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Dynamics of granular flows in volcanic environments: insights from analogue experiments

Rigoberto Aguilar Contreras 1, 2, Olivier Roche1, Pablo Samaniego1

  • Affiliations: 1Laboratoire Magmas et Volcans, Université Clermont Auvergne - IRD - CNRS, Aubière, France; 2Dirección de Geología Ambiental y Riesgo Geológico, Instituto Geológico Minero y Metalúrgico (INGEMMET), Arequipa, Perú

  • Presentation type: Poster

  • Presentation time: Friday 16:30 - 18:00, Room Poster Hall

  • Poster Board Number: 200

  • Programme No: 3.9.26

  • Theme 3 > Session 9

Abstract

Volcanic dense granular flows, such as pyroclastic density currents and debris avalanches, pose major hazards around volcanoes. Field-based, experimental, and numerical studies commonly deal with the dynamics of these flows but few of them address the physical processes of granular fingering that cause remarkable surface structures. Here, we investigate granular fingering using laboratory experiments with polydisperse materials released on an inclined rough substrate. A statistical analysis of the results reveals how the initial parameters (particle size range, volume of material, and slope angle) and the flow parameters (volume flux) control the geometry of the granular fingers that form ridged deposits. The flows require a critical slope angle (24° - 30° for glass beads) and a critical volume to travel down and form deposits with finger patterns. The slope angle, the material volume as well as the particle size distribution control the onset of granular fingering but these parameters have little effect on deposit morphology. However, the width of the fingers is controlled by the volume flux of the flows. We find a well-defined power law relationship between the finger width and the volume flux. Considering finger widths observed in nature, we use this power law relationship to infer the volume flux and hence the velocity of some volcanic granular flows. Application to pyroclastic ridged deposits of the last eruption at Tutupaca volcano, Peru, gives parent flow velocities of 8-30 m/s.