Investigating the thermophysical properties of the ice–snow interface under a controlled temperature gradient: Part I: Experiments & Observations

Abstract

Of critical importance for avalanche forecasting, is the ability to draw meaningful conclusions from only a handful of field observations. To that end, it is common for avalanche forecasters to not only have to rely on sparse data, but also on their own intuitive understanding of how their field-based observations may be correlated to complex physical processes responsible for structural instability within a snowpack. One such well-documented basis for mechanical instability to increase within a snowpack is that caused by the presence of a buried ice lens or ice crust. Although such icy layers are naturally formed and frequently encountered in seasonal snowpacks, very little is known about the microstructural evolution of these layers and how they contribute toward weak layer development. Furthermore, in terms of assessing the structural integrity of the snowpack, there is at the present time no consistent treatment for identifying these layers a priori as problematic or benign. To address this issue, we have created an idealized laboratory scenario in which we can study how an artificially created ice lens may affect the thermophysical and microstructural state of the interface between the ice lens and adjacent layers of snow while under a controlled temperature gradient of primarily −100Km−1. Utilizing in situ micro-thermocouple measurements, our findings show that a super-temperature gradient exists within only a millimeter of the ice lens surface that is many times greater than the imposed bulk temperature gradient. Such large temperature gradients on such a small scale would not be measurable by most field-based instrumentation and to our knowledge these laboratory-based in situ measurements are the first of their kind. Additionally, we have also investigated and characterized the microstructural evolution of the ice–snow interface with X-ray Micro-computed Tomography and Scanning Electron Microscopy. In our analysis, we have been able to identify distinct regions of simultaneous ice crystal growth, sublimation, and kinetic snow metamorphism. We hold that these observations are both consistent with previous laboratory studies and observations made in the natural environment.