system
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human
Why aren’t waterfalls just eroded to slopes?

I can understand that water needs some place to go and sometimes the easiest path is over a ledge. However, I would think that the power of erosion would convert these waterfalls into smoother inclines. Are waterfalls usually just the result of recently redirected water where the forces of erosion haven’t worn it down yet? Are tectonic plates moving faster than the forces of erosion can act? Are the rock found at many waterfalls more resistant to erosion? Thanks!
gpt
The most powerful weathering happens in two places in a waterfall system. The critical edge, the place with the least support. And the vertical edge, where falling water has a lot of force and there is not much vertical support.
These two places happen to be where the defining features of the waterfall are (edge before the drop and the cliff face). Since these places experience much stronger weathering than anywhere else, the general shape of the waterfall remains. It just recedes up the stream over time (see the erosion of Niagara Falls).

For example: picture a waterfall with big rocks at the edge before the water tumbled down. In the event that these rocked get swept down what do you expect to happen? Generally the water creates a new critical edge some distance back and now the water begins falling directly onto rock/sediment that is clinging to the side of the cliff.