JDR Vol.17 No.5 pp. 768-778
doi: 10.20965/jdr.2022.p0768


Numerical Simulations of Dome-Collapse Pyroclastic Density Currents Using faSavageHutterFOAM: Application to the 3 June 1991 Eruption of Unzen Volcano, Japan

Hiroyuki A. Shimizu

National Research Institute for Earth Science and Disaster Resilience
3-1 Tennodai, Tsukuba, Ibaraki 305-0006, Japan
Corresponding author

December 27, 2021
June 16, 2022
August 1, 2022
pyroclastic density current (PDC), dense granular current, depth-averaged model, OpenFOAM, Unzen volcano

Pyroclastic density currents (PDCs) are one of the most dangerous but least understood phenomena of volcanic eruptions. An open-source numerical depth-averaged model of dense granular currents controlled by physical processes such as energy dissipation, basal deposition, and erosion (faSavageHutterFOAM) was applied to investigate the basal concentrated region of a dome-collapse PDC generated on June 3, 1991 at Unzen volcano (Japan) to assess the effects of the physical processes (and their interplay) on the flow dynamics and run-out area of the PDC. Numerical simulations show that energy dissipation process decreases the flow velocity and increases the basal deposition rate, which reduces the run-out distance. The simulations also reveal that erosion process during flow propagation decreases the flow velocity and increases the run-out distance. The numerical results are sensitive to the parameters of energy dissipation (dry friction coefficient μ and collisional or turbulent friction coefficient χ) and erosion (specific erosion energy eb). The results are fitted to field data for run-out distance and flow velocity when μ is between 0.01 and 0.1 with χ∼103 m-1 s-2 (or when χ is between 104 and 105 m-1 s-2 with μ∼0.2) and eb∼102 m2 s-2. The estimated value of eb suggests that re-entrainment of deposit mass played an important role in controlling the flow dynamics and run-out area of the PDC. The estimated values of μ and χ are correlated, but the estimation of these parameters might be improved by further constraints from field data. The presented results serve as a basis to make further quantitative estimations of the model parameters (μ, χ, and eb) for applying the faSavageHutterFOAM model to hazard assessments of PDCs.

Cite this article as:
H. Shimizu, “Numerical Simulations of Dome-Collapse Pyroclastic Density Currents Using faSavageHutterFOAM: Application to the 3 June 1991 Eruption of Unzen Volcano, Japan,” J. Disaster Res., Vol.17, No.5, pp. 768-778, 2022.
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