Publications
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Constraints on the source parameters of low-frequency earthquakes on the San Andreas Fault
Low-frequency earthquakes (LFEs) are small repeating earthquakes that occur in conjunction with deep slow slip. Like typical earthquakes, LFEs are thought to represent shear slip on crustal faults, but when compared to earthquakes of the same magnitude, LFEs are depleted in high-frequency content and have lower corner frequencies, implying longer duration. Here we exploit this difference to estima
Authors
Amanda M. Thomas, Gregory C. Beroza, David R. Shelly
At the foot of the smoking mountains: The 2014 scientific investigations in the Islands of the Four Mountains
An interdisciplinary research team conducted archaeological, geological, and biological investigations in the Islands of the Four Mountains, Alaska during the summer of 2014 as part of a three-year project to study long-term geological and ecological patterns and processes with respect to human settlement. Researchers investigated three archaeological sites on Chuginadak Island (SAM-0014, SAM-0016
Authors
Virginia Hatfield, Kale Bruner, Dixie West, Arkady Savinetsky, Olga Krylovich, Bulat Khasanov, Dmitry Vasyukov, Zhanna Antipushina, Mitsuru Okuno, Susan Crockford, Kirsten Nicolaysen, Breanyn MacInnes, Lyman Persico, Pavel Izbekov, Christina A. Neal, Thomas Bartlett, Lydia Loopesko, Anne Fulton
Dimensionless erosion laws for cohesive sediment
A method of achieving a dimensionless collapse of erosion-rate data for cohesive sediments is proposed and shown to work well for data collected in flume-erosion tests on mixtures of sand and mud (silt plus clay sized particles) for a wide range of mud fraction. The data collapse corresponds to a dimensional erosion law of the form E∼(τ−τc)mE∼(τ−τc)m, where EE is erosion rate, ττ is shear stress,
Authors
Joseph S. Walder
Monogenetic volcanoes fed by interconnected dikes and sills in the Hopi Buttes volcanic field, Navajo Nation, USA
Although monogenetic volcanic fields pose hazards to major cities worldwide, their shallow magma feeders (<500 m depth) are rarely exposed and, therefore, poorly understood. Here, we investigate exposures of dikes and sills in the Hopi Buttes volcanic field, Arizona, to shed light on the nature of its magma feeder system. Shallow exposures reveal a transition zone between intrusion and eruption wi
Authors
James D. Muirhead, Alexa R. Van Eaton, Giuseppe Re, James D. L. White, Michael H. Ort
Geochemical characterization and dating of R tephra, a post-glacial marker bed in Mount Rainier National Park, Washington, U.S.A.
The oldest postglacial lapilli–ash tephra recognized in sedimentary records surrounding Mount Rainier (Washington State, USA) is R tephra, a very early Holocene deposit that acts as an important stratigraphic and geochronologic marker bed. This multidisciplinary study incorporates tephrostratigraphy, radiocarbon dating, petrography, and electron microprobe analysis to characterize R tephra. Tephra
Authors
Mary Samolczyk, James W. Vallance, Joel Cubley, Gerald Osborn, Douglas H. Clark
Apatite fission-track evidence for regional exhumation in the subtropical Eocene, block faulting, and localized fluid flow in east-central Alaska
The origin and antiquity of the subdued topography of the Yukon–Tanana Upland (YTU), the physiographic province between the Denali and Tintina faults, are unresolved questions in the geologic history of interior Alaska and adjacent Yukon. We present apatite fission-track (AFT) results for 33 samples from the 2300 km2 western Fortymile district in the YTU in Alaska and propose an exhumation model t
Authors
Cynthia Dusel-Bacon, Charles R. Bacon, Paul B. O'Sullivan, Warren C. Day
Long period seismicity and very long period infrasound driven by shallow magmatic degassing at Mount Pagan, Mariana Islands
Long period (LP) seismicity and very long period infrasound (iVLP) were recorded during continuous degassing from Mount Pagan, Mariana Islands, in July 2013 to January 2014. The frequency content of the LP and iVLP events and delay times between the two arrivals were remarkably stable and indicate nearly co-located sources. Using phase-weighted stacking over similar events to dampen noise, we find
Authors
John J. Lyons, Matthew M. Haney, Cynthia A. Werner, Peter J. Kelly, Matthew R. Patrick, Christoph Kern, Frank A. Trusdell
Tomographic image of a seismically active volcano: Mammoth Mountain, California
High-resolution tomographic P wave, S wave, and VP/VS velocity structure models are derived for Mammoth Mountain, California, using phase data from the Northern California Seismic Network and a temporary deployment of broadband seismometers. An anomalous volume (5.1 × 109 to 5.9 × 1010m3) of low P and low S wave velocities is imaged beneath Mammoth Mountain, extending from near the surface to a de
Authors
Phillip B. Dawson, Bernard A. Chouet, Andrew M. Pitt
Radiocarbon dating of silica sinter deposits in shallow drill cores from the Upper Geyser Basin, Yellowstone National Park
To explore the timing of hydrothermal activity at the Upper Geyser Basin (UGB) in Yellowstone National Park, we obtained seven new accelerator mass spectrometry (AMS) radiocarbon 14C ages of carbonaceous material trapped within siliceous sinter. Five samples came from depths of 15–152 cm within the Y-1 well, and two samples were from well Y-7 (depths of 24 cm and 122 cm). These two wells, at Black
Authors
Jacob B. Lowenstern, Shaul Hurwitz, John McGeehin
A thermodynamical model for the surface tension of silicate melts in contact with H2O gas
Surface tension plays an important role in the nucleation of H2O gas bubbles in magmatic melts and in the time-dependent rheology of bubble-bearing magmas. Despite several experimental studies, a physics based model of the surface tension of magmatic melts in contact with H2O is lacking. This paper employs gradient theory to develop a thermodynamical model of equilibrium surface tension of silicat
Authors
Simone Colucci, Maurizio Battaglia, Raffaello Trigila
Water-magma interaction and plume processes in the 2008 Okmok eruption, Alaska
Eruptions of similar explosivity can have divergent effects on the surroundings due to differences in the behavior of the tephra in the eruption column and atmosphere. Okmok volcano, located on Umnak Island in the eastern Aleutian Islands, erupted explosively between 12 July and 19 August 2008. The basaltic andesitic eruption ejected ∼0.24 km3dense rock equivalent (DRE) of tephra, primarily direct
Authors
Joel A. Unema, Michael H. Ort, Jessica D Larsen, Christina A. Neal, Janet R. Schaefer
Volcano-tectonic earthquakes: A new tool for estimating intrusive volumes and forecasting eruptions
We present data on 136 high-frequency earthquakes and swarms, termed volcano-tectonic (VT) seismicity, which preceded 111 eruptions at 83 volcanoes, plus data on VT swarms that preceded intrusions at 21 other volcanoes. We find that VT seismicity is usually the earliest reported seismic precursor for eruptions at volcanoes that have been dormant for decades or more, and precedes eruptions of all m
Authors
Randall A. White, Wendy McCausland