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).
Tunnel valleys were formed by subglacial erosion by water and served as subglacial drainage pathways carrying large volumes of melt water. Their cross-sections exhibit steep-sided flanks similar to fjord walls, and their flat bottoms are typical of subglacial glacial erosion.
They presently appear as dry valleys, lakes, seabed depressions, and as areas filled with sediment. If they are filled with sediment, their lower layers are filled primarily with glacial, glaciofluvial or glaciolacustrine sediment, supplemented by upper layers of temperate infill. They can be found in areas formerly covered by glacial ice sheets including Africa, Asia, North America, Europe, Australia and offshore in the North Sea, the Atlantic and in waters near Antarctica.
Tunnel valleys appear in the technical literature under several terms, including tunnel channels, subglacial valleys, iceways, snake coils and linear incisions.
Read more about Tunnel Valley: Significance, Formation of Tunnel Valleys/channels, Temporal Distribution
Famous quotes containing the words tunnel and/or valley:
“The only way to find out anything about what kinds of lives people led in any given period is to tunnel into their records and to let them speak for themselves.”
—John Dos Passos (1896–1970)
“Down in the valley,
Valley so low,
Hang your head over,
Hear the train blow.”
—Unknown. Down in the Valley (l. 1–4)