Detailed Mapping of Pyroclastic Flows and Lahars for an Active Volcano Using RADARSAT SAR and ASTER Image Data

摘要

Merapi eruption is characterized by the persistent growth of a summit dome and partial or total collapse of the dome to generate hot pyroclastic flows. In this paper, we aim at detecting the latest pyroclastic flows deposit and assessing its possibility to generate lahars during and after rainy season. We used RADARSAT SAR scenes and ASTER images acquired on the dates soon after the eruption. The analysis of two type image data proved the high capability of detecting the small-scale volcanic flows in spite of the bad atmospheric condition. The RADARSAT SAR scattering intensity changes through beta nought calculation for SIX product before and after the eruption, and the n classifications using NDVI threshold methods were applied to delineate the pyroclastic flows and lahars distribution. Moving image calculation was also adopted to simulate vector of lahars flow direction. The results deduced that the coverage of lahars deposit changed from parental pyroclastic deposits was about 5.5 km2. The lahars commonly flowed towards the SE-SW direction and elongated more than 10 km. The lahars flow from the nearest height topography to the lower part with gathering and filling the river banks. This study can be effective for environment and hazard assessments associated with pyroclastic flows and lahars after the eruption.