Littoral Sedimentary Processes on Kauai, A Subtropical High Island

Abstract

Beach and shallow water sand samples from the island of Kauai, Hawaiian Islands, were studied to ascertain the effects of climate on the supply of sediment, and of wave action on the dispersal and transport of sand along the shores of this circular island. The littoral sediment s of the island are made up of two components: biogenous material, such as shell, coral, and foraminiferal sands, formed near the shoreline; and terrigenous material, consisting mostly of volcanic mineral and rock fragments brought to the beach by rivers. The northeast trade winds play a dominant part in the climatic and oceanographic processes affecting the island. On the windward side of Kauai, the annual rainfall ranges from 30 inches near the coast to over 460 inches at higher elevations; on the leeward side, annual rainfall is less than 20 inches. This large variation in rainfall results in a climatic range from tropic-humid to semi-arid. Rivers draining the wet, windward port ion of the island carry relatively little sand, and the shoreline on this side is characterized by intermittent fringing reefs and beaches of calcareous sand. A detail ed study of several reefs on the windward side of the island shows that each pair of fringing reefs, divided by a relatively deep inlet, constitute separate cells for the circulation of water and distribution of sediments. The highest concentrations of volcanic sand occur on the lee side of the island , where streams draining the semi-arid region enter the coast. The concentration of volcanic material in the beach sands decreases logarithmically with distance along the coast from the rivers.