Recently (2-3 August 2013) I went for a travel with a friend, around the region of Hofsjökull and then to Skrokkalda and Haganga, and near Hamarinn and Veiðivötn, and then passing by Hekla. This is my small report about it 🙂 and hopefully the first of several to come.
It was a nice volcanic trip but we catch the rather common but somewhat crazy sandstorm, with extreme wind gusts, blowing sand, ash and even rocks, and very cold (but thankfully no snow – we knew it was forecast so he return back ahead of it). The weather made our trip difficult, and even more for the pictures (the camera was ruined with the ash inside) and we though it was not worth of trying our way directly to the edge of Hamarinn or Haganga; it was extremely windy, foggy and ashy there. Hopefully next year I will repeat the attempt. Nevertheless I loved to have seen those mountains as they are rather prominent and well visible from afar.
My impression was that all of this dead zone region is a volcanic field with plentiful of Pleistocene ridges, tuyas and Holocene lines of volcanic hills. Eruptions seem to occur everywhere, sort of a monogenic field – or rather let’s call them monogenic fissures and ridges.
I can’t see Skrokkalda or Haganga being a central volcano. They seem the product of just one or a couple eruptions, under the ice cap during the Pleistocene, while Hamarinn is large enough to could be considered a central volcano. Hamarinn stands out like a huge table mountain, just at the edge of Vatnajökull, but seemingly hiding a caldera beneath the glacier.
Pic: http://www.vedur.is/media/frettir/jardskjalftar_eldgos/medium/hamar_221008.jpg Hamarinn central volcano. Credit: Jóhann Friðrik Kristjánsson.
Tungnafellsjökull is also large enough to be considered a central volcano, and it has a deep caldera at its top, completely ice-filled. I have a feeling because it stands out of the large ice cap of Vatnajökull, and with the ice in the whole of Iceland retreating every year, this could be one of the first big volcanoes to awaken to activity in the near future.
Behind it I could have a glimpse of the mighty ice-filled dome of Bárðarbunga, but it was mostly hidden in the haze. From all of these large central volcanoes, the fissures and ridges seem to pop out here and there, across a vast region to their southwest. There are a lot of hills just similar to Skrokkalda but mostly unknown to us here at volcanocafe. Each was a product of a different sub-glacial eruption.
Skrokkalda is the only one with a SIL station on its top – we saw it from afar, but the track leading to the SIL had a “just for staff” sign and so we did not go there. (I did not want to cause a tremor myself and cause a stir in volcanocafe . Anyways its quite a clever position to have a SIL but personally I would place it further south and i will tell you why.
It seems older eruptions were the ones at Skrokkalda or Haganga (Pleistocene), while the newest eruptions occurred further south, around Veiðivötn (870, 1477 eruptions) or Trollagigar (the eruptions of 1862). I wonder if this is a trend or not. However, Pleistocene ridges also occur further south, like alongside the Langsjór lake.
To which volcano each ridge belongs is a matter of guess, and as Carl posted (Laki), it is my opinion too, that these eruptions come from a source of magma independent from what it is thought to be a central volcano.
I also found some evidence of what seemed to be pumice around that region, but little; mostly tiny whitish volcanic gravel but the weather was nasty when I found it and I just returned quickly to the jeep. Mostly, black basalt is everywhere across that region and it seems it is gas-rich (lots of holes in those volcanic rocks).
Hofsjökull surprised me because it poses such a large caldera, and it displays evidence of recent early Holocene eruptions to its southeast (and also southwest) side. Those are mostly lavas and some mountains look like rhyolite. I could not find any evidence for recent big ash eruptions. I would love to have gone closer to it, but the glacier is surrounded by large outgoing rivers and seems almost impossible to drive or hike over there, without expert help (furthermore off-road driving is strictly forbidden). It is quite an astonishing beautiful volcano and enters my “worth to keep an eye on” list of volcanoes.