The island of Maui is the second-largest of the Hawaiian Islands at 727.2 square miles (1883.5 km2) and is the 17th largest island in the United States. Maui is part of the state of Hawaii and is the largest island in Maui County. Three other islands, LÄnaÊ»i, KahoÊ»olawe, and MolokaÊ»i, also belong to Maui County. Together, the four islands are known as Maui Nui. In 2000, Maui had a population of 117,644, the third-largest of the Hawaiian islands, behind that of OÊ»ahu and HawaiÊ»i. Kahului is the largest town on the island with a population of 20,146. Wailuku is the seat of Maui County.
Maui's wide variety of landscapes have resulted from a unique combination of geology, topography, and climate. Each volcanic cone in the chain of the Hawaiian Islands is built of dark, iron-rich/quartz-poor rocks, which poured out of thousands of vents as highly fluid lava, over a period of millions of years. Several of the volcanoes were close enough to each other that lava flows on their flanks overlapped one another, causing several volcanoes to merge into a single island. Maui is such a "volcanic doublet", formed from two shield volcanoes that overlapped one another to form an isthmus between them.