Basis of erosion (from the Greek. Βάσις - base) - the level at which the water flow loses its energy and below which it cannot deepen its course (loses its eroding ability).
The general basis of erosion is considered the level of the oceans. Local erosion bases are levels of lakes into which rivers flow, the level of the main river for inflow into it, etc. Changes in the height of the basis of erosion due to fluctuations in sea level, secular fluctuations of the earth's crust are accompanied by incision of the valley (with decreasing erosion basis) or filling it with river sediments (when it rises). The change of these processes leads to the formation of river terraces .