Mount Sinabung produced strong eruptions for two consecutive days, with plumes of ash and steam soaring a mile and a half into the sky. Some air traffic had to divert around the ash cloud.

Sinabung last erupted in 1600, leaving today’s scientists with little or no historic information to determine its eruptive pattern and help predict what it might do. Vulcanologists had only begun to monitor the mountain a few days before the first blast, as it showed initial signs of awakening.

People began to evacuate the area around the rumbling mountain on Friday, almost two days before the country’s National Disaster Management Agency advised them to flee.

It had been so long since Sinabung was active that officials initially downplayed the threat of an explosive eruption. Even as it spat steam and produced loud noises the following day, officials remained confident that it would not erupt.

When the mountain did explode after midnight Saturday night, no one was injured as hot volcanic debris blanketed areas up to nearly 20 miles away. Lava flowed for a short distance down Sinabung’s slopes. Residents in the region were forced to wear facemasks and cloths over their nose and mouth as ash fell for the following three days.

On Tuesday, residents began to return home and to work the fields near the volcano as the color of Sinabung’s plume changed from gray to white. That indicated that more steam than ash was being emitted, according to vulcanologists.

Photo: Achmad Ibrahim