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By Kathy Cashman
This lecture was on November 2, 2022.
A major challenge in volcanology is knowing what lies beneath a volcano: Where is the magma? What are its chemical and physical properties? How, when and how fast does it migrate to the surface to erupt? Addressing these questions requires us to combine insights from physical measurements of what’s beneath the Earth’s surface with chemical measurements of erupted lava and pumice. Additional insights come from cores drilled into cooling and solidifying lava lakes in Hawaii. Dr. Cashman will review all of these approaches and resulting implications for (1) detection and evolution of magma in the subsurface, (2) eruption triggers and (3) controls on eruption style and duration.
By Kathy Cashman
This seminar was on November 3, 2022.
Magnitude 7+ eruptions (≥ 40km3 DRE) occur globally at a rate of 1-2 per 1000 years and are large enough to cause devastating global impacts. Yet we know little about either the conditions that lead to very large eruptions or the long-term impacts of such events. Here I address these questions using data from the c.7700 ybp eruption of Mount Mazama that produced Crater Lake, Oregon, which had a magnitude M≥7.1 and deposited ash over >1 million km2 of northwestern North America. The pre-climactic and climactic eruptive sequences of this event have been interpreted to comprise a Plinian eruption followed by effusion of a large (0.5 km3) obsidian flow at the Cleetwood vent, followed weeks to a few months later by the climactic eruption (comprising lower and upper pumice units followed by widespread pyroclastic flows). New data from the lower pumice unit, however, suggests that the "climactic" sequence involved at least three eruptions, two of which were, like the Cleetwood, precursory to the climactic phase, and at least one of which tapped a distinct, although related, magma reservoir. In this way, the eruptive sequence resembled the four-month buildup to the 1883 eruption of Krakatau, Indonesia, and lends support to the idea that evacuation of large magma volumes may often require either pre- or syn-eruptive amalgamation of multiple melt lenses within a larger magmatic system. New data on the distal ash deposit provides new constraints on the eruptive volume, conditions of ash transport and deposition, and types of post-eruption redistribution of the widespread ash that supports archeological interpretations of disruption to Native American communities throughout the region, probably for centuries.
Kathy Cashman is a professor in the Department of Earth Sciences at the University of Oregon and the University of Bristol who has studied volcanoes on all seven continents to learn how they erupt and why eruption styles vary. From 1980 to 1982, she was the Public Information Scientist at the Cascades Volcano Observatory in Washington, and has worked with all of the volcano observatories in the U.S. Prior to coming to University of Oregon, she was a Fulbright scholar studying igneous petrology in New Zealand, and was on the faculty at Princeton University. She is a member of the National Academy of Sciences and a Fellow of the Royal Society. Cashman is also a Fellow of the American Geophysical Union and the American Academy of Arts and Sciences, and a member of the Academia Europaea.
The Thomas Condon Lecture honors the legacy of its namesake, a minister, a university teacher and Oregon’s first State Geologist. Thomas Condon used the free public lecture to disseminate scientific knowledge to the general public throughout his career. To honor that legacy, the Oregon Board of Higher Education established the Thomas Condon Lecture in 1944. The generous support of CEOAS and the Research Office allows OSU to bring world-class scientists to campus each year.
The George Moore Seminar is named to honor the career and contributions of Dr. George Moore. Dr. Moore spent his career working for the U.S. Geological Survey where he focused on regional tectonic and structural problems. After retirement, he moved to Corvallis, where he volunteered for the Department of Geosciences in a wide variety of capacities. At the time of his death, George was working on a book about the geology of wine in Oregon.