This hyaloclastite (moberg) ridge rises 550 m above sea level to the east of the waterfall Hrauneyjafoss on both sides of River Tungnaa. Late during the ice age, three explosive sub-glacial fissure eruptions created the ridge and about 3,000 years ago, lava flows blocked the few passes through it. Gradually a lake was created to the east and soon its discharge started spilling over the ridge. Later, more recent lava flows blocked the discharge and diverted it to the present location, where it quickly eroded through the ridge and the lake was emptied. As a result of the rather quick excavation of the gorge, the material was carried by the water to create the flat area down to the waterfall Hrauneyjafoss. The track across the ridge leads to one of the most popular spots in the interior, Landmannalaugar, about 27 km away.
In 1973, the construction of the hydroelectric power station at Sigalda commenced and the work was finished in 1978. A 925 m long and 40 m high earth dam was constructed just southeast of the station houses and covered with asphalt to minimize leakage. Behind the dam a lake was gradually created. The access channel from the lake is about 1,060 m long. At its end, three steel lined pipes, allowing for a drop of 74 m, supply the hydro power for the generators (50 MW each). The plans for the power station allow for the addition of one more generator in the future.
A short distance beyond the bridge across River Tungnaa (1968), the discharge from the power station enters the river. In the channel and the gorge is a layer of pillow lava, which is usually created in water under great pressure during submarine or sub-glacial eruptions. The road from the bridge continues north on the eastern and newer route over the Sprengisandur track all the way to the northern part of the country. After the construction of the so-called Hrauneyjar hydroelectric power station, an easier and shorter route connects with this route just north of the Sigalda ridge.