Volcanic summer in Iceland, Part II


The almost obscenely inconspicious volcano of Bárdarbunga seen in all it's icy glory.

The almost obscenely inconspicious volcano of Bárdarbunga seen in all it’s icy glory.

The Bárdarbunga volcanic system is the largest in Iceland and it has erupted more lava than any other volcano on the planet in the last 10 000 years. The volcanic system is 200 kilometers long and 25 kilometers wide.

The central volcano has a seventy square kilometer caldera that is ten kilometers across. Technically it is a highly complex type of volcano that is a mixture between a shield volcano, a strato volcano, tuya formations, volcanic ridges, radial volcanic fissures and a truly astounding volcanic fissure swarm extending in a NNE/SSW direction out from the central volcano.

The largest effusive eruptions has come from the fissure swarm where the Thjorsahraun is the largest lava eruption on the planet in the last 10 000 years. The largest explosive eruption occurred in 1477 during the Veidivötn basalt flood eruption in the southern part of the fissure swarm. During that eruption a VEI-6 explosive eruption occurred in the caldera that was the largest explosive eruption in Iceland since Grimsvötn suffered another VEI-6 almost 10 000 years ago. The 1477 eruption is the largest explosive eruption in Iceland since settlement and also the second largest effusive eruption only bested by the Lakí eruption. I think I just set a new record in using the word “largest” in a single paragraph.

The faulting mechanism of the M5 1996 Bárdarbunga earthquake. This is how a double-couple earthquake with no volumetric change looks like.

The faulting mechanism of the M5 1996 Bárdarbunga earthquake. This is how a non-double-couple earthquake with no volumetric change looks like.

Bárdarbunga is understudied since very little was known about the volcano until satellite imagery revealed the true scale. The reason behind this is a combination between it being remote, it having had small and benign eruptions for the last 537 years. The small scale of the eruptions are probably due to damages to the volcanic chamber system in the caldera after the large explosive eruption in 1477. The last reason is that the entire volcano is covered in ice completely.

The last confirmed eruption in Bárdarbunga occurred in 1996 during the Gjálp eruption. That eruption was a short duration VEI-2 eruption with a 3.5km high eruption column. It is also possible that the entire Gjálp eruption was a radial fissure eruption from Bárdarbunga and that Grimsvötn erroneously had that eruption attributed to it. The jury is out on that one.

Bárdarbunga is also by far the most seismically active of the volcanoes on Iceland. Not in numbers, that is the Gódabunga Cryptodome near Katla Volcano, but in the amount of Cumulative Seismic Release. CSR is the same as the amount of earthquake energy released over time.


Image from the 1996 Gjálp eruption.

Image from the 1996 Gjálp eruption.

During the decade leading up to the Gjálp eruption Bárdarbunga suffered from a very peculiar set of earthquakes ranging between M4 and M5.1 ending with the M5 earthquake that set of an intense earthquake swarm consisting of continuous earthquakes ranging between M3 and M4 as the Gjálp fissure ripped open.

After the Gjálp eruption Bárdarbunga has suffered several seismic swarms. These swarms can be short bursts, or longer swarms that can last for months. The current swarm has now been running for 2 months, it has consisted of several different loci. One is around Kistufell where predominantly deep earthquakes (>20km) have occurred with earthquakes well spaced out in time, this swarm was the first part of the current seismic unrest cycle. After that a more vigorous swarm started on a radial fissure between Kistufell and Bárdarbunga. This swarm mainly consisted of earthquakes between 12km and 5km and the strength of the individual earthquakes have mostly been small (M1 to M2). In the last month a third swarm has started in the Bárdarbunga caldera with events ranging from M1 to M2.7. The depths have ranged from 14km to 0.5km, and the earthquakes have mainly been tectonic but with a few showing more magmatectonic signatures.


Image from Icelandic Met Office. Dyngjuháls GPS.

Image from Icelandic Met Office. Dyngjuháls GPS.

Sadly the nearest GPS has suffered a malfunction with the last data point coming from 19th of June this year for the long-term plot. Anyways it shows a rather interesting pattern. The Dyngjuháls GPS-station is directly north of Bárdarbunga. Since October 2008 the station has been pushed 140mm straight north and 100mm straight up. That would be 17mm of north motion per year and 23mm of uplift. If we now imagine that the station had been on top of the hypocenter of inflation we would probably see values in the range of 5cm of yearly uplift.

If one instead look at the short term plot there is not a lot to be had, it seems like the general uplift has not changed due to the current seismic activity.


A smal part of the 1477 eruption of Veidivötn. Photograph by Rajan Parrikar.

A smal part of the 1477 eruption of Veidivötn. Photograph by Rajan Parrikar.

Even though this is far from the largest earthquake swarm at Bárdarbunga, neither is it the longest, it is still a bit of an oddity. First of all the earthquakes are deeper than normal (even though they have happened before). But the main oddity is the distribution of the individual swarms since they follow directly along the path of the main northern fissure swarm of Bárdarbunga. Also, the earthquakes have grown slightly larger and more numerous over time instead of abating.

One should not have feelings around volcanoes; one should instead look sternly at the facts at hand. And a slightly unusual set of swarms is far from a definite sign. Especially at a volcano that can be orders of magnitude more energetic. Still the feeling lingers that this could be the start of the run up. I might of course be totally wrong and it all putters out without even letting out a fart. But, still it could be fun to go through what I think would happen if the volcano erupted and what I think the signs would be for that eruption.

I think that Gjálp is a good indication of what to expect. I think we will see a non-double-couple earthquake with no volumetric change happening inside the caldera with strength between M4.5 and M5.5, after that an intense swarm will occur between Bárdarbunga and Kistufell as the fissure opens up. Expect to see continuous earthquakes above M3 for a day or two. After that the eruption will break through the ice. I also expect that intermittent earthquake swarms will strike at Bárdarbunga and that a VEI-2 eruption will occur there too. I expect the eruption to run for anything between 1 week and 4 months and that between 0.1 and 4 cubic kilometers of lava will be erupted. It is guesswork, but I think I am pretty much on the football field with my guesstimate.

I will though reiterate, there are currently no definite signs for a coming eruption. But if an eruption is around the corner we will not be guessing, we will know for sure because one thing is a definite and that is that it will be noisy.


This week the answers to Matt´s riddles are volcanoes and volcanic features. 2 points are awarded for each correct answer, 1 point after a clue was given. Good luck!

#1 I’m really going to lead you down the wrong path with this riddle!

2 points Bobbi  It’s in the South Shetland islands, and those are Shetland ponies. Leading someone down the wrong path, of course, is deception. It used to be a great refuge for ships seeking to avoid storms and icebergs.

#2 On this American battleground, the invaders left dogs and fresh-brewed coffee. Most of the casualties were from the weather. Sissel 2 points his Aleutian volcano was the only part of the United States successfully invaded by an axis power during WWII. The Japanese knew about the allied invasion forces, and evacuated, leaving “Nothing but dogs and fresh-brewed coffee” according to the admiral in charge of the allied campaign. Although the Japanese boobytrapped the place, and although the Canadians and Americans accidentally shot at each other during the operation, weather-related illness took the heaviest toll.

#3 Unfortunately, this island played a role in the Falklands conflict. 2 points Frances. Ans: San Felix (Part of the Desventuradas Islands, or “unfortunate islands,” it was the base for some British reconnaissance missions. The islands were formed in a volcanic eruption about 100,000 years ago.)

#4 This extinct volcano was the site of the last tree of its species, (at least in the wild.) The cutting of the rest was part of the residents’ downfall. Irpsit 2 points Rano Kau on Easter Island. The last wild Toromiro tree, endemic to Easter Island, grew in its crater. The ecological pillage of the land that led to its extinction in the wild also led to the collapse of the island’s civilization.

#5 This one will be forever etched into your mind… and your sheep. 2 points KarenZ 

This volcanic gas is emitted in large quantities by Icelandic volcanoes. During the Laki fissure eruption, it poisoned a lot of sheep and other livestock, leaving the residents to starve. Plenty of the residents died or were weakened by this gas as well. Hydrofluoric acid is commonly used to etch glass and silicon wafers.

In its air-diluted form, or with sufficient amounts dissolved in the water you drink, far more than in fluoridated drinking water, chronic exposure damages bones and teeth, causing painful lesions on them, eventually leading to death.
In its concentrated form, this acid can be quite deadly. It readily passes through the skin, where it pulls calcium ions out of the tissue and blood. This means the nerves can’t transmit signals, so you don’t feel the pain of the burn, at least until the fluoride goes away. More than a few square inches of burn area can pull enough calcium out of your blood to stop your heart.

Score board: Updated Scoreboard (missing 1 Answer on #3)
24 Sissel
8 Inannamoon667
5 KarenZ
5 Bobbi
5 Dinojura44
4 Dorkviking
1 RenatoRio
1 Talla
26 Sissel
8 Inannamoon667
7 KarenZ
7 Bobbi
5 Dinojura44
4 Dorkviking
2 Frances
2 Irpsit
1 RenatoRio
1 Talla
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