Selected geological features near the Brennisteinsfjöll volcanic system (approximate outline in red). Clicking on the image enables mouse-over with more detail where shading also shows: other fissure swarms, central volcanoes, calderas subglacial terrain above 1,100 m (3,600 ft), seismically active areas between 1995 and 2007.
The mountain range is located at about 20 to 25 km (12 to 16 mi) from Reykjavík as well as Hafnarfjörður and to the south of the cities on the Reykjanes peninsula of Southwest Iceland.[2]
Brennisteinfjöll is not high. The highest mountain is Vífilsfell with 655 m.[3]
Geology
Position within Iceland’s volcano-tectonic environment
In Iceland there are about 32 volcanic systems.[1] Volcanic system means a volcano-tectonic fissure system and – very often a bigger volcano, a so-called central volcano which in most cases is a stratovolcano and may contain a caldera.[4] Brennisteinsfjöll does not include such a central volcano.[1] The existence of the fissure systems in Iceland is explained by its situation, located on top of the Mid-Atlantic Ridge, a divergent plate boundary. There is most probably also a magmatic hot spot under the island which stands for increased magma production.[5]
These volcanic systems are arranged en echelon and in a ca. 45° angle to the direction of rifting, scientists define this as an oblique arrangement.[8] The volcanic systems of Reykjanes, Brennisteinsfjöll included, are stretched out in northeast-southwesterly direction over the rift on the peninsula.[7]
General description of the Brennisteinsfjöll volcanic system
The volcanic system of Brennisteinsfjöll is 45 km (28 mi) long, has a width of about 10 km (6.2 mi) and covers about 280 km2 (110 sq mi). Most to the south are the Stóra Eldborg crater row and to the north Nyðri Eldborg.[9] The volcanic system was the most productive of all the volcanic systems of the Reykjanes peninsula during the Holocene with 30-40 eruptions and around 10 since the settlement of Iceland in the 9th century.[9]
Eruptions and current situation
One of the bigger lava flows of the system run south from Brennisteinsfjöll to the coast at Herdísarvík bay forming lava falls on their way.[10] Previously it was thought that this lava flow had ceased before the settlement of Iceland (i.e. the end of the 8th century), but this is now thought that this was not the case as the coastal trail (now Route 42) was covered in lava at one stage.
The last eruption in the Brennisteinsfjöll volcanic system was a VEI-2 eruption in 1341.[11]
It is a possible cause of St. Mary Magdalene’s flood 1342 in Central Europe und following bad years with Black Death to 1350.
Brennisstein is the word for sulfur on Iceland, so great sulfur emissions with worldwide cooling for some years are possible and quite normal by this volcanic system.
There is a high temperature geothermal area in Brennisteinsfjöll, but it is rather remote, about 20 km (12 mi) southeast of Reykjavík in the inner part of the Reykjavík peninsula.[12] Fumaroles are to be found within an area of a few acres, and two more areas show signs of hydrothermal alteration. The surface conditions are complicated with a rough lava surface and the geothermal features which are located at a height of 450–500 m (1,480–1,640 ft) can only be reached on foot.[12] The stratigraphy of the region includes hyaloclastite, older and younger lava flows.[12]
In a fault, not far from Grindarskörð [ˈkrɪntarˌskœrθ], there are traces of a former geothermal area which is no more active.[12]
Sulfur mining
As the name (Brennisteinsfjöll = Sulfur Mountains) suggests, sulfur is found here, though today in small amounts.[1] But in the 19th century, a sulfur mine was run in the region by people from the United Kingdom.[13] Mining was carried out just til the 1880s.[12]
The mine was situated in a lava slope. The sulfur “was deposited into holes and fractures in the lava and between lava layers”.[12] It was therefore difficult to reach and mine. The miners had first to break up the lava to get to the sulfur.[12] The current geothermal activity is above this area.[12]
The place of the former mine can be found by hiking the old trail Selvogsgata [ˈsɛlˌvɔksˌkaːta] and the following the so-called Draugahlíðar [ˈtrœyːɣaˌl̥iːðar̥] between the lava and the slope. There are still some ruins of the former mine and traces of transportation paths.[12]
Known mountains, craters and other volcanic landforms
Some protected areas are to be found in the region of Brennisteinsfjöll. These are Herdísarvík Nature Reserve, Reykjanes Country Park, Bláfjöll Country Park and the two Natural Monuments Eldborgir undir Geitahlíð and Eldborg í Bláfjöllum.[12][16]
^ abcdef[1]Archived 2017-02-04 at the Wayback Machine Brennisteinsfjöll. Detailed description. In: Catalogue of Icelandic Volcanoes. Retrieved 27 July 2020
^Íslandshandbókin. Náttúra, saga of sérkenni. Reykjavík 1989, p.44-45
^Ari Trausti Guðmundsson, Pétur Þorsteinsson: Íslensk fjöll. Gönguleiðir á 152 tind. Reykjavík 2004, p. 300
^Þorleifur Einarsson: Geology of Iceland. Rocks and landscape. Reykjavík 1991, pp.61–63
^Thor Thordarson, Armann Hoskuldsson: Iceland. Classic geology of Europe 3. Harpenden 2002, pp.6–8
^Thor Thordarson, Armann Hoskuldsson: Iceland. Classic geology of Europe 3. Harpenden 2002, p.9
^ abThor Thordarson, Armann Hoskuldsson: Iceland. Classic geology of Europe 3. Harpenden 2002, p. 14
^ abDaníel Páll Jónasson: Hraunflæði á höfuðborgarsvæðinu Saga hraunflæðis á svæðinu á nútíma og kortlagning mögulegra farvega til byggða. BS ritgerð. Leiðbeinandi:Ármann Höskuldsson. Háskóli Íslands, Reykjavík 2012.
^Íslandshandbókin. Náttúra, saga of sérkenni. Reykjavík 1989, p. 797