Brennisteinsfjöll

Brennisteinsfjöll
	View over the pseudocraters Rauðhólar, located in lavas of the same volcanic system, to the Bláfjöll and part of the actual Brennisteinsfjöll in the background
height	621 m
location	Iceland
Mountains	Brennisteinsfjöll
Coordinates	63 ° 55 '12 " N , 21 ° 49' 48" W Coordinates: 63 ° 55 '12 " N , 21 ° 49' 48" W.
Type	Crevasse volcano
Last eruption	1341 (active)

Brennisteinsfjöll to the left behind the Hellisheiði power station, which uses its energy with a few boreholes

The volcanic system of the Brennisteinsfjöll , to which the mountain range of the same name belongs, is located in Iceland . It is located in the southwest of the island about 20 km away from the capital Reykjavík on the Hellisheiði plateau and southwest of the Hengill volcano system to which it is adjacent.

location

The Brennisteinsfjöll are located approx. 20–40 km southeast of Reykjavík on the border between the districts of Gullbringasýsla in the west and Árnessýsla in the east.

Brennisteinsfjöll volcanic system

Delimitation: mountain massif and volcanic system

It is necessary to distinguish the Brennisteinsfjöll mountain range, which runs from SW to NE on the east side of Lake Kleifarvatn , from the volcanic system of the same name.

The mountain massif of the same name is located in the municipality of Grindavíkurbær and a small part in the municipality of Ölfus ; it is shorter than the active volcanic system following a column , which also includes the mountain range of Bláfjöll (in the municipality of Reykjavíkurborg , Kópavogur and Ölfus).

The volcanic system belongs to the Western Volcanic Zone of Iceland - like most of the volcanic systems active in Iceland today, it is elongated and laid out in a SW-NE direction.

The volcanic system stretches from the east bank of Lake Kleifarvatn to about the ring road on Hellisheiði , a little west of it, however, further parallel to the Hengill system up to Mosfellsheiði . At the level of the power station, the ring road forms the boundary between this and the adjacent system of the Hengill. The Vífilsfell tabular volcano west of the Hringvegur still belongs to the Brennisteinsfjöll system, while the Reykjafell mountain with the old ski hotel on the east side of the Hringvegur belongs to the Hengill system.

Basic characteristics

The Brennisteinsfjöll system does not have an actual central volcano and - as far as is known - has only produced mafic magmas, not Felsic . Basalt rocks with different compositions are therefore typical. The igneous rocks to be found in the area of the volcanic system are mainly hyaloclastites and lavas from interglacial ages , some of which are covered by modern lavas.

Since this is a part of the Mid-Atlantic Ridge lying on Reykjanesskagi , a plate-tectonically active zone, one can also find tectonically induced earthquakes and swarms of earthquakes. A known tectonic fold runs z. B. in NS direction from Stóra-Kongsfell to the south and west of the Heiðin há shield volcano . There you put z. B. At the end of August 2012 a new series of earthquakes began, which began with a stronger earthquake of magnitude 4.6.

The active center of the system, if not yet a properly developed central volcano, is the Heiðin há shield volcano , on the western side of which there is also a high-temperature area.

Types of volcanoes

The oldest recorded types of volcanoes in the Brennisteinsfjöll system are Tuyas and hyaloclastite ridges or cones from the Ice Age.

The occurring interglacial and post-glacial volcanoes include shield volcanoes , volcanic crevices and rows of craters .

Eruption story

Overall, traces of around 20-30 series of eruptions have been found in the volcanic system, of which around 10 took place after the colonization of Iceland.

Lava flows from here last flowed to the sea in the late Middle Ages - more precisely in the 14th century - and formed lava falls on the steep slopes similar to those on Snæfellsnes , which have been preserved in a hardened state.

Well-known eruptions begin about 7000 years ago with an eruption on the Heiðin há shield volcano, which is part of the Brennisteinsfjöll volcanic system . It is an eruption that came out of the main crater, but also from crevices and produced lava flows. A lava lake was also created. The volume of the eruption was 980 million m³.

About 4600 years ago, there was an eruption in the Leitin shield volcano , which is part of the system , and it was an effusive eruption that produced 300 million m³ of lavas. This eruption is mainly known because its lavas crossed today's urban area of Reykjavík until they poured into the sea ( Faxaflói ) in the Elliðavogur bay, which is also in the urban area . The eruption also formed the Rauðhólar pseudocrater groups .

The cinder crater Eldborg í Bláfjöllum was formed about 3040 years ago. The fissure eruption produced about 70 million m³ of lavas.

The eruption of the Tvíbollar crater group at the time of the conquest of Iceland around 875 AD was also a fissure eruption (37 million m³).

Further eruptions took place in the years 910 (volcano Kista, lava field Breiðdalshraun ).

To 960 the number of craters produced Tvíbollar the Pahoehoe -Lavafeld Hellnarhraun in Hafnarfjordur .

In the year 1000, after another eruption from two small craters in the valley south of the Vífilsfell, the Svínahraun lava field was created , over which the Hringvegur runs at the Hellisheiðarvirkjun power station and which is also called Kristnitökuhraun (= the lava field of the acceptance of Christianity) because a messenger passes over it its origin in the parliament in Þingvellir reported when negotiations were being carried out on the general acceptance of Christianity by the population.

The last lava fields created in the Brennisteinsfjöll system date from 1200 and 1341. The latter, the Selvogshraun , embodies the last volcanic eruptions on the Reykjanes peninsula to date . However, H. Torfason, ea, consider the lavas of Selvogshraun to be older (originated before 1226, as they were covered by a known layer of ash from 1226).

Another well-known group of craters or hyaloclastite domes are the eigentríhnúkagígar in the actual Brennisteinsfjöll west of the Bláfjöll ski area. At one of the craters, the Þríhnúkagígur , the magma slot is now accessible.

Use of the volcanic system

Brennisteinn is the Icelandic word for sulfur . In the 19th century there was a sulfur mine in Brennisteinsfjöll, which was run by the English. However, around 1880 it was given up again because exploitation was no longer profitable.

Today, the Bláfjöll , another volcanic mountain range that forms part of the same volcanic system, is a well-known ski area. The whole area is partly within four different nature reserves and is used for hiking. For example, an old connection route, the Selvogsgata, serves this purpose.

High temperature area

A high-temperature area lies at heights between 420 and 450 m at the foot of the Kistufell and the Heiðin há with corresponding sulfur precipitations , hence the name of the volcanic system (German sulfur mountains ).

Around 1880 the sulfur was extracted there by the English. There was a mine below the eastern slopes, but it didn't pay off for long.

The lake Ástjörn

20 m above sea level M. is the small lake Ástjörn (5 ha) in the area of the town Hafnarfjörður.

It was formed about 3,000 years ago when pahoehoe lavas flowed west of Mount Ásfjall from Brennisteinsfjöll to the sea and dammed the drain. The lava field called Skúlatúnshraun extends between the town of Hafnarfjörður and the aluminum plant in Straumsvík . The pond changed due to the influence of other thin-flowing lavas during a series of eruptions in the Brennisteinsfjöll around the year 950.

Like most of the lakes on the Reykjanesskagi peninsula, it has no runoff, but adapts to the respective groundwater level.