Coastal Bench Formation at Hanauma Bay, Oahu, Hawaii
Coastal bench formation at Hanauma Bay, Oahu, Hawaii WILFRED B. BRYAN Department of Geology and Geophysics, Woods Hole Oceanographic Institution, Woods Hole, Massachusetts 02543 ROBERT S. STEPHENS* Hawaii Institute of Geophysics, Honolulu, Hawaii 96822 ABSTRACT rainfall about 4-8 cm per year. Prevailing winds are from the east- northeast, so that the inner north shore is normally the most sheltered A coastal bench that developed from 1 to 6 m above sea level in part of the bay. basaltic tuff at Hanauma Bay conforms to the upper limit of wetting by Many rock benches have been described from Australia, New wave wash at high tides associated with present sea level; it does not Zealand, and on islands in or around the Pacific basin. Such benches constitute evidence for a recent Holocene highstand on Oahu. Variations are usually ascribed to "cutting" by waves and often are called in bench width and elevation are related to differences both in exposure '' wave-cut platforms.'' Typically they are < 1 to > 3 m above sea level to waves and in exposure to daily heating and drying of the cliff behind and have been cited as evidence for a "2-meter" global eustatic high- the bench. Salt weathering of the sort usually invoked to explain weath- stand. They also have been attributed to storm waves, a mechanism ering effects in deserts is a major factor in the retreat of the cliff and the strongly endorsed by Bartrum (1926) and Edwards (1951). However, consequent formation of the bench. The waves do not "cut" the bench others (for example, Hills, 1949) have noted that coastal benches and but, instead, by daily wetting, protect it from desiccation.
[Show full text]