Háifoss (64°12’28.07″N 19°41’12.71″W) of the river Fossá is situated near the volcano Hekla and has a height of up to 122 m. It is after Morsárfoss and Glymur the third highest waterfall of Iceland. The second waterfall deeper in the valley, called Granni (64°12’33.20″N 19°40’58.59″W), is not as tall as Háifoss. The area is situated on the core of the extinct Þjórsárdalur central volcano. The southernmost part of the valley is mostly filled by prehistoric postglacial basic and intermediate lavas older than AD 871. The lava flow belongs to the Búrfellshraun and Drekahraun lava fields, which are around 3,200 years old and originates from the Veiðivötn volcanic field (also called Tungnaárhraun). The lava field in the Þjórsádalur valley (around 10 km²) is covered by several rootless craters (also called pseudocraters). These pseudocraters were formed when the hot lava flow covered the water-saturated fluvial planes of the valley and the heat initiated intense steam eruptions and explosions. These rootless craters were formed by steam explosions rather than magmatic eruptions (www.isor.is). Down into the valley to the Northeast, it is filled-by undefined surface deposits, most likely deposited or re-deposited by the river Fossá, which flows to the Southwest (light grey in geologic map). The hills around the valley are mainly build-up by hyaloclastites older than Bruhnes (brown in geologic map), intersected by grabbro and dolerite intrusions (green in geologic map), andesites (organe in geologic map), and rhyolites (yellow in geologic map).

How to get  from the Commonwealth farm Stöng to Háifoss?

The hike starts in Stöng (64° 8’58.99″N 19°45’23.13″W) a reconstructed farm, which is based on the excavated farmhouse Stöng from the Commonwealth Era in Iceland. The parking lot of stöng can be reached by the Road 327. The hike goes northeast into the gorge of the river Fóssa and follows the trail (marked with orange poles) until the waterfall Háifoss after about 8 km  (ca. 2.5 hours). The way back follows the same trail back as the way to the waterfall. The entire hike back and forth takes about 5 hours.

Hiking map: Háifoss

Thordarson, T., and Höskuldsson, Á. (2015). Classic geology in Europe 3 – Second Edition. Dunedin. 256 pp.