Java and Bali to the east. Borneo lies to the north and Christmas Island is to the south. It is the world's 13th largest island. Java is surrounded by the Java Sea to the north, Sunda Strait to the west, the Indian Ocean to the south and Bali Strait and Madura Strait in the east. Java is almost entirely of volcanic origin; it contains thirty-eight mountains forming an east–west spine that have at one time or another been active volcanoes. The highest volcano in Java is Mount Semeru (). The most active volcano in Java and also in Indonesia is Mount
Ryukyu Trench margin right up to the northeastern Taiwan coastline, also without the existence of a dextral north-south trending fault. Ocean bottom seismography methods combined with earthquake studies of the Benioff zone constrain the dip angle of the Philippine Sea Plate along the Ryukyu trench. In the Northern part of the Ryukyu trench, the dip of the Philippine Sea Plate is shallow at shallow depth, reaching only about 11° in the first 50 km, and steeper at deeper depths, reaching 70° below about 70 km. In contrast, the slab dip in the central and southern parts of the Ryukyu trench is more