The level down to which running water flows on a landscape, and therefore the level that the landscape would be reduced to by erosion, if no other process intervened. The ultimate base level is sea level, though any part of the land surface where a stream‐gradient is effectively zero, may act as a local, temporary base level. Planar landscapes formed by base levelling include some of the oldest land surfaces on earth (for example in the interiors of the Gondwanaland continents), and may have had continuous soil forming processes since the end of the Mesozoic (Adams, 1975).
- Adams, G.F., 1975. Planation Surfaces: Peneplains, Pediplains, and Etchplains. Stroudsburg, PA: Dowden, Hutchinson & Ross, 476 pp.Google Scholar