Drift prediction of pyroclasts released through the volcanic activity of Fukutoku-Okanoba into the marine environment

On August 13, 2021, a submarine volcano Fukutoku-Okanoba erupted, and there was massive release of pyroclasts into the Pacific Ocean. Pyroclasts are chemically stable and continue to float near the surface of the sea, which can affect vessel navigation. Here, a simulation model that predicts the behavior of pyroclasts in the marine environment with practical accuracy is proposed. This is a simple model based solely on the terminal velocity of pyroclasts without being weathered by external forces. On the whole, the model simulation reproduces the drifting positions obtained by actual observations. By using the results, the behavior of pyroclasts around the hull is organized based on the Stokes number. The results indicate that the maximal diameter of the pyroclasts moving along the streamline increases with the overall length of the ship but decreases with its speed.