The seabed (also known as the seafloor, sea floor, or ocean floor) is the bottom of the ocean. At the bottom of the continental slope is the continental rise, which is caused by sediment cascading down the continental slope. The seabed has been explored by submersibles such as Alvin and, to some extent, scuba divers with special apparatuses. The process that continually adds new material to the ocean floor is seafloor spreading and the continental slope. The acronym "mbsf" meaning "metres below the seafloor" is a convention used for depths below the seafloor.