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Collapse and entrainment of perched, metastable, volcaniclastic sequences as a key PDC generation mechanism: Volcán de Fuego June 2018 PDCs and analogue experiments

Symeon Makris1 , Eric C.P. Breard2, Eliza S. Calder2, Rudiger Escobar-Wolf3

  • Affiliations: 1 British Geological Survey (BGS), Edinburgh, UK; 2 School of GeoSciences, University of Edinburgh, UK; 3 Department of Geological Engineering and Sciences, Michigan Technological University, USA 

  • Presentation type: Talk

  • Presentation time: Friday 16:00 - 16:15, Room R380

  • Programme No: 3.9.6

  • Theme 3 > Session 9

Abstract

During the June 3rd, 2018, eruption of Volcán de Fuego (Guatemala), incremental collapse of perched volcaniclastic sequences generated PDCs which travelled ~12 km with total volume of ~50 Mm³. PDCs originating from collapse of metastable deposits which accumulate near the summit on slopes of 25°--40° over months to years, have occurred at Fuego again since, and are also known elsewhere. The specific triggering mechanism and dynamics by which material mobilises and is entrained remains poorly understood. The process is potentially common at persistently active explosive volcanoes, and is important due to the potential to form significantly larger flows than might otherwise be generated. Limited availability of observational and geophysical data means analogue experiments are vital for exploring these processes. Here, we use experiments of sand avalanches to investigate entrainment of erodible beds, employing high-speed imaging and Particle Image Velocimetry (PIV) to measure granular temperature---a key factor in rheology and flow-substrate interactions. We investigate how granular temperature transfer destabilises erodible substrates, weakened through granular heating. When shear stresses in flowing material reach sufficient levels, flows initiate collapse of underlying deposit, which trigger retrogressive dilation waves inducing wholescale pile failure. This represents a PDC generation mechanism which previously has not been recognised. We have also examined material accumulation in the ravine Las Lajas over time to understand the dynamics of metastable piles. An improved understanding of this generation mechanism highlights the importance of monitoring the accumulation of such 'piles' in order to understand how PDC hazard levels vary over time.