It is about 15 km to the south of the southwestern most tip of the Reykjanes peninsula. The structure of Eldey is basaltic hyaloclastites, and it is 0,3 km2 in area. It is the innermost of a chain of skerries standing on a shallow, submarine ridge, which stretches 45 seamiles offshore to the southwest. The name of this chain is Fuglasker or Eldeyjar. One of those skerries was Geirfuglasker, where the last breeding colonies of the Great Auk was located. Geirfuglasker disappeared mostly from the surface during submarine eruptions in 1830. One of the biggest gannet colonies of the world is still surviving on Eldey. According to a count which was made in 1949 the number of gannets breeding there during the summer was 70.000.