In situ measurements of Antarctic snow compaction compared with predictions of models

We describe in situ measurements of the compaction of Antarctic snow. At three different sites in Antarctica, the rate of compaction was measured hourly, over various depth intervals, for up to two years. These measurements show that compaction at each of the sites occurs through slow, viscous deformation of the snowpack, with no significant contribution from sudden collapse of weak layers. The measured rates of compaction at the coldest site exhibit a strong seasonality, consistent with a temperature-dependent sintering mechanism having activation energy of 70 kJ mol(-1). At the two warmer sites, activation energies of 80 and 120 kJ mol(-1) provide slightly better agreement with the observations. Published models of snow compaction underestimate the temperature sensitivity. A good match to our observations is provided by a semi-empirical model, based on rate equations for lattice-diffusion (Nabarro-Herring) creep of material around pores, combined with normal grain growth. This model also provides a theoretical basis for a widely used empirical model of snow compaction. The rate coefficient for lattice-diffusion inferred from our measurements is considerably higher than published values, however, and other creep mechanisms cannot be ruled out.