Factors Controlling Landform Development: Structure, Process, Time and Relief

• Landform development is the result of several controlling factors acting together: the geological structure on which work is done, the geomorphic processes that do the work, the time over which they act, and modifiers such as climate, slope–altitude–relief, base level, biota and human activity.
  • Classical geomorphology reduced these to William Morris Davis’s (1899) trio: structure, process and stage.
  • Modern geomorphology treats them as interacting variables whose relative importance changes with the scale of time and space being studied.
• The controls explain why the same process makes different landforms on different rocks, and why different processes can make similar landforms. The basic vocabulary (agent, base level, grade, relief) is set out in our terminology note on fundamental concepts in geomorphology.

The Geomorphic Equation

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Davis’s Trio: Landscape = f (Structure, Process, Stage)

• William Morris Davis (1899), in The Geographical Cycle, argued that every landscape can be described through three variables. The full model is in the Davis cycle of erosion.
  • Structure: used in a wide sense, the rock type, its hardness, porosity, jointing and its disposition (folds, faults, tilt).
  • Process: the agents of weathering, mass movement and erosion (rivers, wind, glaciers, waves, groundwater).
  • Stage: the time elapsed since uplift, expressed as youth, maturity and old age.
• Davis gave most weight to stage.
  • He treated time as a process in itself: landforms were expected to pass through an inevitable, orderly and largely irreversible sequence towards a peneplain.
  • Structure was the passive material, and process was mainly “normal” fluvial erosion in a humid temperate climate.

Thornbury’s Three Concepts on the Factors

• William David Thornbury (1954) turned the trio into separate propositions, which remain the standard way of stating the factors (the full set is in Fundamental Concepts of Geomorphology).
  • Geological structure is a dominant control factor in the evolution of landforms and is reflected in them.
  • Geomorphic processes leave their distinctive imprint upon landforms, and each process develops its own characteristic assemblage of landforms.
  • As the different erosional agents act, a sequence of landforms with distinctive characteristics appears at successive stages of development.

Balancing the Equation: How Later Models Rewrote It

• The equation has been re-weighted by almost every later model. Each changed which variable is treated as independent and which as the outcome.

• Critique of “structure, process and stage”:
  • Strengths: it gave a genetic classification of landforms, a simple explanatory framework, and a vocabulary (young, mature, old valleys) still in use.
  • Weaknesses:
    • Time is overemphasised and treated as a cause rather than a span within which causes act.
    • The climate of the region is folded into “process” as if one normal climate applied everywhere.
    • Uplift is assumed to be rapid and complete before erosion starts, which plate tectonics contradicts.
    • Structure is treated as passive, although tectonics keeps renewing relief.
    • Rates of processes were described, not measured.

The Uniformitarian Basis

• The equation assumes that the processes of the past were the same in kind as those of today, an idea from James Hutton (1785), but their intensity and location have changed.
  • Climates have shifted: the Talchir glacial boulder beds underlie the Gondwana coal seams of Odisha, recording glaciation followed by warm, humid conditions.
  • Volcanism has varied in time: the Deccan basalts were erupted around 66 million years ago, far more extensively than any volcanism in India today.
  • Mountain building is episodic (Precambrian, Caledonian, Hercynian and Tertiary orogenies), each followed by long quiescence. This is why landscapes carry inherited forms from earlier cycles, as in the polycyclic surfaces of Peninsular India.

Geological Structure

Meaning of Structure

• In the narrow sense, structure means only the deformation and arrangement of rocks by earth movements.
• In the wide sense used in geomorphology, it has three parts:
  • Lithology: the kind of rock (igneous, sedimentary, metamorphic), explained in our classification of rocks.
  • Attitude or arrangement: horizontal, tilted, folded, faulted or domed beds.
  • Rock characteristics: chemical and mineral composition, joints, permeability, porosity and relative hardness.
• Structure acts through differential weathering and erosion: resistant rocks stand up as ridges, scarps and plateaus, while weak rocks are worn into vales and lowlands.
  • The influence is so strong that some landscapes are named after rocks: granite landforms, karst (limestone) landforms, chalk landforms and basalt (trap) landscapes.
  • Variations in lithology can be local, a single outcrop of a few square metres, or regional, covering hundreds of square kilometres.

Lithology

Igneous Topography

• Lava plateaus form where extensive basalt flows cool into near-horizontal sheets.
  • Early drainage partly sinks underground through joints, vesicles and ash layers, so plateau tops are at first little dissected.
  • Once rivers are established they cut deep gorges. The source streams of the Krishna and Savitri around Mahabaleshwar have carved canyon-like valleys in the Deccan traps. Abroad, the Snake River’s Hells Canyon cuts through the Columbia River basalts.
  • Dissection breaks the plateau into mesas (large flat-topped hills with cliffed sides) and buttes (smaller remnants).
  • Indian examples: the Mahabaleshwar and Panchgani tablelands in Maharashtra, and the lava- and laterite-capped “pats” of western Chotanagpur, Jharkhand (Netarhat, Jamira, Bagru and Khamar pats).
• Stepped (trap) topography: successive lava flows of unequal resistance weather into stair-like benches.
  • The Mahabaleshwar escarpment exposes a stack of more than 40 flows.
  • The Deccan Traps at Panchgani and Mahabaleshwar were placed on India’s UNESCO World Heritage Tentative List in 2025.
• Granite landforms reflect unloading and jointing:
  • Exfoliation domes: deeply intruded granites expand as the cover is removed and peel off in curved sheets. Examples are the gneissic domes around Ranchi (for example near Kanke and Pithoria), Yosemite’s domes, Stone Mountain (Georgia) and Sugar Loaf (Rio de Janeiro).
  • Exposed batholiths: the Ranchi batholiths, intruded into Dharwar sediments, now stand as dome-shaped hills after the cover rocks were stripped off.
  • Tors: piles of joint-bounded blocks on hilltops and valley sides, with block trains (clitter) on the flanks.
    • Their origin is disputed: deep chemical weathering followed by stripping (David L. Linton, 1955), periglacial frost shattering and solifluction (Jack Palmer and R. A. Nielson, 1962), and scarp retreat and pedimentation (Lester Charles King).
    • Tors also occur on basalt, sandstone and limestone from the humid tropics to periglacial zones. This shows that joint spacing, not just rock type, is decisive.
• Intrusions exposed by erosion:
  • Sills and dykes harder than the host rock stand out as ridges, cuestas and hogbacks.
  • Volcanic necks and diatremes survive as isolated volcanic buttes. Shiprock (New Mexico) is a diatreme of volcanic breccia rising about 482 m above the plain.
• Joint patterns leave their imprint too:
  • Rectangular joints in granite produce blocky relief and rectangular drainage.
  • Columnar joints in basalt produce hexagonal columns.
  • Cones are shaped by their material: eroded scoria and ash cones develop radiating rills, and old composite cones develop deep radial valleys (barrancos).

Sedimentary Landforms

• Arenaceous rocks (sandstones, siltstones) behave according to their cement:
  • Silica-cemented sandstones resist chemical attack and give bold relief with low drainage density.
  • Iron- or lime-cemented sandstones weather quickly into rolling country.
• Argillaceous rocks (clay, shale) are weak and impermeable, so they produce low relief, but the form depends on climate:
  • In humid areas: gentle slopes (often under about 8°), dendritic drainage and convexo-concave hills.
  • In semi-arid and sub-humid areas: badlands with very high drainage density and gully walls often steeper than 30°. The ravines of the Chambal, Yamuna and Mahi are the Indian type example, though they are cut in alluvium rather than shale.
• Calcareous rocks (limestone, dolomite, chalk) are attacked by solution in humid climates, forming karst.
  • Surface forms: sinkholes, swallow holes, dolines, uvalas, poljes, and disrupted surface drainage.
  • Underground forms: caves with stalactites, stalagmites and other speleothems.
  • Tropical types: cone karst (Cockpit Country, Jamaica) and tower karst (Guilin, China; Ha Long Bay, Vietnam).
  • Indian examples: the Borra Caves (Eastern Ghats, Andhra Pradesh), and Krem Liat Prah in the Jaintia Hills of Meghalaya, the longest known cave in the Indian subcontinent.
• Where resistant sandstone overlies weak shale, escarpments, mesas and buttes result.
  • Examples are the Vindhyan scarps of Rewa, Bhander and Kaimur–Rohtas.
  • The Bhander plateau is itself one very large mesa, and Morcha Pahar (Hazaribagh plateau, Jharkhand) is a sandstone-capped mesa. So mesas are not confined to basalt.

Metamorphic Landforms

• Metamorphism usually raises resistance: shale becomes slate, and sandstone becomes quartzite.
  • However, a distinct class of “metamorphic landforms” is hard to identify, because many metamorphic rocks resist erosion fairly uniformly.
• Quartzite forms bold ridges and high relief. The Delhi Ridge and the Aravalli ridges are quartzite-held.
• Quartzitic sandstone over shale gives a classic escarpment profile: a free face on the hard cap, a straight debris slope, and a concave basal pediment on the weak rock beneath.
• Slate tends to form subdued relief, schist can hold up highlands, and gneiss forms domes and tors, as on the Chotanagpur and Karnataka plateaus.

Attitude of Rocks (Structural Arrangement)

• The disposition of beds, produced by tectonic, orogenic and isostatic movements, guides both drainage and relief.
  • Detailed forms are covered in Folds, Faults, Nappes and Structural Landforms. Here only their role as a control is summarised.

• Inversion of relief: prolonged erosion of a folded belt can lower the anticlines, which are stretched and cracked at the crest, into anticlinal valleys. The more compact synclines are left standing as synclinal ridges.
• Fault scarps and fault-line scarps show how a structural form becomes an erosional one:
  • The original fault scarp is purely tectonic.
  • A consequent fault-line scarp faces the same way as the original, because erosion has removed weak rock from the downthrown side.
  • An obsequent fault-line scarp faces the opposite way. It forms when a fall in base level exposes weak rock on the upthrown side to erosion.
  • A resequent fault-line scarp faces the original direction again after a further fall in base level. It is a later, not an earlier, form.

Rock Characteristics

• Chemical composition decides the type and speed of chemical weathering.
  • Limestone and dolomite dissolve in carbonated water.
  • Feldspar-rich granite decays to kaolinite clay, and limestone to terra rossa.
  • Thick clay mantles encourage soil creep, which rounds hilltops into convex forms.
• Joints and bedding planes control permeability, weathering and block size.
  • Closely jointed rocks let water in and decay faster.
  • Widely jointed granite breaks into large blocks and tors.
  • Joint patterns guide rectangular and trellis drainage.
• Permeability and porosity:
  • Permeability is the capacity to transmit water, mainly through joints and bedding planes.
  • Porosity is the proportion of pore space between grains.
  • Permeable rocks (many sandstones and limestones) absorb rainfall, reduce surface runoff and stand as uplands. Impermeable clays and shales shed water and are eroded into vales.
• Hardness is always relative to the environment.
  • Limestone is weak in humid climates because it dissolves, but resistant in hot deserts where water is scarce.
  • In Meghalaya’s extreme rainfall even sandstone hosts Krem Puri, a sandstone cave of about 24.5 km, reported as the world’s longest in that rock.

Structural Control in India

• Deccan traps: flat-topped plateaus, stepped escarpments, mesas and deep headwater gorges of the Western Ghats reflect horizontal basalt flows of unequal resistance.
• Aravalli: some of the oldest fold belts in India survive as quartzite ridges after very long denudation. They show structure outlasting relief.
• Himalaya:
  • Longitudinal valleys and duns (Dehradun) follow the strike of thrust-bounded belts, and the Siwalik ridges mirror the folded molasse.
  • The Main Central Thrust and Main Boundary Thrust separate belts of contrasting relief.
• Peninsular drainage:
  • The Narmada and Tapi flow west through fault-guided troughs.
  • The Damodar follows a Gondwana graben.
  • The eastward tilt of the peninsula sends the Godavari, Krishna and Kaveri to the Bay of Bengal.
• Vindhyan and Chotanagpur plateaus: sandstone scarps (Kaimur, Bhander, Rewa), lava- and laterite-capped pats, and granite-gneiss domes show lithological control.

Geomorphic Processes

Meaning

• Geomorphic processes are all the physical and chemical changes that affect the earth’s surface and create, modify or destroy landforms.
  • A geomorphic agent is the mobile medium (running water, ice, wind, waves, groundwater) that erodes, transports and deposits material.
  • In practice, process and agent are often used interchangeably.
• A process involves forces applied across gradients: gravity acting on slopes, flowing water on a channel bed, or wind over sand. Its effectiveness depends on energy, frequency and duration.

Classification of Processes

• Endogenetic (hypogene) processes originate inside the earth, driven by internal heat. They are constructional, creating vertical irregularities such as mountains, plateaus, rift valleys and volcanic cones. See endogenic forces.
  • Diastrophism:
    • epeirogenic movements (broad emergence and submergence)
    • orogenic movements (folding, faulting and warping)
  • Sudden movements: earthquakes and volcanism.
  • Landscape role of vulcanism and diastrophism:
    • Vulcanism builds cones, lava plateaus and islands, and its products then control later erosion. Examples are the Deccan traps and Barren Island, India’s only active volcano.
    • Orogeny builds fold–thrust mountain belts such as the Himalaya, and faulting creates rift valleys and horsts (Narmada–Son trough, Satpura).
    • Earthquakes reshape relief at once. The 1819 Kutch earthquake raised the Allah Bund, a ridge about 80 km long, and left the fort of Sindri partly submerged.
• Exogenetic (epigene) processes are driven by solar energy and gravity through the atmosphere. They are gradational, working to remove the irregularities made by endogenetic forces. See exogenic forces.
  • Degradation (“levelling down”): weathering, mass movement and erosion by rivers, groundwater, waves, wind, glaciers and periglacial processes.
  • Aggradation (“levelling up”): deposition by the same agents, in plains, deltas, dunes, moraines and beaches.
• Extraterrestrial processes: meteorite impact, unrelated to either interior or atmosphere.
  • Lonar crater (Buldhana, Maharashtra), about 1.8 km across, is a rare impact crater formed entirely in basalt. It became a Ramsar site in 2020.
• Anthropogenic processes: human action as an agent of excavation, deposition and change in process rates.
• Endogenetic and exogenetic processes are competing forces. Landscapes are the balance between relief-building and relief-reducing work at a given moment.

Mechanism of Processes

• Exogenetic work proceeds in three phases: erosion → transportation → deposition.

• Abrasion depends on the “tools”: their size, quantity and calibre (angularity), plus gradient and velocity.
  • River abrasion is most effective in steep, youthful channels carrying large angular boulders.
  • Wind abrasion is concentrated within about a metre of the ground, where saltating sand travels. It undercuts rocks into pedestal forms.
• Transportation differs by agent:
  • Rivers: one-way (downstream), by traction, saltation, suspension and solution.
    • Competence rises steeply with velocity: under the classical sixth-power relation, the mass of the largest particle moved varies roughly as the sixth power of velocity.
    • This is why floods move boulders that normal flows cannot.
  • Waves: two-way, with swash landward and backwash seaward. Longshore currents move material along the coast.
  • Wind: multi-directional. Silt and clay travel in suspension over long distances, while sand moves by saltation and surface creep.
  • Glaciers: debris is carried on, within and beneath the ice (supraglacial, englacial, subglacial).
  • Periglacial areas: movement is by gelifluction (solifluction over permafrost) and cryoturbation. Kirk Bryan (1946) introduced much of this terminology.
• Deposition occurs when energy falls or load exceeds capacity.
  • Rivers deposit where gradient, velocity or discharge falls, where flow spreads, or where it is obstructed. The results are fans, floodplains, levees and deltas.
  • Groundwater deposits when it becomes saturated or evaporates, forming speleothems: stalactites, stalagmites, travertine and tufa.
  • Waves constantly rework their deposits (beaches, bars, spits) towards a profile of equilibrium.
  • Wind drops sand where it slows or meets obstacles, forming sand shadows, drifts and dunes. Finer dust accumulates as loess.
  • Glaciers deposit till (unsorted), either as lodgement till at the base or ablation till from melting ice. Meltwater leaves stratified drift and outwash.

Process and Form: The Process–Response Idea

• Each process leaves a diagnostic assemblage of landforms, which makes a genetic classification of landforms possible (an approach begun by Davis).
  • Fluvial: gorges, alluvial fans, meanders, levees, deltas.
  • Karst: sinkholes, dolines, poljes, caves, stalactites.
  • Aeolian: dunes, loess, blowouts.
  • Glacial: cirques, arêtes, U-shaped valleys, hanging valleys, moraines, drumlins, eskers.
  • Periglacial:
    • patterned ground (circles, nets, polygons, stripes)
    • pingos, thermokarst, solifluction lobes and terraces
    • nivation hollows, altiplanation terraces, blockfields
• Descriptive terms hide different origins. Naming the process restores the genesis:
  • Plains: floodplain, peneplain, panplain (lateral fluvial planation), pediplain (scarp retreat), etchplain (deep weathering and stripping), karst plain, outwash plain, cryoplain.
  • Scarps: fault scarp (tectonic) versus fault-line scarp (erosional).
  • Valleys: V-shaped (fluvial), U-shaped (glacial), rift (tectonic), blind or dry valleys (karst or periglacial).
  • Terraces: river, marine, solifluction and altiplanation terraces.
• Mono-process versus poly-process origin:
  • In theory a landform can be tied to one process. In reality most landforms are poly-process, because processes rarely act alone. Patterned ground, for example, needs both frost heave and solifluction.
  • Hillslopes are the classic case. Grove Karl Gilbert (1909) linked summit convexity to soil creep, and basal concavity is linked to rainwash and gullying. Most slopes reflect creep and wash working together.
• Process geomorphology since the mid-twentieth century studies each process and its rate by measurement.
  • Climatic geomorphology, by contrast, groups all processes active under one climate. An example is Louis C. Peltier’s (1950) nine morphogenetic regions.

Time, Stage and Scale

Stage in the Davisian Sense

• Stage is a relative phase of development, not a fixed number of years.
  • In Davis’s scheme, a rapidly uplifted block is a closed system with maximum potential energy and minimum entropy at the start.
  • Erosion then spends that energy until relief is uniform, entropy is maximum, and a peneplain remains.
  • Each stage was subdivided into early, middle and late.

• Criticism of stage:
  • Landscapes are open systems with continuous inputs of energy and matter: uplift, precipitation, solar and chemical energy. A one-way decay to a peneplain is therefore unlikely.
  • Stages have no fixed duration. Weak rocks pass quickly from youth to maturity, while resistant rocks prolong youth. Two regions at the “same stage” are similar, not identical.
  • Walther Penck (1924) set stage aside and read landforms as the ratio between the rate of uplift and the rate of removal:
    • aufsteigende Entwicklung (waxing development)
    • gleichförmige Entwicklung (uniform development)
    • absteigende Entwicklung (waning development)
  • John T. Hack (1960) went further. Under dynamic equilibrium, forms adjust to rock resistance and process energy and become time-independent.
• Evaluation: the stage idea survives as relative description (youthful valley, mature drainage). It is useful for long-term, large-area reconstruction such as denudation chronology.

Time Scales: Cyclic, Graded and Steady Time

• Stanley A. Schumm and Robert W. Lichty (1965), in Time, Space and Causality in Geomorphology, reconciled the historical (Davisian) and equilibrium (Hack) views.
  • Their argument: which variables control a landscape depends on the time span considered.
  • The absolute length of each span matters less than its relative size.
  • Cyclic time covers an entire erosion cycle (millions of years). Graded time is a short part of it (roughly hundreds of years), in which self-regulation (negative feedback) keeps forms oscillating around a mean. Steady time is a brief span (days or less), in which forms do not change at all.

• Implications:
  • Over cyclic time, time is the most important independent variable, alongside geology, climate and initial relief.
  • Over graded time, time and initial relief drop out, and hydrology, vegetation and relief become controls.
  • Over steady time, only the outputs of water and sediment remain dependent.
  • Space scales with time. A whole basin keeps losing relief and is never graded as a whole, but a river reach or slope segment can be graded or steady.
  • Modern work, which is mostly concerned with graded and steady time, treats time as a parameter to be measured (for example with cosmogenic nuclide dating), not as a process.
• General resolution levels: macro (millions of years, the scale of megageomorphology), meso (thousands of years) and micro (tens to hundreds of years). Studying processes at these levels allows postdiction (extending present process–form relations into the past) and prediction of future forms.
• Response time:
  • Some responses are instantaneous, like channel change in a large flood.
  • Others involve “dead time” before any change shows.
  • The interval a system takes to respond is its reaction time. The period needed to reach a new equilibrium is its relaxation time.
• Equilibrium types that follow from these time scales:
  • Decay equilibrium: slow progressive decline (the Davisian path).
  • Steady-state equilibrium: oscillation about a constant mean.
  • Dynamic equilibrium: oscillation about a mean that itself changes over time.
  • Dynamic metastable equilibrium: dynamic equilibrium punctuated by sudden jumps when geomorphic thresholds are crossed.
    • Schumm’s episodic erosion is the example. Sediment stored in a valley steepens the channel until a threshold is passed, erosion flushes the fill, and deposition resumes.
    • The result is a stepped valley floor and small terraces that need no external cause (complex response).

Spatial Scales

• The unit of study has shrunk as geomorphology moved from history to process:
  • Macro scale: physiographic regions of Nevin M. Fenneman (1914), defined by structure and geological history.
  • Meso scale: the drainage basin of Robert E. Horton (1945), the standard unit for morphometry and process studies.
  • Micro scale: site assemblages and morphotopes, which are small homogeneous units of uniform shape, lithology, origin and present-day processes.
• Conclusions do not transfer freely across scales, because the dominant variable changes from one scale to the next.

Climate, Relief and Other Controls

Climate

• Direct control:
  • Temperature governs freeze–thaw, glacial and chemical activity.
  • Precipitation amount and intensity govern runoff, solution and mass movement.
  • Wind governs aeolian work.
• Indirect control: through vegetation cover, soil and weathering depth, and runoff regime.
• The same rock behaves differently under different climates. Deep laterite caps on the Deccan and Chotanagpur tablelands contrast with periglacial frost-shattering in Ladakh and dunes in the Thar.
• Relict landforms of past climates show that climate change is part of the time factor.
• Details are in Climatic Geomorphology and Morphogenetic Regions.

Slope, Altitude and Relief (SAR)

• Slope, altitude and relief decide how much energy is available to processes. They are therefore controls on process intensity and the pace of landscape development.

• Slope:
  • Steepness sets the shear stress on slope material and the speed of overland flow. Beyond threshold angles, creep gives way to sliding and flowing.
  • The 30 July 2024 Wayanad disaster (Mundakkai–Chooralmala, Kerala) was a set of channelised debris flows. Around 570 mm of rain in two days fell on steep, regolith-mantled slopes, and the flows ran out for about 8 km.
  • The Landslide Atlas of India (ISRO–NRSC, 2023) mapped about 80,000 landslides (1998–2022). Rudraprayag and Tehri Garhwal ranked highest on its exposure index.
• Altitude:
  • Temperature falls with height, so process zones are stacked vertically:
    • chemical weathering and fluvial work in the foothills
    • mass movement in the Lesser Himalaya
    • frost action and glaciers at high altitude
  • This vertical stacking is why glacial-lake outburst floods occur only at high altitude. The South Lhonak GLOF in Sikkim (October 2023) is an example.
• Relief:
  • Available relief is the store of potential energy.
  • Frank Ahnert (1970) found that the mean denudation rate of mid-latitude basins is directly proportional to mean basin relief, while mean annual precipitation had no noticeable effect.
  • Relative relief, dissection index and slope maps are therefore standard morphometric measures of erosional potential.
  • Relief has also become a legal criterion. In November 2025 the Supreme Court accepted a definition of the Aravalli hills as landforms rising at least 100 m above local relief. On 29 December 2025 it stayed that definition and ordered expert review.
• SAR together: high altitude usually brings high relief and steep slopes. Their combined energy explains why the Himalaya is eroding rapidly while the Peninsula evolves slowly.

Base Level

• Base level, a term introduced by John Wesley Powell (1875), is the lowest level to which a stream can erode.
  • The ultimate base level is sea level.
  • Local or temporary base levels include lakes, resistant rock bars, reservoirs and trunk-stream junctions. The Tehri reservoir is an artificial local base level for the Bhagirathi above the dam.
• Changes in base level reset the process–form balance:
  • A fall (uplift or sea-level drop) causes rejuvenation: knickpoints, incised meanders, paired terraces and obsequent fault-line scarps.
  • A rise causes aggradation and drowned valleys (rias, estuaries), as after the post-glacial sea-level rise.

Biota and Human Agency

• Biota:
  • Vegetation binds soil and slows runoff, and roots wedge joints.
  • Burrowing animals and termites move soil.
  • Organisms build landforms, such as the coral atolls of Lakshadweep and the reefs of the Gulf of Mannar.
• Humans are now a major geomorphic agent. They change runoff, slope loading, sediment supply and base levels through mining, dams, embankments and construction.
  • Joshimath (Uttarakhand) subsided by about 5.4 cm in 12 days (27 December 2022 to 8 January 2023), according to ISRO’s satellite assessment.
  • Details are in Anthropogenic and Environmental Geomorphology.

Evaluation: Is Structure the Dominant Control?

• Structure is dominant where rocks contrast sharply and processes are slow:
  • Vindhyan scarps on sandstone over shale
  • Aravalli quartzite ridges
  • stepped Deccan traps
  • fault-guided Narmada–Tapi valleys
  • strike-guided Himalayan duns
• Structure is not always principal, and never the only control:
  • Convergence: mesas form on basalt and on sandstone; tors on granite, sandstone and basalt; laterite plateaus across many rock types. Similar forms from different rocks point to process and climate.
  • Climate changes rock resistance. Limestone forms karst in Meghalaya but ridges in deserts, and extreme rainfall hollows out even sandstone.
  • Process can override structure. The Indus, Sutlej and Brahmaputra are antecedent rivers: they kept their courses and cut deep gorges across the rising Himalayan ranges.
  • Structure is not passive. Erosion and tectonics are coupled: rapid river incision at the Nanga Parbat and Namcha Barwa syntaxes is linked to rapid rock uplift (the “tectonic aneurysm” of Peter Zeitler and co-workers, 2001).
• Present view:
  • Structure is the stage and the material, process is the tool, and time and scale decide which of them dominates.
  • Over cyclic time and large areas, structure, tectonics and initial relief dominate. Over graded and steady time, process, climate and hydrology dominate.
  • A landscape is therefore a function of interacting factors, not a single master control.