Grímsnes
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Grímsnes () is a relatively small
fissure A fissure is a long, narrow crack opening along the surface of Earth. The term is derived from the Latin word , which means 'cleft' or 'crack'. Fissures emerge in Earth's crust, on ice sheets and glaciers, and on volcanoes. Ground fissure A ...
or crater row volcanic system located in South
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 ...
, located south–east of Lake Thingvallavatn and east of the en echelon group of volcanic systems extending across the
Reykjanes Peninsula Southern Peninsula (, ) is an administrative unit and part of Reykjanesskagi (pronounced ), or Reykjanes Peninsula, a region in southwest Iceland. It was named after Reykjanes, the southwestern tip of Reykjanesskagi. The region has a populatio ...
, that erupted last in the
Holocene The Holocene () is the current geologic time scale, geological epoch, beginning approximately 11,700 years ago. It follows the Last Glacial Period, which concluded with the Holocene glacial retreat. The Holocene and the preceding Pleistocene to ...
.


Geography

The lava fields are spread out to the south-east of the older edifice of Búrfell being bounded to the east by the water body of Álftavatn , on the river Sog (Sogið) and reaches to the south the confluence of the Sog with the Hvítá. From these river boundaries at about the field reaches its highest point at the Seyðishólar cone of . Most of the lava fields are covered by birch and willow.


Geology

Tephrochronology 250px, Tephra horizons in south-central Iceland. The thick and light coloured layer at the height of the volcanologist's hands is rhyolitic tephra from Hekla. Tephrochronology is a Geochronology, geochronological technique for dating archaeolo ...
approximates the volcano's last eruption as about 7000 years ago. There are at least ten vents and all have erupted
olivine The mineral olivine () is a magnesium iron Silicate minerals, silicate with the chemical formula . It is a type of Nesosilicates, nesosilicate or orthosilicate. The primary component of the Earth's upper mantle (Earth), upper mantle, it is a com ...
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 ...
in effusive eruptions although one small tephra eruption is known. It has been classified as part of the Western Volcanic Zone, but is also part of the
South Iceland seismic zone 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. ...
. The northern parts of the lava fields overlay lava fields erupted before the last ice age by the
shield volcano A shield volcano is a type of volcano named for its low profile, resembling a shield lying on the ground. It is formed by the eruption of highly fluid (low viscosity) lava, which travels farther and forms thinner flows than the more viscous lava ...
Lyngdalsheiði to the north. This is known as the
maar A maar is a broad, low-relief volcanic crater caused by a phreatomagmatic eruption (an explosion which occurs when groundwater comes into contact with hot lava or magma). A maar characteristically fills with water to form a relatively shallow ...
volcanic crater A volcanic crater is an approximately circular depression in the ground caused by volcanic activity. It is typically a bowl-shaped feature containing one or more vents. During volcanic eruptions, molten magma and volcanic gases rise from an ...
of
Kerið Kerið (; also Kerith or Kerid) is a volcanic Volcanic crater lake, crater lake located in the Grímsnes area in south Iceland, along the Golden Circle (Iceland), Golden Circle. It is one of several crater lakes in the area, known as Iceland's W ...
towards the middle of the field has of the distinctive Lyngdalsheiði basalt exposed. The maar has a total depth of with being water filled.. In a crater row line extending to the south–east from Kerið are the Tjarnarhólar craters. These erupted what was historically called the Tjarnarhólahraun lavas, a name not currently used in this context, extending mainly to the south of about , now covered by up to four more recent lava flows in part. This central area of the field also has the vent Rauðhólar to the south–east, that contributed some of the youngest lavas in the area, which is part of the many vent Rauðhólahraun flow, although true young Rauðhólar lava flows (Svönkuhraun ), that erupted more recently that 7050 BP, at a volume of are much smaller. To the east of the Rauðhólar vent are the also young Kolgrafarhóll and Borgarhóll vents and east of that the Selhóll I (Selhóll south) vent that is one of oldest vents and erupted more than 9500 years BP (cal). Kolgrafarhóll had a small eruption at more recent than 7050 years BP (cal) and so did Borgarhóll . To the south of Selhóll I is the most southern vent of the field Álftarhóll (Álftarhólar ) that produced the larger () Álftarhólshraun flow, that is less than 7050 years BP (cal). The most eastern vent and its Borgarhólar lava field (Borgarhólahraun ) is separate from the rest of the Grímsnes lava fields with a small eruptive volume of and dated to 8200 years BP (cal). The largest lava field to the north and east of Kerið is the Seyðishólar-Kerhólahraun field. Its vents are Seyðishólar that produced a volume of dated accurately by tephrochronology to 9500 years BP (cal) and Kerhóll that produced a volume of also dated well to 7050 years BP (cal). The Kálfshólar vent just to the east of Seyðishólar and Kerhóll produced the Kálfshólahraun field that flowed to the east to the Sog within area of () and is more recent than 7050 years BP (cal).. The most northerly vent to the north of Kálfshólar is old at 9500 years BP (cal) or more and called Selhóll-north (Selhóll II) with a lava erupted volume of . To the east of this is Rauðhóll (Kerlingarhóll ) lava field (Rauðhólshraun ) dated earlier than 7050 BP (cal). The total volume of lava produced in the lava flows of Grímsnes has been estimated at .


References


Sources

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See also

*
Geography of Iceland Iceland is an island country at the confluence of the Atlantic Ocean, North Atlantic and Arctic Ocean, Arctic oceans, east of Greenland and immediately south of the Arctic Circle, atop the constructive boundary of the northern Mid-Atlantic Ridg ...
*
List of lakes of Iceland Iceland has over 20 lakes larger than 10 km2 (4 sq mi), and at least 40 others varying between 2.5 and 10 km2 (1 to 4 sq mi) in size. This list also includes a few smaller lakes and ponds that are considered notable (for example Tjörnin ...
*
Volcanism of Iceland :''The volcano system in Iceland that started activity on August 17, 2014, and ended on February 27, 2015, is Bárðarbunga.'' :''The volcano in Iceland that erupted in May 2011 is Grímsvötn.'' Iceland experiences frequent volcanic activity, ...
**
List of volcanic eruptions in Iceland This is an incomplete list of volcanic eruptions in Iceland. Please see External links below for databases of Icelandic eruptions which include over 530 events. ''For latest information about the current/ongoing series of eruptions near Grindav ...
**
List of volcanoes in Iceland There are too many presumed extinct or now inactive volcanic features to list all of these below, so most monogenetic volcanoes can not be mentioned individually. This list of volcanoes in Iceland only includes major active and dormant volcano, ...


External links


Grímsnes
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 ...

Volcano Live
* Volcanoes of Iceland Fissure vents Dormant volcanoes South Iceland Seismic Zone Volcanic systems of Iceland VEI-3 volcanoes {{DEFAULTSORT:Grimsnes