How do river terraces reveal former valley floors?
A river terrace is a step-like remnant of a former valley floor or floodplain above the present channel. Several terrace levels may occur along one valley.
Incision and preservation of older surfaces
A river first develops a valley floor, then cuts down into it, leaving fragments along the valley sides. Tectonic uplift, changes in base level, or shifts in water and sediment balance can contribute. Some terraces are cut into bedrock, while others are carved from thick alluvial fills. Surface shape alone does not always distinguish them.
What the steps can tell us
Terraces help reconstruct former river levels and stages of valley development. Similar elevations on opposite valley sides may belong to the same period, but matching them requires sediment characteristics and age evidence. Each terrace should not automatically be attributed to one earthquake or a particular climate episode. Their elevation above the active floodplain can reduce exposure to some floods, yet slope stability, ground conditions and extreme flood limits require separate assessment.