Maui’s wide variety of landscapes 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, 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. Maui’s last eruption (originating in Haleakalā’s Southwest Rift Zone) occurred around 1790; two of the resulting lava flows are located at Cape Kīnau between Āhihi Bay and La Perouse Bay on the southwest shore of East Maui, and at Makaluapuna Point on Honokahua Bay on the northwest shore of West Maui. Although considered to be dormant by volcanologists, Haleakalā is certainly capable of further eruptions.