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Constraints on landscape evolution from slope histograms

¹ Earth and Ocean Sciences, Nicholas School of the Environment and Earth Sciences, Duke University, Durham, North Carolina 27708, USA

We analyzed >10,000 topographic slope histograms subsampled from digital elevation models (DEMs) of 28 landscapes throughout the continental United States. These landscapes are made up of diverse lithologies and have different climatic and tectonic histories, but their slope distributions are consistently unimodal and collectively exhibit a systematic change from positively skewed to negatively skewed as mean slope increases. This change not only occurs between landscapes, but can also occur within them, and is recorded in DEMs of different spatial resolution. The transition from positive to negative skewness cannot be accounted for by scaling of relief, but requires a fundamental change in landscape morphology. Process-based landscape modeling reproduces the trend and suggests that a change in the dominant hillslope process—from creep and/or wash to slope failure—is responsible for the transition from positive to negative skewness with increasing mean slope. This process transition is governed by a dimensionless uplift number that reflects the balance between processes of relief generation and denudation. The uplift number provides a basis for understanding the morphologic similarity between landscapes in our analysis, illustrating how different combinations of climate, tectonics, and lithology can lead to equivalent morphologies.

Key Words: geomorphology • landscapes • processes • slopes • statistics