Large Landslides in Ethiopia: Spatial Distributions, Influencing Factors, and Cascading Effects

Abstract Landslides and associated ground failures are among the major geohazards causing huge economic, social and environmental damage in many countries in the Global South such as Ethiopia. As part of the long-term research and database development for geohazards in Ethiopia, large landslides (areal sizes greater than 3 ha; n = 306) were studied over the years (1997–2024) with several objectives: (i) evaluate the spatial distributions and characteristics of slope failures, (ii) identify the causes and effects of the landslides, and (iii) recommend mitigation/management options. The methods used included: (a) detailed inventory and characterizations of the large landslides (including types, dimensions, and mechanisms of failures), (b) field and lab-based investigations: geological, geomorphological, geotechnical, and hydrological conditions of the sites, (c) assessments of effects of landslides on sediment delivery to streams/rivers: measurements of suspended sediment concentration in streams at downstream and upstream areas of landslide-affected sites, (d) assessments of human-induced factors which influence the stability of slopes (e.g. excavations, loading, deforestation, expansion of settlements, etc), (e) inventory and assessments of the damages due to landslides and cascading hazards, and (f) assessments of existing landslide mitigation/management practices and their performances. Results show that debris/earth slides (n = 291; 95.1%) and debris/earth flows (n = 15; 4.9%) are the dominant types of failures. These landslides occurred in unconsolidated sediments underlain by different bedrock types: Metamorphic rocks (n = 18; 5.9%), Paleozoic glacial/Post-glacial sediments (n = 13; 4.2%), Shales (n = 36; 11.8%), and Volcanic rocks (n = 239; 78.1%). The dominant modes of failures were: translational (n = 125; 40.9%); rotational/quasi-rotational (n = 86; 28.1%); and complex types (n = 95; 31%). The main factors causing landslides could be categorized into: (i) preconditions: lithology (soil and bedrock type), slope angle, and slope shape, (ii) preparatory: gully erosion/scouring, land use change/deforestation, unplanned expansions of settlements, unintended negative effects of soil and water conservation, and poor irrigation water management, and (iii) triggering: rainfalls, excavations, and loadings. The landslides and cascading hazards have caused: (i) loss of lives: human (n = 175) and animals (n = 350), (ii) displacement of people (n = 58,760), (iii) damage on churches (n = 41), (iv) damage on dwelling houses (n = 13,820), (v) damage on agricultural land (over 1785 ha), (vi) damage on schools (n = 32), and health centers (n = 12), (vii) damage on dry weather rural roads (95.4 km), (viii) damage on water supply systems (groundwater wells, ponds, etc) and irrigation infrastructures, and (ix) environmental problems. This paper gives insights on the scale, causes, and significance (economic, social and environmental) of large landslides and cascading hazards in Ethiopia, and calls for action to address such major geohazards through proper industry practice, research, capacity building, and innovations.