Publications
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Three-dimensional geophysical mapping of rock alteration and water content at Mount Adams, Washington: Implications for lahar hazards
[1] Hydrothermally altered rocks, particularly if water saturated, can weaken stratovolcanoes, thereby increasing the potential for catastrophic sector collapses that can lead to far-traveled, destructive debris flows. Evaluating the hazards associated with such alteration is difficult because alteration has been mapped on few active volcanoes and the distribution and intensity of subsurface alter
Authors
C. A. Finn, M. Deszcz-Pan, E. D. Anderson, D. A. John
Investigation of magnesium isotope fractionation during basalt differentiation: Implications for a chondritic composition of the terrestrial mantle
To investigate whether magnesium isotopes are fractionated during basalt differentiation, we have performed high-precision Mg isotopic analyses by multi-collector inductively coupled plasma mass spectrometry (MC-ICP-MS) on a set of well-characterized samples from Kilauea Iki lava lake, Hawaii, USA. Samples from the Kilauea Iki lava lake, produced by closed-system crystal-melt fractionation, range
Authors
F.-Z. Teng, M. Wadhwa, Rosalind T. Helz
Danger lurks deep: The human impact of volcanoes
Near midnight of March 28, 1982, El Chichón — an obscure, little-studied volcano in Chiapas State, southern Mexico — violently erupted, terrifying local villagers and prompting a confused, poorly executed evacuation. For the next five days, the volcano remained intermittently but only weakly active, so many evacuees were allowed to return to their homes. Then, on April 3 and 4, two powerful and le
Authors
J. Feldman, Robert I. Tilling
Microearthquake streaks and seismicity triggered by slow earthquakes on the mobile south flank of Kilauea Volcano, Hawai'i
We perform waveform cross correlation and high precision relocation of both background seismicity and seismicity triggered by periodic slow earthquakes at Kilauea Volcano's mobile south flank. We demonstrate that the triggered seismicity dominantly occurs on several preexisting fault zones at the Hilina region. Regardless of the velocity model employed, the relocated earthquake epicenters and trig
Authors
Cecily J. Wolfe, Benjamin A. Brooks, James H. Foster, Paul G. Okubo
Late Quaternary distal tephra-fall deposits in lacustrine sediments, Kenai Peninsula, Alaska
Tephra-fall deposits from Cook Inlet volcanoes were detected in sediment cores from Tustumena and Paradox Lakes, Kenai Peninsula, Alaska, using magnetic susceptibility and petrography. The ages of tephra layers were estimated using 21 14C ages on macrofossils. Tephras layers are typically fine, gray ash, 1–5 mm thick, and composed of varying proportions of glass shards, pumice, and glass-coated ph
Authors
C.S. de Fontaine, D. S. Kaufman, Anderson R. Scott, A. Werner, Christopher F. Waythomas, T. A. Brown
Young cumulate complex beneath Veniaminof caldera, Aleutian arc, dated by zircon in erupted plutonic blocks
Mount Veniaminof volcano, Alaska Peninsula, provides an opportunity to relate Quaternary volcanic rocks to a coeval intrusive complex. Veniaminof erupted tholeiitic basalt through dacite in the past ∼260 k.y. Gabbro, diorite, and miarolitic granodiorite blocks, ejected 3700 14C yr B.P. in the most recent caldera-forming eruption, are fragments of a shallow intrusive complex of cumulate mush and se
Authors
C. R. Bacon, T.W. Sison, F.K. Mazdab
Massive edifice failure at Aleutian arc volcanoes
Along the 450-km-long stretch of the Aleutian volcanic arc from Great Sitkin to Kiska Islands, edifice failure and submarine debris-avalanche deposition have occurred at seven of ten Quaternary volcanic centers. Reconnaissance geologic studies have identified subaerial evidence for large-scale prehistoric collapse events at five of the centers (Great Sitkin, Kanaga, Tanaga, Gareloi, and Segula). S
Authors
Michelle L. Coombs, S.M. White, D.W. Scholl
40Ar/39Ar ages of the AD 79 eruption of Vesuvius, Italy
The Italian volcano, Vesuvius, erupted explosively in AD 79. Sanidine from pumice collected at Casti Amanti in Pompeii and Villa Poppea in Oplontis yielded a weighted-mean 40Ar/39Ar age of 1925±66 years in 2004 (1σ uncertainty) from incremental-heating experiments of eight aliquants of sanidine. This is the calendar age of the eruption. Our results together with the work of Renne et al. (1997) and
Authors
Marvin A. Lanphere, Duane E. Champion, Leone Melluso, Vincenzo Morra, Annamaria Perrotta, Claudio Scarpati, Dario Tedesco, Andrew T. Calvert
Mount St. Helens Petrology Workshop
Following seismic activity in late September 2004, the current eruption of Mount St. Helens began with an explosive steam and ash emission on 1 October 2004, with hot dacite emerging from the crater floor on 11 October 2004. Nearly two years later, with more than 80 million cubic meters of erupted dacite, accompanied by rare explosions and predominantly shallow seismicity questions still remain ab
Authors
Michael C. Rowe, John S. Pallister, Anita Grunder
Drag-out effect of piezomagnetic signals due to a borehole: The Mogi source as an example
We show that using borehole measurements in tectonomagnetic experiments allows enhancement of the observed signals. New magnetic dipoles, which vary with stress changes from mechanical sources, are produced on the walls of the borehole. We evaluate such an effect quantitatively. First we formulate a general expression for the borehole effect due to any arbitrary source models. This is valid everyw
Authors
Y. Sasai, M.J.S. Johnston, Y. Tanaka, R. Mueller, T. Hashimoto, M. Utsugi, S. Sakanaka, M. Uyeshima, J. Zlotnicki, P. Yvetot
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