BJ Deming

…Meeting Askja

Edited March 21, 2023.

There are so many good videos of eruptions and flowing lava online nowadays — what a pity they weren’t available back in the trippy Sixties so someone could set them to weird music!

Oh wait —

The music starts at around the middle of the video. The narrator uses no science terms, but per this source, the Icelandic/Hawaiian term for that blocky lava is apalhraun/aa and the rope-like stuff is helluhraun/
pahoehoe.

Unfortunately, the Smithsonian’s Global Volcanism Program Askja page doesn’t have much information about this Hawaiian-style eruption in the snow, but according the Iceland Review:

On October 26 1961 the Askja volcano suddenly started erupting. Even though the volcano had brought misery to the nation a hundred years earlier, not many were afraid this time.

Two days later, on Saturday afternoon, a group of men in the fishing town of Norðfjörður in the East Fjords of Iceland decided to travel to the once dreaded volcano.

Why fear? That was a lovely eruption!

Well, Askja has many moods.

While mellow and full of basalt in 1961, it went into a plinian-style VEI 5 rhyolitic rage in 1875. (GVP; Hartley and Thordarson)

As the Icelandic Wikipedia puts it (via Google Translate):

An enormous volcanic eruption began there on March 29, 1875. This eruption is called Öskjugosið 1875 , or Dyngjufjallagos . Ash fall from the eruption had a great impact on the East [1] and played a role in the fact that a large group of people moved from there to the West . After the eruption ended, there was a lot of land subsidence in Öskja, and then Öskjuvatn was formed . On the eastern bank of Lake Öskjuvatn is the Víti crater , and it is believed that the ash from the 1875 eruption came up there [ source missing ]

A crater lake, a volcanic crater, and rolling barren landscape.

Note that Lake Öskjuvatn — the part that slowly, over decades, subsided into a caldera (Source) — is much larger than the actual 1875 vent: the Víti crater, which hosts a small lake of its own just now. For scale, see the people standing on Viti’s lower rim? (Image:
wolfgangbeyer via Wikimedia, CC BY-SA 3.0.)

Okay. With something that big and potentially that violent, I can understand why, as mentioned, there isn’t much public discussion yet of Askja’s unrest by other volcanologists.

It appears to me, and perhaps also to Dr. Thordarson, as mentioned at the link above, that part of the magmatic intrusion responsible for the 2014-2015 Holuhraun basaltic eruption didn’t come all the way up and now, perhaps, it is moving through Askja’s shallow plumbing system.

But 1875 wasn’t that long ago, in geologic terms. Could there be something else going on at this remote volcano, so inaccessible in wintertime?

The boffins, of course, have forgotten more about Askja and Icelandic volcanoes than I will ever know.

What really puzzled me — it puzzles experts in other ways (divergent boundary magma) — was how one volcano could erupt such different igneous products as basalt in the 1960s and rhyolite in the 1870s.

After reading the YVO article referenced below, and drawing on other reading and my own meager background of undergrad courses from four decades ago, I see now that, in general, this can be due to depth and temperature.

  • Mafic magma, from a deep source close to the mantle or (foreshadowing) near a mantle plume, is hot and basaltic, with lots of magnesium and iron.
  • Felsic magma, from a shallower source, one that’s had time to sit in the crust and undergo geochemical changes, is more like granite, a little cooler in temperature and containing feldspar and quartz crystals; rhyolite, I think, is the extreme end member of this group.

So, something about Askja’s underground plumbing must be — understatement of the month — complicated.

We can’t just ignore it, though, because rhyolite does not come out in pretty glowing rivers, and who in the world needs this in the North Atlantic and northern Europe air traffic lanes:

It would be terrible for Iceland, too. This is Chaiten 2008, an order of magnitude below Askja 1875 at VEI 4 per the GVP.

Iceland is too complex for me to be able to figure out what’s going on with Askja, and many other laypeople probably feel the same way.

We can, however, talk dirty about the volcano (well, a little).

Askja sits out there openly, covered in fresh snow at the moment and looking all sweet and innocent, while all the while it might be having underground illegitimate magma transfer with Bardarbunga, skulking nearby underneath the Vatnajokull ice cap.

Who says science is boring?

Sincere apologies to Sigmarsson and Halldórsson (see source list); I wanted to make that as provocative as possible to draw eyes to an amazing possibility they suggest.

Remember how we leveled up last time and saw Iceland as a part of the Mid-Atlantic spreading ridge but located above sea level because of a mantle plume?

There’s all this spreading going on, separating North America and Eurasia, with magma welling up in between the two tectonic plates, right?

Well, that happens over geologic time, so we can all relax: Iceland isn’t suddenly going to dissolve into a lava lake.

BUT — there’s that mantle plume coming up, too AND it turns out that the general Bardarbunga-Askja region may sit right over the center of the plume.

So you’ve got all that spreading from the ridge, and all that magma rising, and to make a long story short, the magma-feeding systems of Askja and Bardarbunga might be mixed together.

That must really mess up both monitoring and building realistic eruption scenarios.

The two scientists put it much more accurately and objectively in their paper, to which I’ve added a couple of videos:

The complicated tectonic structure of the region N of Vatnajökull glacier, more or less directly above the Iceland mantle plume, was highlighted during the 2014–2015 rifting event.

This event was characterized by two-week seismicity progressing over 40 km and up to 2 m spreading as monitored by Icelandic Meteorological Office and Institute of Earth Sciences, University of Iceland and collaborators (e.g. Sigmundsson et al., 2015). The northward propagation of the rifting from the Bárðarbunga central volcano along the northern branch of the associated fissure swarm, caused seismicity in the neighbouring volcanic system of Askja several days before the fissure eruption at Holuhraun. This tectonic evolution caused uncertainty about where an eruption would occur, with an explosive eruption at Askja as a possible scenario.

Fortunately, the magma came up through existing craters at the Holuhraun lava field…

…which had previously been associated with the southern fissure swarm of Askja (e.g. Einarsson and Sæmundsson, 1987), a proposition questioned by Hartley and Thordarson (2013). The question of illegitimate magma transferred from one volcano to another, such as observed at Galapagos and between Kilauea and Mauna Loa (e.g. Rhodes et al., 1988; Geist et al., 1998), and in this case from Bárðarbunga to Askja, is thus a possibility. Alternatively, as discussed by Hartley and Thordarson (2013) and developed below, the delimitation of the Bárðarbunga and Askja volcanic systems needs revision…

Askja is still restless, at the time of writing, and the ending of this post remains to be written.

In the meantime, some update links:

Lagniappe (short):

This one actually is more like another main course instead of dessert, but it seemed fitting to me.

Feel free to skip it, but you’ll miss the cats (and, on a more positive note, the spider).

Featured image: Andriy Blokhin/Shutterstock

Sources:

Hartley, M. E., and Thordarson, T. 2013. The 1874–1876 volcano‐tectonic episode at Askja, North Iceland: Lateral flow revisited. Geochemistry, Geophysics, Geosystems, 14(7): 2286-2309.

Sigmarsson, O., and Halldórsson, S. A. 2015. Delimiting Bárðarbunga and Askja volcanic systems with Sr-and Nd-isotope ratios. Jökull, 65: 17-27.

Yellowstone Volcano Observatory (YVO). 2020. Yellowstone’s shadow. https://www.usgs.gov/news/yellowstones-shadow Last accessed March 16, 2023.

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