The climate is subtropical and mild, with little seasonal differentiation. The island is the eroded remnant of a basalticvolcano active around 2.3 to 3 million years ago,21 - with inland areas now consisting mainly of rolling plains. It forms the highest point on the Norfolk Ridge, part of the submerged continent Zealandia. The area surrounding Mt Bates is preserved as the Norfolk Island National Park. The park, covering around 10% of the land of the island, contains remnants of the forests which originally covered the island, including stands of subtropical rainforest. The park also includes the two smaller islands to the south of Norfolk Island, Nepean Island and Phillip Island. The vegetation of Phillip Island was devastated due to the introduction during the penal era of pest animals such as pigs and rabbits, giving it a red-brown colour as viewed from Norfolk; however, pest control and remediation work by park staff has recently brought some improvement to the Phillip Island environment.