Reactivating ancient landslides through reservoir construction – the Hoseynabad-e Kalpush landslide in Iran
A known potential issue with the construction of reservoirs is the reactivation of ancient landslides that have lain dormant in the landscape. There are literally hundreds of documented examples, but as dam construction continues at a high pace, this problem continues to recur.
There is a very good example described and analysed in a recent edition of the journal Engineering Geology (Vassileva et al. 2023 – available open access). This focuses on a very interesting example in March 2019 at Hoseynabad-e Kalpush village in north–central Iran, caused by the construction of a dam and the subsequent impounding of the lake. Unusually, this landslide occurred on slopes on the back side of the dam. What is really nice about this example is that the authors have been able to use InSAR data to examine in detail the ways in which reactivation of the landslide occurred over a long tine period.
The location of the site is [37.1943, 55.7435]. Google Earth imagery from June 2019 picks it out beautifully – note the amazing offset in the road in the upper midsection of the landslide!
The beautiful thing about InSAR is that the archive record can be used to trace the movement history of the landslide prior to final failure, and this is what Vassileva et al. (2023) have done. No movement was detected in the slope prior to 2010.
The time series shows that in the lower part of the slope, movement could be detected in 2015, with velocities in the region of 3.5 cm per year. However, the upper portion had no detectable deformation.
The first movement of the upper part of the slope was seen in 2017, by which time the lower portion was moving at about 5 cm per year. By 2019, the lower portion was moving at 8.4 cm per year, whilst the upper part was moving at about 1.6 cm per year.
The final failure was triggered by exceptional rainfall in early 2019, generating horizontal movement of over 40 m in parts of the slope. Movement finally ceased in October 2021.
The landslide at Hoseynabad-e Kalpush village is a beautiful example of a failure that was caused by dam / reservoir construction, but triggered by rainfall. The higher groundwater levels that resulted from impoundment of the reservoir reactivated the landslide, which then failed during heavy rainfall. There are many lessons here for other paces around the world.