A dense ash cloud moves downwind from the Soufrière Hills
volcano, Montserrat, in early 1997. The volcano continued its
activity into 1999.
Simon Young, Montserrat Volcano Observatory.
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Published by the American Geological Institute |
Newsmagazine
of the Earth Sciences
July 2000 |
John Stix
| Last year was relatively quiet for volcanoes. Guagua Pichincha and Tungarahua in Ecuador began magmatic eruptions by the early fall. Guagua Pichincha is only 12 kilometers west of Quito, but the city is reasonably well protected from the volcano. On the other hand, the residents of Baños, located at the northern foot of Tungarahua, are at risk from potentially deadly pyroclastic and debris flows that may erupt from the volcano. Mount Cameroon in western Cameroon erupted in March and April 1999, sending lava flows close to villages and the Atlantic Ocean. Mayon in the Philippines erupted explosively in June. Pacaya in Guatemala showed high levels of explosive activity in 1999 and the early part of 2000, and Fuego also erupted. The year 2000 is the 20th anniversary of the May 18, 1980, eruption of Mount St. Helens, a watershed event in many respects for volcanologists and the science of volcanology. |
A dense ash cloud moves downwind from the Soufrière Hills volcano, Montserrat, in early 1997. The volcano continued its activity into 1999. Simon Young, Montserrat Volcano Observatory. |
New research directions
Magma and volcano instability are currently major themes in volcanology. The timing and mechanisms by which magma can fragment have been a source of much debate. Several new studies suggest that fragmentation is the result of brittle processes. Youxue Zhang of the University of Michigan proposes that fragmentation occurs when the tensile stress at the inner walls of bubbles in the magma exceeds the tensile strength of the magma as a whole (Nature, v. 402, p. 648, 1999). Joan Martí of Spain’s Consejo Superior de Investigaciones Científicas, along with colleagues, provides evidence consistent with Zhang’s ideas. Martí’s group investigated tube pumices with stretched vesicles; these may record a change from viscous through plastic to brittle behavior immediately before fragmentation (Nature, v. 402, p. 650, 1999).
On a larger scale, our understanding of explosive activity associated with lava domes continues to grow. Much of this growth can be attributed to the well-studied Soufrière Hills eruption on the island of Montserrat in the Caribbean. A common theme of the various studies is one of overpressure developed within or below highly viscous, partly solidified domes. Using polymer analogues, Roger Denlinger and Rick Hoblitt, both of the U.S. Geological Survey, propose a model for regular cyclic behavior at silicic volcanoes, many of which have active lava domes. The model shows that magma is injected into the conduit, causing pressure increases. After a certain threshold, the magma slips along the conduit wall, pressure is relieved and the cycle begins anew (Geology, v. 27, p. 459, 1999). Oleg Melnick and Steve Sparks of the University of Bristol show that, during lava dome extrusion, large pressures are developed in the shallow conduit system, and these pressures can lead to explosive eruptions. Pressurization at shallow levels, rather than at deeper levels in the magma reservoir, has implications for monitoring such volcanoes (Nature, v. 402, p. 37, 1999). Barry Voight and Derek Elsworth, both of Pennsylvania State University, propose a model of dome collapse in which dome failure is driven by pressurization within the dome’s interior. They suggest that major explosive eruptions associated with lava domes are generated at deeper levels, where pressurization energies are comparatively high (Geophysical ResearchLetters, v. 27, p. 1).
Beyond research of collapse and disruption of
lava domes, large-scale volcano instability continues to be a hot topic,
in part because these large-scale collapses can be devastating to areas
surrounding the volcano. Ben van Wyk de Vries of the Université
Blaise in Pascal, France, along with colleagues, shows that hydrothermal
alteration in the central part of Nicaragua’s Casita volcano has promoted
slow deformation that may lead to sector collapse. This deformation could
become a tool for monitoring a volcano that has a potential to fail catastrophically
(Geology, v. 28, p. 167). Guido Ventura and colleagues of the Osservatorio
Vesuviano in Italy documented a flank failure on Somma-Vesuvius. The modified
morphology of the volcano after collapse favored the development of a shallow
magma reservoir from which explosive activity ensued (GeophysicalResearchLetters,
v. 26, p. 3681, 1999). Mark Reidand colleagues at the U.S. Geological Survey
have developed a 3-D slope stability analysis for volcanoes. Their approach
appears to be useful in hazard analyses for identifying areas prone to
collapse (Journal of Geophysical Research, v.
105, p. 6043, 2000). Plans are afoot in the United States, Europe and Canada
to create large, multidisciplinary research groups in volcanology. These
international initiatives have the potential to significantly advance our
science through integrated research efforts, education and outreach. Involvement
of developing countries in these efforts is vital for their success.
Stix is an associate professor of volcanology in the Department of Earth and Planetary Sciences at McGill University. E-mail: stix@eps.mcgill.ca.
1999 Volcano Books
Encyclopedia of Volcanoes, edited by H. Sigurdsson (University of Rhode Island), Bruce Houghton (University of Hawaii), Steve McNutt (University of Alaska), Hazel Ryumer (Open University) and John Stix (McGill University), is a comprehensive volume treating all aspects of volcanology (Academic, 2000).
Vulcan’s Fury by Alwyn Scarth (University of Dundee) takes a look at case histories of 15 notable historic eruptions (Yale, 1999).
Jacques-Marie Bardintzeff (University of Paris) and Alexander McBirney (University of Oregon) have a new book entitled Volcanology (Jones & Bartlett, 2000).
Volcanoes in the Quaternary is a collection of papers edited by C.R. Firth (Brunel University College) and W.J. McGuire (University College London) that relates volcanic activity to Quaternary environmental change (Geological Society, 1999).
Santorini Volcano by Tim Druitt (Université
Blaise Pascal) and colleagues synthesizes recent work at this well-known
caldera (Geological Society, 1999).
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