Krakatau gave warning before it erupted, and the warning did not become a plan

Anak Krakatau was not a surprise. The volcano in the Sunda Strait was already under a raised alert when it began what the Geological Agency called a 25-hour continuous eruption on Friday, and by Monday the ash column had reached about 50,000 feet, roughly 15 kilometres up. Nearly 3,000 flights were disrupted and more than 340,000 passengers were left waiting. The South China Morning Post asks a narrower question: what happens in the gap between a warning and an eruption, because here the warning came first and not much else followed.

An expert quoted in the report gives a small, concrete answer rather than a sweeping one. Once a pre-eruption alert is issued, the government should announce evacuation routes and release hazard maps, so people living near the mountain already know where to go before anyone has to decide in a hurry. None of that depends on predicting the exact hour an eruption starts. It depends on treating a change in alert level as the beginning of work.

This is also not over. The volcano remains at the country's second-highest alert level, and the Geological Agency puts the chance of further eruptions as high, with hot glowing rock thrown from the crater, heavy ashfall and lava flows all possible. The same wind that shut airports last week can push ash back over Java on any morning.

Why it matters

If you live near the Sunda Strait, the useful thing to find now is your district's hazard map and evacuation route, and to ask the local disaster agency for it if nobody has published one. Anyone with flights through Jakarta in the coming weeks should keep plans loose, since the alert has not been lowered. The wider point reaches past this one mountain: Indonesia has plenty of volcanoes on raised alerts, and an alert level only protects people if something changes on the ground when it moves.