Earthquakes both large and small had rocked the entire island of Sumatra for a year before Mount Toba started to blast out a few small eruptions of steam and ash that blanketed the surrounding jungle.

The evacuations come after steam eruptions have been seen since Thursday from the long-dormant volcano of Mount Dofen, raising fears of a volcanic eruption that could put many people at risk.

For example, in March 1980, Mount St. Helens in the US began to show some precursor events, such as seismic activity, and dozens of steam eruptions ejecting ash and gas into the atmosphere.

The summit eruption at Kilauea exhibited more vigorous fountaining Saturday evening, with spatter rising 60 to 100 feet high, mainly from the more southerly of the two active vents, according to ...