Hrómundartindur

Hrómundartindur is a mountain in Iceland north of Hveragerði  with an elevation of 540 m. It to the east of Hengill and is the central volcano of an adjacent 25 km long Hrómundartindur volcanic system, which contains the Ölkeduháls geothermal field. 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. To the north-east are multiple tindars, and there is a Holocene lava flow called Tjarnahnúkshraun which covers 4 km2 with a volume of 0.03 km3. The lava ranges from picrite basalt, being predominantly tholeiite basalt with some basaltic andesite.

Activity
During 2017 and 2018 GPS and seismic studies were consistent with either hydrothermal fluid or magma increase at a depth of approximately 5 – 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 north-west from an area of uplift between 1993 and 1999.