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Slow and Steady or Sudden? Integration of Crystal Records and Geophysical Signals prior to the 2008 eruption of Okmok Volcano (AK)

Terry Plank1, Daniel Lee1, Shuo Ding1,2, Yves Moussallam1, Euan Mutch3, Jamshid Moshrefzadeh4, Nathan Graham5, Jessica Larsen5, Jeffrey Freymueller6

  • Affiliations:  1Lamont Doherty Earth Observatory, Columbia University, Palisades, NY,USA; 2Department of Geological Sciences, University of Florida, Gainesville, FL, USA; 3Earth Observatory of Singapore, Nanyang Technological University, Singapore; 4Alaska Division of Geological and Geophysical Survey, State of Alaska, Fairbanks, AK, USA; 5Geophysical Institute, University of Alaska Fairbanks, AK, USA; 6Department of Earth & Environmental Science, Michigan State University, East Lansing, MI, USA 

  • Presentation type: Talk

  • Presentation time: Monday 09:30 - 09:45, Room R280

  • Programme No: 1.2.5

  • Theme 1 > Session 2

Abstract

One physical model for eruption is reservoir inflation reaching a critical threshold, successfully employed to forecast Axial Volcano's 2011 eruption [1] and to hindcast Okmok Volcano's 2008 eruption (OK08) [2]. However, OK08 was also preceded by a five-hour seismic swarm, extending to ~16 km depth [3]. Was OK08 driven by slow and steady inflation or a sudden event? To answer this question, we investigated OK08 melt inclusions (MIs) and olivines to constrain the depth and timing of magmatic events. A bespoke piston-cylinder technique was used to resorb CO2 in shrinkage bubbles. Some restored MIs contain > 1700 ppm CO2, reflecting volatile saturation pressures (~380 MPa or ~16 km depth) that coincide with the deepest seismicity during the 5hr swarm. The high CO2 MIs also have unusual compositions (CaO > 11 wt%) only found in ash erupted within the first hours of eruption [4]. The complete lack of zonation in some olivines that are otherwise out of equilibrium in host melt requires rapid transport (< days), while other olivines record mixing events that occurred days to years prior to eruption. Thus, the 5hr precursory seismicity corresponds to a deep and chemically distinct magmatic input, which forged a new vent from that which hosted the prior century's eruptions. The OK08 eruption was triggered by a sudden recharge event, distinct from earlier magmatic inputs events (largely aseismic but driving inflation) that may have nonetheless primed the system for eruption. [1] Chadwick 2022. [2] Albright 2019. [3] Garza-Giron 2023. [4] Larsen 2013.