Monitoring of the remobilisation of the May Ntebteb landslide near Hagere Selam

Abstract

During the last decade, slope failures were reported in a 500 km2 study area in the region of Hagere Selam, Mekelle, northern Ethiopia (Nyssen et al., 2002; Tesfahunegn, 2008; Moeyersons et al., 2008; Van Den Eeckhaut et al., 2009; Shimelies, 2009). The majority of the landslides are old debris flows, affecting the plateau basalts and flowing over the plateau edge, producing a sometimes km-long landslide foot, covering the steep plateau escarpment and often reaching the plain 200 to 400 m lower. For a limited number of these landslides reactivations were reported endangering roads and other infrastructure. One of these reactivations concerned the Amba Raeset debris flow in 1999. Nyssen et al. (2002) attribute the general tendency of reactivation of landslides in the region to changes in land use which contribute to a general increase in the soil water content (i.e. soil and water conservation measures such as conversion of rangeland into exclosures). This decreases the values of the apparent cohesion and of the angle of internal friction and can eventually lead to an increase of the hydrostatic pressures at the base of the landslide. The land use changes on the May Ntebteb flow in 2002-2004 were a unique occasion to test the hypothesis that the installation of stone bunds on the landslide lobe and the consequent increase of water infiltration into the soil (Nyssen et al., 2004) resulted in an increasing landslide activity. The displacement of the flow has been monitored between October 1998 and March 2001 (Nyssen et al., 2002). This note discusses the result of an ongoing monitoring campaign which started in 2007.