Beach - Encyclopedia

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BEACH, a word of unknown origin; probably an old dialect word meaning shingle, hence, by transference, the place covered by shingle. Beach sometimes denotes the material thrown up by the waves, sometimes the long resulting ridge, but more frequently the area between high and low water, or even the area between land and sea covered with material thrown up by exceptional storms.

The actual character of beach material depends upon the nature and structure of the rocks inshore, the strength and direction of currents, and the force of the waves. The southern shore of the Isle of Wight furnishes a good example. The island ends westward in the well-known "Needles," consisting of chalk with flints. The disintegration of this rock by wave action separates the finer chalk, which is carried seawards in suspension, from the hard flint, which is piled in rough shingle upon the shore. The currents sweep constantly eastward up channel, and the rough flint shingle is rolled along by wave action toward the Ventnor rampart, and ground finer and finer until it arrives as a very fine flinty gravel at Ventnor pier. The sweep of Sandown Bay follows, where the cliffs are composed for the most part of greensand, and here the beach at low water is sandy and smooth. The eastern end of the island is again composed of chalk with flints, and here the beach material as at the western end consists of very coarse flint shingle. In this, as in similar cases, the material has been dragged seawards from the land by constant action of the undertow that accompanies each retreating tide and each returning wave. The resulting accumulated ridge is battered by every storm, and thrown above ordinary high-water mark in a ridge such as the Chesil Bank or the long grass-grown mound that has blocked the old channel of the Yar and diverted its waters into Yaverland Bay. Sandown furnishes an instructive example of the power of the eastward currents carrying high-storm waves. The groins built to preserve the foreshore are piled to the top with coarse shingle on the western side, while there is a drop of over 8 ft. on to the sands east of the wall, many thousands of tons of shingle having been moved bodily by the waves and deposited against each groin. The force of the waves has been measured on the west coast of Scotland and found to be as much as 3 tons per square foot. Against these forces the preservation of the shore from the advance of the sea becomes an extremely difficult and often a hopeless undertaking, since blocks of rock over ioo tons in weight have been moved by the waves. The beach is therefore unstable in its position. It advances in front of the encroaching sea, burying former beaches under the sand and mud of the now deeper water, or it retreats when the sea is withdrawn from the land or the land rises locally, leaving the old shingle stranded in a "raised beach," but its formation is in all cases due to the form and structure of the shore, the sapping action of the waves, the backward drag of the undertow plastering the shore with material, which is in turn bombarded by waves and swept by currents that cover the finer debris of the undertow with a layer of coarse fragments that are re-sorted by the daily action of currents and tides.

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