Hverahlíð south of highway 1, half an hour drive east of Reykjavík, is representative. Here, facing the north, the margin is round in outline. Hyaloclastite breccia crops out locally below the sheet lava of the shield, clearly foreset bedded where it is best exposed some 500 m east of a solitary cluster of fumaroles.
The lava shield, which is thought to date from the last glacial period, has a well preserved deep crater at its apex west of Mt. Skálafell. The surface is hummocky and ice scoured. The main margin of the shield is continuous and highest in the northwest, nearest to the crater, but slopes off to the east and south with distance from it. Lower lava levels occur, indicating lower stands of the melt water lake, the most prominent one forming a step below the high northern margin. The lava from the shield flowed down to the lowland in the east. Its base there consists of hyaloclastite breccia, the transition being at about 30 m above present sea level. During transgression of the sea at the close of the last glacial period, a boulder beach formed on top of the lava at about 50 m above present sea level. The fumaroles line up along a northeast-southwest fault.
Drilling has proven that underground there is a geothermal reservoir with temperature over 300°C below 2000 m depth, which means it is the hottest known reservoir south of Mt. Hengill.
Kristján Sæmundsson, 2010