Koyaguchi, Takehiro

Suzuki, Yujiro

小屋口, 剛博

鈴木, 雄治郎

Earth Simulator Research Results Repository

3-D numerical simulations of eruption clouds: 
 The critical condition for column collapse 
 
 
Y. J. Suzuki1, T. Koyaguchi1 
1ERI, University of Tokyo, Tokyo, Japan  
 
 
During an explosive volcanic eruption, an eruption cloud forms a buoyant eruption column 
or a pyroclastic flow. We investigated the critical condition that separates these two 
eruption styles (column collapse condition) by performing a series of three-dimensional 
numerical simulations. We identified two types of column collapse in the simulations: 
collapse from a turbulent jet which efficiently entrains ambient air (jet-type collapse) and 
that from a fountain with a high concentration of ejected materials (fountain-type collapse). 
Which type of collapse occurs depends on whether the critical mass discharge rate for 
column collapse (MDRCC) is larger or smaller than that for the potential core near the flow 
axis to be eroded by shear (MDRJF). When the magma temperature is low, MDRCC is 
smaller than MDRJF for a given exit velocity; therefore, the jet-type collapse occurs before 
the fountain develops with increasing mass discharge rate. In this case, the column 
collapse condition depends only on the Richardson number. When the magma 
temperature is high, on the other hand, MDRCC is larger than MDRJF; the fountain 
develops when the column collapse occurs (i.e. fountain-type collapse). In this case, the 
collapse condition depends not only on the Richardson number but also on the Mach 
number. When the flow is supersonic (the Mach number is larger than 1.0), the standing 
shock waves developing in a fountain inhibit the entrainment of ambient air, which 
enhances column collapse. 
 


3-D numerical simulations of eruption clouds: The critical condition for column collapse

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