How to explore Iceland through the eyes of a geologist: Part 3 – Glaciers and volcanoes of the centre and south
Intro: The last part of my Iceland geology blog series ventures from the centre to the south of the island. These areas contain the youngest rocks in Iceland (i.e., Nornahraun 2014/15 lava field), glacier-covered volcanoes (i.e., Vatnajökull), geothermal altered mountains (i.e., Landmannaluagar) and the scar of one of the most violent eruptions ever (i.e., Laki)!
This post is part 3 in the continuation of my series “How to explore Iceland through the eyes of a geologist” which is based on the field trip to Iceland that I co-organized as part of our university’s SEG student chapter. For an intro to the geology and tectonic setting of Iceland, check out my first post here and my second post here.
Part 1: A Land of Ice and Fire
(Intro to Iceland, Reykjavík, the Golden Circle, Snæfellsnes Peninsula)
Part 2: Volcanic Landscapes of the North
(Mývatn, Dimmuborgir, Krafla, Námafjall, and Askja)
Part 3: Glaciers and Volcanoes of the South
(Nornahraun 2014/15 lava field, Central Highlands, Landmannaluagar, Laki, Vík)
Part 3: Glaciers and Volcanoes of the South
There are some pretty hairy river crossings when traveling through the north centre of Iceland. The main road is F88 and requires a 4-wheel drive vehicle… and a bit of courage. These roads are also frequently closed due to floods and bad conditions, so make sure to check ahead of time if it’s good to go.
Holuhraun (aka. Nornahraun) lava field
The most recent eruption in Iceland was part of the 190 km long Bárðarbunga volcanic system, located in the rift zone part of the Eastern Volcanic Zone. One third of the volcanic system lies below the Vatnajökull ice cap. On August 16th 2014, intense earthquake swarms associated with magmatic activity and deformation were detected at the Bárðarbunga system (Sigmundsson et al., 2014). Over the next 13 days dykes propagated 45 km northeast to the Holuhraun lava field where it breached the surface and formed a small 4 hour effusive eruption (Dumont et al., 2015). A couple days later, more intense gas-rich eruptions started and continued until February 27th 2015. What remains now is a tholeiite basalt lava field that is more than 84 km2. Textures of the lava vary from a’a to slabby pahoehoe (Lavallee et al., 2015).
The volcanic eruption also produced large amounts of wind-spun, thread-like tephra known as Pele’s hair. In Icelandic, Pele’s hair is known as Nornahár, which means “witches’ hair”, and thus the new official name of the lava field is Nornahraun or “witches’ lava” (Thordarson, 2015).
Ice caps and glaciers
Heading south through the interior of Iceland reveals some of the most amazing glaciers and ice caps. The largest glacier, which covers a fair bit of Iceland, is Vatnajökull. Two of the other large glaciers are Mýrdalsjökull and Eyjafjallajökull. Active volcanoes are often underneath these ice caps. Eyjafjallajökull (a tongue twister of a name to pronounce), for example, is where the infamous 2010 eruption occurred. This dispersed volcanic ash into the atmosphere which eventually reached Europe and caused a shut down in air traffic for a week! Recently there have been reports on some rumbling at the even larger neighboring Katla volcano…
Further along south is the 8 km long Sólheimajökull temperate outlet glacier, which descends from ~ 1500 m at its parent glacier Mýrdalsjökull, to ~ 100 m (Russell et al., 2010).
Landmannalaugar (yet another Icelandic name that is a mouthful to pronounce), is a geothermally active area in Iceland know for its amazing colourful mountains. Whereas most of Iceland is composed of mafic rocks, the Landmannalaugar area (i.e., within the Torfajökull central volcanic complex) has the most silicic rocks in Iceland. It has been active for ~ 1 million years, and more than 250 km3 of rhyolite has been erupted in numerous, mostly sub-glacial eruptions (Sæmundsson, 1972; McGarvie, 1985). An example of one of the rhyolitic mountains is Bláhnjúkur. Bláhnjúkur formed by a sub-glacial rhyolitic eruption, which overlaid older rhyolite.
The Námshraun lava flow at Landmannalaugar is an interesting mixed compositions lava flow. It is a mixed rhyolite-basalt composition. It is volumetrically dominated by metaluminous rhyolite, with sub-decimetre scale inclusions of icelandite and basaltic icelandite, which may have increased the temperature of the original magma and influenced its rheology (Wilson et al., 2007).
Laki is one of the most impressive sites in Iceland, as here remains the preserved scar that really gives you a sense of how destructive these volcanic eruptions can be. The Laki fissure eruption occurred over an 8 month period in 1783 to 1784. It occurred along ten en-echelon fissure segments that opened toward the northeast to form a 27 km long cone row. There were over 140 eruption sites which include scoria cones, spatter cones, and tuff cones. The most common features are the scoria cones (40 to 120 m high) which consist of several thick (2 to 15 m) scoria fall layers, and capped by a thin (0.5 to 1.5 m ) spatter layer (Thordarson and Self, 2003).
The Laki eruptions were the second largest basaltic lava flow in historic times. It produced 10 to 13 km high columns of volcanic ash and SO2 that dispersed into the westerly polar jet steam to then be dispersed over Europe. The produced sulfur emissions casted a veil over Europe and caused climate perturbations, including a drop in temperature of 1.3°C for 2 to 3 years (Thordarson and Self, 2003). The noxious fumes emitted by the eruption also stunted grass growth and killed more than half of the livestock in Iceland through fluorine poisoning. The consequences ultimately resulted in the disastrous ‘Haze Famine’ that killed 20% (10,000 folks) of the Icelandic human population (Thordarson and Hoskuldsson, 2002).
Lastly along the south coast, near Vik, there are more beautiful examples of columnar basalt… as well as puffins you can spot if you get lucky!
Some of the major waterfall in the area are Fagrifoss “beautiful falls” and Skogáfoss. Skogáfoss is sourced from both Mýrdalsjökull and Eyjafjallajökull glaciers and travels down the Skóga River (Jóhannesson and Sæmundsson, 2009). The cliffs that Skogáfoss fall over (60 m tall) represent the former shoreline of Iceland before sand-rich deposits from recent jökulhlaup (i.e., catastrophic floods) extended the islands length to the south.
Final Thoughts: Iceland’s precarious position on the Mid-Atlantic Ridge has lead to a constantly changing landscape formed from violent volcanism. This post concludes my 3-part geology series of Iceland. I hope I have shed a bit of “geological” light on this dramatic, volcanic, island country that is Iceland! Even though I covered a fair bit of ground, there is still so much more to see and explore in Iceland (hence I would love to return one day). I regard Iceland as one of the neatest places I have ever travelled to, and I reckon that anyone who travels there would have a similar feeling, whether you are a geologist or not!
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Table of Icelandic Geology Terms
|á (s) ár (pl), fljót (large river)||River|
|aur (glacial outwash)||Sandur|
|bjarg (s), björg (pl)||Cliffs/Rocks/Crags|
|borg (s), borgir (pl)||Rocky hill|
|eldborg (s), eldborgir (pl)||Lava ring|
|fjall (s), fjöll (pl)||Mountain|
|vatn (s), vötn (pl)||Lake|
|víti (also used for explosive volcanic craters or maars)||Hell|
|völlur (s), vellir (pl)||Field/plain|