Volcanic action has resulted in the burial of the surfaces of Mauna Loa and Kilauea, Hawaii, by new lava flows at rates as high as 90% per 1000 years. Local populations of organisms on such volcanoes are continually being exterminated; survival of the species requires colonization of younger flows. Certain populations of the endemic Hawaiian species Drosophila silvestris exemplify such events in microcosm. Local populations at the base of an altitudinal cline were destroyed by two explosive eruptions within the last 2100 years. Natural recolonization restored the cline except for one young population that is genetically discordant with altitude.