Saturday, April 19, 2008

Cliffs, Sea Caves, Stacks, and Natural Bridges

Coastal hikes are always a pleasure. The configuration of coastlines and shorelines are changing from day to day. Hiking along beaches or on cliff trails brings you in touch with the sculptural power of wind and waves. One of my favorite descriptions of this scenery and how it forms is by Rachel Carson [1]:

... we owe some of the most beautiful and interesting shoreline scenery to the sculpturing effect of moving water. Sea caves are almost literally blasted out of the cliffs by waves, which pour into crevices in the rocks and force them apart by hydraulic pressure. Over the years the widening of fissures and the steady removal of fine rock particles in infinite number result in the excavation
of a cave. Within such a cavern the weight of incoming water and the strange suctions and pressures caused by the movements of water in an enclosed space may continue the excavation upward. The roofs of such caves (and of overhanging cliffs) are subjected to blows like those from a battering ram as the water from a breaking wave is hurled upward, most of the energy of the wave passing into this smaller mass of water. Eventually a hole is torn through the roof of the cave, to form a spouting horn. Or, on a narrow promontory, what began as a cave may be cut through from side to side, so that a natural bridge is formed. Later, after years of erosion, the arch may fall, leaving the seaward mass of rock to stand alone—one of the strange, chimneylike formations known as a stack.

[1] Rachel L. Carson: The Sea Around Us. Special Edition, Oxford University Press, New York, 1989; page 124. The Sea Around Us was originally written in 1951, bringing together, in flowing style, the state of the knowledge of the ocean world at that time.

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