole-rock samples and mineral separates provide unique insights into the time scales and processes of magma mixing, storage, and crystallization. We present 238U- 230Th-226Ra data for whole-rock dacite and gouge samples and for plagioclase separated from two dacite samples, all erupted from Mount St. Helens between October 2004 and April 2005. We also...

We report the results of in-situ laser ablation ICP–MS analyses of anorthite content, trace-element (Li, Ti, Sr, Ba, La, Pr, Ce, Nd, Eu, Pb) concentrations, and Pb-isotope compositions in plagioclase from eight dome-dacite samples collected from the 2004-5 eruption of Mount St. Helens and, for comparison, from three dome samples from 1981-85. For 2004-5 samples, plagioclase phenocrysts...

During the ongoing eruption at Mount St. Helens, Washington, lava has extruded continuously at a rate that decreased from ~7-9 m3 /s in October 2004 to 1-2 m3 /s by December 2005. The volume loss in the magma reservoir estimated from the geodetic data, 1.6-2.7×10 7 m3 , is only a few tens of percent of the 7.5×10 7 m3 volume that had erupted by the end of 2005.

We investigated plagioclase phenocrysts in dacite of the 2004-5 eruption of Mount St. Helens to gain insights into the magmatic processes of the current eruption, which is characterized by prolonged, nearly solid-state extrusion, low gas emission, and shallow seismicity. In addition, we investigated plagioclase of 1980-86 dacite. Light and Nomarski microscopy were used to texturally

The process of lava-dome emplacement through a glacier was observed for the first time as the 2004-6 eruption of Mount St. Helens proceeded. The glacier that had grown in the crater since the cataclysmic 1980 eruption was split in two by the new lava dome. The two parts of the glacier were successively squeezed against the crater wall. Photography, photogrammetry, and geodetic...

The 2004-5 eruption of Mount St. Helens exhibited sustained, near-equilibrium behavior characterized by nearly steady extrusion of a solid dacite plug and nearly periodic occurrence of shallow earthquakes. Diverse data support the hypothesis that these earthquakes resulted from stick-slip motion along the margins of the plug as it was forced incrementally upward by ascending, solidifying...

Oblique, terrestrial imagery from a single, fixed-position camera was used to estimate linear extrusion rates during sustained exogenous growth of the Mount St. Helens lava dome from November 2004 through December 2005. During that 14-month period, extrusion rates declined logarithmically from about 8-10 m/d to about 2 m/d. The overall ebbing of effusive output was punctuated, however...

Major element, trace element, and volatile concentrations in 187 glassy melt inclusions and 25 groundmass glasses from the 1980-86 eruption of Mount St. Helens are presented, together with 103 analyses of touching FE-Ti oxide pairs from the same samples. These data are used to evaluate the temporal evolution of the magmatic plumbing system beneath the volcano during 1980-86 and so...

Frictional properties of gouge bounding the solid dacite plug that extruded at Mount St. Helens during 2004 and 2005 may have caused stick-slip upward motion of the plug and associated seismicity. Laboratory experiments were performed with a ring-shear device to test the dependence of the peak and steady-state frictional strength of the gouge on shearing rate and hold time. A remolded...

An unusual feature of the 2004-6 eruptive activity of Mount St. Helens has been the continuous growth of successive spines that are mantled by thick fault gouge. Fault gouge formation requires, first, solidification of ascending magma within the conduit, then brittle fragmentation and cataclastic flow. We document these processes through field relations, hand samples, and thin-section

Textural, compositional, and mineralogical data are reported and interpreted for a large population of clinoamphibole phenocrysts in 22 samples from the seven successive dacite spines erupted at Mount St. Helens between October 2004 and January 2006. Despite the uniformity in bulk composition of magma erupted since 2004, there is striking textural and compositional diversity among...

Images from a Web-based camera (Webcam) located 8 km north of Mount St. Helens and a network of remote, telemetered digital cameras were used to observe eruptive activity at the volcano between October 2004 and February 2006. The cameras offered the advantages of low cost, low power, flexibility in deployment, and high spatial and temporal resolution. Images obtained from the cameras...