A kind of urban legend has it that the sand on the beaches of Hawaii nowadays comes by barge from California. Given recent evidence of significant coastline erosion seen along many beachfronts around the world, one can understand the concept behind the story. However, inasmuch as the sandy stretches garlanding the islands of Hawaii mainly come either from the breakdown of coral reefs, ground up residue of lava and particles of iron, the importing of sand composed primarily of quartz does not seem a likely scenario.
As suggested, beach sand originates from natural sources of diverse characteristics. The perceived coloration of sand – white, tan, copper, dark brown – depends on the makeup of the material from which it has come. If the source material contains iron, the sand likely will have a reddish or light brown color. Dark green sand may have as its origin certain olivine crystals. Very dark or black sand normally results from the disintegration and distribution of lava rock. White sand suggests a large share of the sand contains particulates of calcium from sea shells broken down by the pounding waves and the mincing effect of sand already deposited. A close-up examination of beach sand reveals a marvelous array of colorful particles.
The sand on ocean beaches derives from three basic sources:
1. Inland. The eroding effect of runoff water on inland areas of a land mass washes different kinds of material to the mouths of rivers emptying into the ocean. By the time this material has become a part of the river’s delta, it will have undergone considerable crushing as it encounters stream bed boulders and rolls and bounces along the bottom of the stream. Once deposited into the shallows of the ocean, the dispersing effect of tides and waves distributes the material along nearby beaches. The color and composition of this type of sand will, of course, depend on the type of material the river has brought down stream and how it has become intermixed along the shoreline.
2. Erosion. Along many shorelines, the sand found on beaches comes from material within reach of the ocean’s waves. The material may consist of rock, prehistoric seabeds or different kinds of sandstone. Over thousands of centuries, the pounding effect of incoming waves eat away at these shorelines, slowly eroding them onto the beachfront. Again, the sand on these beaches will have the same diversity as the eroded material directly behind the beaches.
3. Offshore. In areas where coral reefs have developed, the beaches will have a composition reflecting that of the underwater structure. The continuous surging sweep and pound of waves works to break down the reefs to repositionable particles. The beaches formed by the gradual breakdown of these formations reflect the coloration and makeup of the local reefs.