Geomorphological assessment of past landslides in tropical highlands – Case studies from Cameron Highlands and Kundasang, Malaysia

Past landslides are old landslides, probably decades or hundreds of years ago that could be reactivated by their original causes or other causes. Their occurrences are often overshadowed by topographic complexity and dense vegetation cover in the hilly tropical terrain. Basic skills in geomorphology and experience is needed to recognize and identify this type of landslide because the associated geomorphic features tend to be mollified by intense tropical weathering, erosion and rapid sedimentation of the tropical region. Infrastructural developments encroached into the hilly terrains of Malaysia recently has indirectly expose various geotechnical problems and geodisaster risks due to reactivation of the past landslides. Landslides often produced visible signs and can be identified through detailed observation on the morphology and hill slope topography. The aid from new and advanced remote sensing technology and drone photogrammetry making geomorphological observation of past landslide in remote natural terrains easier and more convincing. A landslide, whether new or past, is often characterized by an assemblage of distinct geomorphic features depending on its type, size, age and scale of observation. Features like arcuate crown and main head scarp, side scarps, concave upper slope, convex lower slope and followed by undulating hummocky topography near toe are amongst the main signature to identify the existence of landslides geohazard. Other signs inclusive of colluvial deposit at the foot of the slope or in the downstream floor valey, Y-shaped bifurcating streamlets in the upstream, the existence of stepped terraces, different vegetation cover to the slope counterparts, can also be used to identify and to estimate the relative age of past landslides, either young, mature or old. Geomorphological assessment from Cameron Highlands and Kundasang areas are presented herein as a guide to recognize and identify the existence of past geohazard and mapped into landslide inventory as part of fundamental information for geohazard.