Hrómundartindur (Icelandic pronunciation: [ˈr̥ouːˌmʏntarˌtʰɪntʏr̥] ) is a mountain in Iceland north of Hveragerði with an elevation of 540 metres (1,770 ft).[1] It to the east of Hengill and is the central volcano of an adjacent 25 km (16 mi) long Hrómundartindur volcanic system, which contains the Ölkeduháls geothermal field.[3][1] Like Hengill this area is close to the south-eastern triple junction of the Hreppar microplate, is seismically active, and associated with the Western volcanic zone and the South Iceland seismic zone.[3] To the north-east are multiple tindars,[3] and there is a Holocene lava flow called Tjarnahnúkshraun which covers 4 km2 (1.5 sq mi) with a volume of 0.03 km3 (0.0072 cu mi).[4][3] The lava ranges from picrite basalt, being predominantly tholeiite basalt with some basaltic andesite.[3]
During 2017 and 2018 GPS and seismic studies were consistent with either hydrothermal fluid or magma increase at a depth of approximately 5–7 km (3.1–4.3 mi) within the inferred brittle-ductile transition zone of the area centred at Ölkelduháls, between Hengill and Hrómundartindur. This volume had had been contracting between 2006–2017, and was about 3 km (1.9 mi) north-west from an area of uplift between 1993 and 1999.[5]