Enormous Mass Movements, and Gravitational Tectonics Model of the North Serayu Mountains, Karangkobar Area, Banjarnegara Regency, Central Java, Indonesia

Abstract

North Serayu Mountains in the Central Java province, Indonesia, stretches with west - east axis, bordered by Slamet volcano to the Bogor Mountains in the west, and delimited by Ungaran volcano to the Kendeng Mountains in the east. In the north of these mountains there is coastal alluvial plain of Java, and in the south there is a depression zone of River Serayu. Overall geomorphostructures of the North Serayu Mountains form a faulted anticlinorium, which one of its flank relatively dipping to the south. In the bottom part of this ranges are such plastic, clastic, clayey sedimentary rocks, Eocene to Miocene aged. While at the upper portion there is a group of elastic, brittle, massive volcanic rocks, andesitic to basaltic composition, Pliocene to Pleistocene aged. A volcano, called Rogo Jembangan stands over the top of the North Serayu anticlinorium, with two of its eccentric cones, namely Mount Telagalele and Mount Pawinihan, situated in the Karangkobar District. North Serayu anticlinorium with a plastic bedrock, which is overlain by elastic, hard, and heavy rock has created such a tectonic model influenced by gravity. Parts of volcano’s body and volcanic rocks blocks in the Banjarnegara Regency area generally move slowly but surely southward over a giant slip plane in the form of orographic fields. Locally, this gravitational tectonic is manifested as mass slides, glides, and creeps, occur any time in the study area. Orogenetics of the North Serayu Mountains is still on going in line with the active tectonism of the Java island, caused by subduction of Indian-Australian plate beneath the Eurasian plate. As long as that is the case, gravitational tectonic will continue to run, and mass movements in the research area will regenerate to happen.