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

摘要: Abstract Boulder quarrying by large waves along steep, high-energy coastlines contributes to erosion both causing inland migration of cliff faces and vertical lowering coastal platform surfaces. It also leads the formation boulder deposits (CBD) above high water mark. We describe mechanisms which hydraulic fracture creates boulders from cliffs bedrock platforms. Intense fluid pressures are induced wave impact on base overhanging ledges, interior surfaces as cracks fill with during runup overtopping. These processes impose loads overlying rock, bending stresses thus can create or propagate microcracks in rock. Repeated loading complete detachment slabs, liberated boulders. consider these using Aran Islands (Ireland) a type locality, because CBD there well documented flat-lying strata orthogonal joint patterns yield tabular geometry, lends itself modelling. The loaded rock is modelled beam microcrack that fractured stress an applied hydrodynamic load. This simple approach allows us examine general scalings dependencies. determine condition for fracture, relating pressure, area, stress, position geometry. In some situations, pressure need only be fraction stress. Fracture most likely occur extreme conditions when exposed has eroded area loading. balance forces suggests larger beams break more easily, facilitating creation