18 May 2021
The Kara-Bogaz-Gol megaslide: the world’s largest active landslide?
A startling paper (Aslan et al. 2021) has just been published, open access (hurrah!), in the journal Scientific Reports, describing what is thought to be the largest active landslide so far identified on Earth. This is remarkable – the scale of the Kara-Bogaz-Gol megaslide is vast but until I read this paper I had no idea of its existence, even though it is clearly visible on Google Earth.
The landslide is located on the banks of the Kara-Bogaz-Gol lagoon in Turkmenistan. The landslide complex can be seen extending along the whole of the bay (and more) in the Google Earth image below, although not all of it is currently active. I have included a Google Earth ruler in the image so that you can appreciate the size of this failure:-
The latitude and longitude of the landslide is given on the image above. The scale bar shows that the landslide is up to about 5 km from crown to toe, and the complex extends for over 40 km along the banks of the lagoon. This is a truly enormous landslide.
The Kara-Bogaz-Gol Megaslide is a rotational failure. Aslan et al. (2021) provide the following cross-section to illustrate its form:-
As the cross-section shows, the landslide consists of thick blocks of limestones and marls failing of a gently dipping layer of weak Eocene marls, clays, silts and sandstones. At the top of the cross-section are two graphs showing the movement rate. In form this is broadly similar to the Ventnor landslide on the Isle of Wight, but on a much larger scale.
Aslan et al. (2021) have used 354 Sentinel IW SAR that span the period from 2014 to 2020 to extract movement data. They have shown that a mass that extends about 25 km along the lake shore and that extends up to 5 km inland is moving at up to 3 cm per year. This means that the volume of rock that is involved in the active part of the the Kara-Bogaz-Gol megaslide is about 10 cubic kil0metres! The movement rate is not constant, but responds to the level of the lake. Thus, when the lake level is high, and the soil moisture level is also high, more movement occurs.
The authors point out that this area is seismically active I would be fascinated to see how the Kara-Bogaz-Gol megaslide responds to a major earthquake.
Aslan, G., De Michele, M., Raucoules, D. et al. 2021. Transient motion of the largest landslide on earth, modulated by hydrological forces. Scientific Reports 11, 10407 (2021). https://doi.org/10.1038/s41598-021-89899-6