Grímsnes

Coordinates: 64°2′N 20°52′W / 64.033°N 20.867°W / 64.033; -20.867
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For the cargo ship, see SS Grimsnes.
Grímsnes
Kerið - One of many volcanic craters within the volcanic system.
Highest point
Elevation200 metres (660 ft)SFr Jakobsson
Coordinates64°2′N 20°52′W / 64.033°N 20.867°W / 64.033; -20.867
Geology
Mountain typeCrater rows
Last eruption~3500 BCE
Map
Selected geological features near the Grímsnes volcanic system (red outline) and its Holocene lava flows (violet shading). Other shading shows:    calderas,   central volcanoes and   fissure swarms,   subglacial terrain above 1,100 m (3,600 ft), and   seismically active areas. Clicking on the image enlarges to full window and enables mouse-over with more detail.[1]

Grímsnes (Icelandic pronunciation: [ˈkrimsˌnɛːs] ⓘ) is a relatively small fissure or crater row volcanic system located in South Iceland, located south–east of Lake Thingvallavatn and east of the en echelon group of volcanic systems extending across the Reykjanes Peninsula, that erupted last in the Holocene.

Geography[edit]

The lava fields are spread out to the south-east of the older edifice of Búrfell (Grímsnes) being bounded to the east by the water body of Álftavatn,[2]: ID 99907  on the river Sog(Sogið) [3] and reaches to the south the confluence of the Sog with the Hvítá. From these river boundaries at about 20 m (66 ft) the field reaches its highest point at the Seyðishólar cone of 214 m (702 ft).[4][2]: ID 7002  Most of the lava fields are covered by birch and willow.[3]

Geology[edit]

Tephrochronology approximates the volcano's last eruption as about 7000 years ago.[5] There are at least ten vents and all have erupted olivine tholeiite basalt in effusive eruptions although one small tephra eruption is known.[3][6] It has been classified as part of the Western Volcanic Zone,[7] but is also part of the South Iceland seismic zone.[5] The northern parts of the lava fields overlay lava fields erupted before the last ice age by the shield volcano Lyngdalsheiði to the north.[2]: ID 78047  This is known as the maar volcanic crater of Kerið towards the middle of the field has 7–8 m (23–26 ft) of the distinctive Lyngdalsheiði basalt exposed.[4] The maar has a total depth of 55 m (180 ft) with 10 m (33 ft) being water filled.[8]. In a crater row line extending 800 m (2,600 ft) to the south–east from Kerið are the Tjarnarhólar craters. These erupted what was historically called the Tjarnarhólahraun lavas extending mainly to the south of about 12 km2 (4.6 sq mi), now covered by up to four more recent lava flows in part.[8] This central area of the field also has the vent Rauðhólar to the south–east,[9] that contributed some of the youngest lavas in the area, which as they cover other lavas mainly are also known as the Rauðhólahraun flow,[10] although true young Rauðhólar lava flows that erupted more recently that 7050 BP at a volume of 0.009 km3 (0.0022 cu mi) are much smaller.[9][11] To the east of the Rauðhólar vent is the also young Kolgrafarhóll vent and east of that the Selhóll I (Selhóll south) vent that is one of oldest vents and erupted 0.01 km3 (0.0024 cu mi) more than 9500 years BP (cal).[11] Kolgrafarhóll also is a small eruption at 0.004 km3 (0.00096 cu mi) more recent than 7050 years BP (cal).[11] To the south of Selhóll I is the most southern vent of the field Álftarhóll (Álftarhólar) that produced the larger 6.2 km2 (2.4 sq mi) (0.126 km3 (0.030 cu mi)) Álftarhólshraun flow,[12] that is less than 7050 years BP (cal).[11]

The most eastern vent and its Borgarhólar lava field is isolated at Borgarhóll with a small eruptive volume of 0.03 km3 (0.0072 cu mi) and dated to 8200 years BP (cal).[11]

The largest lava field to the north and east of Kerið is the 23.5 km2 (9.1 sq mi) Seyðishólar-Kerhólahraun field. Its vents are Seyðishólar that produced a volume of 0.26 km3 (0.062 cu mi) dated accurately by tephrochronology to 9500 years BP (cal) and Kerhóll that produced a volume of 0.36 km3 (0.086 cu mi) also dated well to 7050 years BP (cal).[11] The Kálfshólar vent just to the east of Seyðishólar and Kerhóll produced the Kálfshólahraun field that flowed to the east to the Sog withan area of 8.0 km2 (3.1 sq mi) (0.14 km3 (0.034 cu mi)) and is more recent than than 7050 years BP (cal).[9][11]. 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 0.04 km3 (0.0096 cu mi).[11][9]

The total volume of lava produced in the lava flows of Grímsnes has been estimated at 1.2 cubic kilometres (0.29 cu mi).[13]

References[edit]

  1. ^ Óskarsson et al. 2022.
  2. ^ a b c "National Land Survey of Iceland (Kortasja)". 2024. Retrieved 2024-05-08.
  3. ^ a b c Jakobsson 1966, p. 5.
  4. ^ a b Jakobsson 1966, p. 6.
  5. ^ a b Jakobsson & Larsen 2019, Short Description.
  6. ^ Jakobsson & Larsen 2019, Detailed Description:1. Geological setting and tectonic context.
  7. ^ Sinton, Grönvold & Sæmundsson 2005, Fig. 1.
  8. ^ a b Jakobsson 1966, p. 11.
  9. ^ a b c d Jakobsson 1966, Pt. V..
  10. ^ Jakobsson & Larsen 2019, Detailed Description:Map Layers.
  11. ^ a b c d e f g h Jakobsson & Larsen 2019, Detailed Description: Eruption history and pattern.
  12. ^ Jakobsson 1966, pp. 14–15.
  13. ^ Jakobsson & Larsen 2019, Detailed Description:4. Eruption history and pattern.

Sources[edit]

See also[edit]

External links[edit]


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