3D numerical simulations of volcanic plume and tephra dispersal: Reconstruction of the 2014 Kelud eruption

Abstract:

The heights and expansion rate of eruption cloud and the dispersal pattern of tephra particles are key observable data for understanding the dynamics of volcanic plume. In general, when the volcanic plume rises in a stationary environment, the plume height and expansion rate of the umbrella cloud increases as the eruption intensity (i.e., the magma discharge rate) increases. On the other hand, when the plume is distorted by the atmospheric wind, it is difficult to quantify the relationship between the eruption conditions and the observable data. Therefore, we aim to develop a three-dimensional numerical model of volcanic plume and directly reproduce the plume dynamics and the tephra dispersal.

We performed a numerical simulation of the 2014 eruption at Mount Kelud, Java, Indonesia, which formed a large volcanic plume and umbrella cloud in the wind field. We employ a 3D numerical model which is designed to simulate the injection of tephra particles and volcanic gas from a circular vent into the stratified atmosphere, using a combination of a pseudo-gas model for fluid motion and a Lagrangian model for particle motion (Suzuki and Koyaguchi, 2013 EPS). Using the estimated total mass (3.9—6.4×10¹¹ kg) and the eruption duration (2.5 – 3 hours), the average mass discharge rate is estimated to be 3.6—7.1×10⁷ kg/s. In this study, the magma discharge rate is set to be 5×10⁷ kg/s. The weather data based on the radiosonde observation in Surabaya is applied to the atmospheric condition.

The simulation results indicate that the top of plume reaches to nearly 30 km and the umbrella cloud radially spreads at the height of 17—20 km high. These simulated heights are consistent with the observations (e.g., NASA Earth Observatory). The particles are transported by the gravity current of the umbrella cloud. Between the umbrella cloud and the ground, the particles separated from the cloud are drifted by the easterly wind. Therefore, the dispersal axis of the main fall deposits simulated by the present model agrees well with the observation. However, the present simulation cannot reproduce the fall deposits on the north and northeast area of the volcano. This inconsistency implies that in reality, unlike the conditions assumed in our model, the eruption intensity and atmospheric condition fluctuated largely with time.