Tunnel valley
![New York's Finger Lakes. Lying south of Lake Ontario, the Finger Lakes formed in tunnel valleys.](/Images/godic/202502/18/New_York's_Finger_Lakes5941.jpg")
![A figure in Dutch showing the cross-section of a tunnel valley which has been refilled after erosion into bedrock.](/Images/godic/202502/18/Tunneldal_Noordbergum5941.jpg")
![The Kawartha lakes in Ontario formed in residual tunnel valleys from the Late Wisconsonian glacial period. The water flow was from upper right to lower left. Close examination shows the existence of buried tunnel valleys as well - they can be identified by contrasting vegetation.](/Images/godic/202502/18/Kawartha_Lakes_w_legend5941.png")
![A Polish ribbon lake formed in a tunnel valley. Note the variable width and the interruption between segments of the course. There is also evidence of other sediment-filled channels adjacent to this (e.g., two smaller lakes to the right)](/Images/godic/202502/18/Lagowski_Park_Krajobrazowy-World_Wind5942.jpg")
A tunnel valley is a large, long, U-shaped valley originally cut under the glacial ice near the margin of continental ice sheets such as that now covering Antarctica and formerly covering portions of all continents during past glacial ages.
A tunnel valley can be as long as 100 km (62 mi), 4 km (2.5 mi) wide, and 400 m (1,300 ft) deep (its depth may vary along its length).