Ribbed grooves, resembling bulldozer tracks and animal ribbed trails, develop in mud tidal flats of the St. Lawrence Estuary, Quebec, during break-up. They are perpendicular to the tidal currents, and are made by ice blocks scratching the surface of tile tidal flat when being carried seaward by ebb currents. A peculiar track 20 cm wide and 50 m long, parallel to ebb currents, was also discovered. The origin of the track is not known but, if it is a natural feature, it may be ice-made.

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