Lightning as a geomorphic agent: Reply to comments by Sumner

Sumnerʹs comments are mainly concerned with the climatic interpretation of angular boulders and associated landforms. This goes beyond the aims and scope of our paper (Knight and Grab, 2014), which are to examine the role of lightning as a geomorphic agent on mountain summits. We critically address three issues raised by Sumner: (1) that we have misinterpreted the literature that we cited in our paper; (2) that the role of lightning during the last glacial maximum can be evaluated; and (3) that studies of processes, geomorphology and palaeoclimate in the Drakensberg, southern Africa, do not make use of circular reasoning. We reiterate that lightning strikes are a significant geomorphic agent in generating angular debris on low-latitude mountain summits, and therefore to make uncritical climatic inferences based on the presence of ‘frost shattered debris’ is erroneous and should be avoided.