Water should smooth out eventually the rocks by the sea or am I wrong?
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river rocks have been there ages and had the edges knocked off them with all the movement. ocean edge rocks are newer and mostly broken bits of cliff etc….and are mostly stationary, not constantly bashed by other rocks. water doesnt do much work by itself on rocks.
It’s all about the flow of water and how that erodes the rocks.
If you think about it, a river tends runs smoothly in a single direction which would wear something down rather uniformly.
The ocean, on the other hand, is much more tumultuous and waves breaking can wear rocks in more unpredictable patterns (splashing up against, then rising upwards and outwards). The tides and currents can also vary the direction wave breaks.
If you try to visualize it you can almost see how it would happen like this.
Further, they way erosion occurs also depends on the mineral type(s) of the rocks themselves and how porous they may be. Salt and sediment content of the water also plays a role.
One point others have touched on is fresh water has more ability to dissolve minerals so it will erode rock faster as it flows over. Salt water is more saturated with salts and minerals and is thus less erosive.
Sea is VERY good at eroding rocks in the right conditions. Depends how long the rock has been there and what it is made of. But look at sand, sand is just very very very smooth rock, smoothed down to tiny particles. There’s no smoother rock in a way. Big chunky rocks by the sea have either got there fairly recently, or are made from harder stuff than the shells and sediments sand are made of. Come back in a million years, they’ll be smooth.
Vice versa with rivers, plenty of jagged rocks. Cut myself on one just last year in fact!
Your question is wrong since what you find in ocean you can find in river. You get smooth rocks in ocean and beaches too. Also sand is the perfect rock.
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