Velocity gradually increases in the fall face and decreases in the colluvial foot slope. The highest velocity occurs in the transportational middle slope. The spatial autocorrelation can be performed with geostatistical techniques. Those which are closer tend to be more alike than those that are far- ther apart. Velocity and energy of rockfall, as a result of gravitational slope phenomena, may be spatially correlated. Then, rockfall trajectory was used to model the rockfall velocity and rockfall energy by using neighborhood and geostatistical analysis. The first derivatives (i.e., slope angle and aspect angle) were employed to compute the rockfall trajectory. Rockfall velocity and energy are secondary derivatives of a DTM (Lan et al., 2007). Derivation of morphometric variables through DTM processing was divided into two parts, i.e., morphometric variables derived from RockFall analyst (velocity, energy) and from the ILWIS script (slope, plan curvature, shape complexity index, stream power index). Experience and former knowledge are involved during the selection of morphometric variables. Prior to the selection of morphometric variables, knowledge of rockfall processes in relation to generic landforms should be utilized. They should reflect the movement and deposition of rockfall boulders. When selecting morphometric variables one should also consider rockfall processes, besides morphology of the landscape. This depends on the local surface and the presence of an obstacle that can stop the movement of boulders. Some high-velocity and high-energy boulders may continue their movement to a colluvial foot slope. Bouncing, rolling and sliding are dominant in a transportational middle slope. In the transportational middle slope, velocity starts to decrease during the contact between boulder and surface. Velocity increases significantly in the fall face and reaches a maximum in the transportational middle slope. A fall face represents the Gunung Kelir escarpment, which is dominated by slope > 60 ◦ and falling processes. A big boulder, which eventually falls, could be part of a convex creep slope and part of a fall face. Consid- ering that its position is adjacent to a fall face, convex creep slopes and the upper part of fall face are the most likely rockfall sources. Convex creep slopes represent a potential rockfall source. A modified 9-slope model was used to represent conceptual entities of rockfall deposition in each slope segment. The final classification of landform elements should represent an appropriate semantic description related to rockfall processes. Prior to data analysis, a fundamental decision should be made in relation to the number of landform class and the selection of morphometric variables to be used. 2a), but do not influence much the final classification of landform elements. Both errors influence the plausibility of slope (Fig. The remaining padi terraces mostly occur in the transportational middle slope and the flat- tening phenomenon mostly occurs in the interfluves. In addition, “flattening” topography can also be found on slopes of less than 2 %. The result of DTM preprocessing shows that padi terraces still exist where the sampling points of elevation data are unavailable. of contour mapping is needed to obtain a plausible geomorphological feature.
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