Scientists on Wednesday raised the alert level for Anak Krakatoa and Tangkuban Prahu -- which regularly spew gas and rumble -- from "normal" to "warning," the middle of three alert levels.
In January 1901, at 1020 feet, almost precisely the depth predicted by Higgins Wild Gas, the well-roared and suddenly ejected mud and six tons of drilling pipe out of the ground, terrifying those present.
In this part of the cave, they could hear an insistent booming sound which they found was caused by a small waterspout shooting down into a pool from the roof of the cave.
Although impure liquid hydrazine doesn't explode, it can certainly boil vigorously and spray hot and chemically toxic liquid around, which can endanger the safety of people nearby.