Slamet volcano is the biggest volcano in Central Java, Indonesia which has stratovolcano type. Starting in 1772 until recent, Slamet volcano was erupted with short cycling so that geochemicals on rock are important to know how the history and erupted type. Method of research was conducted by geological survey (surface) and geochemical analysis of sample rocks. Geological condition is consist of lava flow, pyroclastic fall, and laharic deposits that was proven by petrography approached, meanwhile geochemical composition shows calc-alkaline and high K calc-alkaline series, genesis of magma was from continental plate with island arc tholeiitic setting. Depth of magma 155-174 km belom the earth’s surface.
The existences of several hot springs between Slamet volcano, Paguyangan, and Cipari Districts raised questions regarding their origin. Several studies have been conducted related to the hydrothermal system at the location. Subsequent studies are needed to understand the hydrothermal system at the research site for the sustainability and conservation of geothermal natural resources. This research has reviewed several previous studies plus the latest information on the origin of hot spring water with the help of deuterium (2H) and 18O isotopes. This study used geochemical analysis of hot springs (geothermal) and local meteoric water to obtain information on isotope values. This was used for the interpretation of the origin of geothermal water. This study also used regional geological analysis methods for the interpretation of the mechanism for the emergence of these hot springs. The results of the analysis informed that the origin of hot water was local meteoric water. The geological structure was weak enough to allow water from the geothermal reservoir to reach the surface and meteoric water into the reservoir.
The PB Sudirman hydroelectric power plant, built in 1988, has fewer than 50 years of operational life. In contrast, the planned operating life for this dam is 50 years. This dam is experiencing intensive sedimentation, which results in siltation. Dredging efforts and catchment area management are conducted to extend the operational life of the dam. Therefore, technical and economic analysis of dredging activities and the potential benefits of dredged sediment is needed to determine the solution's effectiveness. We use the site survey method to conduct an environmental impact analysis and interviews with dam managers. The identification of the extent and distribution of erosion-sedimentation was carried out as part of the technical assessment. In the economic study, we calculate the dredging costs and profits from selling dredged sediments, mainly sand. The analysis results show that the dredging of deposits in the foreset slope area is not profitable. There are 17 areas of bank spoil that have economic benefits. This study concludes that the need for dredging costs on foreset slopes is higher than the profit from selling dredging sediments.
The research location is in the western of Yogyakarta-Central Java Basin, where limestone of Jonggrangan and Sentolo Formation are found with the same age but have different depositional facies characteristics. These differences will be interesting to study the historical process of its formation. The research was conducted through a series of methods. Starting from geological mapping to determine the order of rock stratigraphy, the depiction of outcrop profiles, and limestone sampling for petrographic analysis. Eventually, the depositional environment of the two rock formations was discovered. Field observation results and laboratory analysis were further integrated to determine the rock facies that make up the two formations. The rock units in the study area from old to young are the pyroxene andesite breccia unit of Upper Oligocene age and limestone. The bioclastic limestone and layered limestone units are deposited by interfingering, unconformity over the pyroxene andesite breccia unit. The Middle Miocene bioclastic limestone unit is equivalent to Jonggrangan Formation in the inner shelf environment (Restricted Lagoon and Open Lagoon facies environment). Whereas layered limestone of Middle Miocene age is equivalent to the Sentolo Formation in the lower slope environment (Restricted Lagoon, Open Lagoon, and Open Sea Shelf) facies.
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