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The Condition of Eruption Column Collapse: 2. Three‐Dimensional Numerical Simulations of Eruption Column Dynamics
Author(s) -
Koyaguchi Takehiro,
Suzuki Yujiro J.,
Takeda Kai,
Inagawa Satoshi
Publication year - 2018
Publication title -
journal of geophysical research: solid earth
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.983
H-Index - 232
eISSN - 2169-9356
pISSN - 2169-9313
DOI - 10.1029/2017jb015259
Subject(s) - impact crater , geology , buoyancy , mechanics , explosive eruption , inflow , flow (mathematics) , explosive material , jet (fluid) , volcano , physics , seismology , magma , chemistry , organic chemistry , astronomy
The scenarios leading to column collapse during explosive volcanic eruptions are diverse because of their complex dependence on geological and petrological factors. In a companion paper, we proposed a reference model to predict column collapse condition on the basis of analytical solutions of one‐dimensional eruption models. Here we perform three‐dimensional (3‐D) simulations of eruption column dynamics to confirm the reference model. In the 3‐D simulations, the velocity and pressure boundary conditions at the crater top are determined from quasi‐1‐D conduit flow. When a gas‐pyroclast mixture erupts from a conduit‐crater system that satisfies the conditions of choked flow at the crater base or top, the mixture exits as either an underexpanded (overpressured) or overexpanded (underpressured) jet. The 3‐D simulations show that the underexpanded jets are accelerated and the overexpanded jets are decelerated due to decompression‐compression processes just above the vent. The total momentum flux after these decompression‐compression processes measured in the 3‐D simulations agrees well with the values estimated using the reference model. The column collapse condition determined by the 3‐D simulations is consistent with the reference model, with an effective entrainment coefficient of k = 0.05. We also find that complex flow patterns in the transitional state of column collapse result from multidimensional compressible fluid dynamical and buoyancy effects.