Hi there,
Negative values for removal rate in the erode hydro node are not possible in H17.5 contrary to what the documentation says.
On the other hand, the volcano example found in the volume wrangle node's documentation should be updated for H17.5
There is an issue heightfield erode precipiation setup and the heightfield erode flow node that should have been replaced by the erode hydro node (allowing negative values for the removal rate parameter).
Didn't found a workaround for now…
Thanks for your answer !

May give a try with the slump node.
Anyway, here is the answer to this as RFE

This is fixed on our next major release.