In Skaftártunguafréttur, in West-Skaftafellssýsla, close to Kirkjubæjarklaustur, the eruptive fissure Eldgjá is to be found.
Eldgjá is an approx. 40 km long eruptive fissure, approx. 600 meters wide in many places, and up to 200 meters deep. When it was formed, probably around 934, there were likely eruptions along the whole extent of it. The fissure is believed to extend from Mýrdalsjökull glacier, to the east towards the lake Lambavatn, which is just west of Laki. From Eldgjá, extensive streams of lava have flowed through Landbrot and Meðalland, reaching sea at Alviðruhamrar in Álftaver. The lava-field is believed to cover 700 km², which makes it one of the vastest lava-fields on earth since the last ice age.
Eldgjá is believed to belong to the same crater system as Katla. Eldgjá is a unique natural phenomenon and is listed as natural remnants. Plans to make Eldgjá and its surrounding area a part of Vatnajökull National Park are in place.

Theories have surfaced that suggest that the Eldgjá eruptions had even more effect in Europe than the Lakagígar eruptions. According to newly discovered evidence, crop failure, plagues and other disasters occurred in both Europe and the Middle East at that time. It has also been speculated that these eruptions caused more damage than the eruptions of Lakagígar.

Eldgjá is by Northern Fjallabaksleið, between Kirkjubæjarklaustur and Landmannalaugar. From Northern Fjallabaksleið it is possible to drive into Eldgjá and walk from there to the waterfall Ófærufoss in the river Nyrðri-Ófæra. A road lies up to the eastern edge of Eldgjá. To get there, one needs to cross the river Nyrðri-Ófæra at a wading place, which can be risky. It is safe to recommend a walk up the mountain Gjátindur, from where there is magnificent view of Eldgjá, mountains by Langisjór and Lakagígur and its surroundings.