The process controlling their formation is the same that is responsible for the development of coarse granular crusts on snow. Due to fluctuations in temperature, the snow crystals on the surface undergo a constant disintegrating metamorphosis. The crystals become rounder in shape and lose their dendritic structure. To the contrary, snow crystals in deeper layers undergo a growing metamorphosis and form larger dendritic crystals, which, due to trapped air, possess only little structural strength. Both mechanisms proceed under conditions below freezing point.
The impact tunnels, which were subsequently filled by a loosely packed sediment of windborne snow crystals, relocated the surface process to the deeper layers and the snow crystals were transformed into coarse, interlocking ice grains. This mechanism was yet intensified by the higher humidity of the air inside the tunnel, resulting in ice cores that filled the impact tunnels and that reached down to the meteorites, embedding them in their bottoms (process suggested by W. Groezinger on jgr-apolda.eu). Around February 25, new snow falls that covered the tiny impact holes on the surface prevented further searching for meteorites.