Factors Controlling Landform Development

No landform is the work of a single cause. Every feature of the surface is the joint product of a set of interacting controls acting through process–response relationships: geological structure, lithology, tectonics, climate, relief, base level, vegetation, drainage, time and — increasingly — human interference. Fix the architecture of the idea: the rocks and their arrangement (structure + lithology + tectonics) supply the material and the resistance; the processes (driven chiefly by climate, relief and gravity) do the carving and building; and time decides how far the work has gone. Two great traditions divide on which controls matter most — structural geomorphology (rocks and tectonics first) and climatic geomorphology (climate-controlled process first).

1. Geological structure

• Structure guides where and how erosion attacks and therefore the pattern of landforms. Horizontal strata give mesas, buttes and structural plateaus; gently tilted beds give cuestas (gentle dip-slope, steep scarp) and, when steeper, hogbacks; folded strata give ridge-and-valley topography and trellis drainage; faults give fault scarps, rift valleys and block mountains; joints guide weathering (tors, karst). Domed structures expose inliers/outliers.

2. Lithology

• Lithology controls resistance to weathering and erosion. Hard, massive rocks (quartzite, granite, basalt) stand out as ridges, hills and plateaus; weak rocks (shale, clay, soft sandstone) are worn into valleys and lowlands. Soluble rock (limestone) produces karst regardless of hardness; permeable/porous rock lets water sink, reducing surface runoff and favouring underground forms; well-jointed rock weathers faster. This selective action is differential erosion.

3. Tectonics

• Tectonics supplies the uplift that renews relief and the gravitational energy for erosion. The balance between uplift rate and erosion rate determines whether mountains grow, hold steady, or are reduced. Active tectonics produces young, high, steep relief (Himalayas); tectonic quiescence allows peneplanation toward low relief (parts of Peninsular India).

4. Climate — the master process control

• Climate decides which processes dominate and therefore the landform assemblage: frost shattering & glaciation in cold lands; deep chemical weathering & mass movement in the humid tropics; wind (aeolian) action in deserts; fluvial action in humid temperate lands. This is the basis of climatic geomorphology, developed by Julius Budel (climato-genetic geomorphology), L.C. Peltier (morphogenetic regions), and J. Tricart & A. Cailleux (morphoclimatic zones), who recognised distinct regions each with a characteristic suite of landforms.

5. Relief, base level, drainage and vegetation

• Relief (available altitude/slope) governs the potential energy for erosion — high, steep relief drives vigorous downcutting and mass movement.
• Base level is the limit of downcutting. There are several: the ultimate base level (sea level), temporary/local base levels (a lake, a resistant rock bar, a trunk-river junction), and structural base level. A fall in base level (tectonic uplift or sea-level fall) rejuvenates rivers (incision, terraces, knickpoints); a rise causes deposition and valley filling.
• Drainage routes the water that does most erosional/transport work; its pattern reflects structure. Vegetation intercepts rainfall, binds soil and slows runoff; its removal (natural or human) sharply accelerates erosion and changes landform evolution.

6. Time and human interference

• Time fixes the stage of evolution (youth–maturity–old age) and whether equilibrium has been reached; the same process gives different forms depending on how long it has acted.
• Human interference is now a leading geomorphic agent — through agriculture, deforestation, overgrazing, mining and quarrying, dam-building, river engineering, urbanisation and terracing. Humans both accelerate natural processes (accelerated soil erosion, induced landslides, reservoir-induced seismicity) and create entirely new landforms (mine spoils, embankments, reservoirs, reclaimed coasts). The scale is such that the present is often called the Anthropocene.

7. Process–response, and the two schools

• These controls work together through process–response relationships: a change in one variable (say, uplift or deforestation) triggers adjustments in process and form until a new balance is reached (dynamic equilibrium). Structural geomorphology (e.g. E.H. Hills) stresses rock structure and tectonics as the prime control; climatic geomorphology stresses climate-driven process. In reality all controls operate simultaneously, their relative importance varying with place and scale — structure dominating at some sites, climate at others.

Tested on differential erosion & structural landforms (cuesta, mesa/butte), base level types, morphoclimatic regions, and the structural vs climatic schools.

Optional Paper I / GS Paper I. The examiner rewards balancing structural and climatic controls with named scholars and examples.