Indonesia Conference Directory

The geology of Menoreh Hills is mainly developed by volcanic rocks, formed in the tertiary era, comprising Kaligesing and Dukuh formations. Overlaying these formations, there are beded limestones of Sentolo Formation, and alluvial deposits. The volcanic rocks consist of andesite pyroclastic breccia, tuffaceous breccia, and lava, as well as laharic breccia and andesite intrusion, generally subjected to quite intensive joint expansion. There are also some lateral slip faults with a general pattern of Northwest - Southeast and Northeast - Southwest. Most of the lithology especially volcanic rocks in the Menoreh Hills are undergone very extensive weathering, forming soil with a thickness of up to 5 meters. The mechanical properties of fresh volcanic rocks, described in the value of friction angle () ranges 40o – 65o, cohesion force (c) 15 kg/cm2 – 40 kg/cm2, while  of the soil ranges 3o – 24o , with c = 2.5 kg/cm2 – 8 kg/cm2. The geological setting and rock mechanical properties of the Menoreh Hills bring about specific characteristics of landslides. General characteristic of slope failures in the Menoreh Hills is involving soil or debri, saturated water conditions,  value less than 25o, slope inclination greater than 20o (36%), and soil thickness more than 3 meters. On the other hand, the model of landslides of Menoreh Hills can be grouped into three types consisting of rotational mass movement, soilslide through the boundary plane between fresh and weathered rocks, and wedges failure with joint intersections act as the sliding plane.