Thermal diffusivity variability in alpine permafrost rock walls

Abstract

Permafrost degradation has been hypothesized as being one of the main causes of rockfalls and rock wall instability in the recent past in high mountain areas. Ongoing rock wall permafrost evolution remains poorly understood because of the lack of systematic measurements; models are often validated and driven by few existing instrumented sites. In rock wall subsurface temperature modeling, thermal diffusivity (κ) is one of the main parameters to be considered. In this study, thermal diffusivity data series were inferred from rock temperature data in order to understand their annual variation, their distribution in different temperature ranges, and their relation to atmospheric conditions. A harmonic analysis was performed to define amplitude and phase of the daily temperature waves at different depths by means of a least square minimizing optimization procedure. The analysis conducted shows that changes in κ values are influenced by different factors such as depth, season, rock temperature, aspect, and snowfall.