Editing Valley (section)

====Tunnel====
{{main|Tunnel valley}}
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.<ref name=J>{{Cite journal  | last =   Jørgensen | first =Flemming   |author2=Peter B.E. Sandersen   | title = Buried and open tunnel valleys in Denmark—erosion beneath multiple ice sheets  | journal = Quaternary Science Reviews  | volume = 25  | issue = 11–12  | pages = 1339–1363  | date = June 2006  | doi = 10.1016/j.quascirev.2005.11.006     |bibcode = 2006QSRv...25.1339J }}</ref> Such valleys can be up to {{convert|100|km|mi|abbr=on}} long, {{convert|4|km|mi|abbr=on}} wide, and {{convert|400|m|ft|abbr=on}} deep (its depth may vary along its length). Tunnel valleys were formed by subglacial [[water erosion]]. They once served as subglacial drainage pathways carrying large volumes of meltwater. Their cross-sections exhibit steep-sided flanks similar to fjord walls, and their flat bottoms are typical of subglacial glacial erosion.