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Clearing up the volcanic history at Clear Lake

April 13, 2020

A group of scientists at CalVO have recently begun a new investigation of the Clear Lake Volcanic Field (CLVF), a seismically and geothermally active volcanic system located just ~150 km (93 miles) north of the San Francisco Bay Area.

A group of scientists poses on the shore of a calm lake. Mount Konocti rises above the lake in the background.
The Clear Lake Volcanic Field research team

The CLVF research group, which includes research geologists and geophysicists, will use a combination of computer, field, and lab-based science to understand the potential hazards of the volcanic field to the region. The CLVF team will combine these data with work by the GMEG (Geology Minerals Energy Geophysics) group in Menlo Park, who study how the tectonic environment of the CLVF might control eruptions and geothermal activity.

Many of the CalVO team’s desired datasets are either gathered directly in the field (i.e., gas measurements, gravity measurements, physical volcanology observations) or are generated from samples collected in the field (i.e., geochronology and geochemistry). With fieldwork playing such a fundamental role in CalVO science, the CLVC crew were planning a number of excursions during April and May when the weather in the Clear Lake area is typically wonderful (and the poison oak and snakes are manageable). Those plans are on hold now that the CLVC team is following precautionary safety measures provided by state and national authorities, but in the meantime, we can still introduce our team leaders and their scientific goals!

Dr. Jessica Ball and the physical volcanology team are hoping to unravel the eruption history and dynamics of the youngest activity at the CLVF, a series of maar craters formed from the explosive interaction of magma and water. The youngest dated maars erupted ~ 10,000 years ago, but many remain undated and may be even younger. Understanding the youngest eruptions at the CLVF will help us model and assess future explosive eruptions in and around Clear Lake.

Dr. Dawnika Blatter and the rock geochemistry team will collect and analyze samples necessary to refine the existing geologic map: The initial focus will be on the early (2.1-0.8 million-year-old) rocks at the SE end of Clear Lake. Better geochemical, isotopic, and petrologic work on these rocks will show how magmas form and evolve in the Clear Lake system.

Dr. Deborah Bergfeld and the gas geochemistry team have been conducting geochemical monitoring in the Clear Lake region since 2015. Clear geochemical signals from their samples indicate inputs of magmatic gases from deep in the system, but show no changes in their amounts. This provides a geochemical baseline against which any potential future changes can be interpreted in the context of volcanic or tectonic activity.

Dr. Jared Peacock and the geophysics team are planning to construct a 3-D geophysical model of the CLVF. This model will depict near surface structure and the deeper magmatic system, including locations of deep crustal magma storage. The 3-D model will be built from various geophysical datasets,including magnetotelluric, gravity, magnetic, and seismic data. Combining this model with the regional tectonic framework created by scientists in GMEG, the geophysics team will build a comprehensive model of the Earth’s structure hosting the CLVF’s magmatic plumbing.

Dr. Seth Burgess and the geochronology team are building an eruption history for the nearly 2-million-year life span of the volcanic field by dating rocks via the U/Pb and Ar/Ar geochronology. Linking a timeline of eruptions with the other science being done will provide insight into why, how, and where the system erupts, and if there are any compositional or behavioral changes with time.