Hum,
it seems that the likelihood that the Sumatran super-volcano Toba, will erupt has increased significantly due to geological stresses generated by the recent quakes.
"These super-volcanoes are potentially the greatest hazard on Earth, the only greater threat being an asteroid impact from space." - Ray Cas, volcanologists from Monash University in Melbourne.
< edit - For similar devastation, the supervolcanos are 5 x more likely >
The supervolcano, similar to the yellowstone caldera, sits directly atop the fault line running down the spine of Sumatra, where seismologists say a third quake might strike.
If it does erupt, the blast will throw hundreds of thousands of cubic kilometres of rock and ash into the atmosphere, dwarfing the eruptions of Krakatoa, Mount St Helens, Pinatubo and any conventional volcanic explosion of the past tens of thousands of years.