The interaction between concentrated pyroclastic density currents and snow: a case study from the 2008 mixed-avalanche f
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RESEARCH ARTICLE
The interaction between concentrated pyroclastic density currents and snow: a case study from the 2008 mixed-avalanche from Volcán Llaima (Chile) E. C. P. Breard 1
&
Eliza S. Calder 2 & Dawn C.S. Ruth 3
Received: 18 June 2020 / Accepted: 6 October 2020 # International Association of Volcanology & Chemistry of the Earth's Interior 2020
Abstract The incorporation of snow and ice by pyroclastic density currents (PDCs) can generate mixed-avalanches and pose significant hazards at snow-clad volcanoes. Commonly, the poor preservation of these thin deposits, combined with the subtle characteristics of PDC-snow interaction, has limited their recognition in the geological record. A small-volume (2.5 × 105 m3), basaltic-andesite, mixed-avalanche deposit formed during the 2008 eruption of Volcán Llaima (Chile) provides insight into PDC and snow interactions. Pyroclasts accumulated on the crater rim and collapsed to form a flow that swept up to 2.8 km from source and spread across 6.09 × 105 m2 of the snow-clad slopes. The PDC-snow interaction at the crater rim or during flow propagation resulted in distinct deposit and pyroclast textures. These included abundant blocky non-vesicular cauliflower clasts and blocky poorly vesicular scoria. The thin and sheet-like mixed-avalanche deposit had a lumpy surface, lacked marginal levees, was very loose, and fine ash depleted. Although the flow likely incorporated snow and/or ice mechanically, the overall coarseness of the mixture precluded effective fluidization related to vaporization. Many of the features described herein are distinctive features of other mixed-avalanche deposits worldwide and should be considered key indicators of PDC-snow interaction. Keywords Pyroclastic density currents . Ice-slurry . Snow . Basaltic-andeiste stratovolcano
Introduction Pyroclastic interactions with snow and ice on snow-clad volcanoes can produce hazardous mixed-avalanches (i.e., flow made of pyroclasts and snow or ice also called ice-slurries) and lahars that travel far from source (e.g., Major and Newhall 1989; Pierson and Janda 1994; Walder 2000a, b; Lube et al. 2009; Vallance et al. 2010). The interaction of both dense and dilute pyroclastic density currents (PDCs) with their substrate is common (Lube et al. 2020), but has only been studied in a Editorial responsibility: G. Lube * E. C. P. Breard [email protected] 1
Earth Sciences Department, University of Oregon, 100 Cascade Hall 1272, Eugene, OR 97403, USA
2
School of Geosciences, Grant Institute, University of Edinburgh, The King’s Buildings, West Mains Road, Edinburgh EH9 3JW, UK
3
U.S. Geological Survey, 345 Middlefield Road MS 910, Menlo Park, CA 94025, USA
handful of cases when the substrate consists in snow or ice (e.g., Pierson et al. 1990; Redoubt, Alaska, Waitt et al. 1994; Ruapehu, New Zealand, Lube et al. 2009, Cronin et al. 1996; Augustine, Alaska, Vallance et al. 2010; Beget, 2010). Indicative criteria for identifying PDCs that directly interacted with ice or snow helps better constrain the hazards
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