5 April 2022
Mount Bolu: an interesting case study of a tunnel portal landslide in Turkey
Posted by Dave Petley
Mount Bolu: an interesting case study of a tunnel portal landslide in Turkey
On 2 April 2022 heavy rainfall triggered an economically significant landslide in at Mount Bolu in Turkey. The landslide occurred after a spell of rainfall that in places has fallen onto snow. This is a recipe for landslides in upland areas.
The Mount Bolu Tunnel landslide is interesting though. It has blocked four lanes of the D-100 road, a critical east-west connection across the north of Turkey. This is an image of the landslide:-
The aftermath of the landslide at Mount Bolu in Turkey. Image by AA via the Daily Sabah.
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This is an alternative view that shows the landslide source more clearly, as well as some of the debris blocking the carriageway:-
The landslide at Mount Bolu in Turkey. Image from https://www.turkiyegazetesi.com.tr/.
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The site of the tunnel is at 40.7578, 31.4504. It is clearly visible on Google Earth. The tunnel was completed in 2007.
There are some very interesting images online of the site of this landslide prior to the 2 April 2022 landslide. This image for example shows the tunnel portals and the slope above:-
Archive image of the site of the Mount Bolu landslide, showing the pre-existing landslide scarps. Image from https://structurae.net/.
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The archive of Google Earth imagery does not seem to indicate that further works have been undertaken to stabilise this slope, although of course satellite/aerial imagery has limitations. But on first inspection this is an ugly slope to be located above a tunnel portal on such an important highway, especially in a region that is seismically active.
The debris has taken 44 hours to clear, but the road has now reopened. The images suggest that further works will be needed on the slopes at this site, both in the scar of the 2 April 2022 landslide and on the slope to the left of it (as seen in the images), which appears to be another potential landslide site.
Northern Turkey has been suffering from a wave of landslides in recent days:-
Rapid snow melts have triggered more than 400 landslides in northern Turkey (in Bolu, Bartin, Samsun, Ordu, and Trabzon) in the last week. This foehn effect looks like will continue along the next week. Continue the landslide watch. Video credit @ihacomtr pic.twitter.com/oUfexjgOJH
— Tolga Gorum (@TolgaGorum) April 3, 2022
Dave Petley is the Vice-Chancellor of the University of Hull in the United Kingdom. His blog provides commentary and analysis of landslide events occurring worldwide, including the landslides themselves, latest research, and conferences and meetings.
wow .. Incredible footage and very close calls. I hope people get expert help on how to rebuild in a safer location and prevent such landslides, undermining homes and sweeping away communities in the future. With a warming climate and increasing population densities, these problems can worsen. Its all too often the poor who suffer the most, and they need our help. There are safe places to live and build. Once such a landslide starts, they are very difficult to prevent in the future. Its best to try to prevent them in the first place. Best wishes to those affected. Get a qualified geoscientist and I would not live in that house any more or any in that vicinity sorry to say.
Those tunnel portals…
Beyond *urgent* slope remediation, looks like they need to extend the portals by ~50 metres, this avalanche-shelter having a series of deep, skewed ‘ribs’ to steer detritus off to left of pictures, into catch basin(s)…
Um, perhaps more than ~50 metres, as rock-face to right of pictured does not look too healthy…
Bolu tunnel has a well know history of problems during construction and collapse after the 1999 Düzce earthquake. The ground it crosses, including its portals has been sheared by fault action plus subjected to very strong vibration during multiple earthquakes. It would be interesting to relate this failure with the behavior during past earthquakes