Similar Folds, Recumbent Folds, and Gravity Tectonics in Ice and Rocks

Under steady state flow in glaciers, a banding will form and tend towards parallelism with the flow lines in basal regions of high shear. A simple mathematical model shows that departures from the steady state cause a reorientation of the flow lines such that they depart from parallelism with the banding. If a suitable bedrock ridge is present, the banding will subsequently become deformed into subsimilar folds, whose axial surfaces are very nearly parallel to the direction of maximum extension of the associated strain. The cleavage pattern, geometry, and orientation of many folds in rocks suggest a similar origin during gravitationally-induced flow away from an orogenic welt. In some cases buckling may be a secondary response, resulting in non-similar folds.