**Abstract**

The current research focused on landslide assessment and hazard zonation in the Birbir Mariam district of the Gamo highlands. The study examined landslide causative factors and used the slope susceptibility evaluation parameter to create a landslide hazard zonation covering an area of 110 km2 . The landslide hazard zonation was classified using facet-wise observation. As a result, the intrinsic and external causal parameters of score schemes have been held responsible for slope instability. Inherent causative elements consist of slope geometry, slope material (rock/soil), structural discontinuities, land use/land cover, and groundwater conditions. Rainfall and human interest have seemed as external elements. The intrinsic and external triggering elements for every facet (a total of 106) were rated for their contribution to slope instability. Finally, an evaluated landslide hazard value was calculated and classified into three landslide hazard classes. According to the findings, the area has a high hazard zone of 18.87% (20.76 km2 ), a moderate hazard zone of 54.72% (60.19 km2 ), and a low hazard zone of 26.41% (29.05 km2 ).

**Keywords:** Ethiopia, landslide, hazard zonation, landslide evaluation, slope stability

## **1. Introduction**

Landslides are a series of events in which a mass of rocks, soil, or debris slides down a slope due to gravitational pull, the mechanisms include sliding, falling, or flowing material down a slope [1–3]. Landslides are one of the most common geological hazards in the world, with a high incidence, a wide range of distribution, and catastrophic severity, resulting in numerous fatalities each year [3–9].

Landslides are caused by inherent causative parameters such as slope geometry, slope material, structural discontinuities, land use, land cover, and groundwater conditions, which define the unfavorable stability conditions within the slope [4, 10, 11]. External causative factors, such as rainfall, volcanism, seismic motion, and human activities, are also relatively variable or dynamic, temporary, and forced by upcoming events [11–14], the slope will be prone to instability when the slope morphometry is steep, and a chance of landslide increases with an increase in slope steepness through landslide occurs in all slope. Landslides such as rock-fall, toppling, and rockslides/ avalanches are common in the area because the slope material has been covered by highly fractured bedrock such as basalt and ignimbrite [15–17].

Discontinuities in the slope, such as bedding, joints, and faults, are potentially weak planes that affect slope stability [9, 15, 18]. As a result, fractured rocks have lower strength than intact rocks. They are the most vulnerable component of slope geology, and knowledge of their orientation, spacing, continuity, roughness, separation, and type of filling material, as well as slope angle, slope direction, and strength along such potential weak planes, is essential. Slope stability is influenced by land use/land cover, and the material's shear strength is reduced by subsoil conditions in the slope [17, 19, 20].

Landslides are one of Ethiopia's most common natural disasters, and the current study area of the Birbir Miriam district is one of the most vulnerable. A variety of factors affect slope stability, including slope angle, lithology, soil type, and hydrologic conditions [21]. Deforestation, changes caused by the construction of engineering structures on the slope, road construction undercutting the toe of the slope, and other human activities all contribute to potential factors. Variations in human activity on the cliff-side can make the slope less stable [4, 22–25]. Landslides harm infrastructure (houses, roads, buildings, irrigation, canals, and so on), as well as cause geomorphological damage, serious injuries, and the death of humans and animals. For minimizing damage to infrastructure, homes, cultivated lands, and human lives, well-organized landslide hazard zonation is critical. These slope failures zonation maps become significant when they are used by decision-makers in land use planning, landslide prevention, and mitigation methods [8, 15, 26–30].

The goal of a landslide study is to determine the essence of predisposition as well as the outcomes for human life, land, roads, buildings, and other resources [4, 31]. As a result, locating landslide-prone areas is critical for ensuring human safety and avoiding negative consequences for regional and national economies [1, 9, 32–36].

Landslides are common in the Birbir Mariam district along riverbanks, slope toes, and slope faces. Landslides are responsible for any losses and also affect much of the farmland and farmers' income. Moreover, landslides in the study area cause significant damage to properties and massive destruction, particularly in Zala Gutisha and Waro localities, among the heights-prone areas.
