Abrasion, also called corrasion, occurs when the sea scrapes smaller rocks and particles against stone cliffs, stones or the beach itself. It is a form of contact erosion, solid to solid, that slowly eats away at the material. Sea glass is often formed in this fashion, as the solid form of the glass is rubbed against the stones and beach again and again, polishing it, rounding its edges and finally wearing it away to nothing.
The sea is a powerful erosional force in nature. The world's coastlines are forever changing, little by little or in sweeping amounts, constantly. A hurricane or typhoon may eat away feet of earth in just 24 hours, but the slow progress of the tides may take less than anyone would notice. The sea has several features of erosion to its waves that can be easily identified.
Abrasion or Corrasion
A wave crashing against the shoreline and sweeping back will take with it small pieces of detritus; however, when waves hit a cliff face, a different process occurs. The water will push itself into cracks and crevices along with trapped air, compress and further crack or loosen the rock. When backwash occurs (the retreat of the wave), the air and water expand with the release of pressure, breaking off pieces of stone. This process is called hydraulic action.
Sometimes the sea cannot quite break loose a stone or breaks it loose in such a way that it cannot pull it back out to sea, but leaves it wobbly or unstable. When this stone is rocked or otherwise moved by the waves to push or scrape against other boulders nearby, the process is called attrition. In this fashion, the large rocks are worn down slowly into smaller sizes with fewer sharp edges.
Solution or Corrosion
One of the first facts children learn about the ocean is that it is made of saltwater. Though this fact makes seawater unsuitable for direct drinking, the salt content makes seawater a chemical force. When saltwater from the sea contacts certain types of stone, such as limestone and chalk, the stone erodes away chemically rather than just through wave action. This process is solution or corrosion, a word often associated with acidic reactions against solids. The acidic quality of saltwater is low enough that erosion occurs slowly.
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