Reimagine Fx shows how you can merge a bunch of displacements using math nodes.
A new tutorial from Amar Shinde (Reimagine Fx) shows how you can procedurally combine more than one displacement input using math nodes in Maya working with Arnold. Shinde uses some noise nodes and then combines them using Add, Multiply, and others.
Using math nodes like this is no different than using a blend mode while compositing. MAth nodes offer a quick and easy way to combine two sources.