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CRAMP Study Sites: Basaltic "Spur and Groove" Formations:

The fingerlike reef structures running perpendicular to the shoreline commonly seen along Hawaiian shorelines appear to be formed from resistant basalt ridges. The islands were formed by successive lava flows running down slope. These pre-existing lava formations consist various layers of dense sheet-like pahoehoe, broken blocks of aa lava, cinder, lava tubes filled with hardened dense lava or as long hollow lava tubes. All of these structures strike seaward due to the down slope direction of the flowing lava that formed the layers. Differential rates of erosion on the various types of lava will create longitudinal ridges and valleys. The basalt ridges become colonized by corals and crustose coralline algae that can eventually form thick layers of overlying carbonate rock. Remote sensing images reveal these structures that can appear to be similar to classic "spur and groove" formations. However, the features off Hawai‘i are generally eroded basaltic features rather than constructive carbonate features known as spur and groove formations. A number of areas, including Kawaihae (Hawai‘i), Olowalu (Maui) and Kailua Bay (O‘ahu) have quite massive spur and groove features that appear to be constructional and may fit the classic definition. Investigators working in Hawai‘i commonly have referred to all of these structures as "spur and groove" regardless of whether they are the result of erosion or biological accretion. In any event, these structures might be functionally similar habitats for organisms inhabiting the area.

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