Indonesia knew a volcano was erupting. Could it have prepared for it?

The eruption of Anak Krakatoa in Indonesia has tested the country’s disaster preparedness, disrupting nearly 3,000 flights carrying more than 340,000 passengers as volcanic ash spread across the region.

Authorities say they are monitoring the volcano, which remains under the country’s second-highest alert status. According to scientists, the event’s exceptional scale makes its impact hard to anticipate.

The eruption has renewed debate on whether Indonesia’s monitoring and disaster planning can...