Natural Dam Hazard in Kundasang, Sabah Mountainous Region

Natural dam built up in mountainous regions is hazardous definatively a potential disaster. Kundasang is located on the highest mount in Malaysia and was hit by the 2015 earthquake. There are numerous kinds of dams that form by natural processes, dams formed from landslides on a mountainous landscape present one of the potential threat to people and property. Landslide dams form in a wide range of physiographic settings. The most common types of mass movements that form landslide dams are rock and debris avalanches; rock and soil slumps and slides; and mud, debris, and earth flows. The most common initiation mechanisms for dam-forming landslides are excessive rainfall and earthquakes. Natural dams may cause upstream flooding as the lake rises and downstream flooding as a result of failure of the dam. Many landslide dams fail and mostly caused by over-topping as the most common cause of failure. The timing of failure and the magnitude of the resulting floods are controlled by dam size and geometry; material characteristics of the blockage; rate of inflow to the impoundment; size and depth of the impoundment; bedrock control of flow; and engineering controls such as artificial spill-ways, diversions, tunnels, and planned breaching by blasting or conventional excavation. One of the rare creation of landslide dams are when a single landslide sends multiple tongues of debris into a valley and forms two or more landslide dams in the same reach of river. These dams pose hazards because back in 2015 there was an earthquake that shock the mount and destabilised the soil. Then, many trees were uprooted and fall. Thus, these phenomenon has shown in 2023 young vegetation has not stabilized mount Kinabalu slopes. There are many dam faces are steeper than the angle of repose, these dams and lakes are immediately downslope from steep crevassed glaciers and near-vertical rock slopes, and downstream from these dams are steep slopes with easily erodible materials that can be incorporated in the flow and increase flood peaks. The most recent reported failure mechanism is overtopping and breaching progressive rainfall.