The volcano Katla is subglacial and has a reputation as one of the most dangerous volcanoes of Iceland. The Laki craters and the Eldgjá are part of the same volcanic system, so it can be regarded as one of the most powerful in the world.

Through the ages many farms have been swept away by Katla eruptions with that of 1311 being recorded as particularly damaging. A farmer named Sturla is said to have survived with his young son by clinging to an iceberg which later drifted back to shore. An eighteenth century eruption killed several people while others were stranded for days on mountains that turned to islands as floods engulfed the plains.

Katla erupted very powerfully in 1918 but Katla erupts on average twice a decade. The eruption was probably the biggest one under glacier. The eruption in 1918 was horrible with tremendous effect on people living in the south of Iceland.

Scientist say that Katla has been ready since 1999 to erupt. As the mountain is expected to erupt twice in a century the next one is expected to be of large scale, as there are now more than 90 years since the last eruption. In the past there have been between 13 and 80 years between the eruptions. It is also not unlikely that it is connected with eruptions in Eyjafjallajokull, as they are close by each other.

Eruptions under glaciers cause immense clouds of volcanic steam, ash and smoke. Mushroom-like columns of volcanic material appear as the basins, that can take some of the water smelted by the heat, will overflow, lift the glacier and release millions of square kilometers of glacial water into extreme floods. The floods will sweep away any thing that get in their way, including any homes, roads or bridges on the way.

Wikipedia on Katla