The Bárðarbunga (or Bardarbunga) volcano has erupted, evoking memories of the 2010 Icelandic ash cloud that caused chaos across European and North American air routes.

What has been happening?

The ice-covered Bárðarbunga volcano has a magma chamber beneath it, and measurements indicate that magma from this chamber has been escaping into a vertical underground crack. In total, the magma has migrated some 40 km northeast of the chamber. We call this process a dyke intrusion. Escape of magma from the chamber has removed support from the chamber roof, which has collapsed to trigger earthquakes in the area.

At the far northeast tip of the dyke intrusion, the magma managed to find a route to the surface on August 29, producing a small eruption at the Holuhraun lava field. After a pause, a larger eruption started in the same place on August 31—that eruption continues at the time of writing. Both of these events occurred along an ancient fissure that had erupted in 1797. So it looks like the magma in the new dyke intrusion met the old and cold 1797 dyke intrusion and followed its path to the surface. Had this not happened, the new dyke intrusion might have kept moving to the northeast.

What is the situation right now?

At the moment a vigorous eruption is taking place along a crack about 1.5 km long, from which lava is fountaining. This is called a fissure eruption—these are common in Iceland. The lava fountains reach up to 70m high; on collapsing they coalesce to form lava flows that are streaming away from the fissure. In total, these flows currently cover an area of 10.8 square kilometres. An eruption plume of steam and volcanic gases has reached 6km into the atmosphere, but there is no ash.

The good news for Iceland is that, although Bárðarbunga is covered with ice, both eruptions took place in the an ice-free area. That means that no ice is being melted and therefore there is no danger from flooding. The good news for international air travel is that small fissure eruptions like these produce lots of lava but little or no ash, so any airspace closure is only local.

Is this a dangerous eruption?

Not really. Near the eruption and downwind there will be a hazard from gases escaping from the eruption if they are in high enough concentrations—mostly sulphur dioxide and possibly also some fluorine and chlorine. Scientists working in certain areas have to wear gas masks. Although the lava is slow-moving, it is best to stay a few hundred metres away. Staying away from the ends of the erupting fissure is also a good idea in case it becomes longer.

The Icelandic scientists working in the area are familiar with this type of eruption and know the hazards and how to minimise their risks. But at present there are no plans to allow any one else into the area.

What happens next?

One big uncertainty is whether new magma is entering the system or not—and, if so, how much and at what rate. For example, if more magma is entering the system than is being erupted, then the dyke intrusion may start moving again. At that point, the new magma could power an eruption elsewhere, such as under the Bárðarbunga volcano itself. The dyke intrusion might also surface under the nearby glacier. Either of these possibilities would involve the melting of lots of ice, triggering floods (magma can melt up to 14 times its own volume of ice).

Another uncertainty is that we don’t yet know whether this is an isolated event or whether it is the start of a prolonged episode involving multiple events of seismic unrest and magma movement. If it is the latter, then we have some idea of what to expect as there was a well-studied episode that occurred between 1975-84 at a volcano called Krafla in north Iceland. During this period, there were 21 stretches of seismic unrest, some of which were accompanied by dyke intrusions moving out from a magma chamber, a few of which broke to the surface and formed eruptions just like the present Holuhraun event.

We also don’t know whether the movement of magma away from the chamber beneath the Bárðarbunga volcano is going to trigger an eruption there. There is a lot of ice at this volcano because it contains a crater(called a caldera) some 10km in diameter and 700m deep. Even a modest eruption here would generate a lot of meltwater.

What is the best-case scenario?

That the dyke intrusion stalls in the crust and cools, and the eruption at its tip ceases.

What is the worst-case scenario?

Unfortunately there is more than one. The first is that an eruption might start at the Bárðarbunga volcano itself, and there is a remote possibility that this could be a large, explosive eruption that produces an ash cloud. Fortunately, because of the ash cloud produced during the Grímsvötn eruption of 2011, we have a fair idea of what this might look like and how best to minimise disruption to air travel. A reassuring fact is that lessons learned and changes made after the Eyjafjallajökull 2010 eruption meant that, even though Grímsvötn erupted twice as much ash as Eyjafjallajökull, it caused fewer disruptions.

The second bad option is that the dyke intrusion continues to the north-east and triggers an eruption at the Askja volcano. Askja's most notorious eruption there was in 1875 when an explosive rhyolite eruption produced an ash cloud that spread over northern Europe. Rhyolite is a “sticky” magma type that fragments more easily into ash, hence has a higher potential to produce ash clouds that cause disruption to air travel.

However, we are unlikely to have a repeat of the 1875 eruption because there is probably not much rhyolite magma left, plus there is a deep crater lake covering the 1875 eruption site. There remains the possibility that some ash could be produced if a dyke intrusion mixed with the remaining rhyolite magma and triggered an explosive eruption.

Have lessons been learned?

The Bárðarbunga volcano didn’t get to be the second largest mountain in Iceland by sitting around doing nothing for centuries. An eruption was inevitable, and recent signs of unrest made it clear that one would occur soon. But as we have so little high-quality data from past eruptions to inform what might happen in the future, it is essential that we gather high-quality data to learn what we can as fast as we can. This is what Icelandic scientists are excellent at doing.

I am aware that there is a lot of anxiety because the disruption caused by Eyjafjallajökull's 2010 eruption is still fresh in everyone’s minds. However, even if we had an exact repeat of this eruption tomorrow only a fraction of the flights would be cancelled because we have already learned so much from past eruptions.

This article was originally published on The Conversation.