The Fjallabak Nature Reserve was established in 1979. It is 47.000 hectares and over 500 meters above see level. The land is mountainous, sculptured by volcanoes and geothermal activity, covered by lavas, sands, rivers and lakes.

The topography of the Torfajökull, central volcano found within the Fjallabak Nature Reserve, is a direct result of the region being the largest rhyolite (liparite) area in Iceland and the largest geothermal area (after Grímsvötn in Vatnajökul). The hot pools at Landmannalaugar are but one of many manifestations of geothermal activity in the area, which also tends to alter the minerals in the rocks, causing the beautiful colour variations from red and yellow to blue and green, a good example being Brennisteinsalda.