Radiocarbon profile of Hanauma Reef, Oahu, Hawaii

Easton and Olson (1976) have offered evidence to prove that the ocean at Hanauma Bay has not stood higher than at present during the past 7,000 yrs. They ignore an important outcrop of beachrock clinging to a basaltic dike on the east shore of the bay 5 to 8 ft (1.5 to 2.4 m) above sea level, coincidental with the elevation of the "2-m" bench so well developed around the east side of the bay and shown in their Figure 1. Fossil coral from this beachrock outcrop has a C14 age of 3,485+160 yr (Geochron Laboratory sample GX-2673; Stearns, 1974). Easton and I examined the outcrop together. The specimen taken as a sample for dating had been transported, but the 2-m bench is ubiquitous in Hawaii and the Pacific and cannot be omitted from their study. The 2-m bench and notches occur only in weak tuff and limestone in the Pacific and are believed to indicate only a short eustatic stand of the sea lasting about 1,000 yr and ending about 3,000 yr ago. There is no way the hard beachrock at Hanauma Bay could have been cemented at this level from storm-tossed sand and gravel, because it adheres to the face of the basaltic dike and shows bedding typical of a beach held at the 2-m level by a higher ocean.