Debris slides were recently found in the Pelangan area at Southern Mountain of Lombok Island, Indonesia. Pelangan is well known as the gold mineralization and hydrothermal alteration area. This study is aimed to identify the mineralogy and geochemistry of altered andesitic tuff that controlled slope instability and induced debris slides. For this purpose, it is necessary to prepare the field observation and laboratory analyses. Landslide inventory reveals that the Pelangan debris slides mostly occur in altered andesitic tuff. Based on the outcrop observations in the field, andesitic tuff found around the Pelangan debris slides have been altered in general. The strong intensity of alteration developed by hydrothermal alteration in this study area produces large amount of clay minerals especially montmorillonite, kaolinite, and illite. The abundance of those clay minerals reflect the intermediate argillic alteration. Montmorillonite is a type of clay mineral that easily swells at wet condition and easily shrinkages at dry condition. Swelling of clay mineral destroys intersheet and interlayer bonds, and reduces shear strength. The presence of clay minerals in the altered andesitic tuff of intermediate argillic zone can be considered as one of the factors that induced to the Pelangan debris slides. Further studies on geotechnical and slope stability analysis of the landslide area are crucial to be done for better understanding of the characteristics of the altered rocks inducing hazardous landslides.

Landslide disasters are abundant in the mountainous areas of Lombok Island, Indonesia. Most landslides frequently occur in areas intensively suffered by hydrothermal alteration including Pelangan Village at Southern Mountain, West Lombok Regency. The objective of this study are to identify the most important factors controlling landslide and also to analyze the landslide susceptibility zones in the hydrothermally altered area. For this purpose, it is necessary to prepare the landslide investigation and landslide susceptibility map. In this study, the AnalyticalHierarchyProcess (AHP) is used to develop landslide susceptibility map. The landslide susceptibility was analyzed by applying weighting and scoring on each factor controlling the landslide occurrence, such as hydrothermal alteration, slope inclination, distance to lineament, and landuse.The result shows that hydrothermal alteration and slope inclination are the most important parameters to landslide occurence (39.35%), and the least important factor are distance to lineament (13.76%), and landuse (7.54%). The high susceptible zones (HS) cover about 34.20% of the total study area. The moderate susceptible zones (MS) cover about 18.40% of the total area, while about 27.80% of the total study area were classified as being the low susceptible zone (LS), and about 19.60% of the total study area are  classified as very low susceptible zone (VLS).

Lombok Island as a tropical region with complex geology conditions included West Lombok Regency intensively undergo rocks weathering that further will be a cause of geological hazard such as landslide. Community knowledge and understanding of landslide hazard needs to be carried out continuosly. Therefore, the role of colleges to provide disaster education are needed. The aim of this community service is to provide knowledge and understanding regarding landslide prone areas in disaster risk reduction efforts. Students of D-3 Study Program in Mining Engineering, Universitas Muhammadiyah Mataram is an activity participant. This activity employed a counseling method through lecture and site visit. It was analyzed using rating scale with Likert scale method. The results showed that participants’ knowledge and understanding had increased. The highest increase is landslide causes 36,40%, followed by landslide impacts 33,33%, landslide type 30,67%, and the lowest is landslide mechanism 28,00%, with an average increase by 32,10%.      Keywords: geological hazard, climate, weathering, Lombok Island