Here we provide some information on Bárðarbunga, the volcano that has now erupted. The eruption is currently not under the glacier, so lava is coming up and ash production is limited. This also reduces the threat of a flood.
However, the small eruption probably which likely occurred under Vatnajökull glacier last Saturday (the eruption we all thought was phoney) has melted a considerable amount of ice, hence making a flood in the near future likely.
The following information comes from the Icelandic Met Office:
There are about 30 known central volcanoes, or volcanic systems, in Iceland. Bárðarbunga, the second highest mountain of Iceland; ca 2000 meters above sea-level, is one of them. The volcano is placed in northwestern Vatnajökull ice cap and therefore covered with ice.
The enormous size and nature of Bárðarbunga was not fully recognized until it was observed in 1973 on an image from a satellite, 800 km above Earth. A caldera in the volcano's crown, 11-km long on the longer side, is covered with approximately 850-m thick glacial ice. Eruptions related to the central volcano can occur anywhere in the caldera, on the sides of the volcano and also in the fissure swarms to the NA and SW of the volcano, for a distance up to 100 km from the central volcano.
Inevitably, immense eruptions and explosive eruptions are a possibility in the system with imminent threat of ice melting in great magnitude causing a huge jökulhlaup (glacial outburst flood). It is presumed that Jökulsárgljúfur and Ásbyrgi were created in such cataclysmic events in prehistoric times. Large jökulhlaup in Kelduhverfi in the 17th century are believed to be related to volcanic activity in Bárðarbunga.
Over the last seven years, seismic activity has been gradually increasing in Bárðarbunga and the fissure swarm north of the volcano. This activity diminished after the Grímsvötn eruption in May 2011, but soon after, the activity started to gradually increase again. The current seismic activity began August 16, 2014.