Magma is close to surface here. Hveradalir Geothermal Area (Hengill Volcano).

Hveradalir at Hellisheidi, Iceland. The gray colour of the mud pool is due to sulphur (clay + sulphur). Hveradalir is the name of the valleys south and south-west of Reykjafell, west of Hellisheiðar and north-east of the highway by the Litla Kafistofa. Up in the so-called Flengingbrekka there was a jumping platform for skiers. The ski lodge is above the mouth of the largest valley, Stóradals, and above it are the hot springs, for which the area is named. Hveradalaflät is in their vicinity and closer to Lakahnúk. It was a resting place for tourists on the way over Hellisheidi. The Ski Association of Reykjavík built the Skíðskálan in 1934 and sold it to the City of Reykjavík in 1971. Twenty years later it burned to the ground (Jan. 21).