Channels of the glacial river Jökulsá á Breiðamerkursandi

The glacial river Jökulsá á Breiðamerkursandi drains the Jökulsárlón tidal lagoon (27 km2), in Southeast Iceland. Despite being the shortest glacial outlet (0.6 km), it is among the most voluminous rivers in Iceland, with an estimated average drainage of 250–300 m3/s and has doubled its volume at peak runoff. Until a bridge was established, this was one of Iceland’s most infamous river and for travellers, cruising on horseback, the greatest obstacle to cross on the main road. The river began shaping its present channel in the late 19th century but was not permanently settled until the mid-20th century. Before that it used to wander around the fan, occasionally in several branches, or as a single heavy moving water. In this paper we present a map of its known runoffs and channels that were formed in the 19th and 20th centuries. Few channels were digitized from old maps, but several of those were identified and recorded by the late Flosi Björnsson (1906–1993), a farmer from the Kvísker, who guided travellers across the river before the bridge was built. The Breiðamerkurjökull outlet glacier of Vatnajökull, Southeast Iceland, advanced 10–15 km during the Little Ice Age. During the LIA advance the wide fan shaped shore in front of Breiðamerkurjökull gradually extended outward by >1 km, mainly due to sediment deposition by the Jökulsá river and few other temporal glacial river branches. At the turn of the 20th century the outlet glacier started to retreat slowly and in the 1930s terminal lakes were formed. With the formation of the Jökulsárlón tidal lagoon river dumping at the shore terminated and was replaced by a progressive coastal erosion. Currently ca. 0.9 km has eroded off the coast since the 1930s. A 0.65 km wide strip now remains between the coast and Jökulsárlón tidal lagoon, where the Jökulsá river and the remains of its former runway channels are located.