Skjaldbreiður

The Prestahnúkur volcanic system is located on the W side of the Langjökull icecap at the west margin of the Western Volcanic Zone, and overlaps with the Hengill volcanic system north of Lake Þingvallavatn. It is about 90 km long and 15 km wide, with a subglacially erupted rhyolite peak and associated rift zones to the N and SW that have erupted during the Holocene. A large part of the volcanic system is underlain by early to mid Pleistocene plateau basalts. Olivine tholeiite basalt lava shields have erupted during the Holocene.