Rock surface temperatures in southern Namibia and implications for thermally-driven physical weathering

摘要

Rock surface temperatures were measured over a three year period on a granite-gneiss boulder on top of an inselberg in the southern Namibia Desert, southwestern Africa. Aspect orientation was considered through diurnal minimum and maximum temperature measurements taken by sensors on the upper, north-facing and south-facing rock surface. In addition, minute-duration temperatures were recorded on a horizontal surface. Although several periods of data are missing, diurnal records indicate a high propensity for thermal fatigue on the upper and northern-facing rock surface. The records from the shaded south-facing surface approximate values measured for air temperature. Rapid changes, as measured over minute-durations, show that thermal shock (where Delta T/t exceeds 2 degrees C/min) is probably limited to cooling during precipitation events but that changes exceeding 1 degrees C/min are frequent and likely to contribute to fatigue throughout the year. Fracture patterns observed on isolated core stone remnants support the contention for thermally-driven mechanical weathering, but more detailed data on field moisture conditions combined with field temperatures and laboratory simulation are still required to elucidate the relative contribution of 'Weathering processes.