ABSTRACT

Hawaiian littoral sand is a mixture of detrital and organic grains, whose relative abundance depends on recency of vocanism, intensity of weathering in the hinterland, and vigor of growth of marine organisms. The size and sorting of the beach sands vary by island, quadrant, locality, and season in relation to exposure to tradewind-driven waves, to storms, and to reef configuration.

Detrital components are mainly fresh grains of basalt, but weathered grains may be preserved on some sheltered coasts. Sands rich in olivine grains from lava phenocrysts or in black basalt glass are significant locally. Calcareous organic grains in general order of abundance are Foraminifera, mollusks, red algae, Echinoids, corals and Halimeda. Most of the sediment on the widest and shallowest fringing reef flats, and on the beaches behind them, does not originate on the reef flats, but rather comes from organisms washed in across the reef edge.