Final answer:
Base level is the lowest point to which a stream can erode its bed, contributing to the formation of valleys and floodplains through erosion, sediment deposition, and influenced by plate tectonics.
Step-by-step explanation:
The concept of base level is crucial when discussing the formations of valleys and floodplains in geomorphology. The base level is defined as the lowest point to which a stream can erode its channel. It plays a significant role in the development of various geological features. For example, the ultimate base level for most streams is sea level, but lakes, resistant layers of rock, and other local conditions can create a local base level.
Valleys are formed by a combination of processes, including erosion by running water, glacier activity, and tectonic movements. Erosion by streams and rivers can create V-shaped valleys as the water cuts into the bedrock, carving the valley over time. Floodplains, on the other hand, develop in the flat areas alongside rivers and streams where sediment is deposited during periods of high water or flooding. As the river reaches its base level and lacks the energy to erode the bedrock further, it begins to meander and spread out, leaving behind sediment which creates the flat, often fertile area known as a floodplain.
Plate tectonics also play a role in the formation of valleys and floodplains. As tectonic plates move, they can lift land, create mountain ranges, and form structural basins which can later become valleys or floodplains. Finally, understanding topography is essential for recognizing how natural features like valleys and floodplains are shaped by these geological processes.