Controls on submarine channel-modifying processes identified through morphometric scaling relationships

Abstract

Submarine channels share morphological similarities with rivers, but observations from modern and ancient systems indicate they are formed under processes and controls unique to submarine settings. Morphologic characteristics of channels-e.g., width, depth, slope, and the relationships among them-can constrain interpretations of channel-forming processes. This work uses morphometric scaling relationships extracted from high-resolution seafloor bathymetry to infer connections between morphology and process in submarine channels. Analysis of 36 modern channels in five geographic regions shows that channel widths vary regionally (from <100 m to >10 km wide) but occupy the same range of aspect ratios (~10:1-100:1). This suggests an autogenic control on aspect ratio, perhaps resulting from feedback processes in levee growth and/or bank erosion, and allogenic (e.g., sediment supply, grain size) controls on channel width. Submarine channel aspect ratios tend to decrease with increasing dimensions, while the opposite relationship has been observed for fluvial channels, likely due to opposing relationships between flow discharge and channel distance. Additionally, observation of an apparent lag between channel thalweg and levee responses to gradient changes suggests that thalweg and levee deposition and erosion may be partially decoupled due to the vertical structure of turbidity currents, with thalweg evolution driven by the basal, higher-shear-stress portion of the flow and levee evolution by the dilute upper portion. The data presented here provide a basis for predicting channel metrics in exploration scenarios, in which data coverage may be sparse. This documentation of a diverse suite of channels also captures the range of scales and variability exhibited globally by submarine channel systems, providing context for local studies.

Entangled external and internal controls on submarine fan evolution: an experimental perspective

“…The volume of overbank (levee) deposition in runs 1-3 stayed relatively high (>10 L for each run) as sediment supply rate increased, despite the channel being progressively widened and deepened by channel erosion and overbank deposition ( Figures 5B and 6; Figure S8). These growing levees would normally be predicted to progressively confine the flows due to the flows becoming smaller with respect to the channel form (Hodgson et al, 2016;Shumaker et al, 2018). Instead, the levees continued to be overtopped; probably due to flows becoming progressively larger, experiencing more turbulent mixing and decreased grain-size stratification as the sediment supply rate was increased between runs (Rouse, 1939;Kneller and McCaffrey, 1999;de Leeuw et al, 2018a;Eggenhuisen et al, 2019).…”

Quantification of the bed‐scale architecture of submarine depositional environments

“…As with levee deposits, differentiating axis, off-axis and margin deposits may lead to better constraints on channel-deposit architecture. The event bed correlation distance in channel deposits is less than 300 m (Figure 3), limited by channel dimensions (Konsoer, Zinger, & Parker, 2013;Shumaker et al, 2018).…”

Levees Formed by Turbidity Currents: A Depth‐Averaged Modeling Treatment

“…In this case, we can speculate that if the levees along the flanks of the structure are formed before significant deposition has occurred downslope along the axis, then these levees could focus the flow, promoting further levee formation downslope, allowing a fully leveed channel to form at arbitrary distances from the canyon mouth. This would further imply that the radial expansion of the channel near the canyon mouth would be much less evident than in the Garcia‐Parker case discussed above, and levee development downstream might lead to the relatively stable channel width seen in observations (Shumaker et al, ). However, without direct evidence regarding the characteristic erosion law in natural systems, this can only remain a speculation.…”

“…Leveed channels are found in submarine fans not only near submarine canyon outlets, but also at considerable distances downslope; a comprehensive and recent review of a variety of systems is found in Shumaker et al (). Clearly, there must be a generic mechanism promoting the formation of leveed channels well away from the expanding flow directly downstream of the canyon mouth, which is modeled by our similarity solution.…”

“…One puzzling feature of our theoretical results is that the erosion-deposition line does not extent arbitrarily far downslope; instead, the regime sufficiently far downslope of the outlet is purely erosional. It is difficult to reconcile this result with the widespread observation of levees far downslope of submarine canyon outlets, as summarized in Shumaker et al (2018). This result, however, emerges from the precise power law for erosion chosen by Garcia and Parker (1991) based on laboratory experiments; this power law has never been validated by measurements from full-scale natural systems in oceans or lakes.…”