At Unzen volcano, rainfall caused lava dome collapses and pyroclastic flow in some cases. Heavier precipitation increases the probability of dome collapses and pyroclastic flows, and increased pyroclastic flows are correlated with precipitation for certain periods, but not others. Dome collapses and pyroclastic flows were clearly triggered on fresh, and not yet cooled lava, and presumable originates in the instability of the lava dome cracked due to rapid cooling by rainwater.
We have done several three-dimensional numerical storm surge simulations using the terrain-following Princeton ocean model (POM) with horizontally uniform stratification in the area of Tosa Bay (maximum depth=4,800m). Results show slightly larger peak surges with finer vertical resolution or stronger stratification. We report the effects of the vertical mixing form on the simulated sea level. The balance of forces in momentum equations are studied in some detail. A simple explanation is proposed as to explain why larger peak surges are found as vertical resolution becomes finer.