Publications
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Hydrothermal circulation at Mount St. Helens determined by self-potential measurements
The distribution of hydrothermal circulation within active volcanoes is of importance in identifying regions of hydrothermal alteration which may in turn control explosivity, slope stability and sector collapse. Self-potential measurements, indicative of fluid circulation, were made within the crater of Mount St. Helens in 2000 and 2001. A strong dipolar anomaly in the self-potential field was det
Authors
Paul A. Bedrosian, Martyn J. Unsworth, Malcolm J. S. Johnston
Annual modulation of seismicity along the San Andreas Fault near Parkfield, CA
We analyze seismic data from the San Andreas Fault (SAF) near Parkfield, California, to test for annual modulation in seismicity rates. We use statistical analyses to show that seismicity is modulated with an annual period in the creeping section of the fault and a semiannual period in the locked section of the fault. Although the exact mechanism for seasonal triggering is undetermined, it appears
Authors
L.B. Christiansen, Shaul Hurwitz, Steven E. Ingebritsen
Vapor transfer prior to the October 2004 eruption of Mount St. Helens, Washington
Dome lavas from the 2004 eruption of Mount St. Helens show elevated Li contents in plagioclase phenocrysts at the onset of dome growth in October 2004. These cannot be explained by variations in plagioclase-melt partitioning, but require elevated Li contents in coexisting melt, a fact confirmed by measurements of Li contents as high as 207 µg/g in coexisting melt inclusions. Similar Li enrichment
Authors
A.J.R. Kent, J. Blundy, K. V. Cashman, K.M. Copper, C. Donnelly, John S. Pallister, M. Reagan, M.C. Rowe, Carl Thornber
Geology and complex collapse mechanisms of the 3.72 Ma Hannegan caldera, North Cascades, Washington, USA
Contiguous ring faults of the 8 × 3.5 km Hannegan caldera enclose the Hannegan volcanics in the Cascade arc of northern Washington. The caldera collapsed in two phases, which each erupted rhyolitic ignimbrite (72.3%–75.2% SiO2). The first collapse phase, probably trap-door style, erupted the ≥900-m-thick ignimbrite of Hannegan Peak at 3.722 ± 0.020 Ma. This single cooling unit, generally welded, h
Authors
David S. Tucker, Wes Hildreth, Tom Ullrich, Richard M. Friedman
Understanding Merapi-type volcanoes
"We have to understand volcano science to know what to monitor.” That simple statement by Antonius Ratdomopurbo, director of the Indonesian Center for Volcano Technology [Balai Penyelidikan dan Pengembangan‐Teknologi (BPPTK)],captured the spirit and content of a recent workshop about Merapi and Merapi‐type volcanoes.Merapi still is experiencing low levels of unrest, following a peak in eruptive ac
Authors
M.A. Purbawinata, Antonius Ratdomopurbo, John S. Pallister, B. Luehr, Chris Newhall
Tsunami warnings: Understanding in Hawai'i
The devastating southeast Asian tsunami of December 26, 2004 has brought home the destructive consequences of coastal hazards in an absence of effective warning systems. Since the 1946 tsunami that destroyed much of Hilo, Hawai‘i, a network of pole mounted sirens has been used to provide an early public alert of future tsunamis. However, studies in the 1960s showed that understanding of the meanin
Authors
Chris E. Gregg, Bruce F. Houghton, Douglas Paton, David M. Johnston, David A. Swanson, B.S. Yanagi
Pre-eruption recharge of the Bishop magma system
The 650 km3 rhyolitic Bishop Tuff (eastern California, USA), which is stratigraphically zoned with respect to temperatures of mineral equilibration, reflects a corresponding thermal gradient in the source magma chamber. Consistent with previous work, application of the new TitaniQ (Ti-in-quartz) thermometer to quartz phenocryst rims documents an ∼100 °C temperature increase with chamber depth at t
Authors
D.A. Wark, W. Hildreth, F.S. Spear, D.J. Cherniak, E.B. Watson
Hydrothermal fluid flow and deformation in large calderas: Inferences from numerical simulations
[1] Inflation and deflation of large calderas is traditionally interpreted as being induced by volume change of a discrete source embedded in an elastic or viscoelastic half-space, though it has also been suggested that hydrothermal fluids may play a role. To test the latter hypothesis, we carry out numerical simulations of hydrothermal fluid flow and poroelastic deformation in calderas by couplin
Authors
Shaul Hurwitz, L.B. Christiansen, Paul A. Hsieh
Subaqueous geology and a filling model for Crater Lake, Oregon
Results of a detailed bathymetric survey of Crater Lake conducted in 2000, combined with previous results of submersible and dredge sampling, form the basis for a geologic map of the lake floor and a model for the filling of Crater Lake with water. The most prominent landforms beneath the surface of Crater Lake are andesite volcanoes that were active as the lake was filling with water, following c
Authors
M. Nathenson, C. R. Bacon, D.W. Ramsey
Waveform inversion of volcano-seismic signals for an extended source
[1] We propose a method to investigate the dimensions and oscillation characteristics of the source of volcano-seismic signals based on waveform inversion for an extended source. An extended source is realized by a set of point sources distributed on a grid surrounding the centroid of the source in accordance with the source geometry and orientation. The source-time functions for all point sources
Authors
M. Nakano, Hiroyuki Kumagai, B. Chouet, P. Dawson
Accelerated uplift and magmatic intrusion of the Yellowstone caldera, 2004 to 2006
The Yellowstone caldera began a rapid episode of ground uplift in mid-2004, revealed by Global Positioning System and interferometric synthetic aperture radar measurements, at rates up to 7 centimeters per year, which is over three times faster than previously observed inflation rates. Source modeling of the deformation data suggests an expanding volcanic sill of ???1200 square kilometers at a 10-
Authors
Wu-Lung Chang, Robert B. Smith, Charles Wicks, J.M. Farrell, C.M. Puskas
Emplacement of a silicic lava dome through a crater glacier: Mount St Helens, 2004-06
The process of lava-dome emplacement through a glacier was observed for the first time after Mount St Helens reawakened in September 2004. 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 measurements document g
Authors
Joseph S. Walder, Richard G. Lahusen, James W. Vallance, Steve P. Schilling