Dune, thank you so much for your reply and suggestion. But no, I don´t think it´s really the effect I´m after.
I would like to add finer detail (smaller scale depressions) on top of a layer with large scale depression. To be clear, I don´t actually want FURTHER depressions than in the underlying terrain. That is, no displacement intersection, I just want both layers to find and colour different scale depressions in a terrain, so to speak. Hope that makes sense.
What I want to achive is this:
First a layer that has large snowfields, in valleys and other larger depressions. That is the green layer in the first image below.
Second, a layer with finer depressions, simulating snow that fills crevasses and smaller depressions. That is the pink in the second image below.
As you can see in the third image, when both layers are enabled, they interact in a way that completely spoils the look. The green is no longer constricted to large patches, instead it nearly covers the whole terrain. It seems the last pink layer somehow destroys or overrides the previous layer. ( But atleast now I can see both colors at the same time, which I didn´t before. Not sure why, but anyway..)
Attached is also a tgd to illustrate the problem. The actual terrain I want to use is a digital surface model from the Japanese Space Agency, but I`ve replaced it with a fractal terrain instead. The idea is the same anyway.
Roberts