Fluvial Channel Branching Enforces Threshold Relief

Abstract

AbstractRelief within mountain belts appears to be limited to a threshold of 1,000–1,500 m. However, it remains unclear definitively where in the landscape this threshold is found. Here we use a new method of analysis, termed Progressive Hypsometry, to show that “threshold relief” is the typical relief of first‐order fluvial catchments. The method tracks changes in the elevation frequency distribution (hypsometry) across nested catchments of all sizes. We find that self‐similar nesting of fluvial catchments leads to quasi‐scale invariance in hypsometry, such that the relief between any catchment's modal and outlet elevation (RMo, mode relief) falls into three groups: the two lower associated with steep upland subcatchments (RMo = 250–1,000 m) and the other with fluvial catchments, which span orders of magnitude in area but maintain an RMo of 1,000–1,500 m. We conclude that threshold relief is the maximum relief a first‐order fluvial catchment can develop without branching.