The 1967 Steinsholtsjökull rockslide and GLOF event in light of climate change in Iceland

One of the most visible consequences of climate changes in Iceland are retreating outlet glaciers and formation of proglacial lakes. It is estimated that Icelandic glaciers have lost about 16% of their mass since 1890 or over a 130-year time interval. Temperatures have been fluctuating over this period with exceptional warm period in the 1920s and 1930s followed by slightly colder interval until beginning of the 1980s. During this time outlet glacier retreated considerably but around 1970 glaciers begun to readvancing which continued until around 1995. At the end of the 20th century another turning point occurred, with higher temperatures and rapidly retreating outlet glaciers. Existing proglacial lakes expanded and many new were formed in front of the rapidly retreating ice margins. Over the last years temperature have become more stable and several outlet glaciers have been showing a readvancing phase. Glacial fluctuations have affected the stability of valley slopes above retreating outlet glaciers and their proglacial lakes. Resulting in increased frequency of mass movements and slope deformation in these high-mountain regions. In 1967 a large rockslide fell onto the Steinsholtsjökull outlet glacier and into its proglacial lake causing a GLOF.

The rockslide was approximately 20 million m³ in volume. The head scarp was around 970 m long and up to 300 m high. It fell onto the western side of the glacier and broke up its snout. Part of the rockslide material fell into a proglacial lake, in front of the ice margin, causing a large GLOF down the valley. Large amounts of sediment were transported and redistributed down-valley with the GLOF. About 20km downstream a maximum flood discharge of 2100-2700 m³/s, was estimated.

The Steinsholtsjökull 1967 GLOF, entirely overprinted the proglacial landscape in the Steinsholtsdalur valley. Similar circumstances to the valley prior to the event, now exist and are forming in glacial environments around Iceland’s present-day outlet glaciers, which highlights the urgent need to study and monitor these environments.