Mysterious tar mounds in the West African deep ocean

Initial surveys of the seafloor of these areas of huge oil reserves revealed some unusual surface features, which were subsequently investigated using underwater robots. In the area of seabed investigated, which was around the size of the Isle of Wight, a total of 2254 mounds were identified by side-scan sonar, covering a total area of 3.7 square kilometres of seafloor, about the area of Golden Gate Park.