A guest post from Salting
I visited Iceland many times in the past to meet friends and take a day off on my way between Europa and US. In summer 2011 I made an extra-long stop and visited a glacier to better understand the forces that shaped the coastline around my Swedish home island. Trekking the glacier tongue Solheimajökull our guide decided to cut our trip short. I never felt anything but the guide claimed he sensed movements in the ice that worried him. Back with access to the internet, he showed me the IMO earthquake page with red dots in Myrdalsjökull and a couple of days later a jökulhlaup swept away a bridge and parts of the main road that runs around Iceland. The events triggered my curiosity for Icelandic geology and resulted in daily visits at the IMO pages and similar. Some years later I found the Volcano Café and the fascination went from serious to a severe case of “volcanitis”. When the seismic activity around Bardabunga increased in 2014 my condition developed from severe to incurable and as I watched the seismic track snaking its way from Bardabunga to the final eruption sites in Holuhraun I knew I had to see the place myself. However, it was not until this July, five years later, that I had the opportunity to make the trip. With a rented jeep, my wife as a “Grand Theft Auto” style driver and an Icelandic friend as a guide, we set off to negotiate the F-roads on a round trip to see Holuhraun and other Iceland volcanic celebrities.
Five years ago: The seismic activity had been gradually increasing in Bárðarbunga and the fissure swarm north of the volcano since 2007. The activity dropped down during the Grímsvötn eruption in May 2011, but soon after, gradually increased again.
An intensive swarm was reported by IMO August 16. Subsequent quakes, seismic tremor and GPS measurements showed that the pressure inside the caldera increased and caused the formation of a dyke and magma movements first to the southeast and after a 90 degree turn to the northeast. August 23rd the dyke reached under the Dyngjujökull glacier and a subglacial eruption with massive ashfall was feared. No eruption surfaced, however, and instead the dyke propagated further 10-12 km northeast outside the glacier with many > 3M quakes at a depth of 5-12 km. https://www.youtube.com/watch?v=VPaF2bxVAv4
August 29, 2014, 02:00 an eruption started from an old volcanic fissure on the Holuhraun lava field, about 5 km north of the Dyngjujökull ice margin Holuhraun north of Dyngjujökull. It was a small fissure eruption and at 02:40 AM the activity appears to have decreased.
New eruptions from longer fissures were reported from August 31.
Some drone footage: https://www.youtube.com/watch?v=8cICS9MtRRw
As we all know, the eruption continued for months causing an expanding lava field (hraun) covering the plains north of Dyngjujökull glacier. The formation of the long dyke and the eruption of lava were accompanied by strong earthquakes around the rim of the Bardabunga caldera and dramatic subsidence of the ice-covered caldera floor. The best explaining model was that fresh injections of magma had gradually increased the pressure in the large magma chamber under Bardabunga. The chamber lid/caldera floor was envisioned as a several kilometres thick plug/piston with a 600-800 of meters icecap on top. When the plug was stuck, the pressurized magma instead of pushing the plug upward broke its way out sideways through weaker rocks in the chamber wall to the south. Soon the dyke/pipe was blocked by another pressurized chamber (that we now discuss as the proto-volcano “Greip”, https://www.volcanocafe.org/greip-june2019/). Instead, the magma found a new way to the north and finally erupted. The magma required to fill the dyke and feed the eruption was flowing from the Bardabunga magma chamber and the loss of pressure and magma caused the plug and caldera floor to subside. While the eruption once started was going smooth without much noise, the subsiding caldera plug caused a series of strong quakes. Calculations based on the size, positions and shrinking of the magma chamber allowed for surprisingly accurate predictions on how long the eruption could be expected to continue and the eruption finished at the end of February 2015.
The subsidence of Bárðarbunga caldera, that was caused by draining of magma away from the volcano and out to feed the lava, dropped from over 80 cm per day to less than 25 cm per day at the new year 2015 and the accompanying magnitude 5 or larger earthquakes there, which used to happen every day, came a week apart or more. Satellite measurements of heat flux show a decline from over 20 gigawatts in early September (to put this amount of energy in context, the average UK electricity demand in 2012 was 36 gigawatts), to fewer than 5 gigawatts by the end of November.
Five years after the outbreak form the Bárðarbunga magma chamber and dyke formation, I finally managed to reach Holuhraun by jeep from the Dreki (dragon) camp at Askja. The hraun (lava) had erupted on a vast plane north of Dyngjujökull glacier formed by erosion material from Dyngjujökull, and several earlier “hrauns” from various sources around.
Most of the plain is covered by black or grey coarse sand, ash, and remains from some older hrauns were visible, most clearly in the northwest.
Several investigations regarding the composition and origin of the lava have been published and reported that the geochemistry of the eruption products firmly locates it within the Bárðarbunga volcanic system. By carrying out careful geothermobarometry, the magma was concluded to be stored at 8 ± 5 km prior to eruption( Hartley et al., 2018; Gudmundsson et al., 2016). Although the erupted magma is extremely homogeneous in composition, complexity in its crystal cargo reveals that it was ultimately assembled from heterogeneous mantle melts that underwent crystallisation and mixing in the lower- to mid-crust. Re-equilibration of melt inclusion H2O contents indicated that crystals spent at least 1–12 days in their carrier liquid before the eruption, consistent with lateral transport in a mid-crustal dyke from the Bárðarbunga central volcano to the eruption site.”
The new Holuhraun, now more than 4 years old, is really impressive. The tourists that arrived when the area was opened after the eruption enjoyed swimming in the heated river/lake north of the hraun but today there is no noticeable heat left on the surface. Warm and wind/sand protecting clothes were badly needed.
The first site we visited (the tourist site on the western edge with a marked route) has large areas where the solidified roof had caved in when liquid lava had moved away underneath.
Some signs of life invading the hraun could also be seen, a few green straws, a tiny patch of lichen. This is, however, a hard place for higher life forms! The sandy ground drains away water very efficiently and sandstorms will bury the small patches of life.
Another site on the south east, closer to the eruption site, has much less of caves. Both sites were extremely rugged and it was hard to move safely around thus limiting our excursions. Most of the solidified lava has a very “spongy” structure, reminiscent of all the gas it held.
This makes it sensitive to erosion. There is a lot of precipitation in the area and many freeze/thaw cycles every year. Strong winds with sandstorms grind the rocks down. The process is obviously very efficient and rapid and Holuhraun has already started to erode. I wonder how many more hrauns have flooded this area just to be quickly degraded or buried by the sand! How long will it take to erode/hide the 2014 Holuhraun? Probably a within an eye blink on a geological timescale!
Where will the next large eruption on Iceland take place? With great respect, we trekked to about 3 km northeast from Hekla. Who knows? Maybe she will be the next erupting volcano in Iceland. She is a real beauty, for now resting in a peaceful green landscape with sheep and lovely Icelandic horses grassing around.
Other hot candidates are Grimsvötn and Katla, but they are unreachable for us ordinary volcano tourists.
However, on the way to Askja and Holuhraun, we passed the fantasy evoking “Upptyppingar“, or Mount Viagra”. Actually, the name is not for one, but for two peaks. Increased unrest here and northward towards Herdubreid may be a prelude for an approaching eruption. So for now waiting for the next upcoming hraun to visit! In the meanwhile, my wife developed a taste for tuff driving in rough terrain and now wants to register for the Dakar rally. Anyone who knows if there are any volcanoes to see along that road?