Geomorphic Processes

Landforms and Their Evolution

Landforms are defined as small to medium-sized tracts or parcels of the Earth's surface, each having distinct physical characteristics such as shape, size, and material composition. Multiple related landforms together constitute a landscape, which is a larger tract of the Earth's surface. The formation and evolution of landforms are primarily governed by geomorphic processes and agents such as running water, groundwater, wind, glaciers, and waves, which act on the Earth's surface materials after weathering has broken them down. These geomorphic agents cause erosion, which modifies the land surface by removing materials, and deposition, which adds materials, thereby continuously reshaping the Earth's surface. The evolution of landforms refers to the stages of transformation that a landform or a part of the Earth's surface undergoes over time. This evolution is influenced by factors like climatic changes and tectonic movements, which can alter the intensity or nature of geomorphic processes. Landforms have a developmental history and can change slowly or rapidly due to ongoing geomorphic activities. The process of landform evolution can be likened to stages of life—youth, maturity, and old age—each characterized by distinct geomorphic features and processes. Two important aspects of landform evolution are: (1) the transformation of one landform into another over time, and (2) the modification of individual landforms after their initial formation. Understanding these aspects helps in comprehending the dynamic nature of the Earth's surface and the continuous interplay of constructive and destructive forces shaping it.

• Landforms are small to medium-sized parts of the Earth's surface with distinct physical features.
• Multiple landforms together form landscapes, which are larger surface tracts.
• Geomorphic agents like running water, wind, glaciers, groundwater, and waves cause erosion and deposition.
• Landform evolution involves stages of transformation influenced by climatic and tectonic changes.
• Landforms can change slowly or rapidly due to ongoing geomorphic processes.
• Evolution includes both formation of new landforms and modification of existing ones.
• 📌 Landform: A small to medium-sized tract of the Earth's surface with distinct physical characteristics.
• 📌 Landscape: A large tract of the Earth's surface made up of several related landforms.
• 📌 Geomorphic agents: Natural forces like water, wind, glaciers that shape the Earth's surface.

Running Water

Running water is the most significant geomorphic agent in humid regions receiving heavy rainfall. It acts primarily in two forms: overland flow and linear flow. Overland flow is the sheet-like movement of water over the general land surface, while linear flow occurs as streams and rivers flowing in valleys. Running water is responsible for both erosion and deposition. In the early stages, especially in youthful rivers flowing over steep gradients, erosion dominates, carving out valleys and other erosional landforms. As erosion continues, the gradient of the river channels becomes gentler, reducing the velocity of water and promoting deposition. Depositional landforms become more prominent in mature and old stages of river development. Overland flow causes sheet erosion, which removes surface materials uniformly. Due to irregularities in the land surface, this flow concentrates into narrow paths forming rills, which develop into gullies, and eventually into a network of valleys. Initially, down-cutting erosion dominates, removing features like waterfalls and cascades. Later, lateral erosion widens valleys and lowers divides between drainage basins, eventually forming nearly flat lowlands called peneplains. Resistant rock remnants called monadnocks may stand out in these plains. The evolution of landscapes under running water can be summarized in three stages: 1. Youth Stage: Few streams with shallow V-shaped valleys, poor integration, narrow or no floodplains, broad and flat divides with marshes and lakes, presence of waterfalls and rapids. 2. Mature Stage: Many streams with good integration, deep V-shaped valleys, wider floodplains with meanders, sharp divides, disappearance of waterfalls and rapids. 3. Old Stage: Few tributaries with gentle gradients, extensive meandering over vast floodplains, broad and flat divides with lakes and swamps, landscape near sea level.

• Running water acts as overland flow (sheet) and linear flow (streams/rivers).
• Early stages dominated by down-cutting erosion forming V-shaped valleys.
• Overland flow causes sheet erosion leading to rills, gullies, and valleys.
• Later stages see lateral erosion widening valleys and lowering divides.
• Peneplains are nearly flat lowlands formed by prolonged erosion.
• Landscape evolution stages: youth, mature, and old, each with distinct features.
• 📌 Overland flow: Sheet-like movement of water over land surface.
• 📌 Linear flow: Flow of water in streams and rivers within valleys.
• 📌 Sheet erosion: Uniform removal of surface soil by overland flow.