Climatic Geomorphology and Morphogenetic Regions

• Climatic geomorphology studies how climate controls geomorphic processes and, through them, the assemblages of landforms that characterise each climatic type.
  • Its core premise: each climate produces its own set of processes, and each set of processes leaves its own characteristic landforms.
• A morphogenetic (morphoclimatic) region is a large area within which a distinctive combination of processes (weathering, frost action, mass movement, running water, wind) operates, so that regional landforms tend to reflect regional climate.
• The field sits within the study of exogenic forces, since temperature and moisture drive weathering, erosion, transport and deposition; its vocabulary is gathered in the terminology of climatic geomorphology and morphogenetic regions.
• It stands against the view that structure and tectonics decide landforms, a debate taken up in factors controlling landform development.

Concept of Climatic Geomorphology

Geography Optional Notes {PDF}

Complete Notes Package (Paper I & II) | 3000+ Pages | Instant Download

Discounted Price | Buy Now @ ₹1,180 →

Premises of the Concept

• Landforms differ significantly from one climatic region to another.
• These differences arise because temperature, humidity and precipitation vary in space and change the nature and rate of weathering, runoff and erosion.
• Diagnostic landforms exist that still reveal the climate–landform link, despite Quaternary climatic change.
• Magnitude and frequency matter: the same process works at different intensities in different climates, and even within one climate, slopes, channels and divides may be shaped by events of different size and recurrence.

Evolution and Proponents

• Roots in exploration (late 19th century): German and French field scientists working outside Europe saw that landscapes changed with climate.
  • Ferdinand von Richthofen (loess and dry landscapes of China), Siegfried Passarge (Kalahari), Johannes Walther (deserts) and Karl Sapper (humid tropics of Central America) built this base.
• William Morris Davis (1899) treated the humid temperate cycle as “normal” and added an arid cycle (1905), so other climates appeared only as deviations from the normal scheme.
• Albrecht Penck (1910) made an early world zoning into humid, arid and nival zones based on the balance of precipitation and evaporation.
• The German school held that each climatic zone carries a distinctive landform assemblage; the French school treated climate as a leading control within a wider set of factors.
• Climatic cycles of erosion: the cyclic idea was carried beyond the humid “normal” cycle into other climates.
  • Charles Andrew Cotton (1942) set out savanna, semi-arid and selva (rainforest) cycles, and developed Davis’s notion of climatic accidents, in which a change of climate interrupts the running cycle and starts a new one.
  • In the savanna cycle, rivers cut little into fresh rock; they strip the red weathered regolith, while lateral migration and seasonal flooding flatten the land into plains studded with inselbergs.
  • Lester Charles King (1953) framed his cycle of pediplanation for the arid and savanna landscapes of Africa, where the Davisian model fitted poorly.

• Later contributors include Pierre Birot (cycle of erosion in different climates), William F. Tanner (1961) and Lionel Wilson, who refined process–climate boundaries.

Diagnostic (Climate-Indicative) Landforms

• Diagnostic landforms are landforms taken to represent one climate, identified by observing whole landscapes and by picking out typical forms.
  • The classic set is duricrusts, inselbergs, pediments and tors; each has proved less diagnostic than first claimed.

• Duricrusts are indurated crusts named by their dominant cement: laterite and ferricrete (iron), alcrete (aluminium), silcrete (silica), calcrete (lime).
  • Indian example: laterite was first named by Francis Buchanan-Hamilton (1807) at Angadipuram, Kerala, now a National Geological Monument; laterite caps the pats of Ranchi and Palamau and the Sahyadri mesas of Mahabaleshwar, Panchgani and Kas.
  • Crusts in cool Europe prove they record past, not present, climates.
• Inselbergs occur from deserts to rainforests, so rock structure (massive, sparsely jointed granite and gneiss) matters more than present climate.
• Pediments: Walther Penck tied piedmont benches to uplift, and Lester Charles King treated pedimentation as a universal process of slope retreat.
• Tors have three rival origins:
  • Periglacial frost shattering: J. Palmer and R. A. Nielson (1962) on Dartmoor.
  • Two-stage origin: David Leslie Linton (1955), deep chemical weathering under a warm humid climate followed by stripping of the regolith.
  • Pediplanation: King, independent of climate.
• Conclusion: climatic control is secure for glacial, periglacial and desert landforms; elsewhere the evidence is thin because most diagnostic forms predate Pleistocene climatic change.

Climatic Controls on Geomorphic Processes

• Temperature and moisture are the master variables; climate acts directly on processes and indirectly through vegetation and soils.
• Louis C. Peltier (1950) plotted mean annual temperature against mean annual rainfall to show where each process peaks.

• William B. Langbein and Stanley Schumm (1958) confirmed the rainwash pattern: sediment yield peaks at about 10–14 inches (250–350 mm) of effective rainfall, because drier basins lack runoff and wetter ones have protective vegetation.
• Weathering processes themselves are treated in weathering and mass movement.

Direct Controls

Temperature Below Freezing

• Freeze–thaw cycles (below 0 °C at night, above by day) expand and contract water in joints, causing frost shattering (congelifraction).
  • Widely jointed rocks break into block fields, scree and tors.
• In the active layer above permafrost, thawed clays lubricated by meltwater creep downslope as solifluction (congelifluction).
• Runoff regime: frost locks water in winter and releases it in a short summer peak; meltwater cannot soak into frozen ground, so brief, heavy overland flow moves coarse debris even on gentle slopes.
• Wind: frozen fine material resists deflation, abrasion is weak, and wind-blown snow and sand mix as niveo-aeolian deposits.
• Coasts: winter shore ice shields cliffs from waves, but freeze–thaw shatters the cliffs themselves.
• Indian example: Ladakh and Lahaul–Spiti show frost-shattered scree, patterned ground and rock glaciers above the tree line.

Temperature Above Freezing

• Large diurnal ranges in hot deserts cause repeated expansion and contraction, producing granular disintegration and exfoliation.
  • Indian example: exfoliation domes on the granite-gneiss of the Ranchi plateau, where a strong dry-season temperature range operates in a monsoon climate.
• Heat speeds chemical reactions, so the same rock behaves differently by climate.
  • Limestone dissolves readily in hot humid climates but stands as bold relief in deserts.

Rainfall Amount, Intensity and Seasonality

• Amount decides whether chemical weathering, runoff and leaching are effective at all; soil creep is nearly absent in arid lands.
• Intensity decides splash, rill and gully erosion; short, heavy storms on bare ground do the most work.
• Seasonality alternates wetting and drying:
  • Montmorillonite-rich clays shrink into polygons in the dry season; rain entering the cracks wets a sliding plane at depth and triggers slumps and earthflows.
  • Kaolinitic clays shrink little and harden when dry, favouring runoff over infiltration.
  • Indian example: the black cotton soils (regur) of the Deccan crack deeply before the monsoon; the Mediterranean climate shows the same wet–dry slumping.

Wind

• Wind is strongest as an agent where vegetation is absent: hot deserts, cold deserts and dry coasts.
• It deflates, abrades and builds dunes and loess, but in most climates it is subordinate to water.

Local Variation: Aspect and Altitude

• Slope aspect changes insolation, snow duration and freeze–thaw frequency, producing asymmetric valleys.
  • Indian example: in the western Himalaya, north-facing slopes hold moist forest and deeper soils, while south-facing slopes are drier, sunnier and more sparsely vegetated.
• Altitude stacks several morphoclimatic belts within one mountain range.

Indirect Controls

Vegetation

• Interception: forest canopy absorbs raindrop energy; water reaches the ground slowly as stemflow and drip, so infiltration rises and splash erosion falls.
  • Bare ground is pelted by full-energy drops; splashed particles seal the surface into a crust, raising runoff.
• Seasonal cover: in tropical deciduous (monsoon) forests trees are leafless in the hot dry season, so pre-monsoon storms cause strong splash erosion; lush monsoon foliage then reduces it.
  • Indian example: this seasonal switch governs the effectiveness of rainwash across peninsular India.
• Grass cover protects soil even better than forest against sheetwash; conversion of the steppe, prairie, pampas, veld and downs into farmland exposed them to sheet erosion and deflation, making humans a leading geomorphic agent.
• Microclimate: forest cover narrows daily ranges of soil temperature and moisture, slowing weathering and desiccation cracking.
• Wind: trees cut near-ground wind speed and so aeolian erosion; taiga and temperate forests also intercept snowfall.
• Forest clearing in the humid tropics removes this shield, so gullying, vertical erosion and landslides accelerate on steep slopes.
• Jean Tricart and André Cailleux argued that vegetation, like climate, produces its own landform assemblage: dense cover promotes chemical erosion but checks mechanical erosion.

Soils and the Weathering Mantle

• Leaching moves material from the A horizon to the B horizon and below; it is maximal in hot humid climates, seasonal in monsoon climates (June–September in India), weak in temperate winters, and nearly absent in deserts.
• Humus and lime bind clay particles, raising cohesion and lowering erodibility.
• A hardened illuvial horizon blocks infiltration, saturates the topsoil and increases overland flow.
• Duricrusts formed this way are resistant caprocks that protect old erosion surfaces and create bold relief in the tropics.
• Weathering depth reflects climate: tens of metres of saprolite in the humid tropics, thin, rocky mantles in deserts and cold regions.
• Palaeosols buried in dunes and alluvium record past processes and help reconstruct former climates.

Three Pathways of Control

1. Climate → vegetation + processes → landforms
2. Climate → soils + processes → landforms
3. Climate → processes → landforms (direct)

Zonal Classification of Geomorphic Processes

• Zonal processes are confined to, or dominant in, one climatic zone.
• Azonal processes work in almost all zones with varying intensity; climate changes their rate, not their presence.
• Extrazonal processes appear outside their normal zone because of local conditions, such as glaciers on tropical high mountains or coastal dunes in humid climates.

Climatically Controlled Agents of Erosion

• Running water, glaciers and wind are the climatically controlled agents: rainfall and temperature decide which of them works, and how strongly.
  • Waves are powered by wind; their work is largely azonal but is halted by sea ice in cold climates and shaped by coral reefs in the tropics.
• They differ as states of matter:
  • Water is a liquid of low viscosity; it flows turbulently, so it lifts and sorts load by size.
  • Glacier ice is a plastic solid; enormous viscosity makes flow slow and laminar, so it carries boulders to clay together, unsorted, and erodes by grinding and plucking.
  • Air is a gas about a thousand times less dense than water; it moves only sand and dust, mostly within a metre or two of the ground, and sorts them finely.

• Each agent’s landforms are detailed in fluvial landforms, glacial landforms and desert landforms.
• Indian example: the Gangotri trough (ice), the Thar dunes (wind), the Chambal ravines (running water under semi-arid, seasonal rain) and the Konkan cliffs (waves).

Climatic Change and Relict Landforms

• The central problem: climate has changed repeatedly, so present landforms need not fit present climate.
  • Relict landforms were made under a past climate; polygenetic landforms carry the imprint of several climates.
• Stoddart (1969) argued climate changed so continuously over 50 million years and so rapidly over the last 2 million that equilibrium landforms can rarely have formed.
• Nikolai Strakhov (1967) saw most landscapes as mosaics of Tertiary-inherited tracts and Quaternary forms.
• Julius Büdel estimated that about 95% of mid-latitude landforms are relict; landscapes are relief generations, layered records of successive climates.
• Pleistocene cold and dry phases are covered in Quaternary geomorphology.

Indian Examples of Relict Landforms

• Thar palaeodunes: the 16R dune section near Didwana records 12 cycles of dune building, soil formation and calcrete growth over about 190,000 years, alternating with monsoon strength; many older dunes are now vegetated and stable.
• Himalayan relict glacial forms: moraines and U-shaped troughs lie far below present snouts, marking larger Pleistocene glaciers.
• Laterite duricrusts of the Western Ghats and Chotanagpur are older than the present climate and now dissected, not forming.
• Peninsular etchplains and inselbergs preserve long spells of deep tropical weathering.

Morphogenetic Regions

• The concept follows from the premise that each climate produces a distinctive process set and landform assemblage.
• Regions tend towards morphoclimatic equilibrium in which regional landforms reflect regional climate.
• Early tropical work by Karl Sapper (1935) began the idea; Büdel, Peltier, Tricart and Cailleux, and Chorley and colleagues built full schemes.

Peltier’s Morphogenetic Regions (1950)

• Louis C. Peltier (1950) defined nine regions by process dominance, not landform geometry, using only mean annual temperature and rainfall.
• Assumption: a given temperature–rainfall field fixes the relative strength of weathering, mass movement, running water and wind.

• Strength: simple, graphable and process-based.
• Weakness: ignores seasonality, intensity, vegetation and relict forms; the ranges overlap widely (savanna spans 10–85 °F).
• Indian example: the Western Ghats and northeast fall in selva–savanna conditions, the Deccan in savanna, western Rajasthan in semi-arid to arid, and the high Himalaya in periglacial and glacial fields.
• The cold end of the scheme is detailed in periglacial landforms.

Büdel’s Climato-Morphological Zones

• Julius Büdel (schemes of 1948, 1963, 1977) zoned the world by the dominant relief-making tendency, chiefly valley cutting versus planation.
• Mechanism in the tropics: his double planation surfaces (1957) have a wash surface at the top and a basal weathering surface at the base of deep saprolite; both lower together, producing etchplains with inselbergs.

Tricart and Cailleux’s Morphoclimatic Zones

• Jean Tricart and André Cailleux (1965) held that climate works directly and through vegetation, so zoning must use climate, vegetation (biogeographic zones) and palaeoclimate.
• They recognised four major zones and nine sub-zones.

• Periglacial sub-provinces range from hyper-periglacial ice deserts to tundra, steppe periglacial (dry, windy; Mongolia) and taiga with relict permafrost.
• Humid tropical rivers carry mainly solutes and fine load, so they cut poorly and keep rapids and falls on hard-rock steps.
  • Indian example: the falls of the Chotanagpur rim and the Western Ghats.

Chorley, Schumm and Sugden (1984)

• Richard Chorley, Stanley Schumm and David Sugden (1984) merged earlier schemes into eight regions, using temperature, precipitation and seasonality.

• Characteristic forms: alpine topography and tills (glacial); dunes, playas and fossil fans (arid); knife-edged ridges and broad flood plains (humid tropical); pediments, inselbergs and fans (wet-dry and semi-arid); smooth soil-covered slopes (humid mid-latitude); cryoplanation surfaces and patterned ground (periglacial).

Morphogenetic Regions of India

• Himalaya (altitudinal zonation): humid subtropical fluvial action in the Siwaliks, forested temperate slopes, periglacial belt above the tree line, glacial zone above the snowline.
  • Ladakh combines periglacial and cold-arid processes.
• Peninsula: savanna-type seasonal tropics dominate, with laterite, pediments, inselbergs and etchplains; the Western Ghats and Meghalaya approach selva conditions.
• Thar: arid to semi-arid, with active and relict dunes.

Critical Evaluation

Strengths

• Explains process contrasts between climates that a purely structural view misses.
• Is secure for glacial, periglacial and desert landscapes.
• Gives a framework for reading palaeoclimate from relict forms and for anticipating landscape response to climate change.

Criticisms

• Weak evidence: Stoddart (1969) found the methods qualitative and the process data too thin to infer landforms from climate.
• Structure over climate: inselbergs, tors and pediments occur across climates; rock type and tectonics often decide form.
• Azonal processes: running water and mass movement work everywhere, blurring zone boundaries.
• Inheritance: relict and polygenetic forms break the assumed climate–landform equilibrium.
• Overlap and scale: annual means hide seasonality and extremes; boundaries are arbitrary, and local aspect and altitude cut across zones.
• Charles Rowland Twidale and Yannick Lageat (1994) accepted only desert, glacial, periglacial and some coastal zones, about half the land surface.
• Michael A. Summerfield argued plate tectonics explains large-scale relief better, and Piotr Migoń noted that planation is absent over large parts of the zones said to be dominated by it.

Current View

• Measured erosion rates favour relief: Eric W. Portenga and Paul R. Bierman (2011), compiling 1,599 beryllium-10 measurements from 87 sites, found slope, not mean annual precipitation, the strongest control.
• Climate still modulates: Byron Adams and colleagues (2020) showed that in the Bhutan and Nepal Himalaya erosion rises with relief at a rate set by rainfall; without monsoon rain the ranges would be steeper.
• Climate change has revived the field by shifting process thresholds:
  • South Lhonak GLOF (3–4 October 2023): about 14.7 million m³ of frozen moraine, weakened by permafrost thaw, fell into the lake; the outburst destroyed the Teesta-III dam at Chungthang.
  • Wayanad debris flows (30 July 2024): about 570 mm of rain in two days mobilised deeply weathered regolith at Mundakkai and Chooralmala, killing more than 200 people.
• Present consensus: climate is one control among structure, tectonics, time and human action; climatic geomorphology survives as a working hypothesis and a process-based science rather than a rigid world zoning.