[6] At the base of the northern flank is a geothermal area,[7] with the rhyolite and hot springs suggesting that a long-lived magma chamber is or has been present.
[8] In 2009 geologists in their research of earthquake events in the area showed that volcanic fissures lie in direction southwest-northeast and reach under the glaciers Þórisjökull and Geitlandsjökull-Langjökull.
[3] The southern extent of the fissure swarm is unclear and may overlap with that of the Hengill volcanic system.
[11] The central volcanoes rhyolite has for Iceland a high silica content of about 77%,[12] and must have come from a single batch of magma over a relatively short time span of less than 20 years.
They explored especially a valley behind the Þórisjökull called Þórisdalur, which had a bad reputation in sagas and folk stories because it was believed to be haunted by ghosts and that lawless people would be living there.