__NOTOC__ The Hofsjökull volcanic system (also Hofsjökull-Kerlingarfjöll volcanic system) contains the largest active

central volcano A central volcano is a type of volcano formed by basalts and silica-rich volcanic rocks. They contain very few or no volcanic rocks of intermediate composition, such that they are chemically bimodal volcanism, bimodal. Large silicic eruptions at c ...

Iceland Iceland is a Nordic countries, Nordic island country between the Atlantic Ocean, North Atlantic and Arctic Oceans, on the Mid-Atlantic Ridge between North America and Europe. It is culturally and politically linked with Europe and is the regi ...

. It is called

Hofsjökull __NOTOC__ Hofsjökull (Icelandic language, Icelandic: "temple glacier", ) is the third largest ice cap in Iceland after Vatnajökull and Langjökull and covers the largest active central volcano in the country, which has the same name. It is si ...

( Icelandic: "

temple A temple (from the Latin ) is a place of worship, a building used for spiritual rituals and activities such as prayer and sacrifice. By convention, the specially built places of worship of some religions are commonly called "temples" in Engli ...

glacier", ), after the icecap of the same name. The system is in the west of the

Highlands of Iceland The Highland (Icelandic language, Icelandic: ''Hálendið)'' or The Central Highland is an area that comprises much of the interior land of Iceland. The Highland is situated above and is mostly uninhabitable. The soil is primarily volcanic as ...

and north of the dormant central volcano of

Kerlingarfjöll Kerlingarfjöll () is a tall volcanic massive in Iceland situated in the Highlands of Iceland near the Kjölur highland road. It is usually regarded as part of a large tuya fissure system of in the southern portion of the Hofsjökull volcanic ...

), which is usually regarded as part of the same volcanic system.

Activity

The volcanic system has for Iceland, low activity. There are high temperature geothermal areas associated with the Hofsjökull central volcano, its northern fissure swarm, and

to its south. A sulfurous

jökulhlaup A jökulhlaup ( ) (literally "glacial run") is a type of glacial outburst flood. It is an Icelandic term that has been adopted in glaciological terminology in many languages. It originally referred to the well-known subglacial outburst floo ...

occurred in the summer of 2013, from the Hofsjökull glacier with a new ice cauldron being formed at the north-east edge of the Hofsjökull central volcano's caldera. There have been earthquake swarms in the period 1996 to 2013 on the western and northern flanks of the Hofsjökull central volcano, extending to the northern fissure swarm but only isolated earthquakes under Kerlingarfjöll to the south. The last effusive eruption was just to the north of the Hofsjökull icecap between 3000 and 4500 years ago.

Geography

The two central volcanoes are mountain massifs. Hofsjökull is between in diameter. From Hofsjökull, fissure mapping has defined fissure swarms that trend NNW-SSE in the north and SW-NE in the south. These extend to the south-west and south by about . Fissure swarms extend to the north by . The Hofsjökull central volcano caldera is located under the south-west portion of the icecap and is wide and about deep.

Nunatak A nunatak (from Inuit language, Inuit ) is the summit or ridge of a mountain that protrudes from an ice field or glacier that otherwise covers most of the mountain or ridge. They often form natural pyramidal peaks. Isolated nunataks are also cal ...

s exposed on the caldera rim are high but probable rim height is about from subglacial mapping that also reveals a maximum thickness of ice of . There are post ice–age lava flows to the south, east and north of the Hofsjökull central volcano. Kerlingarfjöll, is eroded, and about in diameter.

Geology

The central volcanoes have

tholeiite basalt The tholeiitic magma series () is one of two main magma series in subalkaline igneous rocks, the other being the calc-alkaline series. A magma series is a chemically distinct range of magma compositions that describes the evolution of a mafic ...

and

rhyolite Rhyolite ( ) is the most silica-rich of volcanic rocks. It is generally glassy or fine-grained (aphanitic) in texture (geology), texture, but may be porphyritic, containing larger mineral crystals (phenocrysts) in an otherwise fine-grained matri ...

components. In the case of Kerlingarfjöll which is not covered by of ice, the rhyolite is found close to the two central caldera. Kerlingarfjöll, is between 68 and 350 thousand years old. In the case of Hofsjökull the basaltic

hyaloclastite Hyaloclastite is a volcanoclastic accumulation or breccia consisting of glass (from the Greek ''hyalus'') fragments (clasts) formed by quench fragmentation of lava flow surfaces during submarine or subglacial extrusion. It occurs as thin marg ...

deposits have rhyolite outcrops at the margins of the glacier, on some of the nunataks east of the caldera, and at the Arnarfell peak at the south-east margin of the glacier. Fissure vents that have erupted basalts form

tuya A tuya is a flat-topped, steep-sided volcano formed when lava erupts through a thick glacier or ice sheet. They are rare worldwide, being confined to regions which were covered by glaciers and had active volcanism during the same period. As lava ...

's to the south. The largest tholeiite basalt lava flow that originates in the southern fissure swarm to the south of Hofsjökull is the 4500 to 7000 years old Illahraun lava, with a composition distinct from Kerlingarfjöll (to its south–west) and covers about . The fissure swarms and a radial pattern of dike intrusions appear to radiate away from the Hofsjökull central volcano suggesting that it is a significant local stress field. To the south the wide western part of the fissure swarm has multiple mainly mostly tensional faults orientated at 30° that are traceable as they extend across the

Langjökull Langjökull (, Icelandic for "long glacier") is the second largest ice cap in Iceland (), after Vatnajökull. It is situated in the west of the Icelandic interior or Highlands of Iceland and can be seen clearly from Haukadalur. It covers the ...

volcanic system's 10,000 years ago origin Kjalhraun lava shield. The south-western part of the southern fissure swarm is orientated at 40° and after a shadow to the south produced by the older Kerlingarfjöll the rest of the southern swarm which is about wide, is orientated at 50°. The northern fissure swam is orientated perhaps at -10° from north with a wider spread.

Tectonics

The Hofsjökull volcanic system is found on the north-eastern edge of the

Hreppar microplate The geological deformation of Iceland is the way that the rocks of the island of Iceland are changing due to tectonic forces. The geological deformation help to explain the location of earthquakes, volcanoes, fissures, and the shape of the island. ...

, so has the North American Plate to its north and the Eurasian Plate to its east. It is classified as being in the Mid-Iceland belt that connects the Western volcanic zone to the intersection of the

Northern volcanic zone The Andean Volcanic Belt is a major volcanic belt along the Andean cordillera in Argentina, Bolivia, Chile, Colombia, Ecuador, and Peru. It is formed as a result of subduction of the Nazca plate and Antarctic plate underneath the South America ...

and the Eastern volcanic zone. The

moho Moho may refer to: Birds * ''Moho'' (genus), an extinct genus of birds in the family Mohoidae * The Hawaiian name of the Hawaiian rail, an extinct species * The Māori name of the North Island takahē, an extinct species * A local name for the o ...

is over deep under Kerlingarfjöll and at the north-east coroner of the system is over deep. The pole of relative rotation of the Hreppar microplate is near the Hofsjökull volcanic system. This implies by geometry that the relative plate velocity across this region is small which geologists usually predict means little seismic or volcanic activity. However the system is also over the current north-eastern area of the

Iceland hotspot The Iceland hotspot is a hotspot that is partly responsible for the high volcanic activity that has formed the Iceland Plateau and the island of Iceland. It contributes to understanding the geological deformation of Iceland. Iceland is one ...

Glacier

The icecap covers an area of about , with the icecap top being .

References

Sources

* * * *

External links

Hofsjökull
in the

Catalogue of Icelandic Volcanoes The Catalogue of Icelandic Volcanoes (CIV) is a web resource that was created to serve as an official source of information about potentially active volcanoes monitored by Iceland. The creation of the website followed the disruptive 2010 eruption ...

* {{DEFAULTSORT:Hofsjokull Highlands of Iceland Mid-Iceland Belt Subglacial volcanoes of Iceland Volcanic systems of Iceland Calderas of Iceland Central volcanoes of Iceland