The island of Maui is the second-largest of the Hawaiian Islands at 727.2 square miles (1,883 km2) and is the 17th largest island in the United States. Maui is part of the State of Hawaiʻi and is the largest of Maui County's four islands, bigger than Molokaʻi, Lānaʻi, and unpopulated Kahoʻolawe. In 2010, Maui had a population of 144,444, third-highest of the Hawaiian Islands, behind that of Oʻahu and Hawaiʻi Island.
Maui's diverse landscapes are the result of 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, merging 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.