Why are there gravel beaches? In thousands of years of waves crashing on the beach shouldn’t all the gravel have become sand?
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Simple answer!! Envi scientist here 🙂 the gravel has been delivered to the beach by a process called long shore drift from a river which is situated down-drift of the beach. It’s not a case of the rocks not eroding (they do this by rolling and chipping bits off more so than waves on their own), but rather a case of the material being freshly delivered to the beach. You’re seeing sand in its first stage of life.
Take a look at New Zealand’s gravel beaches along the east coast of the South Island, you will see them most commonly north (down drift) of the major braided rivers, and you’ll see sandy beaches in sheltered areas. The sand is delivered from off shore as it’s easier for the waves to delivery this kind of lighter material for long distances to sheltered coves – there’s less energy in the wave which means it doesn’t have the power to lift heavy boulders/gravel, hence why sand travels more readily and settles in places where wave energy is lower.
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