There are strong indications that magma is gathering in the volcano under the Öræfajökull glacier, which may be a sign that an eruption will happen soon, but eruptions are notoriously difficult to predict.
RÚV reports that there have been numerous tremors at and around Öræfajökull, and they have increased in recent weeks. Magma pressure also appears to be building up within, which is usually an indication that an eruption is coming.
Sigurlaug Hjaltadóttir, a natural disaster specialist at the Icelandic Met Office, told Fréttablaðið that while it is clear that Öræfajökull is preparing for an eruption, it is impossible to know whether and when that eruption will happen—it could be after some months, years or even decades from now.
Further, there is the possibility that the eruption will not result in flowing lava or ash clouds; it may result in rapid melting of glacial ice and subsequent flooding.
Öræfajökull has also erupted before, to devastating effect. Twice, in fact: in 1362 and 1727. The former eruption was enormous – some 10 cubic kilometres of material was blown into the atmosphere, and the district around the volcano was uninhabited for about 40 years afterwards. It was the largest eruption in Iceland since Hekla erupted in 800 BC.
The eruption in 1727 was smaller, but was nonetheless devastating. Three people and many farm animals were killed in the ensuing glacial flooding that the eruption provoked.
Glacial flooding is probably the greatest danger posed now, should Öræfajökull erupt. The ice that covers the caldera is estimated to be about 550 metres thick, and rests hundreds of metres above sea level. Even a small eruption would be likely to provoke massive flooding into the region. Fortunately, not many people live in the area, and preparedness and evacuation procedures are much better now than they were in the 18th century.