The third volcanic cycle began with the Mývatnseldar eruptions in 1724-1729 which commenced with an explosion that formed the crater lake Víti. Later lava flowed from Leirhnjúkur down to the north end of Lake Mývatn, destroying two farms. The Mývatnseldar eruptions are quite similar in character to the recent volcanic activity near Krafla in 1975-1984. The source of both is a central volcano lying between Krafla and Gæsafjöll. Inside the volcano resides a magma chamber from which molten magma periodically bursts into a swarm of fissures that cut through the volcano from north to south.