Numeric Simulations of Glacial Quarrying
Abstract
Subglacial bedrock erosion primarily occurs through a combination of abrasion and quarrying. In quarrying heterogenous stresses along the ice-bed interface cause preexisting fractures to extend or in some instances new fractures may be created. If fractures extent sufficiently they can intersect with other preexisting fractures or bedding planes causing bedrock blocks to become isolated from the surrounding bedrock, at which point the glacier can entrain them. It is generally assumed that fracture propagation is the rate limiting process for quarrying, but the fracture mechanics associated with quarrying are poorly constrained. To improve our physical understanding of quarrying we use the finite element modeling (FEM) package COMSOL to simulate a subglacial setting in which quarrying might occur. We estimate the stresses within a stepped bed and then use the J1 integral and a mode-mixing ratio calculated from the crack tip displacement to estimate strain energy density at the tips of preexisting fractures. We do this for a range of fracture lengths and orientations to investigate K1 and K2 stress intensity factors. With K1 and K2 stress intensity factors we evaluate how mixed mode fractures affect fracture propagation and fracture propagation direction compared with only the mode 1 fractures typically assumed in quarrying. To test the FEM model, we compare the modeling results with published observations of quarrying from a subglacial experiment at Engabreen glacier Norway. We drive the model with their recorded subglacial conditions. We find that in the subglacial setting mixed mode fractures dominate the quarrying process and that by using mixed mode fractures we can replicate the fracture pattern observed at the Engabreen experiment. This works supports the need for considering mixed mode fractures and not only mode-1 fractures when assessing the mechanics of glacial quarrying.
- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2022
- Bibcode:
- 2022AGUFMEP35D1366Z