Geomorphological study of ternate island and landslide risk assessments

Abstract

Ternate Island is an active volcano (Gamalama Volcano) where the capital city of Ternate Municipality located. The island has however highest population density in compare to other regencies in North Maluku Province. The population tend to grow by time and the demand of land for settlements increase following the population growth. Some of the lower part of volcanic slope has recently been occupied by settlement and unfortunately it triggered landslides in recent days. The purposes of this research are to study geomorphology of Ternate Island and to analyze landslide hazard and risk. To achieve this purposes the satellites imageries, i.e. Geo Eye (Google Earth) and SRTM imagery, were used for geomorphological visual interpretation. The landforms were used as a parameter for landslide hazard analysis along with other parameters such as slope steepnes, soil texture, and land use. The landslide hazard then used together with community vulnerability parameter to analize the landslide risk. In this study, the method of weighting and scoring were applied to each parameter and its variables to assess landslide hazard and risk, and all of data analyzed using Geographic Information Systems. The results showed that the geomorphology of the study area is dominated (71.15%) by volcanic landform following the morphogenesis of Ternate Island, while the rest are fluvial landform (26.1%), marine landform (2.5%), and anthropogenic reclamation landform (0.25%) occupied by settlements and commercial area. Based on geomorphological conditions, 18.2% of study area considered safe area from landslide hazard, but 23.7% classified as low hazard, 29.8% as moderate, and 28.1% as high hazard. In compare to landslide susceptibilty assessment result, it appears that land use changes in the study area are quite a major effect provoking landslide hazard. The result of landslide risk analysis showed that 96.3% of study area is far from risk, but 1.16% classified at low risk, 2.2% at moderate risk, and 0.44% at high risk. In relation of these zones of risk, there are of about 2.0221 houses at low risk area, 4.041 houses at moderate risk area, and 826 houses at high risk area. All these numbers of risk can however be increased by time when the value of each parameter change. Therefore monitoring of land use changes, particularly for residential, is very important for study area, especially in relation to the government mitigation program and spatial planning.