Revealing the key role of the substrate in pyroclastic flows using small-to-large scale experiments
^^Alexis Bougouin^1^, Fabio Dioguardi2, Giovanna Capparelli1, Eugenio Nicotra1, Roberto Sulpizio2
Affiliations: 1DIMES, Università della Calabria, Rende, Italy; 2Department of Earth and Geo-environmental sciences, University of Bari, Bari, Italy
Presentation type: Poster
Presentation time: Friday 16:30 - 18:00, Room Poster Hall
Poster Board Number: 170
Programme No: 3.9.9
Abstract
During explosive volcanic eruptions, the collapse of lava domes or eruptive columns can generate pyroclastic density currents, which then propagate at high velocity over considerable distances, destroying everything in their path. While the upper dilute cloud, often referred to as pyroclastic surge, can be satisfactorily described as a turbulent gravity current, the basal concentrated granular avalanche, known as pyroclastic flow, is more difficult to model, suggesting that physical processes are still missing. The interaction between the pyroclastic flow and the substrate, which can vary considerably due to the nature of the deposits in past events, is one of the mechanisms that may explain their high mobility compared with experimental flows. To better understand and model the flow-substrate interaction, we investigate the role of the substrate roughness on the dynamics of concentrated granular flows using small-to-large scale experiments. We reveal that the nature of the substrate can significantly affect the stability, dynamics and deposition of granular flows. More specifically, we identify three types of substrate - smooth, rough and macro-rough - based on the size ratio between the flowing material and the substrate roughness, for each of which we characterize the macroscopic flow properties. This study offers guidelines for improving the modelling of pyroclastic flows and, more generally, of geophysical granular flows.