Tuesday, 26 July 2022

While I had intended to report on the trip in this blog, it turned out, since I was writing on my phone, to be easier to do a series of daily posts to Facebook. So this is the last bit on Iceland here, at least for the moment. I plan to edit and expand the FB posts, and will eventually post them here, or in a another of my blogs.

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Geology of the Peninsula*

*Much of this is adapted from https://en.wikipedia.org/wiki/Geology_of_Reykjanes_Peninsula

The Reykjanes Peninsula is the continuation of the submarine Reykjanes Ridge, a segement of the Mid-Atlantic ridge. It reaches from the Esja volcano in the north to hengill in the east and Reykhanesta in the west. It originated 6-7 Ma in a rift-jump, after the Snæfellsnes-Skagi rift had drifted to the west out of range of the presumed location of the mantle plume.

Reykjanes Peninsula was formed by glaciers and volcanism, with lava fields made of a characterisitic grey basalt. Volcanic systems are submarine, subglacial  (tuyas and hyaloclastic ridges or tindars) and subaerial (shield volcanoes).

Subglacial volcanos are either tuyas (larger, with subaerial ‘tops’) or subglacial cones (rare) or ridges (both, of course, consisting of hyaloclastite, lapilli tuff and pillow lavas)., Reykjanes examples include Sveifluháls, Núpshlíðarháls, Undirhlíðar , Helgafell and Vífilsfell. Most of these  volcanoes produce mafic basalt, though there are also some basaltic andesite or andesite volcanoes on Reykjanes, like Húsmúli and Stapafell in the Hengill Volcanic System.

Central shield volcanoes erupted after the Weichselian glaciation (<11-15Ka); they are situated at the periphery of fissure systems and have produced most of the volcanic landforms in the region.They are mostly circular and consisting of low cones and aprons of pahoehoe lavas; the older shields are made from picrite, the younger, bigger ones from olivine-tholeiite. Olivine tholeiites constitute about 60% by volume of all post-glacial lava products on the Reykjanes Peninsula.” Examples include Selvogsheiði, Þráinskjöldur , Heiðinhá and Sandfellshæð and Leitin.

Areas we will visit

Geldingadalur eruption site. Geldingadalur is an area on the Reykjanes Peninsula, notable for being home to the Fagradalsfjall volcano, which erupted in 2021. Geldingadalur’s 2021 Eruption. The Reykjanes Peninsula in southwest Iceland is a very volcanic area, renowned for its conic mountains, craters, hot springs, and lava fields.

Krýsuvík Geothermal Area. This is a fissure sytem without a central volcano. It includes an expanse of steaming volcanic vents, hot springs, mud pools, colorful crate lakes, all framed dramatically by a range of multi-coloured hills.  The Grænavatn, Gestsstaðavatn, and Augun lakes are old explosion craters formed by volcanic eruptions. Colors in springs and lakes are due to the presence of photpsynthetic thermal algae and dissolved minerals.The volcanic system has a length of 55 km, a width of around 13 km,and is arranged in en echelon and in a certain angle (20–45°) to the rift zone of the divergent plate boundary traversing Reykjanes.

The Seltún geothermal area is situated next to Krýsuvík at the foot of Sveifluháls hyaloclastite ridge. It is a geothermal high temperature ares fed by rain and snow melt (Guðmundsson, 2017)t. Here solfataras, fumaroles, mudpots and hot springs are formed; the soil is coloured bright yellow, red, and green caused by iron oxidation, sulfur and calcite precipitation. See: https://en.wikipedia.org/wiki/Kr%C3%BDsuv%C3%ADk_(volcanic_system)

Undirhlíðar glaciovolcanic ridge. A lava field formed around 1100 due to a fissure eruption underneath pillow-lava hills Undirhlíðar. The lava then flowed north of the cove to the sea, forming a spit. Kapelluhraun classifies as A’a or block lava; its phenocrysts mostly consist of plagioclase, pyroxene and olivine

Gunnuhver is an area of Reykjanes UNESCO Global Geopark with hundreds of mudpots, craters and lava fields, and black sand beaches, and other features such as geothermal energy generation. The groundwater at Gunnuhver consists to 100% of seawater. Carbon dioxide and hydrogen sulfide, accompanied gases, make the water acidic and alter the fresh lavas to clay. Throughout the entire hydrothermal field, evaporites and sulfuric minerals are visible. Metal ores, like copper sulfates, are more concentrated at depths. See https://geosturm.com/gunnuhver/

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