Leirhnjúkur is a small hill in the middle of the Krafla caldera. It is the point of origin of the Krafla fires of 1975 to ’84. It is located close to the maximum vertical movement during the Krafla fires which was closely monitored. Here is also the centre of Krafla's magma chamber. Leirhnjúkur was the centre of the Mývatn fires which occurred in the 18th century and gave rise to the Leirhnúkshraun lava. Lying along the somewhat scoured and oxidized summit of Leirhnúkur are the crater rows of the Krafla and Mývatn fires in conjunction with older eruptive fissures. Several mud-pits and steam vents are located on the northern slopes of Leirhnúkur. Lavas from the initial phase of the Krafla fires are preserved at Leirhnjúkur. They are thin and of small volume, and were followed by eruptions lasting a few hours, covering them with the grayish sticky mud, still evident today.