The eastern flank of the Merapi volcano (Central Java, Indonesia): Architecture and implications of volcaniclastic deposits

Abstract

Merapi volcano in central Java Island is considered to be the most active and dangerous andesitic volcano in Indonesia. The volcanic history of Merapi volcano is complex, and often perturbed by frequent episodes of eruptive edifice building and subsequent erosion and collapse. In this paper, we present a detailed field, literature, and GIS-study of the well-preserved eastern flank of Merapi, which has been spared from major eruptions, in order to reconstruct the geologic and geomorphic history of the edifice. Here, the most recent deposits arise from the remobilization of the old volcanic materials by lahar, gravitational collapse of massive lava flow and local landslide processes.In this study, we describe the specific deposits and subsequent alteration and removal processes. The stratigraphic analysis was performed with respect to the distinct phases of construction due to eruptions and dismantling of the volcano by erosion, gravitational collapse and the associated local to distal re-sedimentation. Based on GIS analysis and field surveys, a drainage network anomaly was detected in two main rivers, the Soka and the Brambang Rivers. We infer that an apex fan of volcaniclastic material was deposited into a central paleo-Pusur river and explains the abnormal divergence of the rivers. A new lithological 3D conceptual model is proposed based on the characterization of the lithological facies and their temporal and spatial evolution along the eastern flank of Merapi volcano.