Geotimes
Highlights
Volcanoes
Tobias Fischer


Dome growth and collapse dominated volcanic activity during the year 2001. At Merapi, one of the most active volcanoes in Java, the 1998 dome collapsed catastrophically, producing an ash-cloud 5 kilometers high and dozens of pyroclastic flows. A new dome extruded and grew to a volume of 1.4 million cubic meters shortly afterwards. Soufrière Hills Volcano on Montserrat continued its dome growth activity at a rate of 3 cubic meters per second. The Soufrière dome collapsed in July 2001 and generated pyroclastic flows travelling over the sea. In Kamchatka, mass wasting from the lava dome at Bezymniany Volcano created an eruption column 10 kilometers high. Dome growth continued at Popocatepetl in Mexico at a rate of 7 cubic meters per second and at Mayon Volcano in the Philippines. The January eruption of Niragongo Volcano in the Congo received considerable attention. And its neighbor, the Niramuragira Volcano, produced small lava flows in February 2001.

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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Fischer is an assistant professor of volcanology at the University of New Mexico in Albuquerque and coordinator of the University of New Mexico-Los Alamos National LAboratory Volcanology program. E-mail.

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