Katla Geopark is home to two of the largest basaltic flood lava eruptions in historical times in Iceland, Laki in 1783-1784 and Eldgjá around 938 AD. The Eldgjá fissure is at least 50 km long, extending from the Mýrdalsjökull ice cap in the southwest (Katla), into the Vatnajökull ice cap in the northeast. The most spectacular part of Eldgjá is a 8 km long part of it in the southwest where the fissure is about 400 m wide and 150 m deep. The fissure is a complex volcanic structure of a graben, an eruptive fissure and an explosive crater row. In the southernmost part the eruption was subglacial, and caused a large glacial outburst flood in association with the eruption, jökulhlaup.
The Eldgjá eruption was a catastrophic eruption that had worldwide impact. The Eldgjá tephra from the eruption is widespread in the northern hemisphere. Total magma volume produced in the Eldgjá eruption has been estimated to be around 19 km3. Lava flowed towards Álftaver on the Mýrdalssandur sand plain, along the Skaftá river course and down to Meðalland (the Landbrotshraun lava) and reached the Atlantic ocean in Alviðruhamrar in Álftaver.
The Eldgjá and Laki lavaflows are not only big on an Icelandic scale, they are also some of the largest lava flows on earth since the end of the ice age about 10.000 years ago. The two lava streams have very different appearance, the Laki lava is covered with thick moss while the Eldgjá lava is often covered with younger material but also characterized by countless number of pseudocraters or rootless vents (Landbrotshólar and Álftavershólar). These have been compared to similar features observed on the planet Mars
Ófærufoss is a distinctive two-tiered waterfall in the Nydri-Ófæru river which falls into Eldgjá Canyon. A natural stone arch once spanned the top of the lower falls until 1993, when it fell into the river during the spring thaw.
Ófærufoss. Video by