Rock‐surface temperatures of basalt in the drakensberg alpine environment, lesotho

Abstract

Grab, S., 2007: Rock-surface temperatures of basalt in the Drakensberg alpine environment, Lesotho. Geogr. Ann., 89 A (3): 185-193.ABSTRACT. Rock temperature data are presented for a variety of topographic localities at a high Drakensberg site. The objective is to investigate the spatio-temporal variations of surface rock temperatures in high Drakensberg basalt. The temperature results are then used to discuss possible implications for thermal stress fatigue and frost-induced weathering. Tinytalk TM data loggers and probes were used for rock-surface temperature recording. Long-term measurements were recorded over 12 months from May 2002 to April 2003, at a 1-hour logging interval and rock depth of 1 cm for a highaltitude (3300 m a.s.l.) interfluve and fracture site. Whilst the north-facing rock surface experiences negligible hours below -3°C, the south-facing rock surface and interfluve sites are subjected to considerable periods below -3°C, which falls within the 'frost cracking window'. It is concluded that the substantial contrasts of recorded rock thermal parameters over small spatial scales between various topographic settings, highlight that site-specific measurements across the broader scale are required for an adequate evaluation of regional weathering and its associated landform development.

Cool barnacles: Do common biogenic structures enhance or retard rates of deterioration of intertidal rocks and concrete?

“…This included steeper vertical gradients in the bare field-exposed limestone and granite (0% cover) relative to bare control blocks ( Figure 6). Given that test structures are comparably light in colour, thermaldampening by barnacles is expected to be greatest for darker-coloured rocks such as mudstones, shales, slates and basalts, which may be especially prone to thermal breakdown (Grab, 2007;Hall et al, 2005;Robinson, 1977). Alongside their influence on evaporative cooling, the influence of barnacle tests on surface albedo probably contributed to the observed thermal dampening, especially for the darker granite and crusted concrete (e.g., Warke et al, 1996).…”

Fine-Scale Variations of Near-Surface-Temperature Lapse Rates in the High Drakensberg Escarpment, South Africa: Environmental Implications

“…Further, given that several of the world's major escarpments consist of basalt, which weathers faster than other silicates, it has been argued that they significantly influence the atmospheric CO 2 budget over long temporal scales (Das et al, 2005). Surface (and associated rock) temperature trends along such escarpments are fundamental to controlling rates and intensity of weathering (Grab, 2007), and thus any future projections of weathering rates that influence CO 2 budgets and rates of landscape evolution need to consider the fine-scale climate trends.…”

Late quaternary moraines along the sekhokong range, eastern lesotho: contrasting the geomorphic history of north‐ and south‐facing slopes

“…The geomorphology along the north-and south-facing slopes of the Sekhokong range thus portrays very different micro-environments during the Late Pleistocene. AMS ages obtained from the moraines along the south-facing slopes suggest emplacement during the LGM, while ages obtained from sediments within north-facing hollows are of Late Holocene age (Marker 1995); this implies that north-facing slopes have undergone greater weathering and seepage than south-facing slopes during the Holocene (Meiklejohn et al 1999;Grab 2007b), consequently permitting slow mass transport and debris accumulation at the base of slopes. The contrasting palaeo-climatic and palaeogeomorphological processes on north-and southfacing slopes along the Sekhokong range are likely to have been major controls on the dissimilar sedimentary and contemporary biophysical attributes represented on such slopes.…”