File:Shore processes and shoreline development (1919) (14760878541).jpg

Identifier: shoreprocessessh00john (find matches)
Title: Shore processes and shoreline development
Year: 1919 (1910s)
Authors: Johnson, Douglas Wilson, 1878-1944
Subjects: Shorelines Coasts
Publisher: New York : John Wiley & Sons, Inc. (etc., etc.)
Contributing Library: University of California Libraries
Digitizing Sponsor: MSN

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shallowing sea floor cast up thebottom material into an initial bar or ridge; later, larger stormwaves break a little farther out in deeper water, and from thene\vly eroded bottom material construct another bar on theface of the earlier one. A preliminary offshore bar is builtup by the storm waves . . . ; and afterwards, at times ofexceptional storms, successive additions may be made on itsouter side^. According to this theory, also, the accumulationoccurs on the face and not on the end of the earlier deposit; butthe material is supposed to be derived from the sea-bottom andnot from the longshore currents upon which Gilbert relied. When a recurved spit develops into a compound spit or fore-land by the addition of successive spits or embankments to itsseaward side, there is produced a beach plain characterized bysub-parallel ridges separated by belts of lower land or strips ofwater. In this case, however, the accumulation may take place 406 SHORE RIDGES AND THEIR SIGNIFICANCE > <
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ORIGIN OF BEACH RIDGES 407 not simultaneously along the entire face of the earlier deposit,but by extension of the ends of the successively formed embank-ments; longshore currents furnish the principal supply of mate-rial; and the individual ridges are evidently not to be correlatedwith a corresponding number of great storms. Davis^i appearsto regard the beach ridges of the Provincelands as having beenproduced in the manner here indicated, although his admirableessay on The Outline of Cape Cod does not explicitly statethat the successive embankments all grew longitudinally fromtheir point of tangency with the mainland cliff. It is highly probable that ridged beach plains have beenproduced in all three of the ways mentioned above. Whereone part of a shore is being cut back and straightened by thewaves, a longshore current may have its course so modified asto depart from an adjacent section of the shore which it pre-viously followed. If the withdrawal is gradual enough, theportion of th

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