The influence of aspect on the biological weathering of granites: observations from the Kunlun Mountains, China

Bedrock and boulder weathering in the higher elevation, permafrost areas of the Qinghai–Tibetan Plateau have usually been ascribed to frost action. For short periods during two summers, an attempt was made to better elucidate weathering processes in this region. A combination of visual observation coupled with rudimentary data regarding removable weathered material from the four cardinal aspects of granite boulders at elevations of 4600–5000 m in the Kunlun Mountains (Qinghai–Tibetan Plateau) showed that there was a distinct aspect influence (south>west>north>east) on weathering. It was also observed that there were aspect-constrained variations in chasmoendolithic communities and for lichen distribution. To further aid understanding, temperature data for the four aspects were collected for several weeks during the summers of 2 years, with data recording at 1-min intervals using ultraresponsive (0.05 s), high precision (0.1 °C), ultrasmall (0.15 mm diameter) thermocouples; humidity data were also collected at the rock face. Based on these data, an attempt is made to evaluate the nature of granite weathering in this region. To better understand what the impact of the lichens/endolithic communities was and how this varies, use is made of XRD and SEM analyses on samples from each aspect. In addition, iron-rich patinas were found on a number of the boulders, and these too were analyzed in an attempt to see their relationship (if any) to the biological action.