Landform Evolution: Rivers, Torrents, Wind, Sea, and Glaciers
River Landforms and Processes
Rivers shape the landscape through erosion and deposition, creating distinct landforms:
- V-shaped valleys: Formed by rivers with high erosive power, cutting deep into the ground.
- Flat-bottomed valleys: Develop as rivers slow, meander, and widen their valleys.
- Peneplains: Result from the merging of river valleys, creating a broad, flat surface.
River systems also produce:
- Hills witness: Isolated remnants of older plains.
- Terraces: Stepped landforms representing successive valley enlargements.
River Sediment Transport
Rivers transport and reduce the size of sediments. Larger clasts are moved in the upper reaches, while finer materials are carried downstream.
Torrential Streams and Wild Waters
Ephemeral streams and wild waters, active after heavy rains, cause significant erosion:
- Gullies: Deep ruts formed on steep slopes with little vegetation.
- Barrancos: Deep, V-shaped valleys in steep areas.
- Ramblas: Channels that carry water during storms, often dry for years.
Torrential Sedimentation
Torrential flows have high carrying capacity, depositing large clasts at the base of slopes. Sedimentation is rapid and unsorted, resulting in:
- Ejection cones: Small, steep accumulations from streams.
- Alluvial fans: Large accumulations of sediment.
- Pediments: Inclined surfaces formed by the merging of alluvial fans.
Wind Action on Landforms
Wind is a primary agent of erosion in deserts and dry areas:
- Deflation: Wind removes fine materials, leaving behind rocky deserts (reg).
- Abrasion: Wind-blown particles sandblast rock surfaces.
Wind Transport and Deposition
Wind carries fine materials over long distances, depositing them as:
- Loess deposits: Accumulations of dust in areas surrounding deserts.
- Dunes: Sand accumulations formed parallel to wind direction.
Coastal Processes and Landforms
Waves constantly erode coastlines:
- Cliff retreat: Waves erode the base of cliffs, causing collapses and creating abrasion platforms.
- Trituration: Waves break down rocks, and currents carry away fine materials.
Coastal Sedimentation
Littoral currents transport sand along the coast, forming:
- Beaches: Accumulations of sand or gravel on gentle slopes.
- Spits and bars: Sandy features that can isolate lagoons and marshes.
Glacial Landforms and Processes
Glaciers erode and transport materials, creating:
- U-shaped valleys: Wide, deep, and rounded valleys.
- Over-excavated zones: Cavities formed by flowing ice.
Glacial Sedimentation
Glacial sediments, known as till, are deposited as:
- Moraines: Accumulations of clasts associated with glacier movement.