Sand on the Virginia Barrier Islands is driven along the coast by waves. Waves from the northeast drive sand southward. Southeast waves drive sand north along the beach. Sand loss from one end of an island may be the gain of the at the other end. Or, one island may harvest sand from the loss of a neighbor island. These ribbons of sand can be seen in the illustration. The sand, the substrate, of these islands is like the air and water, fluid. It moves from place to place. One time it is there and another it is not. Building a house on such a fluid is a risky thing to do.
