Sinabung on Sumatra erupting on August 29, 2010.
Eruptions readers were quick on the news about the new eruption at Sinabung in Indonesia. There isn't much known about the eruptive history of the volcano - checking out the Global Volcanism Program, the last activity at Sinabung might have been an explosive event in 1881 with persistent fumaroles up until 1912. However, most news sources are quoting 400 years as the last known eruption of the volcano, apparently information from the Indonesian government.
The eruption itself appears to be an ash-rich explosion with ash fall reported up to 30 km from the volcano although the ash column from the explosion was only 1.5 km (~5,000 feet) tall. The volcano had been showing signs of activity with smaller explosions and minor steam-and-ash plumes on Friday, but the explosion on Saturday was much larger than expected. From the details I've read, [speculation] I wouldn't be surprised if there is no new magma (juvenile material) in this eruption, but rather just older material that was in the conduit. 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 (think about the events leading to the eruption at Redoubt).[speculation] However, Surono, head of the Indonesian Center for Volcanology and Geological Disaster Mitigation, warned that "we have little knowledge in terms on its eruptive patterns and general forms."
A closer look at the August 29, 2010 eruption of Sinabung. Image by Binsar Bakkara/AP.
Thousands of people have needed to evacuate their homes around the volcano on Sumatra after this explosion - however, some have stayed behind to prevent the looting of their property. A 6-km exclusion zone has been set up around the volcano by the Center for Volcanology and Geological Disaster Mitigation as well.