The distribution of soil morphological characteristics for landslide-impacted Sumbing Volcano, Central Java - Indonesia

Landslides are the second biggest natural disasters in Indonesia, occurring mostly in volcanic area with thick and clay rich soils. Examining the changes of land surface and soil morphology brought about by a particular landslide is usually the first step required for vegetative rehabilitation. Most examinations to date, however, have been based on general characters rather than on soil morphology, including physical and chemical characteristics of the soil, which are usually locally specific. This study investigates the morphological characteristics of soil in a landslide-prone slope region of Sumbing Volcano, in Central Java Province of Indonesia. The field investigations are conducted at three landslides sites. It starts with interpreting small format areal-photographs which have been geo-corrected, followed by the delineation of landslide zones (i.e. crowns, main scarps, heads, bodies and toes) based on morphological analysis of the landslide sites. Finally, identification of morphological, physical and chemical characteristics of the soil in each of the landslide zones are conducted in the field, along with laboratory tests. The results demonstrate that soil morphology is unique for each of the landslide zones. The characters of the undisturbed soil, as indicated by well-defined genetic horizons, are found in the crown zones. Outcrop of high clay content soil material layers are seen in the main scarp zones. Meanwhile pedoturbation processes are evident in the zone of bodies and toes, suggesting that the soil is prone for erosion. If natural erosions in these zones are not controlled and/or unmitigated, the situation will trigger landslide reactivations. We suggest that in studying landslide, one also considers the characters of soil morphology, as this additional information provides a more complete understanding of both land surface morphology and soil morphology to inform landslide vegetative rehabilitation.