However, if a flow transports granular material, those grains impact and erode irregularities in underlying materials, an effect that is demonstrably unstable. This mechanism, associated with catastrophic flooding, can have an overnight effect on the landscape. The clays that are produced are an important agent in the formation of topography and have an especially complex rheology. Wind and ice can operate in a similar way, completing the triad of aeolian influences. Water, even in microscopic quantities, has a dramatic influence on the strength of rocks and could contribute to the migration of seismicity and the triggering of seismic events at great distances from an earthquake.
Sea ice is another excellent example of a material with a nonlinear rheology.
Nonlinear rheology, taken in the broadest sense, may be the single most important aspect of the behavior of earth materials. While rheology is not an issue for flows in the earth's liquid outer core, understanding the mechanisms and nonlinear interactions involved in the generation and reversal of the earth's magnetic field by dynamo action in the core remains a great challenge in geophysics. Though progress has been made toward the solution of the coupled nonlinear equations of motion and electrodynamics for the extreme parameter values appropriate to the rapidly rotating and relatively inviscid core of the earth, novel approaches are required to proceed substantially further.