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Sectors: Haena -- Hanalei -- Na Pali -- Po‘ipū

Study Sites: Miloli‘i -- Nu‘alolo Kai

A unique submarine feature on Kaua‘i is the massive submarine ridge located along the northwestern coast of the island. This ridge occurs directly off Polihale Beach and is approximately 10 nautical miles long running from north of Mana (Barking Sands) in the south to Nu‘alolo in the north. The top of the ridge varies in depth from 7 to 10 fathoms (42-60 feet). The trough between the ridge and shore reaches depths of from 12 to 15 fathoms (70- 90 ft). The area is characterized by deeply fractured basalt with deep crevices running along the crest. The bathymetry resembles that of a sunken barrier reef with associated lagoon. One hypothesis is that this area represents a relict barrier reef formed during a previous lower sea level stand. Numerous drowned sea level terraces do occur at 20-60 m around the island. Others suspect that its origin might actually be the result of faulting and erosion or subsidence of a large section of shoreline. Regardless of origin, the Mana ridge structure may have been functionally acting as a barrier reef at lower sea level stands. The area presently has unique coral formations and abundant fish life. Jacks, sharks and other large fish are observed here (Andrew Ellis, Personal Communication). The area is notable because corals of the genus Acropora, have been found along the "Crack".

Chart showing the Mana Crack area.

Chart showing the Mana Crack area. (Click image for larger view.)

 

Last Update: 04/21/2008

By: Lea Hollingsworth

Hawai‘i  Coral Reef Assessment & Monitoring Program

Hawai‘i  Institute of Marine Biology

P.O. Box 1346

Kāne‘ohe, HI 96744

808-236-7440 phone

808-236-7443 fax

email: jokiel@hawaii.edu