Jokulsargljufur - Hljodaklettar
About 8-9,000 years ago, two volcanic fissures erupted, one of which ran parallel to today’s river for a distance of some 6 km and is named after the Rauðhólar and Hljóðaklettar formations. The other fissure is named after Randarhólar hills, where, just north of Dettifoss waterfall at Hafragil, the river has cut through the feeder channel of a volcanic crater.
Iceland - Island Iceland - Island Iceland - Gufudalur
Iceland - Island Iceland - Island Iceland - Island

This opened a unique cross-sectional view of the magma channel in the canyon’s east wall. Both of these fissures produced broad lava fields; however, catastrophic river floods washed large parts away, leaving cliff-edged hills behind, such as Vígabjarg in Forvöð, Eyjan in Vesturdalur and Eyjan in Ásbyrgi, all remains of former lava flows.
Iceland - Island Iceland - Island  Iceland - Island 
Iceland - Island  Iceland - Island  Iceland - Island 

Source: www.vatnajokulsthjodgardur.is