DEEP SEA MINERALS - Vol 1 - Sea-Floor Massive Sulphides

The potential extent of impacts 3.6

If a sediment plume is created through dispersal by currents, it will have a larger footprint than the physical mining area. There is also the possibility of plumes extending upwards into the water column, although engineering design should mini- mize such movement. Similarly, the area affected by discharge of the waste-water and fine materials could be more extensive than the mined area. Sediment and water-column plumes will disperse with distance, and this dilution will mean there is a gradient of impact, with effects lessening with distance from the mining site. In addition to potential impacts from normal operation, it is important to consider accidental events and natural haz- ards. These include such possible problems as spills and oil leaks from the vessel/platform, which enter the sea, and leaks from the riser pipe or from sea-floor equipment (e.g., hydraulic oil leaks). Although unlikely, such extreme events as a ship sinking or collisions between vessels or with marine mammals are possible. Commercial operators and national management agencies must reduce the risk of these sorts of events and must be prepared to respond in the event they do happen. Such precautions are generally covered under national and/or international regulations and are not detailed here. Natural hazards, such as ex- treme weather events, volcanic activity, etc., will also need to be considered in the management plans. Accidental Events and Natural Hazards

The Integrated Ocean Drilling Programme has conducted nu- merous scientific investigations of hydrothermal sites around the world. Pictured here is the Deep Sea Drilling Vessel JOIDES Resolution. Photo courtesy of Elaine Baker.

THE GEOLOGY OF SEA-FLOOR MASSIVE SULPHIDES 39