Characterization of bedrock mass-wasting at fault-bound abyssal hills

Abstract

Fault-bound abyssal hills form at mid-ocean ridges and cover ∼65 % of Earth's surface, but few studies have characterized the extent to which bedrock erosion controls their morphology. Here, we use bathymetry data to characterize the morphology of fault-bound abyssal hills on a global scale, and employ numerical modelling and seismicity catalogues to quantify how simultaneous rock uplift and bedrock erosion sculpt deep-ocean landscapes. By generating a global database on abyssal hill morphology, we show that most large abyssal-hill scarps (>100 m in height) within the near-axis zone of seismicity (i.e., <30 km from axis) have slopes between 10 and 30°, well below the expected range of underlying normal fault dips of 45–60°. We interpret this as a manifestation of efficient bedrock mass wasting on near-axis growing faults, a process that operates from fault inception. Using a non-linear topographic diffusion model to parameterise the effects of erosion, we find a balance between erosion and rock uplift that is similar for slow, intermediate, and fast spreading rates. We express the ratio of erosion to uplift as an inverse Peclet number that ranges between 0.06 and 0.82 for abyssal hills. We also calculate a global bedrock diffusivity for abyssal hills in the range 0.01–1.51 m² yr⁻¹. These results imply that bedrock erosion is a significant process that sculpts abyssal hill morphology and reshapes the oceanic crust. Overall, this study provides a framework to incorporate bedrock mass wasting into future models of ocean-floor evolution and, more generally, to active extensional settings on Earth and beyond.