Ribbed grooves and tracks in mud tidal flats of cold region

Ribbed grooves, resembling bulldozer tracks and animal ribbed trails, develop in mud tidal fiats 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 the tidal fiat 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.