 The eastern flanks of both volcanoes are cut by deeply incised valleys and steep-sided ravines that run downslope to the rocky, windswept shoreline.The valley-like Isthmus of Maui that separates the two volcanic masses was formed by sandy erosional deposits.Maui's last eruption (originating in Haleakalā's Southwest Rift Zone) occurred around 1790; two of the resulting lava flows are located (1) at Cape Kīnau between Āhihi Bay and La Perouse Bay on the southwest shore of East Maui, and (2) at Makaluapuna Point on Honokahua Bay on the northwest shore of West Maui.