Hence, the main stream may be eroding laterally rather than vertically, while the tributaries are still involved in downcutting or vertical erosion. The Cycle of Erosion Early stage - rivers are above base level and are actively engaged in vertical erosion. This stage is generally initiated either by uplift, so the area is raised above base level, or by climate change which adds to the discharge of rivers. The latter change most often involves the melting of glacial ice in a region which increases runoff to river systems and enables them to perform vertical erosion. The early stage can also be initiated by covering over an older landscape by deposits such as glacial till, resulting in a new landscape for streams to begin dissecting.
Rivers are very sluggish and meander widely across very broad floodplains.
This stage is seldom if ever reached , because uplift or climate change will result in renewed downcutting by streams, and the landscape is said to be rejuvenated. One good line of evidence for rejuvenation in the landscape is stream terraces some stream terraces, such as those along the Mississippi River in SE Minnesota, are evidence of rejuvenation brought about by the melting of glaciers which increased the river's discharge and enabled it to downcut into floodplain deposits of the glacial period.