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Mount Edgecumbe (L\'úx Shaa) volcano magma storage conditions

Claire Puleio1 , Jessica Larsen1,2, Matthew Loewen2,, Behnaz Hosseini3

  • Affiliations: 1Department of Geosciences, University of Alaska Fairbanks Geophysical Institute, Fairbanks, Alaska, USA; 2Alaska Volcano Observatory, Anchorage, Alaska, USA; 3Department of Earth Sciences, Montana State University, Bozeman, Montana, USA 

  • Presentation type: Poster

  • Presentation time: Thursday 16:30 - 18:30, Room Poster Hall

  • Poster Board Number: 177

  • Programme No: 1.8.8

  • Theme 1 > Session 8

Abstract

Mount Edgecumbe is a stratovolcano located in Southeast Alaska which last erupted in the mid-Holocene.  A new magma intrusion was observed in 2018 resulting in increased seismicity and ground deformation. This study will provide petrologic and experiment-based data on the magma plumbing system at this volcano using late Pleistocene dacite, rhyolite, and basalt samples. Temperature estimates from Fe-Ti oxide equilibrium pairs yield 922 to 975 °C in the dacite and 866 to 928 °C in the rhyolite, with fO2 NNO 0.5 to -0.9 log units in the dacite.  FTIR analyses returned ~2.8 wt.% H2O in pyroxene-hosted melt inclusions from the rhyolite and ~1 wt.% H2O in olivine-hosted inclusions from the basalt. The experiments will utilize dacite starting material at pressures ranging from 75 to 300 MPa and temperatures between 800 to 1100 °C at water-saturated conditions. For temperatures below 900 °C, we will use Waspaloy cold seal pressure vessels and above 900 °C we will use TZM and MHC alloy pressure vessels. Waspaloy runs will be buffered at ~ NNO+0.5 log units using a nickel filler rod. TZM/MHC runs will be buffered by adding ~2.5 bars CH4 gas to buffer hydrogen diffusion, monitored with a separate capsule containing buffer compounds. The results from these experiments will be used along with Rhyolite-MELTS modelling to replicate the mineral assemblages and abundances in the natural sample. Once the experimental study is complete, our petrology-based model for magma storage at Mount Edgecumbe will provide context for recent and potentially future geophysical unrest.