The remote Barðarbunga volcano viewed from Askja volcano in southeast Iceland. An intense earthquake swarm started Aug. 16, 2014, signaling magma traveling underground. The volcano is buried beneath the Vatnajökull glacier, meaning an eruption could melt some of the ice, causing a jökulhlaup, or a huge meltwater flood.
A winter's view of Barðarbunga volcano. Barðarbunga is surrounded by the Vatnajökull ice cap.
A Barðarbunga flood could wipe out this bridge. Officials have evacuated tourists downstream from the volcano.
A Barðarbunga flood could also escape through the Kverkfjöll mountains into the Jökulsá á Fjöllum river, said Dave McGarvie, a volcanologist at the Open University in Scotland.
Barðarbunga volcano, the fourth most active volcano in Iceland, on the right with Kistufell volcano in front.
Bardarbunga volcano overflight
An aerial view of Barðarbunga volcano and the Jökulsá á Fjöllum river on Aug. 20. Iceland's second longest river, Jökulsá á Fjöllum spans a length of 128 miles (206 kilometers) and is fed by the Vatnajökull glacier.
Heart of a volcano
A radar image of Barðarbunga volcano's caldera lake, captured Aug. 20.
Hole in the ice
The 2011 Grímsvötn volcano eruption formed a hole in the Vatnajökull ice cap.
This spectacular pattern formed when river water cooled a lava flow in southern Iceland.