Publications
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Trace element and Pb isotope composition of plagioclase from dome samples from the 2004-2005 eruption of Mount St. Helens, Washington
We report the results of in-situ laser ablation ICP–MS
analyses of anorthite content, trace-element (Li, Ti, Sr, Ba, La,
Pr, Ce, Nd, Eu, Pb) concentrations, and Pb-isotope compositions
in plagioclase from eight dome-dacite samples collected from
the 2004-5 eruption of Mount St. Helens and, for comparison,
from three dome samples from 1981-85. For 2004-5 samples,
plagioclase phenocrysts range
Authors
Adam J. R. Kent, Michael C. Rowe, Carl R. Thornber, John S. Pallister
Constraints on the size, overpressure, and volatile content of the Mount St. Helens magma system from geodetic and dome-growth measurements during the 2004-2006+ eruption
During the ongoing eruption at Mount St. Helens, Washington, lava has extruded continuously at a rate that decreased
from ~7-9 m3
/s in October 2004 to 1-2 m3
/s by December
2005. The volume loss in the magma reservoir estimated from
the geodetic data, 1.6-2.7×10
7
m3
, is only a few tens of percent
of the 7.5×10
7
m3
volume that had erupted by the end of 2005.
Authors
Larry G. Mastin, Evelyn Roeloffs, Nick M. Beeler, James E. Quick
Plagioclase populations and zoning in dacite of the 2004-2005 Mount St. Helens eruption: Constraints for magma origin and dynamics
We investigated plagioclase phenocrysts in dacite of the
2004-5 eruption of Mount St. Helens to gain insights into the
magmatic processes of the current eruption, which is characterized by prolonged, nearly solid-state extrusion, low gas
emission, and shallow seismicity. In addition, we investigated
plagioclase of 1980-86 dacite.
Light and Nomarski microscopy were used to texturally
character
Authors
Martin J. Streck, Cindy A. Broderick, Carl R. Thronber, Michael A. Clynne, John S. Pallister
Effects of lava-dome growth on the crater glacier of Mount St. Helens, Washington
The process of lava-dome emplacement through a glacier
was observed for the first time as the 2004-6 eruption of
Mount St. Helens proceeded. 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 doc
Authors
Joseph S. Walder, Steve P. Schilling, James W. Vallance, Richard G. LaHusen
Dynamics of seismogenic volcanic extrusion resisted by a solid surface plug, Mount St. Helens, 2004-2005
The 2004-5 eruption of Mount St. Helens exhibited
sustained, near-equilibrium behavior characterized by nearly
steady extrusion of a solid dacite plug and nearly periodic
occurrence of shallow earthquakes. Diverse data support the
hypothesis that these earthquakes resulted from stick-slip
motion along the margins of the plug as it was forced incrementally upward by ascending, solidifying, gas
Authors
Richard M. Iverson
Extrusion rate of the Mount St. Helens lava dome estimated from terrestrial imagery, November 2004-December 2005
Oblique, terrestrial imagery from a single, fixed-position
camera was used to estimate linear extrusion rates during
sustained exogenous growth of the Mount St. Helens lava
dome from November 2004 through December 2005. During
that 14-month period, extrusion rates declined logarithmically
from about 8-10 m/d to about 2 m/d. The overall ebbing of
effusive output was punctuated, however, by ep
Authors
Jon J. Major, Cole G. Kingsbury, Michael P. Poland, Richard G. LaHusen
Evolving magma storage conditions beneath Mount St. Helens inferred from chemical variations in melt inclusions from the 1980-1986 and current (2004-2006) eruptions
Major element, trace element, and volatile concentrations in 187 glassy melt inclusions and 25 groundmass glasses from the 1980-86 eruption of Mount St. Helens are presented, together with 103 analyses of touching FE-Ti oxide pairs from the same samples. These data are used to evaluate the temporal evolution of the magmatic plumbing system beneath the volcano during 1980-86 and so provide a frame
Authors
Jon Blundy, Katharine V. Cashman, Kim Berlo
Frictional properties of the Mount St. Helens gouge
Frictional properties of gouge bounding the solid dacite
plug that extruded at Mount St. Helens during 2004 and 2005
may have caused stick-slip upward motion of the plug and
associated seismicity. Laboratory experiments were performed
with a ring-shear device to test the dependence of the peak
and steady-state frictional strength of the gouge on shearing rate and hold time. A remolded gouge s
Authors
Peter L. Moore, Neal R. Iverson, Richard M. Iverson
Chemistry, mineralogy, and petrology of amphibole in Mount St. Helens 2004-2006 dacite
Textural, compositional, and mineralogical data are
reported and interpreted for a large population of clinoamphibole phenocrysts in 22 samples from the seven successive
dacite spines erupted at Mount St. Helens between October
2004 and January 2006. Despite the uniformity in bulk composition of magma erupted since 2004, there is striking textural
and compositional diversity among amphibole ph
Authors
Carl R. Thornber, John S. Pallister, Heather Lowers, Michael C. Rowe, Charlie Mandeville, Gregory P. Meeker
From dome to dust: shallow crystallization and fragmentation of conduit magma during the 2004-2006 dome extrusion of Mount St. Helens, Washington
An unusual feature of the 2004-6 eruptive activity of
Mount St. Helens has been the continuous growth of successive spines that are mantled by thick fault gouge. Fault gouge
formation requires, first, solidification of ascending magma
within the conduit, then brittle fragmentation and cataclastic
flow. We document these processes through field relations,
hand samples, and thin-section texture
Authors
Katharine V. Cashman, Carl R. Thornber, John S. Pallister
Remote camera observations of lava dome growth at Mount St. Helens, Washington, October 2004 to February 2006
Images from a Web-based camera (Webcam) located 8
km north of Mount St. Helens and a network of remote, telemetered digital cameras were used to observe eruptive activity
at the volcano between October 2004 and February 2006. The
cameras offered the advantages of low cost, low power, flexibility in deployment, and high spatial and temporal resolution. Images obtained from the cameras provided i
Authors
Michael P. Poland, Daniel Dzurisin, Richard G. LaHusen, Jon J. Major, Dennis Lapcewich, Elliot T. Endo, Daniel J. Gooding, Steve P. Schilling, Christine G. Janda
Photogeologic maps of the 2004-2005 Mount St. Helens eruption
The 2004-5 eruption of Mount St. Helens, still ongoing
as of this writing (September 2006), has comprised chiefly
lava dome extrusion that produced a series of solid, faultgouge-mantled dacite spines. Vertical aerial photographs
taken every 2 to 4 weeks, visual observations, and oblique
photographs taken from aircraft and nearby observation
points provide the basis for two types of photogeolo
Authors
Trystan M. Herriott, David R. Sherrod, John S. Pallister, James W. Vallance