Each frame the erosion is being resimulated....and the simulation itself involves computing a procedural flow of water cascading down the terrain and taking sediment with it. As soon as you change anything about the terrain, you get a butterfly effect of changes to the end result. There's not much flickering on the peaks because they don't represent areas where the changes between frames accumulate.
You can attempt to increase evaporation and such, to prevent large accumulations of (invisible) liquid at the bottom of the valleys, which may reduce flickering as less sediment will accumulate there, but there's not going to be a sure-fire way to get rid of all the flickering in a simulation with continually changing terrain just due to how the simulation works.
You can attempt to increase evaporation and such, to prevent large accumulations of (invisible) liquid at the bottom of the valleys, which may reduce flickering as less sediment will accumulate there, but there's not going to be a sure-fire way to get rid of all the flickering in a simulation with continually changing terrain just due to how the simulation works.