Interpreting erosion frequency and magnitude from luminescence profiles in boulders

Exposed bedrock is ubiquitous on terrestrial and planetary landscapes, yet little is known
about the rate of bedrock erosion at a granular scale on timescales longer than the
instrumental record. As recently suggested, using the bleaching depth of luminescence
signals as a measure of bedrock erosion may fit these scales. Yet this approach assumes
constant erosion through time, a condition likely violated by the stochastic nature of erosional
events. Here we simulate bleaching in response to power-law distributions of removal
lengths and hiatus durations. We compare simulation results with previously measured
luminescence profiles from boulder surfaces to illustrate that prolonged hiatuses are unlikely
and that typical erosion scales are sub-granular with occasional loss at mm scales,
consistent with ideas about microflaws governing bedrock detachment. For a wide range of
erosion rates, measurements are integrated over many removal events, producing
reasonably accurate estimates despite the stochastic nature of the simulated process. We
hypothesize that the greater or equal erosion rates atop large boulders compared to rates at
ground level suggest that subcritical cracking may be more influential than aeolian abrasion
for boulder degradation in the Eastern Pamirs, China.