Volcanoes remind us of their power

Volcanic Mount Sinbung in Sumatra, Indonesia, has sprung to life in a series of massive eruptions over the last few days.

The volcano had lain dormant for more than 400 years before a few minor eruptions three years ago. But over the past week, more than 5,000 people have been evacuated from nearby towns and villages as Sinbung makes her presence felt.

The volcano erupted an ash cloud more than 6km (4mi) into the air, and a super-heated avalanche of lava, ash and rock raced down its flanks at terrifying speeds.

There have been reports of a stream of red hot lava extending a kilometre or so from the vent.

Sinabung's activity is fed by the slow tectonic descent of rocks forming the floor of the Indian ocean, drawn down and northward into the Earth's mantle beneath Indonesia. This geological feature is called the Sunda Arc and it is home to some of the largest volcanic eruptions ever seen.

The 1815 eruption of Mount Tambara, above the Sunda Arc, remains the largest recorded volcano ever.

But it is topped by the super-eruption of Toba, also in Sumatra, which scientists place at 70,000 years ago as the largest in human history.

The eruption of Indonesian Krakatoa was smaller than both, yet was heard 5,000km (3,000mi) away and caused widespread devastation. More than 35,000 people are thought to have been killed.

Indonesia, the world's fourth most populous nation, sits atop a geological powder keg. This week's eruption of Sinabung serves as a reminder.

As Sinabung puts on her show of power, in the Mediterranean the volcano Etna has also been active. But the view of Etna's summit is far more gentle, as extraordinary smoke rings have been puffed into the Sicilian sky, as if the volcano is sitting back and relaxing for a while.

Photographer Tom Pfeiffer managed to capture the scene in his fantastic shots.