Sveifluháls is one of the largest multi-summit hyaloclastite ridges in the Geopark A lava flow formed it in a eruption in the year 1151 AD. In that year a 25 km long fissure opened obliquely across the Reykjanes peninsula. It is interesting for its variety of hyaloclastite formations; layered tuff, breccia and pillow lava. The rocks bear witness to interaction between magma, glacier ice and water.
Sveifluháls or Austurháls is 395 m high palagonite rigg in Reykjanesfjallgarð, west of Kleifarvatn. Steep hammers are down to Kleifarvatn. On the south and east site of the neck are high geothermal areas mainly at Krísuvík. The highest peaks at Sveifluháls are Hellutindar, Stapatindar og Miðdegishnúkar.