| Summary: | In the upper basin of the Porcupine River, the subhorizontal caves of Bear Cave and Tsi-it-toh-Choh mountains are characterized by a very rich ice zone. The authors propose a model for the build-up of ice based on the formation of hexagonal ice sublimation crystals on the cold walls of underground passages. In this model, water freezes and thaws many times, causing a series of different forms from the ceiling to the floor of the caves. This process will sometimes provoke total obstruction of a passage due to particular topoclimatic conditions or a change of climate, notably an increase in atmospheric humidity. During the summer the passage where the ice is located is preceded by a warm and humid passage and is followed by a cold and extremely dry passage, in which are preserved fragments of wood, animal faeces and remains of small mammals.Key words: Yukon, Porcupine River, Bear Cave and Tsi-it-toh-Choh mountains, caves, climate, cave ice Mots clés: Yukon Rivière Porcupine, massifs de Bear Cave et de Tsi-it-toh-Choh, cavernes, climat, glaces de cavernes
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