The violent eruption of Krakatoa Volcano located in the Sunda Strait, Indonesia, in 1883 represents one of the deadliest eruptions in human civilization. Although lots of data have been reported, the trajectory of the subducted slab and the upper mantle structure beneath this volcano are still rather poorly known. We combined geochemical data, major, trace and rare earth elements with seismic tomograms to characterize the deep structure of Krakatoa Volcano at the junction of Sumatra and Java subduction systems. Geochemical data are in agreement with the partial melting of mantle wedge in these subduction systems, based on previous studies, and this conclusion is also supported by inferences from P-wave tomographic model. Whereas, the tomographic image of S-wave suggests that subducted slab has been intruded by hot material of mantle upwelling. The presence of both partial melting of mantle wedge and mantle upwelling in the upper mantle might be caused by the thinning of subducted slab beneath Krakatoa Volcano.

The research area is within the territory of Nature Preserve and Marine Preserve region of Krakatoa Islands, South Lampung District, Lampung Province. The study aims to determine the surface geological, mapped on a scale of 1: 20,000, and to determine the geological history that forms the Krakatoa Islands. Volcanostratigraphy is made by combined from literature studied, shoreline analysis, petrographic analysis and field observation. From these results, it is poured into a map of geological outcrops, maps of volcanostratigraphy profiles, geological maps and geological sections. Volcanostratigraphy on the research area is divided into 30 rock units that consists of 22 lava, 8 pyroclastic and allvuial. Geological structure that developed in the research area in the form of secondary structure that is crater and caldera, and the primary structure that is sheeting joinnt, columnar joint, vesicular and autobreccia. New and detailed geological map of Krakatoa volcano is presented.

Krakatoa Islands is one of the results of high activity volcanic islands located in the Sunda Strait, Indonesia. Volcanic activity of the research area is highly influential on the typical morphological conditions. Rocks produced from this volcano activity a role in the formation of geomorphology that is typical of areas with high volcanic activity. Rocks in the study area were the result of volcanic activity such as lava, pyroclastic alluvial. Geomorphology analysis was conducted by analyzing river flow pattern, slope criteria analysis and shoreline analysis since 1984. East Anak Krakatoa island which is dominated by lava, in contrast to the krakatoa west of which the rock formers are dominantly pyroclastic fall. Unconsolidated rocks form west Sertung island, east Panjang island and south Rakata island which the rock formers are dominantly pyroclastic flow. Evidence of 1883 catastrophic eruption is highly visible on the north Rakata island, east Sertung island and west Panjang island shown by vertical high cliff which is indicated as a caldera structure. The results of the geomorphological analysis are poured into geomorphological maps. Geomorphology unit in research area consist of 9 (nine) geomorphology units of Krakatoa Islands. Krakatoa Islands in this geomorphological case, is still controlled by climate change, erosional of sea water wave, 1883 catastrophic eruption which produces rock in the form of lava and pyroclastic and volcanic activity still continues to this day.

Krakatau is one of Quaternary volcanoes that has catastrophic eruption histories including the eruption in 1883 causing fatalities about 36.500 people. Such an Krakatau is one of Quaternary volcanoes that has catastrophic eruption histories including the eruption in 1883 causing fatalities about 36.500 people. Such an