Geologic structures control geomorphic patterns: Linking rectangular drainage evolution, underground pipe systems, and clastic dikes

Rectangular drainage networks are characterized by right-angle channel bends and confluences. The formation of the rectangular pattern is commonly associated with orthogonal sets of fractures, making rectangular drainages an outstanding example of structurally controlled landform evolution. However, the association between geologic structures and rectangular patterns remains circumstantial. So far, no specific mechanisms were suggested to explain the linkage between the emergent right-angle bends and confluences and the preexisting fracture system. This gap is particularly significant for planetary rectangular drainages, where the association with preexisting structures can not be directly observed.

We investigated the mechanistic linkages between geologic structures and the geomorphic drainage pattern in the hyper-arid Ami'az Plain located within the Dead Sea Basin in SE Israel. The Ami'az Plain is incised by a seemingly rectangular canyon system and is also penetrated by hundreds of sub-vertical clastic dikes (mode-I opening cracks infilled with sedimentary material), that reach a width of up to 0.18 m. Additionally, many caves and cavities extend from the banks and heads of the canyon system. Based on field surveys and analysis of a high resolution LiDAR based DEM, we mapped and characterized the Ami’az Plain drainage network and associated geomorphic structures including sinkholes. Our analysis revealed that the canyon system exhibits rectangular characteristics and its tributaries share dominant orientations with the strike of the clastic dikes. Surface and subsurface mapping assisted by Ground scanning LiDAR, together with field experiments, demonstrated that the caves and sinkholes are spatially associated with clastic dikes and that the caves formed by piping erosion along dikes.

Based on these findings, we propose a three-component hydrologic-geomorphic model for the formation of the Ami’az Plain rectangular drainage network: First, clastic dikes act as efficient infiltration pathways for surface runoff into the subsurface, where subsurface flow along clastic dikes induces internal erosion and forms piping caves. Second, collapses of cave roofs create sinkholes. Coalescence of sinkholes and seepage erosion in places where dikes intersect canyon banks and canyon heads generate new tributaries and extend existing ones. Finally, fluvial erosion and bank collapse modify the drainage network. Our observations and model emphasize the critical role of subsurface erosion and the formation of caves and sinkholes in linking fractures to drainage pattern evolution. This linkage could be highly consequential for our understanding of rectangular drainage evolution on planetary and terrestrial surfaces.