Modeling cave cross‐section evolution including sediment transport and paragenesis

Abstract

Summary Deposits within caves are often used to interpret past landscape evolution and climate conditions. However, cave passage shapes also preserve information about past conditions. Despite the usefulness of passage shape, no previous models simulate cave cross‐section evolution in a realistic manner. Here we develop a model for evolving cave passage cross‐sections using a shear stress estimation algorithm and a shear stress erosion rule. Our model qualitatively duplicates observed cave passage shapes so long as erosion rates vary with shear stress, as in the case of transport limited dissolution or mechanical erosion. This result provides further evidence that erosion rates within caves are not typically limited by surface reaction rates, even though current speleogenesis models predict surface‐rate limitation under most turbulent flow conditions. By adding sediment transport and alluviation to the model we successfully simulate paragenetic channels. Simulations duplicate the hypothesized dynamics of paragenesis, whereby: 1) the cross‐section of a phreatic passage grows until shear stress is sufficiently reduced that alluviation occurs, 2) the floor of the passage becomes armored and erosion continues on the ceiling and walls, 3) negative feedback produces an equilibrium cross‐sectional area such that shear stress is sufficient to transport incoming sediment. We derive an approximate scaling relationship that indicates that equilibrium paragenetic channel width scales with the square root of discharge, and weakly with the inverse of sediment supply. Simulations confirm this relationship and show that erosion mechanism, sediment size, and roughness are secondary controls. The inverse scaling of width with sediment supply in paragenetic channels contrasts with surface bedrock channels, which respond to larger sediment supplies by widening. Our model provides a first step in simulating cave cross‐section evolution and points to the need for a better understanding of the dominant erosion mechanisms in soluble bedrock channels. © 2020 John Wiley & Sons, Ltd.

Potential Caves: Inventory of Subsurface Access Points on the Surface of Titan

“…In addition, conduits formed by liquid flow yield information about the moon's climate history. In the same way that sedimentary deposits in fluvial caves can reveal terrestrial flow history (e.g., through detailed analysis of passage keyhole shapes in the karstic system), Titan caves could indicate processes of speleogenesis, paragenesis, and even climate cycles (Cooper & Covington, 2020; Ford & Williams, 2007).…”

Carbonates in the Critical Zone

“…Such integrated flow paths, or karst conduits, are characterized by elevated permeability and exhibit rapid and turbulent flow that transports large quantities of solutes and gases between the surface and subsurface. High flow rates also allow the conduits to transport sediment through the subsurface (Cooper & Covington, 2020; Farrant & Smart, 2011; Herman et al., 2012). Once the capacity of the subsurface conduit network is sufficient to carry available surface runoff and sediment, closed basins develop on the land surface that route water and sediment into the subsurface.…”

Carbonates in the Critical Zone

“…Such integrated flow paths, or karst conduits, are characterized by elevated permeability and exhibit rapid and turbulent flow that transports manuscript submitted to Earth's Future large quantities of solutes and gases between the surface and subsurface. High flow rates also allow the conduits to transport sediment through the subsurface (Cooper and Covington, 2020;Farrant and Smart, 2011;Herman et al, 2012). Once the capacity of the subsurface conduit network is sufficient to carry available surface runoff and sediment, closed basins develop on the land surface that route water and sediment into the subsurface.…”