Terrace (geology)

They are formed by the downcutting of a river or stream channel into and the abandonment and lateral erosion of its former floodplain.

The most common sources of the variations in rivers and streams that create fluvial terraces are vegetative, geomorphic, and hydrologic responses to climate.

It can be formed by marine abrasion or erosion of materials comprising the shoreline (marine-cut terraces or wave-cut platforms); the accumulations of sediments in the shallow-water to slightly emerged coastal environments (marine-built terraces or raised beach); or the bioconstruction by coral reefs and accumulation of reef materials (reef flats) in intertropical regions.

This process happens by either change in sea level due to glacial-interglacial cycles or tectonically rising landmasses.

[8][9][10] Finally, glaciolacustrine kame terraces are either the relict deltas or bottoms of ancient ice marginal lakes.

The preferential removal of softer material exposes the flat surface of the underlying harder layer, creating the tread of a structural terrace.

Sediments underlying fluvial terrace exposed in cutbanks along the Manú River , Peru
Hypothetical valley cross-section illustrating a complex sequence of aggradational (fill) and degradational (cut and strath) terraces and deposits (upland gravels). Note ct = cut terraces, ft = fill terraces, ft(b) = buried fill terrace, fp = active floodplain, st = strath terrace, and ug = upland gravels.