Soft Matter and Complex Systems Seminar
sala 1.40, ul. Pasteura 5
2020-10-23 (09:30) 
Max Cooper (IFT UW)
Modeling cave cross-section evolution and the effect of mechanical versus chemical erosion
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, numerical models of cave formation neglect cross-section evolution. To address this gap a model for evolving cave passage cross‐sections is developed using a shear stress estimation algorithm and a shear stress erosion rule. The 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. Existing scaling relationships from bedrock channel literature of width to discharge are duplicated, and further explored for varying erosion mechanism. Additionally, this scaling relationship is explored for natural distribution of discharge instead of treatment as a single mean value.
When sediment transport and alluviation is added to the model we successfully simulate paragenetic channels, a type of passage that forms when sediment armors the floor of the cave, forcing upwards erosion under pressurized conditions. An approximate scaling relationship indicates that equilibrium paragenetic channel width scales strongly with discharge, and weakly with the inverse of sediment supply. Simulations confirm the relationship and show that erosion mechanism, sediment size, and roughness are secondary controls.
The model is also adapted to simulate cross-sections of cave meander bends. Simulations of meander cross-sections reveal that the relationship between the contrast in shear stress on either wall and the incision angle of the meander record erosion mechanisms, allowing mechanisms to be determined in the field. Field measurements of such data indicate mechanical erosion plays a larger in the formation of caves than assumed in the karst literature. Totality of modeled cave cross-sections and measured data strongly indicate previous hypotheses of cave formation in turbulent flow need adjustment, and further data must be collected to determine erosion mechanisms in caves.
The seminar will be conducted on Zoom
https://zoom.us/j/92987083349?pwd=YTZLSFVWUnJzdE4xS1drR3dqMVFDdz09
Meeting ID: 929 8708 3349
Passcode: a8QhyS
When sediment transport and alluviation is added to the model we successfully simulate paragenetic channels, a type of passage that forms when sediment armors the floor of the cave, forcing upwards erosion under pressurized conditions. An approximate scaling relationship indicates that equilibrium paragenetic channel width scales strongly with discharge, and weakly with the inverse of sediment supply. Simulations confirm the relationship and show that erosion mechanism, sediment size, and roughness are secondary controls.
The model is also adapted to simulate cross-sections of cave meander bends. Simulations of meander cross-sections reveal that the relationship between the contrast in shear stress on either wall and the incision angle of the meander record erosion mechanisms, allowing mechanisms to be determined in the field. Field measurements of such data indicate mechanical erosion plays a larger in the formation of caves than assumed in the karst literature. Totality of modeled cave cross-sections and measured data strongly indicate previous hypotheses of cave formation in turbulent flow need adjustment, and further data must be collected to determine erosion mechanisms in caves.
The seminar will be conducted on Zoom
https://zoom.us/j/92987083349?pwd=YTZLSFVWUnJzdE4xS1drR3dqMVFDdz09
Meeting ID: 929 8708 3349
Passcode: a8QhyS