Abstract Ridgeline longitudinal profiles map elevation along drainage divides from headwaters to basin outlets. Despite being present in every landscape on Earth and across many planetary bodies, it is unclear whether ridgeline longitudinal profiles have a characteristic morphology and how that morphology adjusts in response to changes in climate, tectonics, or the competence of underlying bedrock. We show that ridgelines have a characteristic two‐part form, consisting of a lower‐gradient, near‐linear “crest” extending from the headwaters to near the basin outlet and a steep‐sloped “snout” that connects the crest to the mouth of the river. We develop a theory that predicts crest morphology as the distribution of relief generated from rivers and hillslopes, and predicts that crest slope, like river slope, is sensitive to basin area as well as rock uplift rate, climate, and lithology. We show that normalizing average ridge crest slope for basin area, a metric we term crest steepness, can isolate changes in external forcing and/or lithology in steady‐state basins. We test these predictions using measurements of natural crests from two quasi‐steady‐state landscapes, where a nearly two‐fold increase in rock uplift rate results in an increase of over a factor of three in crest steepness, consistent with theory. Our results suggest that ridge crest steepness represents a topographic proxy of rock uplift rate, which can be combined with, or used in lieu of, other topographic proxies (e.g., channel steepness, hillslope angle, and hilltop curvature) to estimate variation in rock uplift across landscapes.
Robinson et al. (Mon,) studied this question.