The Hveravellir central volcano lies at the northern end of an active volcanic zone that extends to the NE from the Reykjanes Peninsula. Hveravellir central volcano occupies the NE half of the massive Langjökull icecap, east of the prominent Pleistocene table mountain, Erikskökull. A summit caldera lies beneath the ice. The Kjalhraun shield volcano east of Langjökull produced about 11 cu km of lava about 7800 years ago. Several small shield volcanoes have been constructed along flank fissure zones, producing postglacial lava flows that flank Langjökull on the northern, western, and eastern sides. One of the most prominent of these is a small shield volcano that was formed at the site of the massive Hallmundahraun lava flow, which covers about 240 sq km and was erupted about 950 AD. The Geysir thermal area, containing Iceland's largest geysers, lies in the Haukadalur basin, near the southern end of the lengthy fissure system extending from the Hveravellir central volcano.