Wave Action on Basalt

December 12, 2006

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Provided by: David Harrington, University of Hawaii, Institute for Astronomy
Summary authors & editors: David Harrington

The photo above shows a frothy wave crashing into a basalt rock platform at Waimea Bay, on the North Shore of Oahu, Hawaii, on October 1, 2006. During the winter season, the ocean produces 20 foot (>6 m) waves that pummel the basalt. Turbulent water from these huge waves (and smaller waves too) flows over the rock and sand as filaments, drops, streams, and sheets. The surface tension of the water as it moves through the air determines the shapes of these forms. Not only is chemical and physical weathering of the basalt occurring from the water, but the motion of sand grains plays a role in physical erosion as well. The small ripples in the lower left hand corner are from the previous wave flowing outward along the sand, moving the sand and leaving ripple marks similar to those found on river and lake beds. Entire beaches can disappear from the waves and ocean currents during the winter months, only to reappear the following summer.

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