Oraefajokull is the highest mountain of the country, 2,110 m, and stretches to the south of the middle of the ice cap Vatnajokull.  The terrain to its south reaches the elevation of about 100 m above sea level.  The mountain is a topless strato volcano with a large, ice filled caldera.  Its ice cover reaches down to the 1,800 m elevation and usually a few precipitous cliffs of the peaks remain ice-free.  This strato volcano is considered to be the second most active in Europe after Mt Etna in Sicily.  The ground diameter of the mountain is about 20 km and its ground area about 400 km².  Its volume is close to 370 km³.  Prior to the enormous eruption in 1362 its name was Knappafell.

The name of the inhabited area between the alluvial plains Skeidararsandur in the west and Breidamerkursandur in the east, Oraefi, dates back to the aftermath of the first eruption in historic times.  That eruption almost totally destroyed the area and killed most of the inhabitants and their livestock.  Afterwards the area looked like a vast desert, which is exactly what the word Oraefi means.  The rhyolite peak Hvannadalshjukur rises about 300 m above the caldera, which is about 5 km long and has an area of 12 km².  The average snow thickness added to the area annually is about 10 m, and the average precipitation up there about 5,000 mm, which exceeds all other parts of the country.  A number of small glacier tongues slowly crawls down the indented slopes of the mountain from about 1,800 m elevation.  The largest are Falljokull, Kviarjokull, Fjallsjokull and Svinafellsjokull.

The strato volcano has erupted twice during historical times, in 1362 and 1727.  Scientists consider the first eruption to be the largest pumice eruption in historical times in the country, but another one took place about 2,800 years ago.  The volume of the tephra was estimated 10 km³, which corresponds to about 2½ km³ of compact rhyolite.  The immense flood waves following the eruption swept most of the farms away in the Little District as the area was called prior to the eruption.  In the North ash fell on the ground and off the northwest coast, boats had difficulties in getting through thick, floating patches of pumice on the sea.  Thick patches of pumice from this eruption are all over the present Oraefi area.

The second eruption started in January 1727 and lasted almost a year.  Its fury was greatest during the first three days and the ash fall so great, that it was impossible to distinguish between night and day.  Fewer people and livestock were killed and no farms were destroyed, because they stood on much higher ground than before.  The volume of tephra emitted was also much less than during the first eruption.  The main flood wave ran eastwards past the parsonage Sandfell and the farm Hof.  Signs of this natural catastrophe are still clearly visible in the area.

Legends about trips across the Vatnajokull ice cap in the ancient past exist.  No sources are available on the Oraefajokull until Sveinn Palsson climbed it in 1794.  When he arrived at the peak and took a look around, he realized how the glacier snouts were created and behaved.  He discovered, that the ice is a viscous mass, which slowly moves downward with gravity.  He also saw the layers of ashes from previous eruptions somewhere in the country, and realized their meaning.

(Saga trail South Iceland)