Volcanic activity has been intense through the ages, and most of the surface of the island (outside of the Bukit Peninsula and Prapat Agung) has been covered by volcanic magma. Some old deposits remain (older than 1 million years), while most of the central part of the island is covered by young volcanic deposits (less than 1 million years), with some very recent lava fields in the northeast due to the catastrophic eruption of Mount Agung in 1963.