River terrace

A river terrace is a step-like surface along a valley wall that marks an abandoned level of a river or its floodplain. It forms when a river cuts down into deposits or bedrock after its former valley floor is left higher and dry.

River incision: The downward erosion of a river channel into its bed or underlying valley deposits. Incision leaves former floodplains stranded as higher surfaces beside the channel.
Floodplain: Low, relatively flat land beside a river that is periodically inundated by floods. A former floodplain can become a terrace when the river cuts below it.
Quaternary glaciation: Repeated expansions of continental ice sheets and mountain glaciers during the Quaternary Period. Glacial changes in runoff and sediment supply helped build and abandon terraces in many valleys.
Terrace dating: The estimation of when a river terrace formed or was abandoned using geological dating methods. Dating terrace deposits constrains the timing of river incision and valley change.
Aggradation: The buildup of a river bed or floodplain through sediment deposition. Aggradation raises valley floors; later incision can preserve those levels as terraces.
River channel: The path through which a river flows, bounded by its bed and banks. The channel's position and elevation define the active valley floor beneath terraces.
Pleistocene: The geological epoch from about 2.58 million to 11,700 years ago, marked by repeated ice ages. Many mapped terrace sequences preserve river changes from Pleistocene climate cycles.
Optically stimulated luminescence: A method that estimates when mineral grains were last exposed to sunlight before burial. It can date sediment deposited on a terrace before the surface was abandoned.
Base level: The lowest level to which a stream can erode its channel. A fall in base level can trigger the incision that abandons a terrace surface.
Alluvium: Sediment deposited by flowing water, including sand, silt, and gravel. Alluvial deposits often form the surfaces or caps of river terraces.

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