The island of Maui comprises two major volcanoes, West Maui and East Maui (Haleakala). But Maui itself is one of four islands that form the once-great island of Maui Nui. The other islands are Kaho`olawe, Lana`i, and Moloka`i. The extent of these islands and the shallow flooded platform that connects them is easily seen in the accompanying bathymetric map, which shows the southeastern part of the Hawaiian Island chain. Maui Nui--roughly coincident with the four islands of Maui County--probably was similar in extent to today's Big Island.
The submergence of Maui Nui resulted from the complex interplay of diminished volcanic upbuilding and continued subsidence as the island complex moved away from the Hawaiian hot spot. A similar fate awaits the Big Island. As the Pacific plate moves relentlessly northwestward, at about 10 cm per year, the Big Island volcanoes will lose their eruptive vigor. Without the benefit of rapid volcanic construction, subsidence will dominate; the sea will slowly encroach on the flanks of the separate volcanoes, then flood the saddles that separate them, creating smaller islands.
The URL of this page is http://hvo.wr.usgs.gov/volcanoes/haleakala/mauinui.html