Loss of Hawaiian Littoral Sand

Abstract

ABSTRACT Temporary losses or gains between individual beach and nearshore sand reservoirs in Hawaii amount to a few cubic meters of sand per meter of beach per month. In addition to these changes of seasonal nature, the littoral sediment system is in dynamic equilibrium, with some new sand entering while other sand is being removed permanently. A principal loss is to deep water by wave and current action mainly along sand-bottomed channels that cross reefs and are generally deeper than the adjacent reef flats and reef slopes. The channels, were cut by streams during lower stands of sea level in the Pleistocene and, because coral and calcareous algal growth has been inhibited on the channel bottoms by the sand trapped and transported downslope in them, have remained as topographic features. On he reef flats and where beaches and deltas agrade, sand is lost by paralic sedimentation. Abrasion experiments suggest that surf abrasion to silt-size is a significant process of sand-loss in Hawaii and that basalt-rich sands abrade faster than calcareous-rich ones. Within calcareous sands, the aragonitic skeletal components abrade markedly faster than the calcitic components. All these local components abrade some three orders of magnitude faster than quartz sand, which is absent in Hawaii. Some additional sand is driven inland to storm beaches or blown inland to dunes, and some is cemented to beaches or exploited commercially by man.