Ófærufoss is a distinctive two-tiered waterfall in the Nydri-Ófæru river which falls into Eldgjá Canyon (fire 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.
From Northern Fjallabaksleið it is possible to drive into Eldgjá and walk from there to the Ófærufoss. Eldgjá can be reached by the mountain road Fjallabaksleið nyrðri (F208) which runs from Hrauneyjar (on road F26), to just east of the farm Búland (on road 208, west of Kirkjubæjarklaustur). All roads in the western part of the national park are mountain tracks, only navigable for vehicles with four wheel-drive; some only for large jeeps. Some sections of road are rocky and full of potholes, and loose gravel is common. It is sometimes necessary to ford (drive through) mountain streams or even glacial rivers which can become suddenly swollen, making them difficult, or even impossible, to cross.
Eldgjá is 40 km long eruptive fissure, approx. 600 meters wide in many places, and up to 200 meters deep. It last erupted in 934 shortly after the Settlement period, with eruptions taking place along the whole extent of it. The fissure is believed to extend from Mýrdalsjökull Glacier, to the east towards Lake Lambavatn, which is just west of Laki. From Eldgjá, extensive streams of lava have flowed through Landbrot and Meðalland, reaching the sea at Alviðruhamrar in Álftaver. The lava-field is believed to cover 800 km², making it one of the most extensive lava-fields on earth since the last ice age. Eldgjá is thought to belong to the same crater system as Katla and is a unique natural phenomenon which is listed as a protected natural monument.