Earth surface systems are characterized by components that are adjusted, and those that aren't. By "adjusted," I mean that they have had time to respond to the most recent change or disturbance, and reach relaxation time equilibrium (Phillips, 2009), are considered to be characteristic of their environment. Non-adjusted components are inherited from past environmental conditions, or are inherently dynamically unstable, nonequilibrium phenomena that basically don't reach a stable condition. You could also add a third category--phenomena that are in the process of adjustment, but haven't have time to complete the process (this corresponds roughly to Renwick's (1992) triad of equilibrium, nonequilibrium, and disequilibrium geomorphic systems). 

The attached describes a simple method for measuring and quantifying the degree of adjustedness in environmental systems--at least the quantification is simple; determining what constitutes adjusted, adjusting, and non-adjusted could get hairy. This was the seed of what was to be a research proposal, but I doubt that I will ever have time to pursue it. Maybe you will!

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Phillips, J.D.  2009.  Changes, perturbations, and responses in geomorphic systems.  Progress in Physical Geography 33: 17-30.

Renwick, W.H., 1992.  Equilibrium, disequilibrium, and nonequilibrium landforms in the landscape.  Geomorphology 5, 265-276.