The island of Maui, the second largest Hawaiian island, is made up of two volcanoes, separated by low lying land. The smaller of the two, the West Maui Volcano is an extinct volcano and rises above 5000 feet out of the sea. The larger volcano, East Maui Volcano, which includes Haleakala Crater, rises above the sea to over 10,000 feet. It covers 75% of Maui's land. The East Maui Volcano is considered dormant, having last erupted a little over 200 years ago. The land that connects the two volcanoes was formed by lava flow from the East Maui Volcano that built up over time.
About 1.2 million years ago, Maui was connected to Lanai, Molokai, Kaho'olawe and Penguin Bank, a bench between Molokai and Oahu, forming a super island known as Maui Nui, Greater Maui. On this super-island, there were 6 to 7 different shield volcanoes, similar to what Big Island looks like today. Erosion and glaciation over time has split the super island into 4 smaller islands that you would see today as you drive the coastal roads of Maui. It is predicted that East and West Maui Volcanoes will also split into separate islands in 15,000 years.