**3.1 Landslide inventory**

Landslide inventory is the base for landslide hazard zonation mapping [5, 28, 33, 35, 42]. A clear understanding of landslide conditions and a more detailed assessment of the landslide hazard of the area concerned are essential to make a systematic landslide inventory. The landslide inventory map depicts the location and characteristics of prior landslides. The geologic, topographic, and climatic conditions that are overcome at the site give an important indication regarding the causes and triggering mechanisms of the past slope failures. Hence, landslide inventory mapping provides helpful insight regarding the potential for future landslide occurrences. Based on relevant literature, historical sources, and classical field survey and mapping, landslide inventory on sliding processes was compiled. The inventory includes 46 different types of mass movements from the past and present that are dispersed throughout the area. The landslide inventories (**Figure 5a**) were collected through the direct field survey method. The density of landslides is very high in the central part of the area which is covered by highly weathered basalt.

*Landslide Assessment and Hazard Zonation in the Birbir Mariam District, Gamo Highlands… DOI: http://dx.doi.org/10.5772/intechopen.108122*

#### **Figure 5.**

*a. Landslide inventory map of Birbir Mariam district, b. slope geo-material map of Birbir Mariam district.*

#### **Figure 6.**

*Landslide causative factor maps, a. groundwater condition manifestation, b. land use land cover, c. slope morphometry, and d. relative relief.*

### **3.2 Landslide causative factors**

Intrinsic factors are the inherent or static causative parameters that define the favorable or unfavorable stability conditions within the slope [4, 11]. The main landslide causative factors selected for the Birbir Mariam area are summarized in **Table 1** and their brief descriptions are presented hereunder.

### *3.2.1 Groundwater condition*

Groundwater has a major influence on slope stability. In hilly terrains, groundwater does not follow a consistent pattern and is generally channeled along rock structural discontinuities. It is difficult and time-consuming to assess the behavior of groundwater in hilly terrains over large areas. Groundwater surface indicators (**Figure 6a**) such as damp, wet, dripping, and flowing provide valuable information on the stability of hill slopes and are helpful for the rating [4].
