Submersible observations have been made on‘ patches’ of the deep-water coral Lophelia pertusa (L.) occurring on Rockall Bank, north-east Atlantic. It is suggested that an initial colony gives rise to a ring of younger colonies. These in turn give rise to further rings of colonies, thus enlarging the ‘patch’. The transition from stage to stage depends on portions of living colonies, weakened by clionid sponge attacks, breaking off and falling away from the colony so providing the substrate for the development of later colonies, thus enabling lateral increase in the size of the ‘patch’ to take place.

A 4000‐km2 area of submarine slump and slide deposits along the west flank of Mauna Loa volcano has been mapped with GLORIA side‐scan sonar images, seismic reflection profiles, and new bathymetry. The youngest deposits are two debris avalanche lobes that travelled from their breakaway area near the present shoreline as much as 100 km into the Hawaiian Deep at water depths of 4800 m. The two lobes partly overlap and together are designated the Alika slide. They were derived from the same source area and probably formed in rapid succession. Distinction hummocky topography, marginal levees, and other features on lower slopes (0.3°–0.6°) of these deposits resemble subaerial volcanic debris avalanche deposits such as 1980 Mount St. Helens and suggest high emplacement velocities. The breakaway area for the Alika slide (10°–15° slopes) is characterized by large block slumps, bounded by normal faults, that probably represent multiple subsidence events before, during, and after the debris avalanches. Lower slopes of the slide contain distinctive lobate‐terraced deposits that are interpreted as having been emplaced more slowly, prior to the debris avalanches. Estimated thicknesses of 50–200 m suggest volumes of 200–600 km3 for the two lobes. The combined volume of the entire slide and slump terrane is probably 1500–2000 km3. The slide deposits predate a 13‐ka coral reef and probably postdate the block‐faulted Ninole Basalt, roughly dated as a few hundred thousand years old. The Alika slide, or a similar deposit recognized on GLORIA images further north along the Hawaiian Ridge, probably triggered a giant wave that washed 325 m high on Lanai at about 100 ka. Slumping on Mauna Loa has been most intense adjacent to the large arcuate bend in its southwest rift zone, as the rift zone migrated westward away from the growing Kilauea volcano. Slumping events were probably triggered by seismic activity accompanying dike injection along the rift zone. Such massive slumps, landslides, and distal submarine turbidity flows appear to be widespread on the flanks of Hawaiian volcanoes.

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