Trolladyngja & Graenadyngja

Mt. Trolladyngja is a hyaloclastite mountain. The shield Volcano Trolladyngja has two main hyaloclastite peaks, 393 and 374m high. Between this ridge and shield volcano Trolladyngja is the shield volcano Graenadyngja with the area Sog in between.

Situated in the Ódáðahraun lava field, Trölladyngja is the biggest of the Icelandic shield volcanoes, reaching a height of 1,468 metres (4,816 ft) above sea level, and rising almost 600 metres above the surrounding desert and lava fields. It also contains major central volcanoes to the south and north. Its lavas have run from there to create various lava fields such as Afstapahraun. There is great thermal activity within this area.

It is about 10 kilometres in diameter and its inclination is 4 to 5° in the lower slopes, but 6 to 8° at higher elevations. Its oblong crater is about 1,200 to 1,500 metres in length, 500 metres broad, and about 100 metres deep.

Most of its lava fields have flowed in a northerly direction, with one branch of it reaching the valley of Bárðardalur, a distance of roughly 100 km.