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Earth Surface Dynamics An interactive open-access journal of the European Geosciences Union
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Preprints
https://doi.org/10.5194/esurf-2020-47
Copyright waived. This work has been dedicated to the public domain (Creative Commons Public Domain Dedication).
https://doi.org/10.5194/esurf-2020-47
Copyright waived. This work has been dedicated to the public domain (Creative Commons Public Domain Dedication).

  15 Jun 2020

15 Jun 2020

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A revised version of this preprint is currently under review for the journal ESurf.

Reconstructing the dynamics of the highly-similar May 2016 and June 2019 Iliamna Volcano, Alaska ice–rock avalanches from seismoacoustic data

Liam Toney1, David Fee1, Kate E. Allstadt2, Matt Haney3, and Robin S. Matoza4 Liam Toney et al.
  • 1Alaska Volcano Observatory and Wilson Alaska Technical Center, Geophysical Institute, University of Alaska Fairbanks, Fairbanks, AK, USA
  • 2U.S. Geological Survey Geologic Hazards Science Center, Golden, CO, USA
  • 3U.S. Geological Survey Alaska Volcano Observatory, Anchorage, AK, USA
  • 4Department of Earth Science and Earth Research Institute, University of California, Santa Barbara, CA, USA

Abstract. Surficial mass wasting events are a hazard worldwide. Seismic and acoustic signals from these often-remote processes, combined with other geophysical observations, can provide key information for monitoring and rapid response efforts and enhance our understanding of event dynamics. Here we present seismoacoustic data and analyses for two very large ice–rock avalanches occurring on the natural laboratory of Iliamna Volcano, Alaska (USA) on 22 May 2016 and 21 June 2019. Iliamna is a glacier-mantled stratovolcano located in the Cook Inlet, ~ 200 km from Anchorage, Alaska. The volcano experiences massive, quasi-annual slope failures due to glacial instabilities and hydrothermal alteration of material near its summit. The May 2016 and June 2019 avalanches were particularly large and generated energetic seismic and infrasound signals which were recorded on numerous stations at ranges from ~ 9 to over 600 km. Both avalanches initiated in the same location near the head of Iliamna's east-facing Red Glacier, and their ~ 8 km long runout shapes are nearly identical. This repeatability – which is rare for mass movements – provides an excellent opportunity for comparison and validation of seismoacoustic source characteristics. For both events, we invert long-period (15–80 s) seismic signals to obtain a force-time representation of the source. We model the avalanche as a sliding block which exerts a spatially-static point force on the Earth. We use this force-time function to derive constraints on avalanche acceleration, velocity, and directionality which are compatible with satellite imagery and observed terrain features. Our inversion results suggest that the avalanches reached speeds exceeding 80 m s−1, consistent with numerical modeling from previous Iliamna studies. We lack sufficient local infrasound data to test an acoustic source model for these processes. However, the acoustic data suggest that infrasound from these avalanches is produced after the mass movement regime transitions from cohesive block-type failure to granular and turbulent flow – little to no infrasound is generated by the initial failure. At Iliamna, synthesis of advanced numerical flow models and more detailed groundtruth combined with increased geophysical station coverage could yield significant gains in our understanding of these events.

Liam Toney et al.

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Liam Toney et al.

Liam Toney et al.

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Latest update: 28 Nov 2020
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Short summary
Large avalanches composed of ice and rock are a serious hazard to mountain communities and backcountry travellers. These processes shake the Earth and disturb the atmosphere, generating seismic waves and sound waves which can travel for hundreds of kilometers. In this study we use the seismic waves and sound waves produced by two massive avalanches on a volcano in Alaska to reconstruct how the avalanches failed. Our method may assist with rapid emergency response to these global hazards.
Large avalanches composed of ice and rock are a serious hazard to mountain communities and...
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