The Kfarnabrakh Landslide of November 30th, 2015

Abstract

During the early hours of November 30th, 2015, the mountain town of Kfarnabrakh experienced a major landslide at one of the town’s rock cliffs. Kfarnabrakh is 1,150 meters above the sea level, 45 km south-east of Beirut, and about 30 km away from the Mediterranean seacoast. The landslide was well documented with multiple cellphone videos captured by the local residents (check link at the end of this email) that were later used to finalize the failure mechanism. The rock cliffs are located at the north-northeast edge of the village with houses constructed within few meters of the cliff edges. Seventeen houses were evacuated and the families were provided temporary housing until the stability and safety of the sliding zone is assessed. In response to this extreme event, a recon team sponsored by the NSF-sponsored Geotechnical Extreme Events Reconnaissance (GEER) Association and the Lebanese National Council for Scientific Research (NCSR-L) authorities, had multiple visits to the location of the landslide and collected information from the local residents on the events of the day of the failure. In addition, the team explored the area and checked for possible locations of future breakoffs. A drone was used for aerial photography acquisition and a Digital Surface Model was generated for the area of interest. Geologic and hydrogeological maps of the area were used to help understand the cause of failure. Rainfall and seismic records didn’t show any major events in the days leading to the failure. The failure occurred in the C3 formation, a highly jointed chalky limestone. The C3 formation has an embedded thin layer (about 0.3-0.5m thick) of high plasticity Blue Marl clay located 20-25 m. from the top of the formation.