Back-arc Seamount Distribution Along the Western Aleutian Volcanic Arc

Seamounts and seafloor volcanoes provide important insights into magma production, fluid flow in the crust, and habitat oases for marine life. In 2005, we obtained the first modern multibeam bathymetric maps, using the 30 kHz Simrad EM300 on the RV Thompson, for large areas of the Aleutian back-arc from west of Attu to Unalaska. Hundreds of previously unknown small seamounts were discovered, and many of the larger previously known seamounts were bathymetrically mapped completely for the first time. Equally important, the high-resolution bathymetry was able to confidently establish areas where no seamounts exist. Our mapping concentrated on several rhombochasms and the general back-arc region. Individual seamounts were identified and characterized using a GIS-based method for detecting local peaks in digital elevation models. Our results indicate that seamounts become progressively smaller but more abundant westward along the arc. Seamounts tend to be organized in linear chains that are subparallel to the local direction of maximum compressive stress indicated by scarps bounding their rhombochasm. Finally, no seamount was found in the Kresta Trough west of Attu, suggesting that this marks the westward limit of (normal?) volcanic production along the Aleutian Arc. These results are correlated to the obliquity of subduction of Pacific Plate beneath the arc.