The Savage Islands, or Ilhas Selvagens in Portuguese, are a small archipelago in the eastern North Atlantic Ocean between the archipelago of Madeira to the north and the Canary Islands to the south. Like these other island groups, the Savage Islands are thought to have been produced by volcanism related to a mantle plume or “hot spot.”
Typically, volcanoes are fueled by magma being generated where tectonic plates are colliding or being pulled apart. The active volcanoes remain at the plate boundaries, even as the plates shift. Mantle plumes, in contrast, are relatively fixed regions of upwelling magma that can feed volcanoes on an overlying tectonic plate. When a tectonic plate passes over the mantle plume, active volcanoes form, but they become dormant as they are carried away from the hot spot on the moving tectonic plate. Over geologic time, this creates a line of older, extinct volcanoes, seamounts, and islands extending from the active volcanoes that are currently over the plume.
These two astronaut photographs illustrate the northern (top) and southern (bottom) Savage Islands. The two views were taken 13 seconds apart from the International Space Station; the geographic center points of the images are separated by about 15 kilometers. Selvagem Grande, with an approximate area of 4 square kilometers, is the largest of the islands. The smaller and more irregularly-shaped Ilhéus do Norte, Ilhéu de Fora, and Selvagem Pequena are visible at the center of the lower image. Spain and Portugal both claim sovereignty over the Savage Islands.
All of the islands of the archipelago are ringed by bright white breaking waves along the fringing beaches. Reefs that surround the Savage Islands make it very difficult to land boats there, and there is no permanent settlement on the islands. The islands serve as nesting sites for several species of seabird including petrels and shearwaters, and they are included on the tentative list of additional UNESCO World Heritage Sites.
Astronaut photographs ISS021-E-11832 and ISS021-E-11833 were acquired on October 22, 2009, with a Nikon D2Xs digital camera fitted with an 800 mm lens, and are provided by the ISS Crew Earth Observations experiment and Image Science & Analysis Laboratory, Johnson Space Center. The images were taken by the Expedition 21 crew. The image in this article has been cropped and enhanced to improve contrast. Lens artifacts have been removed. The International Space Station Program supports the laboratory to help astronauts take pictures of Earth that will be of the greatest value to scientists and the public, and to make those images freely available on the Internet. Additional images taken by astronauts and cosmonauts can be viewed at the NASA/JSC Gateway to Astronaut Photography of Earth. Caption by William L. Stefanov, NASA-JSC.
In one frame International Space Station astronauts were able to capture the evolution of fringing reefs to atolls. As with the Hawaiian Islands, these volcanic hot spot islands become progressively older to the northwest. As these islands move away from their magma sources they erode and subside.