Second-generation studies of Cascade volcanism

T Sisson, C Bacon, M Clynne, J Donnelly-Nolan, C Gardner, VHZ

**Statement of problem --** Beginning in the mid-1950s, and accelerating
in the late 1970s, Geological Survey scientists conducted whole-edifice
mapping and geochronologic studies of the major volcanoes of the
Cascades in Washington, Oregon, and northern California. This work has
reached a high level of maturity, providing a knowledge base of time --
volume -- composition -- eruptive-style unmatched in other
subduction-related volcanic arcs. As access, analytical technology, and
conceptual understanding of volcanic and tectonic processes have
advanced, major research issues and opportunities have arisen, and the
time is appropriate for a new generation of more process-oriented
studies of Cascade volcanism, capitalizing on the comprehensive geologic
mapping. Opportunities include: producing more complete estimates of
Holocene eruptive histories through detailed field and geochemical
studies of thin proximal tephras and of eruption generated lahars;
investigating the rates of magma ascent and the depths of magma
fragmentation through experimental, analytical, and textural studies of
explosive eruption products; establishing the durations and causes of
highly active eruptive periods by applying improved ^14^C,
^40^Ar/^39^Ar, and paleomagnetic instruments, methods, and calibrations;
developing evidence to test proposed associations between seismic and
volcanic events; evaluating regional differences in volcanic style,
composition, and rate in light of new results on real-time tectonic
deformation zones along the arc (GPS); determining the timing and
explosiveness of regional mafic volcanism between the stratovolcano
edifices in Oregon; and designing and conducting joint geologic --
petrologic -- geodetic -- geophysical studies to image and interpret
magma reservoirs and conduits.

Objectives -- To advance understanding of the frequency, style, and
causes of hazardous volcanism through multidisciplinary process-oriented
studies building upon the framework volcanic histories developed during
mapping studies.

# Work strategy -- The USGS Volcano Hazards Team is understaffed to meet its Congressionally mandated obligations, and probably needs to hire several new research geologists with skills bridging between field volcanology and geochemistry/petrology, who would collaborate closely with geochronologists, geodesists, and seismologists. These persons should be leading young scientists in their disciplines, and as such, the positions could be opened to non-U.S. citizens, perhaps as long-term contract hires. These persons would be given broad mandates to examine well-mapped volcanic areas of the Cascades with emphasis on establishing the frequencies and causes of the spectrum of volcanic events.

**Relevance and impact** -- The public has an expectation that the USGS
will be knowledgeable, informed, and prepared for even small volcanic
events in the Cascades. This work will address that expectation by
moving beyond studies of exclusively large or historic eruptions, and by
increasing understanding of processes driving hazardous volcanism.

# Partnerships -- Opportunities could be developed with academic colleagues to direct NSF --supported Ph.D. students on selected topics/areas. The National Park Service and National Forest Service are potential partners.