A previous study (Pr¿vost et al., 1990) has shown that a lowering in the soil infiltrability index improves hydrograph snowmelt runoff peaks simulation of the Lac Laflamme basin. The hypothesis that explains this phenomenon is as follows: when the snowpack becomes discontinuous or thin during the spring, cold air temperatures during the night (<-10 ¿C) freeze the water at the soil surface. To test this hypothesis, four plots were instrumented to follow the evolution of water table fluctuations, snow cover area, soil and air temperatures, and liquid and total water contents at different levels in the soil. Transect lines were also established to monitor snow depth, percentage of soil free of snow, and presence of basal ice and different types of soil frost (porous or concrete). Our results show that the minimum nightly air temperature of -5 ¿C during snowmelt did not produce soil ice. It was not possible to validate or invalidate the hypothesis. The results of the survey at the basin scale show that concrete frost is prevalent throughout the basin, is associated with forest floors dominated by sphagnum or hypnobryale mosses, and originates from winter meteorological events.