| Abstrak/Abstract |
The 1257 CE eruption of Samalas volcano, Indonesia, buried the entire island of Lom- bok beneath various thicknesses of pyroclastic material during this Volcanic Explosivity Index (VEI) 7 event. This study aims to reconstruct the paleo-topography of western Lombok before the Samalas eruption in 1257 CE and analyse the sedi- mentation processes that led to its landscape evolution over the last 700 years. Strat- igraphic data were collected from various surveys, such as outcrops, coring, drilling, hand auger and wells observation. Electrical resistivity tomography (ERT) measure- ments were performed to complement the stratigraphic data. A combination of stra- tigraphy, ERT and topographic data from various sources (topographic map, Digital Elevation Model Nasional [DEMNAS] and Real Time Kinematic [RTK] measurement) is employed to determine the depth of the paleo-surface. Topographic modelling was performed by subtracting the delta-DEM (DDEM) from the current-DEM (CDEM). The result of this operation is a paleo-DEM, which is used to reconstruct the paleo- hydrographic features such as shoreline positions and river channels. Modelling results demonstrate that the relief has not been significantly modified, except in low- land areas, which is the sediment accumulation zone. River channels have experi- enced minor changes, except for the location of the river mouth and the degree of meandering. Significant changes occurred at the shoreline that has prograded by approximately 1.6 km during the last 700 years. A schematic model is built to illus- trate the evolution processes of the study area, consisting of the pre-eruption condi- tion, the immediate post-eruption condition and development of the current condition. This model further develops the previously proposed model with a higher resolution and simultaneously revises the estimated boundary of the pyroclastic den- sity current (PDC) deposit from previous work. |
