We congratulate our NORDRESS partners who recently published the paper Rockslide in Askja, C-Iceland, on 21st July 2014 in the Icelandic periodical The Naturalist. Jón Kristinn Helgason, Sigríður Sif Gylfadóttir, Sveinn Brynjólfsson, Harpa Grímsdóttir, Ármann Höskuldsson, Þorsteinn Sæmundsson, Ásta Rut Hjartardóttir, Freysteinn Sigmundsson & Tómas Jóhannesson.
Rockslide in Askja, Iceland, on 21st July 2014
Abstract
A large rockslide fell from the south-eastern rim of the Askja caldera, Central Iceland, in the evening of 21st of July 2014 and into the Öskjuvatn lake. The rockslide covered most of the Suðurbotnahraun lava and reached the edge of the Kvíslahraun lava. The slide caused a tsunami with run-up of 20–40 m at many locations along the shoreline and up to 70–80 m in a couple of places. The tsunami wave propagated hundreds of metres up the flat shore near the Víti crater, in the Kvíslahraun lava, in the Mývetningahraun lava and by the Ólafsgígar craters. Model simulations show that the tsunami run-up along the coast is determined by complicated interference of waves on the lake surface. The rockslide tongue on the bottom of the Öskjuvatn lake is ca. 600 m wide, extends ca. 2.1 km into the lake, and the thickness of the outermost 800 m is ca. 8 m on average. The volume of mobilized material is estimated at ca. 20 million m3. The bedrock around the Öskjuvatn lake is extensively fractured and may be unstable in places. There is a danger of further rockslides near the location of the 2014 slide and also both to the north and to the west of the slide. Rockslides and tsunamis endanger travellers in the Askja Caldera, which is a popular tourist destination. The risk to individuals due to potential rockslides and tsunamis in Askja is, however, not considered very high due to the low frequency of the slides and the fact that people typically do not stay long in the caldera. Nevertheless, precautionary measures are advised to ensure the safety of people visiting the area. Travellers should, for example, not stay long down by the coast. Model simulations indicate that tsunami waves induced by a somewhat larger rockslide than in 2014 could overtop the northern caldera rim by the Víti crater and flow some distance to the north beyond the rim.