Long periods of exceptionally high temperatures in California and Finland this summer have been associated with the formation of large ‘exfoliation’ or ‘sheeting’ fractures in bedrock surfaces that may have remained largely unchanged since the last ice age.
Predicted distribution of various types of fracture beneath an Alpine valley. Here we start with a ‘V’ shaped topography, introduce ice, and manually cut out the center of the valley. Fractures forming in tension and shear are coloured yellow and orange, respectively, while active ‘micro-cracking’ is purple, and regions in which we predict explosive fracturing are marked in red under the ice. Note how the area of explosive fracturing increases as we remove ice, and the difference in fracture distribution between model Stages 14 and 32, for which the only difference is the relief of stresses during the intermediate period of deglaciation (Leith et al. 2014).
Leith, K., Moore, J.R., Amann, F., Loew, S., 2014. Sub-glacial extensional fracture development and implications for Alpine valley evolution. J. Geophys. Res. 119, 62-81.
A revised compilation of in situ stress measurements indicates maximum differential stress magnitudes are limited by micro crack initiation.
Leith, K., Moore, J.R., Amann, F., Loew, S., 2014. In situ stress control on micro-crack generation and macroscopic extensional fracture in exhuming bedrock. J. Geophys. Res. 119, 594–615.