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Marine Places

South Sandwich Trench

Although discovered by James Cook in 1775, the South Sandwich Islands were not visited until 1818, when seal hunters landed. They were never permanently settled and remain uninhabited. With volcanic peaks rising up to 3,300 ft (1,000 m) above sea level, the islands are mostly composed of basaltic lava and covered by glaciers. North of the islands is the Protector Shoal—an undersea volcano that rises to within 100 ft (30 m) of the surface. The South Sandwich Islands mark the eastern boundary of the Scotia Sea, and the South Sandwich Trench lies a little farther to the east. Both features are caused by tectonic processes occurring where the Scotia and South Atlantic plates meet. The Scotia Plate is split and spreading at the East Scotia Ridge, forming a new plate at its eastern end—the South Sandwich microplate. This plate is geologically young, at about eight million years old, and buoyant. Moving eastward at about 2.75 in (7 cm) per year, it is converging with the South Atlantic Plate, resulting in the older South Atlantic Plate sinking beneath the South Sandwich Plate at a subduction zone. This zone is marked by the South Sandwich Trench and the volcanic island arc of the South Sandwich Islands (or the Scotia Arc).

South Sandwich Trenchzoom image
  • Length 600 miles (965 km)
  • Maximum Depth 27,300 ft (8,325 m)
  • Rate of Closure 2.75 in (7 cm) per year