南三明治海沟（South Sandwich Trench）为一个在大西洋拱形的深海海沟，位于南三明治群岛以东100公里。因为南美洲板块（South American Plate）的南端隐没在细小的南三明治板块（South Sandwich Plate）下方的关系，形成隐没带，从而形成南三明治海沟。南三明治群岛拥有一个因为活跃隐没带而形成的火山弧（Volcanic arc）。蒙塔古岛（Montagu Island）上的贝琳达山（Mount Belinda）正是一个活火山.

The South Sandwich Trench is a deep arcuate trench in the South Atlantic Ocean lying 100 km to the east of the South Sandwich Islands. The trench is produced by the subduction of the southernmost portion of the South American Plate beneath the small South Sandwich Plate. The South Sandwich Islands constitute a volcanic island arc which results from this active subduction. Mount Belinda on Montagu Island is an active volcano.