Askja represents a volcanic system with nested calderas north of Vatnajökull. A major eruption in 1875 resulted in the formation a huge caldera which was later filled by lake Öskjuvatn (in the background), 11 square kilometres large and more than 200 m deep. The small geothermal lake Víti (in the foreground) fills an explosion crater that goes back to the same eruption. It has a temperature of 20-30 degrees Centigrade. The main crest of the mountain range Dyngjufjöll (1510 m) appears in the very background.