On the Askja rockslide
Preliminary results of observations
The rockslide which occurred in Askja 21 July 2014 and descended into the caldera lake is one of the largest known rockslides since the settlement of Iceland (see preliminary results).
The slide triggered a tsunami in the lake that washed up on the lakeshores all around the lake, reaching up to 20–30 m and even higher in places. The wave travelled farthest around 400 m into the flatland SE of the crater Víti.
It was fortunate that the rockslide occurred late at night and nobody was close to the water, otherwise it would have been extremely hazardous. A few hours earlier, tens of people were at the lakeshore who might not have been able to escape the tsunami.
There were no eyewitnesses to the slide, but members of a search- and rescue team saw a white plume rise up above Askja at 23:27. The steam plume was created when the slide exposed shallow geothermal areas in the release area. In addition, a dust cloud created by the rock slide may have contributed to the plume.
Askja consists of 3–4 calderas. The youngest one hosts Lake Öskjuvatn and was formed over a period of 30 years after an eruption in 1875. Before that, Öskjuvatn did not exist and, therefore, the rims of the caldera are geologically a very young area. Such slopes are more unstable than slopes in older landscape. It is clear from geological evidence that rockslides similar to the one that fell in July 2014 have been released before from the rims of Askja, although people have not noticed them.
Further rockslides in Askja should, therefore, be expected within the next years, decades or centuries. Consequently, travel near the lake is associated with a certain risk. A person by the lake that notices a landslide should move immediately up the hill and away from the lake. It takes a tsunami wave about 1–2 minutes to travel across the lake and sound takes about 10 sec to cover that distance. Thus, people have a very short time to escape if a big rockslide is released from the other side of the lake.
The Icelandic Meteorological Office and the University of Iceland have compiled a collective memo with the preliminary results of observations of this largest rockslide since the settlement of Iceland. These results are presented on the web with photos, maps, graphs and thorough explanations.