Rock thermal data at the grain scale:: Applicability to granular disintegration in cold environments

Consideration of the mechanisms associated with the granular disintegration of rock has been limited by available data. In most instances, both the size of the transducer and the nature of the stud have negated any applicability of the resulting data to the understanding, of grain-to-grain separation within rock. The application of microthermocouples (less than or equal to0.15 mm diameter) and high-frequency logging (20 s intervals) at a taffoni site on southern Alexander Island and from a rock outcrop on Adelaide Island (Antarctica) provide new data pertaining to the thermal conditions, at the grain scale, of the rock Surface. The results show that thermal changes (DeltaT/t) can be very high, with values of 22 degreesC min(-1) being recorded. Although available data indicate that there can be differences in frequency and magnitude of fluctuations as a function of aspect, all aspects experienced some large magnitude (greater than or equal to2 degreesC min(-1)) fluctuations. Further, in many instances, large thermal changes in more than one direction could occur within 1 min or in subsequent minutes. These data suggest that the surface grains experience rapidly changing stress fields that may, with time, effect fatigue at the grain boundaries; albedo differences between grains and the resulting thermal variations are thought to exacerbate this. The available data failed to show any indication of water freezing (an exotherm) and thus it is suggested that microgelivation may not play as large a role in granular breakdown as is often postulated for cold regions, and that in this dry, Antarctic region thermal stress may play a significant role. Copyright (C) 2003 John Wiley Sons, Ltd.