Fagradalsfjall is an active tuya volcano formed in the Last Glacial Period on the Reykjanes Peninsula, around 40 kilometres (25 mi) from Reykjavík, Iceland. Fagradalsfjall is also the name for the wider volcanic system covering an area 5 kilometres (3 mi) wide and 16 kilometres (10 mi) long between the Eldvörp–Svartsengi and Krýsuvík systems. The highest summit in this area is Langhóll. No volcanic eruption had occurred for 815 years on the Reykjanes Peninsula until 19 March 2021 when a fissure vent appeared in Geldingadalir to the south of Fagradalsfjall mountain. The 2021 eruption was effusive and continued emitting fresh lava sporadically until 18 September 2021.

A tuya is a flat-topped, steep-sided volcano formed when lava erupts through a thick glacier or ice sheet. They are rare worldwide, being confined to regions which were covered by glaciers and had active volcanism during the same period.