Shaping Planetary Surfaces: The Impact of Liquid and Frozen Water on Hillslope Topography

The availability of liquid water plays a primary role in controlling the development of topography. Hillslope asymmetry (HA), or slope differences between terrain aspects, has been well-documented in small-scale and field-based studies throughout the world. In this study, we apply a consistent HA analysis method across the entire globe and find that poleward facing hillslopes are on average steeper than equator-facing hillslopes, with the exception of high-latitude, high-elevation, and low-temperature regions where equator-facing slopes tend to be steeper.

To test the impact of different land cover and climate regimes on HA, we use global and high-resolution elevation, vegetation and land-surface temperature data to examine erosional process differences between poleward- and equator-facing hillslopes. We find that vegetation supports poleward-steepening, and that low temperatures and high freeze-thaw cycle frequencies enhance equator-steepening of hillslopes. We further show that HA is propagated into the size and form of fluvial drainage networks. We posit that insolation plays a key role in controlling soil-water availability and retention, and thus drives asymmetries in vegetation cover, soil formation rates and landscape form at the planetary scale.