The southernmost province of Indonesia comprises the eastern portion of the Lesser Sunda Islands, facing the Indian Ocean in the south and the Flores Sea in the north. It has 566 islands, with the largest ones being Sumba, Flores, and the western part of Timor. The islands are part of the the Banda Arc. The northern islands belong to inner volcanic arc and are of volcanic origin. They also have active volcanism. The southern islands belong to the outer accretionary arc and were formed by the accumulation of sedimentary rock at the sea floor due to the convergent movement of the two plates. As a result it is composed of Cenozoic and Mesozoic formations and has some metamorphic complexes.