Abstract
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.
