Maori tradition speaks of the Marlborough Sounds as the shattered prow of an intracately adorned canoe by which the gods came from heaven.
The Sounds are unique in New Zealand as the only land area sinking into the sea. The Sounds are a continuation of the Richmond Range, which has tipped into the sea. The bedrock they consist of formed 280 million years ago and has moved 53km since the Pliocene 7.7 million years ago. Sedimentary, volcanic, and mineral belts are found in close proximity. Concentrated deposits of nickel, chromium, cobalt, molybdenum and manganese are found in the mineral belts, and cause stunting of vegetation at low altitudes. Movement continues northwards at a rate of 6.6mm per year. This movement is a result of the Sounds being on the boundary of the Pacific and Indo-Australian plates. This active geology has led to dramatic ridges rising out of the sea, and a sheltered marine environment. This environment provides a home to a rich diversity of marine life. Crabs, paua, kina, shrimps, starfish and anemone's, blue mussels, and bladder kelp are all common. Over 200 species of fish and three sea mammals also inhabit the Sounds, including snapper, blue cod, terakihi, moki, and in the outer reefs, grouper. Blue cod and snapper suffered from over fishing, however with effective management fish stocks are returning.
Several predator free islands in the Sounds are used for recovery programs for a variety of endangered species including the kakapo, tuatara, and giant weta. On land, much of the Sounds are covered in regenerating bush after being cut over, however there are also many reserves of original podocarps and broadleafed trees, lianas, orchids and ferns.
Commercial use includes mussel and oyster farming. The former is one of Marlborough's largest industries. In addition, the Sounds are extremely popular as a recreational playground and there are a number of holiday homes and resorts located throughout the Sounds. The rich mineral deposits of the Sounds have also encouraged past efforts at mining, including copper mining on D'urville Island, and gold mining at Cape Jackson.