Time for Herðubreið to erupt? + Riddles

Few volcanoes portray the same raw beauty as Herðubreið. Photograph by Thrainn Vigfusson.

Serendipity seems to have really cursed this series of the five most likely volcanoes and areas to erupt in Iceland. So far all 3 I have written about have shown signs of unrest (Hekla, Grimsvötn and Reykjanes Volcanic Area), and yesterday I would have written and published this piece on Herðubreið and Askja, but work got in the way.

It is though not that I have grown psychic powers, the scientific signs have been there all the time. I just tried to put my thinking cap on and figure out which volcanoes in my opinion are the most likely to make an appearance. So, even though Herðubreið put in an appearance slightly before I got to it, here is a bit of information on her and Askja and what the signs are for a future eruption.

I have here clumped them together even though they are not belonging to the same volcanic system. Askja is on her own fissure swarm and Herðubreið is a volcano in her own right between the Kverkfjöll and Askja fissure swarms.

Askja

The crater of Viti infront of the Caldera of Öskjuvatn all of it inside the two Calderas of Askja. Photograph by Wolfgangbayer, taken from Wikimedia Commons.

Askja is one of the Big Five in Iceland together with Theistareykjarbunga, Bárdarbunga, Grimsvötn and Katla. These have all had eruptions transcending the 10 cubic kilometer range, and all of them except Theistareykjarbunga have suffered from VEI-6 eruptions, and all of them have had that size of activity after deglaciation.

Major lava fields of Iceland and the Odadhahraun lava field surrounding Askja. Image from Encyclopedia Britannica.

Askja is a much understudied volcano compared to Grimsvötn and Katla even though she has ample capacity for destructive behavior. Just as an example, the Odadhahraun lava field is Iceland’s largest single lava field covering 3681 square kilometers; still it is not known if it is from a single eruption, or several eruptions. Visual evidence seems to point towards it mainly being from one eruption but no petrochemical testing has so far been done. Nor is it known when this eruption happened.

Why would now Odadhahraun be important? Well, normally we point towards Thjorsahraun out of Bárdarbunga being the largest lava flow after deglaciation on earth.  It was an estimated 21 to 30 cubic kilometers of lava and covers 950 square kilometers. If we assume the same thickness for Odadhahraun we get a discharge of about 81 to 116 cubic kilometers of lava, and that would be a low score since the thickness obviously would be greater in a larger field (if the viscosity is the same).

Personally I feel that there is place for a driven PhD. student to do a dissertation on Odadhahraun, it certainly merits it. After all it feels pretty useful to know if it was erupted in one go and when it was erupted. I do though think that it is from several eruptions, but one of them might still be the largest in Iceland after deglaciation.

Askja has a couple of features the other volcanoes does not have, it for instance inflates and deflates independently of its eruptions and as such behaves a bit more like a resurging dome volcano. The deflative phases have been paired conclusively with activity in volcanoes to the north of Askja. After the 1961 eruption she started to slowly deflate as the area around Krafla inflated, and as the Krafla Fires died out the Askja deflation slowed until a minor inflation occurred. That deflation stopped as Theistareykjarbunga started to inflate when Askja once more deflated slightly.

Askja today

The dark blue beauty of Lake Öskjuvatn with the surrounding outer caldera wall clearly visible. Click on image to see it clearly. Image by unknown.

The volcano is today suffering from intermittent seismic activity centered around the magma reservoir indicating changes in magmatic pressure, no large earthquakes are taking place, nor are there large earthquake swarms happening.

There is though evidence of slightly increased hydrothermal activity and the hydrothermal energy release into Lake Öskjuvatn has increased leaving the lake ice free during the last two winters as evidenced by satellite imagery.

Sooner or later Askja will erupt again, but at this time it is probably more than 10 years away unless a large intrusion occurs, if that happens Askja can probably erupt pretty quickly, especially if the new magma heats up old magma left in the system.

Herðubreið

This beautiful black and white image shows Herðubreið with snow on top and the small top tuff cone is clearly visible. Photograph by Skarphéðinn Þráinsson. Click on imge for larger view.

Herðubreið is a tuya that was deposited during the last glaciation. It is a contender for the title of being the world’s most beautiful volcano; it certainly is the most beautiful tuya volcano. A tuya is also called a table top volcano due to its shape. The surrounding ice shaped the erupting lava and worked as a mold for it giving the characteristic round steep sided shape with the flat top. There is though a slight chance that Herðubreið erupted at the end of glaciation or even after deglaciation; there is after all a small tuff cone on the top. But, largely it is an unaltered tuya.

In 2007 a swarm of 5 300 earthquakes took place at a depth of 14 to 21 kilometers under Upptyppingar volcano, this swarm has after that progressed laterally at a slight upwards angle towards Herðubreiðartögl and Herðubreið. The type of earthquakes was brittle earthquakes as rock fractured from the inrushing magma, or magmatectonic earthquakes of type B.

The persistency of later swarms have given ample signals to track this intrusion as it moved upwards towards the surface and all signs so far has pointed to an area from Herðubreiðartögl to Herðubreið as being the likely ground zero if it pops up in the form of an eruption. There have also been smaller swarms indicating new intrusions into the area, both following the same path and also going more straight up from locations under Herðubreið and Herðubreiðartögl.

Herðubreið and Herðubreiðartögl today

Image of the current ongoing earthquake swarm. Image by the Icelandic Met Office.

Seismic signals combined with sparse GPS data released from the area seems to suggest that an eruption very well can occur at any time now, the time period could be anything from weeks to years. We will not really know until we see a persistant swarm moving from the current depth of 5km upwards to 2km or less.

During the last few days a slow earthquake swarm has been running at about 5 km depth, the earthquakes were small but rather persistant. During the night a brief spike in activity occurred at about midnight local time and at 05.38 a major earthquake swarm started with the maximum magnitude of M3.2 occurring 11 minutes later.

So far the swarm is counted in about 100 earthquakes and counting. The depth is though still not manually checked by the Icelandic Met Office and might very well be moved towards the 5km depth line, several of the earthquakes during the last week has been set at shallow depth by the automatic system and was later manually corrected to about 5km. Do not be surprised if that will be the case for the earthquakes from this swarm.

A slightly different view of the activity. Image by Icelandic Met Office. Thanks to Islander for sending me the image.

It is still too early to say if this is the start of the run up towards an eruption, but to be honest I would not be surprised if it was. We will most likely know in a few days if this is it or just a volcanic teaser.

If the volcano would erupt we would not know how she would behave. The most likely behavior would though be an effusive fissure eruption like the one that happened at Herðubreið around 8 000 years ago.

Update

Here is a plot made by Cryphia, in green are all the earthquakes since 1995 coded in green, the earthquakes during the last month is color-coded yellow to blue. In this plot the earthquake swarm of today form a rather neat dyke intrusion going from 10km depth up to 2km. There is also evidence of deeper quakes following what is likely a deep conduit that is being pressurised. One should though note that the earthquakes used in this plot has as of yet not been manually checked by seismologists.

Riddles

As usual there are one faultline, one volcanologist and three volcanoes amongst the riddles. Two points will be awarded until I append any clues, after that there will be one point. Good luck to everyone!

1. Savate against + image – Kick’Em Jenny (Sissel, 2pt). Savate is a french kickboxing discipline, and Sigrud Undseth on the image wrote a novel named “Jenny”.
2. The new Lady of Madrid that blows sand – Marianna Fault (Inannamoon667, 2pt). Fault associated with the New Madrid Fault, it is supposedly only 6000 years old and it suffers sandblows.
3. Domed tents near the white water (The real clue hides in the “Domed tents”) – Khorgo, also known as Taryatu-Chulutu (Diana Barnes, 1pt) is situated near Terkhiin Tsagaan Nuur (White Water Lake). A yurt is dome shaped tent, and the volcano has created Yurt-basalts
4. From K-T to a town lost in the mist of coke – Haraldur Sigurdsson (Inannamoon667, 2pt), won the Coke award, found tekite at the K-T boundary in Haiti supporting the impact theory and also helped to find the lost village of Tambora
5. Truly a volcano in your male pants (Clue, think common male trouser fabric from the land of male clothing and HP) – Cheviot Hills (Sissel, 1pt)

Score board
7 Sissel 5 KarenZ 5 Kelda	4 Shérine France 2 Alison	2 Dinojura44 2 Evan Chugg

CARL