Indonesian Volcano's Forked Eruption: Big Pics

UPDATE: Sept. 7, 2010 -- Sinabung experienced a round of larger explosions over the weekend that again dusted nearby towns and flung ash 3 miles into the atmosphere. By this morning, the mountain had quieted again (middle), but the risk of a major eruption remains high.

Aug. 30, 2010 -- Over the weekend, Indonesia's Mount Sinabung awoke on Sumatra with a series of explosions that hurled ash over a mile into the air and sent it raining down on local communities up to 20 miles away. Authorities have established a six-kilometer (3.7-mile) zone of exclusion around the volcano and evacuated 30,000 people.

On Monday, a six-hour-long eruption produced an unusual sight: two plumes of ash spewing out of the top of the volcano (bottom). Little is known about the volcano's history, which is last thought to have erupted 400 years ago, but the forked ash clouds are likely due to a blockage in the volcano's main vent.

The ash cloud has forced rerouting of some regional flights, but so far it has not reached an altitude that affects larger planes. On the ground, authorities are scrambling to distribute gas masks to help prevent respiratory distress among the local population.

Government officials have also repeatedly stressed that because of Sinabung's sparse history, they cannot predict what it will do next. On his blog Eruptions, geologist Erik Klemetti echoed that uncertainty, but added the following speculation: "My hunch is that this explosion might be the start of more and the heat from the magma interacted with groundwater near the summit to cause the explosion - a very common precursor activity at a composite cone like Sinabung..."

Indonesia is one of the most volcanically active places in the world. Before the eruption of Sinabung, the country already boasted 76 historically active volcanoes, the most of any place on Earth.

Images: all AP: top, Achmad Ibrahim; middle, Binsar Bakkara; bottom, Roone Patikawa