Compositional Insights from the Precursory Cleetwood Eruption on the Lead-Up to Mount Mazama's Caldera Collapse
Sophia Wang1 , Adam Kent1, Katharine Cashman2, Camille Pastore2
Affiliations: 1College of Earth, Ocean, and Atmospheric Sciences, Oregon State University, Corvallis, Oregon, U.S.A; 2Department of Earth Sciences, University of Oregon, Eugene, Oregon, U.S.A
Presentation type: Poster
Presentation time: Monday 16:30 - 18:30, Room Poster Hall
Poster Board Number: 39
Programme No: 1.7.26
Abstract
The magmatic architecture and processes that produce and mobilize the large volumes of magma required for a caldera collapse eruption can be extremely complex. Precursory activity provides valuable insight into the state of a magmatic plumbing system immediately prior to climactic eruptions. Mount Mazama, in southwest Oregon, USA, produced a VEI 7 caldera collapse during its climactic eruption, resulting in one of the largest eruptions of the Holocene epoch. At least four precursor eruptions have been identified in the 200 years leading up to the climactic eruption. Of the four, the Cleetwood eruption occurred immediately prior to the climactic activity and is compositionally identical. However, although having seemingly tapped the climatic magma reservoir, the Cleetwood eruption terminated in an effusive flow before the system destabilized and triggered the climatic eruption only weeks later. Here we present new major and trace element data across multiple Cleetwood units to better understand: 1) the state of the precursory magmatic system immediately prior to the climactic eruption; and 2) the controls that determine whether an eruption from a system primed for a caldera collapse results in effusion and temporary quiescence, as with the Cleetwood, or large-scale collapse. Preliminary results from plagioclase and orthopyroxene compositions indicate that different Cleetwood units were derived from a variety of liquid compositions, suggesting a range of magma sources may have been involved.