Bárðarbunga is the second highest mountain in Iceland; more presicely, it´s a subglacial volcano. "Subglacial" means that it is located under a glacier. This glacier that covers Bárðarbunga is called Vatnajökull. It´s the biggest glacier of Iceland. The last time Bárðarbunga erupted was in 1910; in 1996 another volcano in immediate proximity erupted.
Since last Saturday, experts have been measuring thousands of earthquakes. On Monday, there was the largest earthquake of the region since 1996 and the volcano alert has been raised to orange. On Tuesday they said that there had been 1600 earthquakes within the last 48 hours. Seismic activity is still great; on Wednesday they have been measured every minute.
But still, nobody knows, whether there will be an eruption at all.
Because the volcano is situated under a glacier, it can lead to a subglacial eruption. That means, that hot magma melts the ice under the glacier. This melt water first accumulates in hollow spaces and then spouts, so that the regions surrounding the volcano are flooded. In case of an eruption of Bárðarbunga, such floods threaten the areas northerly of Bárðarbunga. Therefore, this region has been evacuated on Tuesday.
You can observe Bárðarbunga via webcam under the following link: