Perpustakaan Digital ITB

Jember Regency in the southeastern part of East Java Province, Indonesia is an area known as the "land of a thousand hummocks" due to the large number of volcanics deposits as hill morphology with a height up to tens of meters scattered around this area. The previous research stated that these hummocks were the product of the greatest avalanche phenomenon in Indonesia, namely the Mt. Raung avalanche. The distribution of these hummocks is divided into two zones, namely the proximal zone which is close to Mt. Raung and characterized by the large and densely distributed hummocks, and the distal zone which is far from Mt. Raung and characterized by the small and scattered hummocks. These hummocks contained some construction materials (sand and gravel) that could be used i.e. for infrastructure development. The objective of this study is to map the potential of the volcanic products as construction materials which are associated with the existing hummocks in the proximal zone. The mapping was conducted by a remote sensing method using watershed segmentation method which is applied to a Digital Elevation Model (DEM) of the area to detect the hummock boundaries. The DEM need to be modified because the segmentation method were originally used to delineate the closed basin boundary, whereas the hummock has a cone shape. A preprocessing step was conducted by changing the shape of hummock from a cone to a “bowl” like shape with the tip of bowl is assumed correspond to the boundary of hummock. The tip of the bowl is generated based on two criterions i.e. has a large slope change and lowest possible elevation on the change. This study also investigating of the subsurface distribution of volcanic materials for three mined hummocks using the geoelectric resistivity method. Wenner configuration was used with ±50 m depth penetration. From the remote sensing analysis, 296 hummocks were detected in study site with total volume of all the detected hummock is about 169.5 million cubic meters. Meanwhile, from the geoelectrical resistivity method, the composition and subsurface shape of three hummocks can be interpreted. The first hummock composition is dominated by tuff with the base depth range of 20 – 40 m. The second hummock composition is dominated by andesite with the depth continues up to more than 50 m in the center part and the edge area is composited by tuff with 20 m base depth. The third hummock composition is dominated by tuff with an inclusion of andesite and has a base depth range of 15 – 40 m.