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.

[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.

[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 is part of the many vent Rauðhólahraun [ˈrœyðˌhouːlaˌr̥œyːn] flow,[10] although true young Rauðhólar [-ˌhouːlar̥] lava flows (Svönkuhraun [ˈsvœyŋkʏˌr̥œyːn]),[2]: ID 84336  that erupted more recently that 7050 BP, at a volume of 0.009 km3 (0.0022 cu mi) are much smaller.

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] To the east of this is Rauðhóll [ˈrœyðˌhoutl̥] (Kerlingarhóll [ˈcʰe(r)tliŋkarˌfjœtl̥]) lava field (Rauðhólshraun [-ˌhoulsˌr̥œyːn]) dated earlier than 7050 BP (cal).