Understanding geomorphological hazard in Watumalang Area post Bisma volcanic era. Denudational or multihazard?

Abstract

The combination of endogenous processes in the form of volcanic and mountainous formation with exogenous processes in the form of wet tropical climate produces very complex geomorphological conditions in Java. From this geomorphological complexity there are various kinds of processes that often cause disasters for people’s lives. Watumalang Area in Wonosobo Regency, is one of the regions in Java Island with complex geomorphological conditions. Based on the genesis, this region was formed by volcanic activity in the past, some of which were affected by the structural process. Bisma Volcano is the last part of volcanism in this region that has stopped since thousands of years ago. At this time landform denudation is a dominating process and causes many disasters. However, does the threat of hazard only come from the denudation process? This paper aims to identify the geomorphological conditions of the Watumalang Area and the potential hazard. To achieve these objectives field observations were carried out using geomorphological survey methods. Observations are supported by remote sensing image interpretation, study literature, and documentation. Spatial analysis with a geomorphological approach supported by GIS analysis was used to describe the geomorphological hazard distribution. The results show that the Watumalang area is geomorphologically arranged by structural and volcanic units. The denudation process is so dominant that the potential for geomorphological hazards comes mainly from this process. However, the presence of faults can also trigger earthquakes. Meanwhile the existence of Bisma Volcano which is currently not active does not act as a trigger. In areas with such complex geomorphological conditions, the multihazard approach needs to be prioritized rather than limited to one type of hazard, although one hazard has a tendency to be more dominant.