Tsunami sirens are built to detect earthquakes, but Anak Krakatau can kill without one, and our warning systems are still waiting for a shake that’s never coming.

Mount Anak Krakatau has erupted since late on Friday, with volcanic ash disrupting hundreds of flights as Indonesia faces a string of natural disasters across the archipelago.

JAKARTA, Sept 6 — Indonesia’s Anak Krakatoa volcano remains highly active and could intensify despite a significant decline in the strength of volcanic seismic signals recorded...