Is Katla Volcano likely to erupt?

Katla volcano in the southern Iceland is one of the countries most active volcanoes. The volcano is located beneath the Mýrdalsjökull ice cap, thus eruptions have the potential to produce large amount of ash and glacial outburst floods (jökulhlaups), potentially repeating the problems experienced in 2010.

I’m currently in Iceland leading a university geology field trip, thus pay close attention to the current activity of the volcanoes. On our first day in Iceland there had been some seismic activity overnight around Katla, which the locals were talking about and had been discussing with us, knowing we would be interested. On awaking on our second day in Iceland, I was greeted with comments like, “Iceland’s biggest volcano Katla set to erupt” on my Facebook feed. I was a little puzzled by this media frenzy I had woken to and wondered if the status of Katla had changed overnight? For we had been sleeping in the shadow of Katla (having checked it was safe to do so), had not been evacuated during the night, so what had happened?

According to the media reports “Iceland raised the alarm after its largest volcano was hit by the biggest tremors since 1977”. Over the following days several further reports followed in The Express (whose headline does not even spell Katla correctly, stating Katia is “on the verge of erupting”). There are a variety of similar reports in The Sun and The Metro and the list could go on. Some of these reports are based on speculation of what may occur if Katla was to erupt, with little science and others after the rather frightening and misleading headlines, go on to accurately report the official information released.

One report even suggests “panic grips Iceland”, although the Icelandic media has taken a more measured approach to the reporting of these events than the British media and certainly this is not the impression I have received from the locals here.

So what is happening?

The Icelandic Metrological Office (IMO) is responsible for monitoring and providing information on Iceland’s volcanoes. At no time in the last week has the status of any of the volcanoes in Iceland changed from ‘Volcano is in normal, non-eruptive state” (with running a field trip currently in Iceland, we check this regularly, we ran the same trip in 2014 during the Holuhraun eruption, when the volcano status was changing daily).

What have been issued by the IMO are several warnings of potential activity.

The IMO on the night of the 28^th-29^th August recorded a series of earthquake swarms with two earthquakes measuring over a magnitude of 4 on the Richter scale. These are the largest earthquakes reported from Katla since 1977. On the 30^th August a further earthquake swarm of over earthquakes occurred with the largest measuring a magnitude of 3.3. Typically earthquakes associated with the Icelandic volcanoes are less than a magnitude 3 (unlikely to be felt by us going about our daily lives) so the two larger earthquakes stood out. However, at no point was volcanic tremor detected at Katla over this period. Volcanic tremor are a specific type of earthquakes that can herald the movement of magma in the crust. We would expect to see such earthquakes if magma was close to the surface.

At the same time as the increased seismicity at Katla, glacial water was also recorded in Múlakvísl River, located south of Mýrdalsjökull. This is one of the rivers that are known to potentially flood in times of eruption. As Katla is located beneath an ice cap, if an eruption takes place, the hot magma melts the overlying ice causing large outburst floods. These are large powerful floods that can sweep away infrastructure within its path. It is not uncommon for glacial water to flow into the Múlakvísl River and this alone does not indicate a potential eruption. The current problem being reported by the IMO along the Múlakvísl River are the high concentrations of hydrogen sulfide (H₂S) and the potential gas pollution this can produce.

The IMO provided an overview of the status of Katla and Mýrdalsjökull on the 31^st August. The IMO have been reporting an increase in seismic activity since June and point out this is an almost annual occurrence at Katla, often associated with the release of glacial water into local rivers. The IMO do go on to point out the two magnitude ~ 4.5 earthquakes recorded at Katla in the last week are the biggest since 1977, but since these and the following earthquake swarm seismicity has decreased. The IMO  commented that several such periods of unrest have been detected since the 1950’s and none have resulted in an explosive eruption. However, Katla long period of quiescence, since 1918 is rather usual and people are beginning to speculate about a future eruption.

Why the speculation?

Katla is one of the most active volcanoes in Iceland. In addition the location of Katla beneath an ice cap may result in additional hazards, such as the eruption of large amount of ash into the atmosphere. Eruptions from Katla have been recorded to last between 2 weeks to over 5 months and occur on average every 47 years (Larsen, 2000). With the last eruption occurring in 1918, an eruption from Katla is long overdue.

In the last 1100 years, Katla has known to erupt 20 times (Sturkell et al., 2010). It’s smaller neighbor to the west, Eyjafjallajökull has erupted twice in the same period, both times simultaneously with Katla (Sturkell et al., 2010). Thus there has been much speculation whether Katla will erupt following the Eyjafjallajökull eruption of 2010 and whether the trend will continue.

So is Katla likely to erupt? It is likely that in the future Katla will erupt again. Did it happen this past week? No, but when the next eruption is likely, is just a matter of time.

References

Larsen, G., 2000. Holocene eruptions within the Katla volcanic system, south Iceland: characteristics and environmental impact. Jo ̈kull 49, 1–28.

Sturkell, E., Einarsson, P., Sigmundsson, F., Hooper, A., Ófeigsson, B.G., Geirsson, H., Ólafsson, H. 2010. Katla and Eyjafjallajökull volcanoes. Developments in Quaternary Sciences. 13:5-21.