lava, which could be a result of the decreasing influence of subduction-related material. A major volcano in East Java is Mount Bromo. Central Java There exist two main arcs at Central Java which are Southern Mountain Arc (SMA) and Modern Volcanic Arc (MVA) which give rise to frequent volcanic activities. Prior studies suggested that SMA is formed during Middle Eocene, followed by the subduction that resulted in the formation of MVA in Late Eocene. Central Java is home to one of the most notorious volcanoes, Merapi, as well as other major volcanoes such as Merbabu, Muria, and Slamet. Mount Merapi is the most active volcano in Indonesia which erupt periodically every 2–6 years and has shown perennial volcanic activities dated back roughly 2000 years ago based on carbon isotropic signatures. The earliest eruption has been approximated to be roughly 40,000 years ago. The most recent significant eruptions occurred in 1994, 2006, and 2010. Mount Merapi is a steep stratovocano situated on Central Java Island with its seismic and volcanic activities that could pose major threats to countless lives and infrastructures in its vicinity. Most recent volcanic activities are induced by the collapse of lava dome, contributing to highly explosive eruption of andesitic materials. West Java The volcanic activities in this region have begun roughly since Pliocene or Pleistocene epoch. There are two major volcanic zones called the volcanic front (VF) and the rear arc (RA) with different chemical imprints. The geochemical study of major and trace elements and isotopic signatures of lava have confirmed the steady-state subduction and ongoing replenishment of magma for about 10 Ma. The volcanic rocks founded on West Java are dated back to the Eocene. The basement of West Java is continental lithosphere which can be inferred from crustal assimilation and contamination in volcanic rocks. Krakatoa The island of Anak Krakatau has grown at an average rate of five inches (13 cm) per week since the 1950s. Quiet periods of a few days have alternated with almost continuous Strombolian eruptions since 1994. In 1883 CE, tsunami were triggered by the eruption of Krakatoa with the run-up of 41 meters. The magnitude of damage reached Panama, which was located almost 19,300 km away from the focus. Sumatra Sumatra island is located on the southwest side of Sunda Arc. The main seismic zone of Sumatra is the Sumatra Fault System (SFS), which trends NW-SE. The subducting oceanic crust