Warning signs block the road to Bardarbunga volcano, some 20 kilometres (12.5 miles) away, in the north-west region of the Vatnajokull glacier August 19, 2014.  (REUTERS/Sigtryggur Johannsson)

Since the weekend, literally thousands of (mostly) small earthquakes have been recorded at the site of a volcano in south central Iceland.  Officials fear the volcano, known as Bardarbunga, could erupt at any time. But it also may not.

An eruption could blow thousands of tons of steam, ash, and dust into the atmosphere. As the volcano sits beneath Iceland’s largest glacier, local flooding is an additional concern.

In anticipation of an eruption, the (largely uninhabited) area surrounding the volcano was evacuated, and the Icelandic Meterological Office raised the risk posed to the aviation industry to the second highest level (on a five point scale) since volcanic ash is a known hazard for aircraft.

“In 2010, the Eyjafjallajökull volcano erupted in Iceland, causing more than 100,000 flights to be cancelled, and costing commercial airlines an estimated $1.7 billion in revenue loss,” writes Mashable.  (Brad Plumer at Vox notes the effect on aviation from a volcano today should be less as “airlines have also changed their policies on dealing with ash since then, and fewer planes are likely to stay grounded.”)

The Icelandic Met Office released a computer animation showing the seismic activity beneath the Bardarbunga volcano from April 16-20. (Icelandic Met Office via YouTube)

The present volcano region, located about 190 miles from the capital of Reykjavik, has been swarming with earthquakes. On Tuesday alone, 1,000 small earthquakes were detected and the Icelandic Meteorological Office reports today that  an “intense earthquake swarm continues”.

Earthquake activity around volcano site in Iceland (Iceland Meteorological Office)
Earthquake activity around volcano site in Iceland (Iceland Meteorological Office)

Still, volcanologists are unsure if and when the volcano will erupt. In a detailed update today, the Icelandic Meteorological Office wavered on such an eventuality, while stressing the threat remains:

There are no measurements to suggest that an eruption is imminent. Previous intrusion events in Iceland have lasted for several days or weeks, often not resulting in an eruption. However an eruption of Bárðarbunga cannot presently be excluded, hence the intense monitoring and preparation efforts. The ongoing monitoring and assessment effort is necessary in case a volcanic eruption occurs. Hazards in the event of an eruption are being assessed, including a glacial outburst flood and dispersal of volcanic ash. Additional seismic, GPS and hydrological stations have been installed in the Bárðarbunga region. Likewise, mobile radars capable of monitoring ash dispersal have been moved to the region. The aviation colour-code for the Bárðarbunga volcano remains unchanged at ‘orange’, signifying that the volcano is exhibiting heightened levels of unrest.

Volcanologists on Twitter have also equivocated some on the volcano threat:

Gísli Pálsson, an anthropologist at the University of Iceland, told Slate’s Eric Holthaus that “there is a risk of false alarm, but on the other hand we should try to be objective and say something immediately.” Kristín Vogfjörð, research director at the Icelandic Meteorological Office cautioned  the volume of magma underground is “incredible” in the Icelandic paper Visir.

Nature has an excellent rundown on the different possible scenarios with Bardarbunga:

Anything could happen. The quietest possibility is that the earthquakes subside, the moving magma solidifies and there is no eruption.

Another scenario is that the magma begins to erupt but stays beneath the overlying ice. The heat from such subglacial eruptions can melt some of the ice, creating floods that rush downhill and pose a hazard to anything in their path.

A third option is an eruption with a lot more magma, enough to break through the ice and form an ash plume. And perhaps the worst-case scenario, according to volcanologist Dave McGarvie of the Open University in Edinburgh, UK, is that an eruption begins along the long fractures that extend beyond the ice cap for tens of kilometres south and west of Bárðarbunga. Much of Iceland’s hydroelectric power comes from rivers in this region.

The timeline remains uncertain. It can take days, weeks or even months, for seismic unrest to develop into a full-fledged eruption — if it happens at all.

Bardarbunga has been quiet for the past 100 years (last eruption in 1910), but “has erupted more lava than any other volcano on the planet in the last 10,000 years” according to the blog Volcano Cafe.