Split Top Mountain, Alaska, USA
(c) 2000 Andrew Alden, licensed to About.com, Inc. (fair use policy)
Split Top Mountain is an important part of the northwest skyline of Unalaska/Dutch Harbor, the twin towns of Unalaska Island in the Aleutian Islands. Its treeless, windblown flanks are typical of the whole Aleutian chain.
The Aleutians are a volcanic island arc, built by magmas welling up from the subducted crust of the Pacific plate. Other island arcs are built this way—the Antilles, the Kermadecs, the Ryukyus, Java and Sumatra, the Japanese archipelago and others—but the Aleutians are distinctive in having been glaciated, too. The scooped-out cirques on either side of the peak, and the deep fiord of Unalaska Bay on the left, were once filled with ice while the sea sat as much as 100 meters lower than today.
When the ice went away, the oversteepened slopes underlain by fragile volcanic rocks often collapsed, as they have on Split Top Mountain's left flank. The resulting landscape is rugged, intricate, and compelling even on rare days like this when it's not shrouded in cold fog from the Bering Sea.
See other pictures of this region in my photo-tour of a 1979 research cruise here.
