THE VOLCANOSTRATIGRAPHY OF THE GEOTHERMAL AREA OF MOUNT UNGARAN, CENTRAL JAVA

Abstract

The Ungaran Geothermal Working Area (WKP) is located in Central Java Province where it is one of the ancient volcanoes with a composite type. In the geothermal exploration stage, it is important to determine the boundaries of volcanic rocks by the interpretation of remote sensing data. This research is to create a volcanostratigraphic unit using ASTER DEM data to create a digital elevation model. This data will be used to create a volcanostratigraphic unit with an explanation of the ridges and rivers that will point to the center of the eruption. The geological history of Java Island is a complex arrangement of basin formations, faults, folds, and volcanism under the influence of different pressure regimes from time to time. Java Island is in the subduction zone, a collision between the Indo-Australian Plate and the Eurasian Plate. The history of Javanese subduction is also the history of magmatism paths that have formed over time, forming a pattern of magmatism that is rich in igneous and volcanic rock formations. The geological structure in the Mount Ungaran area is controlled by a collapse structure that extends from west to southeast of Mount Ungaran. The volcanostratigraphic method is used using the source of the eruption center that can still be identified, for example, the existence of circular features and the morphological shape of the volcanic cone that is clear in satellite images. The sources of the eruption centers that can be identified are closely related to the relatively young age, generally in the Quaternary Period. On the regional scale of the Mount Ungaran WKP with a scale map of 1:100,000, three Brigades were identified around the Mount Ungaran WKP, namely Sumbing Brigade which is on the southwest side consisting of Sumbing Crown and Sindoro Crown. Based on the 1:50,000 scale map on the Ungaran WKP, it was identified into 2 Crown (Main Eruption Center), namely Young Ungaran Crown (Kh. Ung. Muda) and Kuluk Old Ungaran Crown (Kh.Ung. Tua) on the scale map of 1:50,000 identified 5 volcanostratigraphic units as Hummock originating from the central eruption and eruptions including Pengion Hummock (Gm. Pgn), Songo Hummock (Gm.Sgo), Godong Hummock (Gm. Gdg), Tungku Hummock (Gm. Tgk) and Kaligesik Hummock (Gm. kgk).