www.zigzagonearth.com/leirhnjukur-iceland
What is called Leirhnjukur is an area of the Krafla caldera around a rhyolite formation (593 meter above sea level). The hill rises less than 50 meters above the surrounding lava field. The rhyolite of the hill is porous due to the geothermal heat and has in several places turned into clay, hence the name “clay hill”.