Near-surface rockwall temperatures in high Drakensberg basalt: spatio-temporal differences and possible implications for weathering

摘要

The objective is to investigate the spatio-temporal differences in rock temperatures along north- and south-facing rock scarps in the high Drakensberg. High frequency monitoring was undertaken during winter 2001 and summer 2002, with logging intervals set at one, two and fifteen minutes, whilst recording depths varied from the surface to 10 cm depth. Mean winter month rock temperatures vary from 11.9 degrees C on the north-face to -6.5 degrees C on the south-face. Mean rock temperatures on both aspects generally increase from the surface towards 10 cm depth. Whilst the maximum rate to temperature change reached 3.6 degrees C min(-1) on the north-face, the maximum recorded value on the south-face was only 1.13 degrees C min(-1). Steep thermal gradients of up to 14 degrees C/5 mm occur on the north-face, and it is suggested that this may initiate thermal stresses. It is proposed that the pronounced spatial variations in rock surface weathering expressions are a product of the corresponding weathering processes, which to a large part are controlled by differences in rock thermal characteristics.