A change in base level leading to formation of stream terraces can come about by uplift of the land over which the stream flows, or a lowering of sea level (stream terraces will develop if base level is lowered). An uplifted erosional remnant of a floodplain that formed when a stream was flowing at a higher level is called a stream terrace. The renewal of erosion which results in creation of stream terraces is generally attributed to a change in base level/a change in climate resulting in greater runoff. Stream flow on the floodplain is a common event. This question is related to Geology.
