TY - JOUR
T1 - The fragmentation-induced fluidisation of pyroclastic density currents
AU - Breard, Eric C. P.
AU - Dufek, Josef
AU - Charbonnier, Sylvain
AU - Gueugneau, Valentin
AU - Giachetti, Thomas
AU - Walsh, Braden
N1 - Funding Information:
E.C.P.B. was supported by UKRI with the NERC-IRF (NE/V014242/1). J.D. was supported NSF EAR 1852569 and EAR 1650382. S.J.C. and V.G. acknowledge funding from the National Science Foundation (NSF) CAREER project #17511905. The present work was conceptualised during the 2019 Cooperative Institute for Dynamic Earth Research (CIDER) summer programme in Berkeley, CA, USA, supported by NSFEAR1135452.
Funding Information:
E.C.P.B. was supported by UKRI with the NERC-IRF (NE/V014242/1). J.D. was supported NSF EAR 1852569 and EAR 1650382. S.J.C. and V.G. acknowledge funding from the National Science Foundation (NSF) CAREER project #17511905. The present work was conceptualised during the 2019 Cooperative Institute for Dynamic Earth Research (CIDER) summer programme in Berkeley, CA, USA, supported by NSFEAR1135452.
Publisher Copyright:
© 2023, The Author(s).
PY - 2023/4/12
Y1 - 2023/4/12
N2 - Pyroclastic density currents (PDCs) are the most lethal volcanic process on Earth. Forecasting their inundation area is essential to mitigate their risk, but existing models are limited by our poor understanding of their dynamics. Here, we explore the role of evolving grain-size distribution in controlling the runout of the most common PDCs, known as block-and-ash flows (BAFs). Through a combination of theory, analysis of deposits and experiments of natural mixtures, we show that rapid changes of the grain-size distribution transported in BAFs result in the reduction of pore volume (compaction) within the first kilometres of their runout. We then use a multiphase flow model to show how the compressibility of granular mixtures leads to fragmentation-induced fluidisation (FIF) and excess pore-fluid pressure in BAFs. This process dominates the first ~2 km of their runout, where the effective friction coefficient is progressively reduced. Beyond that distance, transport is modulated by diffusion of the excess pore pressure. Fragmentation-induced fluidisation provides a physical basis to explain the decades-long use of low effective friction coefficients used in depth-averaged simulations required to match observed flow inundation.
AB - Pyroclastic density currents (PDCs) are the most lethal volcanic process on Earth. Forecasting their inundation area is essential to mitigate their risk, but existing models are limited by our poor understanding of their dynamics. Here, we explore the role of evolving grain-size distribution in controlling the runout of the most common PDCs, known as block-and-ash flows (BAFs). Through a combination of theory, analysis of deposits and experiments of natural mixtures, we show that rapid changes of the grain-size distribution transported in BAFs result in the reduction of pore volume (compaction) within the first kilometres of their runout. We then use a multiphase flow model to show how the compressibility of granular mixtures leads to fragmentation-induced fluidisation (FIF) and excess pore-fluid pressure in BAFs. This process dominates the first ~2 km of their runout, where the effective friction coefficient is progressively reduced. Beyond that distance, transport is modulated by diffusion of the excess pore pressure. Fragmentation-induced fluidisation provides a physical basis to explain the decades-long use of low effective friction coefficients used in depth-averaged simulations required to match observed flow inundation.
U2 - 10.1038/s41467-023-37867-1
DO - 10.1038/s41467-023-37867-1
M3 - Article
SN - 2041-1723
VL - 14
JO - Nature Communications
JF - Nature Communications
IS - 1
M1 - 2079
ER -