Publications
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Bacon receives 1999 Bowen Award
Charles R. Bacon received the 1999 Bowen Award, presented by the Volcanology Geochemistry, and Petrology Section during the 1999 AGU Fall Meeting.
Authors
Wes Hildreth, Charles R. Bacon
Geochemical evidence for a magmatic CO2 degassing event at Mammoth Mountain, California, September-December 1997
Recent time series soil CO2 concentration data from monitoring stations in the vicinity of Mammoth Mountain, California, reveal strong evidence for a magmatic degassing event during the fall of 1997 lasting more than 2 months. Two sensors at Horseshoe Lake first recorded the episode on September 23, 1997, followed 10 days later by a sensor on the north flank of Mammoth Mountain. Direct degassing f
Authors
K.A. McGee, T.M. Gerlach, R. Kessler, M.P. Doukas
Revised age of the Rockland tephra, northern California: Implications for climate and stratigraphic reconstructions in the western United States: Reply
Sarna-Wojcicki suggests that the 40Ar/39Ar age of 614 ± 8 ka for the Rockland tephra (Lanphere et al., 1999) is too old because of the presence of xenocrystic plagioclase. The Rockland tephra is indeed full of lithic debris that can be seen at any well-exposed outcrop of ash-flow or air-fall deposits. In order to minimize contamination, we selected pumice lumps known to be representative of the Ro
Authors
Marvin A. Lanphere, Duane E. Champion, Michael A. Clynne, L. J. Patrick Muffler
Formation of submarine flat-topped volcanic cones in Hawai'i
High-resolution bathymetric mapping has shown that submarine flat-topped volcanic cones, morphologically similar to ones on the deep sea floor and near mid-ocean ridges, are common on or near submarine rift zones of Kilauea, Kohala (or Mauna Kea), Mahukona, and Haleakala volcanoes. Four flat-topped cones on Kohala were explored and sampled with the Pisces V submersible in October 1998. Samples sho
Authors
D. Clague, James G. Moore, J.R. Reynolds
Rhyolite themobarometry and the shallowing of the magma reservoir, Coso volcanic field, California
The compositionally bimodal Pleistocene Coso volcanic field is located at the western margin of the Basin and Range province ∼60 km north of the Garlock fault. Thirty-nine nearly aphyric high-silica rhyolite domes were emplaced in the past million years: one at 1 Ma from a transient magma reservoir, one at ∼0·6 Ma, and the rest since ∼0·3 Ma. Over the past 0·6 My, the depth from which the rhyolite
Authors
C.R. Manley, Charles R. Bacon
Deep magmatic structures of Hawaiian volcanoes, imaged by three-dimensional gravity models
A simplified three-dimensional model for the island of Hawai'i, based on 3300 gravity measurements, provides new insights on magma pathways within the basaltic volcanoes. Gravity anomalies define dense cumulates and intrusions beneath the summits and known rift zones of every volcano. Linear gravity anomalies project southeast from Kohala and Mauna Kea summits and south from Hualālai and Mauna Lo
Authors
J. Kauahikaua, T. Hildenbrand, M. Webring
A model for the magmatic-hydrothermal system at Mount Rainier, Washington, from seismic and geochemical observations
Mount Rainier is one of the most seismically active volcanoes in the Cascade Range, with an average of one to two high-frequency volcano-tectonic (or VT) earthquakes occurring directly beneath the summit in a given month. Despite this level of seismicity, little is known about its cause. The VT earthquakes occur at a steady rate in several clusters below the inferred base of the Quaternary volcan
Authors
S.C. Moran, D. R. Zimbelman, S. D. Malone
Late Pleistocene granodiorite beneath Crater Lake caldera, Oregon, dated by ion microprobe
Variably melted granodiorite blocks ejected during the Holocene caldera-forming eruption of Mount Mazama were plucked from the walls of the climactic magma chamber at ∼5 km depth. Ion-microprobe U-Pb dating of zircons from two unmelted granodiorite blocks with SHRIMP RG (sensitive high-resolution ion microprobe–reverse geometry) gives a nominal 238U/206Pb age of100+78−80100−80+78ka, or174+89−11517
Authors
C. R. Bacon, H.M. Persing, J. L. Wooden, T. R. Ireland
Magma storage and mixing conditions for the 1953-1974 eruption of Southwest Trident volcano, Katmai National Park, Alaska
Between 1953 and 1974, approximately 0.5 km3 of andesite and dacite erupted from a new vent on the southwest flank of Trident volcano in Katmai National Park, Alaska, forming an edifice now known as Southwest (or New) Trident. Field, analytical, and experimental evidence shows that the eruption commenced soon after mixing of dacite and andesite magmas at shallow crustal levels. Four lava flows (58
Authors
Michelle L. Coombs, John C. Eichelberger, Malcom J. Rutherford
Mount Mageik: A compound stratovolcano in Katmai National Park: A section in Geologic studies in Alaska by the U.S. Geological Survey, 1998
Mount Mageik is an ice-clad 2,165-m andesite-dacite stratovolcano in the Katmai volcanic cluster at the head of the Valley of Ten Thousand Smokes. New K-Ar ages indicate that the volcano is as old as 93±8 ka. It has a present-day volume of 20 km3 but an eruptive volume of about 30 km3, implying a longterm average volumetric eruption rate of about 0.33 km3 per 1,000 years. Mount Mageik consists of
Authors
Wes Hildreth, Judy Fierstein, Marvin A. Lanphere, David F. Siems
Preliminary volcano-hazard assessment for the Katmai volcanic cluster, Alaska
The world’s largest volcanic eruption of the 20th century broke out at Novarupta (fig. 1) in June 1912, filling with hot ash what came to be called the Valley of Ten Thousand Smokes and spreading downwind more fallout than all other historical Alaskan eruptions combined. Although almost all the magma vented at Novarupta, most of it had been stored beneath Mount Katmai 10 km away, which collapsed d
Authors
Judy Fierstein, Wes Hildreth
A numerical program for steady-state flow of magma-gas mixtures through vertical eruptive conduits
This report presents a model that calculates flow properties (pressure, vesicularity, and some 35 other parameters) as a function of vertical position within a volcanic conduit during a steady-state eruption. The model idealizes the magma-gas mixture as a single homogeneousfluid and calculates gas exsolution under the assumption of equilibrium conditions. These are the same assumptions on which cl
Authors
Larry G. Mastin, Mark S. Ghiorso