A hole dug into snow or firn to facilitate observation and sampling of density, snow and firn structure and associated grain sizes, layering and other attributes. Snow-pit measurements are part of the basis of the glaciological method (see stake). A snow pit can be excavated by hand using shovels (common on most smaller glaciers) or by trenching using a larger machine such as a tracked vehicle or caterpillar (now common in work on ice sheets). Coring by means of a barrel corer is a much less labour-intensive alternative to, and can to some extent replace, snow pits in determining bulk density of the snow and firn. Cores, however, are not as well suited for detailed observations of stratigraphy because of their small size relative to what can be observed on a snow-pit wall.