A global quantification of submarine mass-wasting at fault-bound abyssal hills

Abstract

<p>Fault-bound abyssal hills form at mid-ocean ridges and cover ~65% of the Earth’s surface on the ocean floor. This makes abyssal hills one of the most common landforms on Earth. Despite their ubiquity, few studies have quantified the role of erosion in the spatial and temporal evolution of abyssal hills. Here, we use freely available shipboard bathymetry data, seismicity catalogs, and deep-tow sonar data to quantify the morphology of mid-ocean ridge faults and fault-bounded abyssal hill scarps. Our study encompasses slow, intermediate, and fast spreading rates. At slow spreading rates, we analyze the axis-facing scarps of abyssal hills where crustal formation is dominated by volcanic accretion rather than more complex areas such as those dominated by detachment faulting.</p><p>For the tallest scarps, scarp morphology data shows a rapid increase in both height and slope within 10 km of the axis and for scarps younger than ~5 Ma. For scarps older than 5–10 Ma and greater than 10 km from the ridge axis, we observe a gradual decrease in height and slope with either increasing distance from the ridge axis or increasing age. Seismicity data indicates that most earthquakes occur within 30 km of the ridge axis. The increase in height and slope for young scarps near the axis must therefore reflect fault growth within a near-axis fault growth window. Most near-axis scarp slopes fall between 10 and 30º, well below the expected range of underlying normal fault dips (45–60º). We interpret this as a manifestation of bedrock mass wasting on actively growing faults, which is supported by the observation of fresh talus in deep-tow sonar data. We find evidence for fresh talus at the ridge axis but limited evidence for fresh talus several hundred kilometers from the axis. We use these observations to infer that earthquakes are the most common trigger for bedrock mass wasting for abyssal hill faults, which implies that most bedrock mass wasting occurs within the near-axis fault growth widow. By contrast, the gradual decline in height and slope with increasing age and distance from the axis likely reflects the decrease in tectonic uplift caused by earthquakes and an increase in topographic smoothing from pelagic sediment.</p><p>For scarps within the 30 km fault growth window, we then apply the global database on scarp morphology to constrain parameters into a numerical model for abyssal hill erosion based on non-linear diffusion laws. Outputs from the numerical models indicate that diffusivity is similar across all spreading rates with a total range of 0.03–0.99 m<sup>2</sup>yr<sup>-1</sup>. By combining the scarp morphology data with the model results, we calculate a global annual mass wasting flux of 31 billion m<sup>3</sup> (total range 6–236 billion m<sup>3</sup>) from earthquake-driven erosion of abyssal hills. This flux is greater than the total sediment flux from terrestrial earthquake triggered landslides and demonstrates that mass wasting of abyssal hills during fault growth is a significant but understudied global surface process that drives local mass flux<em>. </em></p>