Askja (means caldera) – is an 8km wide volcanic depression formed from a collapsed subterrean magma chamber. In the centre it has 217 m deep lake oskuvatn – steel grey waters in the middle of a colossal lava field. Öskjuvatn is a large lake that fills much of the smaller caldera resulting from the 1875 eruption. Its surface lies about 50 m below the level of the main caldera floor and covers about 12 km². When the lake originally formed it was warm, but today it is frozen over for most of the year. Öskjuvatn is the second deepest lake in Iceland at 220 m 721 ft deep.
Follow the Jökulsá á Fjöllum is the second longest river in Iceland from the glacier to Dettifoss & Selfoss.