Publications
Filter Total Items: 2692
Age of the youngest volcanism at Eagle Lake, northeastern California—40Ar/39Ar and paleomagnetic results
The age of the youngest volcanism at Eagle Lake, California, was investigated using stratigraphic, paleomagnetic, and 40Ar/39Ar techniques. The three youngest volcanic lava flows at Eagle Lake yielded ages of 130.0±5.1, 127.5±3.2 and 123.6±18.7 ka, and are statistically indistinguishable. Paleomagnetic results demonstrate that two of the lava flows are very closely spaced in time, whereas the thir
Authors
Michael A. Clynne, Andrew T. Calvert, Duane E. Champion, L. J. P. Muffler, Michael G. Sawlan, Drew T. Downs
Long Valley Caldera-Mammoth Mountain unrest: The knowns and the unknowns
This perspective is based largely on my study of the Long Valley Caldera (California, USA) over the past 40 years. Here, I’ll examine the “knowns” and the “known unknowns” of the complex tectonic–magmatic system of the Long Valley Caldera volcanic complex. I will also offer a few brief thoughts on the “unknown unknowns” of this system.
Authors
David P. Hill
Regional patterns of Mesozoic-Cenozoic magmatism in western Alaska revealed by new U-Pb and 40Ar/39Ar ages
In support of regional geologic framework studies, we obtained 50 new argon-40/argon-39 (40Ar/39Ar) ages and 33 new uranium-lead (U-Pb) ages from igneous rocks of southwestern Alaska. Most of the samples are from the Sleetmute and Taylor Mountains quadrangles; smaller collections or individual samples are from the Bethel, Candle, Dillingham, Goodnews Bay, Holy Cross, Iditarod, Kantishna River, Lak
Authors
Dwight Bradley, Marti L. Miller, Richard M. Friedman, Paul W. Layer, Heather A. Bleick, James V. Jones, Steven E. Box, Susan M. Karl, Nora B. Shew, Timothy S. White, Alison B. Till, Julie A. Dumoulin, Thomas K. Bundtzen, Paul B. O'Sullivan, Thomas D. Ullrich
Electrical resistivity investigation of fluvial geomorphology to evaluate potential seepage conduits to agricultural lands along the San Joaquin River, Merced County, California, 2012–13
Increased flows in the San Joaquin River, part of the San Joaquin River Restoration Program, are designed to help restore fish populations. However, increased seepage losses could result from these higher restoration flows, which could exacerbate existing drainage problems in neighboring agricultural lands and potentially damage crops. Channel deposits of abandoned river meanders that are hydrauli
Authors
Krishangi D. Groover, Matthew K. Burgess, James F. Howle, Steven P. Phillips
Oxygen isotope geochemistry of mafic phenocrysts in primitive mafic lavas from the southernmost Cascade Range, California
Previously reported whole-rock δ18O values (5.6–7.8‰) for primitive quaternary mafic lavas from the southernmost Cascades (SMC) are often elevated (up to 1‰) relative to δ18O values expected for mafic magmas in equilibrium with mantle peridotite. Olivine, clinopyroxene, and plagioclase crystals were separated from 29 geochemically well-characterized mafic lavas for δ18O measurements by laser fluor
Authors
Sandra J. Underwood, Michael A. Clynne
Paleomagnetism and 40Ar/39Ar geochronology of the Plio-Pleistocene Boring Volcanic Field: Implications for the geomagnetic polarity time scale and paleosecular variation
Paleomagnetic directions and 40Ar/39Ar ages have been determined for samples of lava flows from the same outcrops, where possible, for 84 eruptive units ranging in age from 3200 ka to 60 ka within the Boring Volcanic Field (BVF) of the Pacific Northwest, USA. This study expands upon our previous results for the BVF, and compares the combined results with the current geomagnetic polarity time scale
Authors
Jonathan T. Hagstrum, Robert J. Fleck, Russell C. Evarts, Andrew T. Calvert
By
Energy and Minerals Mission Area, Natural Hazards Mission Area, Energy Resources Program, Geomagnetism Program, Mineral Resources Program, National Cooperative Geologic Mapping Program, National Laboratories Program, Science and Decisions Center, Volcano Hazards Program, Geologic Hazards Science Center, Geology, Minerals, Energy, and Geophysics Science Center, Geosciences and Environmental Change Science Center, Volcano Science Center
Soil data for a thermokarst bog and the surrounding permafrost plateau forest, located at Bonanza Creek Long Term Ecological Research Site, Interior Alaska
Peatlands play an important role in boreal ecosystems, storing a large amount of soil organic carbon. In northern ecosystems, collapse-scar bogs (also known as thermokarst bogs) often form as the result of ground subsidence following permafrost thaw. To examine how ecosystem carbon balance changes with the loss of permafrost, we measured carbon and nitrogen storage within a thermokarst bog and the
Authors
Kristen L. Manies, Christopher C. Fuller, Miriam C. Jones, Mark P. Waldrop, John P. McGeehin
High-resolution climate of the past ∼7300 years of coastal northernmost California: Results from diatoms, silicoflagellates, and pollen
Piston core TN062-O550, collected about 33 km offshore of Eureka, California, contains a high-resolution record of the climate and oceanography of coastal northernmost California during the past ∼7.34 kyr. Chronology established by nine AMS ages on a combination of planktic foraminifers, bivalve shell fragments, and wood yields a mean sedimentation rate of 103 cm kyr−1. Marine proxies (diatoms and
Authors
John A. Barron, David Bukry, Linda E. Heusser, Jason A. Addison, Clark R. Alexander
Thermodynamic properties in the Fe(II)-Fe(III)-As(V)-HClO4–H2O and Fe(II)-Fe(III)-As(V)-HCl–H2O systems from 5 to 90 °C
Fe-As mineral solubility and associated aqueous species have been intensively studied because of the environmental need to immobilize arsenic. The thermodynamic data for aqueous iron-arsenic species are inadequately characterized, however. The Gibbs free energy, enthalpy, entropy, and heat capacity and activity coefficients were refined in the Fe(II)-Fe(III)-As(V)-HClO4-H2O and Fe(II)-Fe(III)-As(V
Authors
Xiangyu Zhu, D. Kirk Nordstrom, R. Blaine McCleskey, Rucheng Wang, Xiancai Lu
Fitful and protracted magma assembly leading to a giant eruption, Youngest Toba Tuff, Indonesia
The paroxysmal eruption of the 74 ka Youngest Toba Tuff (YTT) of northern Sumatra produced an extraordinary 2800 km3 of non-welded to densely welded ignimbrite and co-ignimbrite ash-fall. We report insights into the duration of YTT magma assembly obtained from ion microprobe U-Th and U-Pb dates, including continuous age spectra over >50% of final zircon growth, for pumices and a welded tuff spanni
Authors
Mary R. Reid, Jorge A. Vazquez
Graphite in the Bishop Tuff and its effect on postcaldera oxygen fugacity
Several cubic kilometers of Paleozoic graphite-bearing argillitic country rocks are present as lithic fragments in Bishop Tuff ignimbrite and fallout. The lithics were entrained by the 650 km3 of rhyolite magma that vented during the 5- to 6-day-long, caldera-forming eruption at Long Valley, California. The caldera is floored by a 350 km2 roof plate that collapsed during the eruption and consists
Authors
Edward Hildreth, Juliet Ryan-Davis, Benjamin Harlow
Thermal mapping of a pahoehoe lava flow, Kilauea Volcano
Pāhoehoe lava flows are a major component of Hawaiian eruptive activity, and an important part of basaltic volcanism worldwide. In recent years, pāhoehoe lava has destroyed homes and threatened parts of Hawai‘i with inundation and disruption. In this study, we use oblique helicopter-borne thermal images to create high spatial resolution (~1 m) georeferenced thermal maps of the active pāhoehoe fl
Authors
Matthew R. Patrick, Tim R. Orr, Gary B. Fisher, Frank A. Trusdell, James P. Kauahikaua