Freezing of beach sediment during exposure to cold air and subsequent thawing upon immersion have been analyzed in a strong tidal environment, near Rimouski in the St. Lawrence Estuary (Québec). Temperature data, recorded at different depths in the sediment over a 25-h period above the high water mark and following a sudden drop of air temperature to −6 °C, indicate that temperatures in the top 15 cm of the beach dropped below the freezing point of seawater (<−1.36 °C). At the mid-tide level station, which was alternately exposed to air and immersed, freezing temperatures were observed to a depth of approximately 5 cm. Observations show that the surface sediment became ice-cemented to a corresponding depth. Temperature changes on exposure to air and immersion were rapid in the surface sandy layer (about 5 cm) and slower in the underlying coarser sediment. Temperature changes were barely perceptible at low tide level and no ice-cemented sediment was observed. Observations on the frozen beach showed that waves undermined the ice-cemented surface sediment and eventually eroded away this frozen layer of beach material.