How does wave impact generate large boulders? Modelling hydraulic fracture of cliffs and shore platforms

We consider these processes using the Aran Islands (Ireland) as a type locality, both because CBD there are well documented and because flat-lying strata and orthogonal joint patterns yield tabular bedrock geometry, which lends itself to modelling. The loaded rock is modelled as a beam with a microcrack that is fractured by a bending stress from an applied hydrodynamic load. This simple approach allows us to examine general scalings and dependencies. We determine a condition for fracture, relating the fluid pressure, loaded area, fracture stress, microcrack position and geometry. In some situations, the fluid pressure need only be a fraction of the fracture stress. Fracture is most likely to occur during extreme wave conditions and when the exposed rock has a large eroded area for loading. The balance of forces suggests that larger beams break more easily, facilitating the creation of large boulders.