Landforms created by running water, also known as fluvial landforms, are shaped by the processes of erosion, transportation, and deposition of sediments by rivers and streams. These landforms are dynamic, continuously evolving as water flows through various landscapes.
1. Erosional Landforms
a. V-Shaped Valleys
- Formation: When a river cuts downwards into its bed through vertical erosion, it creates a steep-sided, narrow valley that resembles a “V” shape.
- Example: The Grand Canyon in the United States.
b. Waterfalls and Rapids
- Formation: Waterfalls form where there are layers of hard and soft rock. The soft rock erodes faster than the hard rock, creating a drop. Rapids are sections of a river with a steep gradient causing turbulent water flow.
- Example: Niagara Falls, USA/Canada.
c. Gorges and Canyons
- Formation: Over time, if a river continues to cut downwards, it can create deep, narrow valleys known as gorges or canyons.
- Example: Fish River Canyon, Namibia.
d. Interlocking Spurs
- Formation: In the upper course of a river, where it cuts through less resistant rock, the river winds around harder rock, creating a series of protruding ridges that interlock from either side of the valley.
- Example: Found in many upland areas.
2. Depositional Landforms
a. Floodplains
- Formation: These are flat areas of land adjacent to a river, formed mainly by the deposition of sediments during periodic floods. When the river overflows, it deposits layers of alluvium (silt, sand, and clay) on the floodplain.
- Example: The Mississippi River floodplain.
b. Levees
- Formation: Natural levees are raised banks formed along the sides of a river channel due to the deposition of coarser sediments during floods. Over time, these levees can become quite pronounced.
- Example: Levees along the Yellow River, China.
c. Deltas
- Formation: When a river enters a standing body of water (like a sea or lake), it loses velocity and deposits sediments, forming a delta. Deltas are typically triangular or fan-shaped.
- Example: The Nile Delta, Egypt.
d. Alluvial Fans
- Formation: These form when a river spreads out and deposits sediments as it flows out of a mountainous region onto a flatter plain. The sediments fan out, creating a cone or fan shape.
- Example: The alluvial fans in Death Valley, USA.
3. Combined Erosional and Depositional Landforms
a. Meanders
- Formation: In the middle and lower courses of a river, lateral erosion and deposition create sinuous curves known as meanders. Erosion occurs on the outer banks (creating river cliffs), while deposition happens on the inner banks (creating point bars).
- Example: The meanders of the Mississippi River.
b. Oxbow Lakes
- Formation: These crescent-shaped lakes form from abandoned meanders. When a river cuts through a narrow neck of a meander during a flood, it creates a new, shorter channel, leaving the old meander loop as an oxbow lake.
- Example: Found along many meandering rivers, such as the Amazon River.
4. Other Notable Features
a. Potholes
- Formation: Circular holes formed in the bedrock of a riverbed due to the grinding action of pebbles and sediment swirled by the river’s flow. They are often found in the upper course of rivers.
- Example: Potholes in the Sooke River, Canada.
b. Braided Streams
- Formation: These occur when a river splits into several channels that intertwine. This typically happens in areas with a high sediment load and a variable discharge.
- Example: The Brahmaputra River in India and Bangladesh.
c. Terraces
- Formation: River terraces are step-like landforms that form along the sides of a river valley. They represent former riverbeds that have been abandoned as the river cuts downward into its floodplain.
- Example: Terraces along the Colorado River.
Summary
Running water is a powerful agent of landscape transformation. Through erosion, rivers carve out valleys and gorges, while through deposition, they create floodplains, deltas, and alluvial fans. The interplay between erosion and deposition leads to the formation of dynamic features like meanders and oxbow lakes, showcasing the river’s ability to continually reshape the land over time.
