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Stability research
Volcano instability and its consequences for potential future hazards is currently
a major theme in volcanology research. The catastrophic collapse of steep volcano
flanks and the resulting debris flows can potentially threaten a large number
of people. Understanding the factors that could result in such a collapse at
Mount Rainier in Washington is the goal of recent research efforts at the U.S.
Geological Survey. Carol Finn and collaborators used airborne magnetic data
in conjunction with detailed geologic mapping to assess the extent of hydrothermally
altered rocks on Rainier. Their work is the first to map, in detail, the internal
distribution of altered zones in an active volcano using geophysical measurements
(Nature, v.409 p. 600-603). Mark Reid and colleagues also from the USGS
incorporated these results into a new three-dimensional slope stability model
to image the distribution of hydrothermally altered (weak) and fresh (strong)
rock of the volcanic edifice. The three-dimensional quantification of the relative
slope stability of different areas on the volcanic edifice allowed the authors
to demonstrate where gravitational collapse is most likely to occur in the future
(Geology, 29; p. 779-784).
During Hurricane Mich in 1998, Casita Volcano in Nicaragua had a catastrophic
flank collapse as a result of excessive precipitation and resulted in a lahar
that killed 2500 people. Norman Kerle and Benjamin van Wyk de Vries from the
University of Cambridge and the Universite of Blaise Pascal reported that analyses
of pre-disaster remote sensing imagery allowed them to identify zones of instability
at Casita. Their work suggests that remote sensing data analysis is an efficient
and cost effective way of assessing such hazards at other volcanoes (Journal
of Volcanology and Geothermal Research, 105 p. 49-63).
In other work related to the issue of volcanic hazards associated with instability,
Pamela de Groat-Nelson and colleagues at Arizona State University are researching
silicic domes. They showed that magmatic water contents increase towards the
center of a dome consistent with the equilibrium pressure dependence of water
solubility. These concentration gradients are significantly higher than the
1 atmosphere saturation value for rhyolite {emdash} implying that the lava did
not equilibrate when it emerged from the vent. Volatile contents high enough
to generate pyroclastic flows during front collapse may be found in the upper
portions of silicic domes (Earth and Planetary Science Letters, v. 185
p. 331-341).
The growth of cryptodomes within a volcanic edifice is an effective way of destabilizing
a volcano as illustrated by the May 18, 1980 collapse of Mount St. Helens. The
group working with Franck Donnadieu at CNRS, in Cerlmont-Ferrant, showed that
the intrusion of the cryptodome dramatically reduced the stability of the edifice
and suggested that it was on the verge of failure even before the triggering
earthquake of May 18 (Bulletin of Volcanology, v.63 p.61-72).
Volcanic Timing
The time scales of magma ascent are difficult to observe directly and their
investigation using indirect methods has received considerable attention. Using
microbeam techniques, Chloe Harford and Stephen Sparks from the University of
Bristol were able to measure the hydrogen isotopic composition of amphiboles
from the Soufrière Hills Volcano. The data in combination with information
on the rates of isotopic exchange between the amphibole and the primary magma,
allowed the authors to constrain magma ascent rates leading to explosive eruptions
(Earth and Planetary Science Letters, v. 185 p. 285-297). Kurt Roggensack
at Arizona State University, showed that melt inclusion volatile saturation
pressures vary with crystal size and crystal age. Using the rate at which crystals
grew in the magma chamber, he calculated magma ascent and decompression rates
prior to eruptions (Earth and Planetary Science Letters, v.187 p. 221-237).
Both approaches are promising and will help to better constrain the temporal
evolution of magmatic systems.
On a much larger scale, the episodicity of eruptions in entire volcanic arc
systems is becoming better constrained with new results from volcanic ash layers
in of deep-sea sediments. Libby Prueher and David Rea from the University of
Michigan established a detailed record of deep-sea ash layers over the past
five million years. They were able to clearly distinguish several episodes of
increased volcanic activity from episodes of relative quiescence, confirming
prior work on circum-Pacific tephra layers (Journal of Volcanology and Geothermal
Research, v. 106 p. 67-84). Knowledge of the large-scale volcanic history
is the first step towards understanding the paleoclimatic effects of explosive
volcanic activity.
2001 Volcanology Books and Special Journal Issues:
Magma degassing through volcanoes: a tribute to Werner F. Giggenbach. Journal of Volcanology and Geothermal Research, special issue v. 108 (2001) edited by Allard, Shinohara and Wallace.
Mechanics of thermalfluid-dynamics of volcanic processes, Journal of Volcanology and Geothermal Research, special issue v. 109 (2001) edited by De Natale, Kilburne and Chouet
From magma to tephra: modeling physical processes of explosive volcanic eruptions by Armin Freundt. and Mauro Rosi (Elsevier, 2001).
Volcaniclastic Sedimentation in Lucustrine Settings by Nancy Riggs and James White, (Malden: Blackwell Science, 2001).
Volcanoes in the National Parks by Robert Decker (Odyssey Publications,
2001).
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