Atol das Rocas
- ISS007-E-9762_2
- 09 July 2003
- 13:05 UTC
Rocas Atoll (Atol das Rocas) is a little-known, isolated atoll formation of the southwestern tropical Atlantic, located 265 km off the northeastern coast of Brazil and 146 km directly westwards from the island of Fernando de Noronha; it is the best example of an Atlantic atoll formation and the only example in the southwestern Atlantic.
The atoll is the emergent portion of a large, flat-topped seamount formation. Rocas atoll is located at the western side of this seamount with the remainder of its summit extending to the east and northeast as a shallow submarine shelf (see large size image). The seamount is part of a chain of seamounts, that also includes the island of Fernando de Noronha, that stretch out in an east to west trending line along the Fernando de Noronha Fracture Zone.
The atoll is oval in outline, measuring 3.7 km in length (east to west) and 2.5 km in width (north to south), consisting of an outer perimeter reef (100 to 800 m in width and dominated by reef-building algae) that encloses a shallow central lagoon of 7.1 km² in area. The encircling reef is almost continuous, being broken by a 200 m wide passage on the northern side and by a smaller channel on the western side. The reef is best developed on the windward margin, becoming less pronounced on the leeward side.
The western side of the atoll contains two small islets: Farol Cay (on the northwest) and the smaller Cemitério Island (on the southwest). They have a combined are of 0.36 km² and are vegetated primarily with grasses and low shrubs.
Protected by the 360 km² Reserva Biológica do Atol das Rocas (to the 1,000 m depth contour) and designated as a World Heritage Site by UNESCO, Rocas Atoll is an important nesting and feeding site for many species of migratory sea bird, and both green and hawksbill turtles.
image: earth sciences and image analysis laboratory, nasa johnson space center
