Abstract:
Insights into the possible effect of lightning strikes on rock breakdown are presented by Knight and Grab (2014)
froma summit area in the Lesotho highlands. Based on their findings, the authors challenge the association of angular
debris with frost shattering and use this as a platform for directing critique against palaeo-geomorphic
studies.While the lightning strike data are not questioned directly here, the palaeo-environmental contextwithin
which the paper is set, the portrayal of former findings and the assumptions regarding weathering mechanisms
in Lesotho are commented on. Frost shattering is the centre of Knight and Grab's weathering critique
but, contrary to that stated in their text, none of the cited authors invoke this process in Lesotho. Other
weathering processes that are speculated upon are not specific to cold climates either and thus cannot be used
in support of their argument. In terms of debris and block distribution, lightning will not account for the preferential
location of relict blocks and debris below the summits on south-facing slopes, or for the extensive valley
floor accumulations that are documented in Lesotho. Knight and Grab also falsely portray former studies by implying
that palaeo-environmental inferences in the area are drawn fromblock origin or morphology alonewhen
the climatic signatures were derived from integrated assessments. In a palaeo-context, the relative contribution
of lightning to debris production under dryer and colder conditions, when convective thunderstorm activity in
the highlands was likely reduced, is also questioned. The weathering context, as well as the critique that Knight
and Grab direct at other studies on relict landforms, is thus shown as inappropriate.
