Chapter 6 — Geomorphic Processes

What are geomorphic processes? Geomorphic processes are natural physical and chemical actions that change the Earth’s surface and produce landforms. They operate at different scales and times and are broadly classified into endogenic (internal) and exogenic (external) processes.

• Endogenic processes (internal): Driven by energy from the Earth’s interior (heat and tectonic stresses). They build and uplift landforms.
  • Tectonic movements — folding and faulting produce mountains, rift valleys and basins (e.g., formation of the Himalayas by continental collision).
  • Volcanism — extrusion and intrusion of magma form volcanic cones, lava plateaus (e.g., Deccan Traps are a large volcanic plateau).
  • Isostatic adjustment — buoyant rise or sinking of the crust in response to loading/unloading (glacial rebound).
• Exogenic processes (external): Powered mainly by solar energy, gravity, climate and organisms; they wear down and redistribute materials.
  • Weathering — in situ breakdown of rocks without transport. Types:
    • Physical (mechanical) weathering: freeze–thaw, thermal expansion, exfoliation. Produces angular debris.
    • Chemical weathering: solution, hydrolysis, oxidation—produces clays, dissolved ions.
    • Biological weathering: root action, organic acids.
  • Mass wasting (mass movement) — downslope movement of rock/soil under gravity. Main types: rockfall, slides (landslide), slumps, creep, solifluction. Often triggered by saturation, earthquakes, removal of support.
  • Erosion — detachment and removal of material by agents: running water (rivers and streams), glaciers, wind, waves, groundwater. Each agent sculpts characteristic landforms (e.g., V-shaped valleys by rivers, U-shaped valleys by glaciers, dunes by wind, sea cliffs by waves).
  • Transportation — movement of sediments as bedload, suspended load, dissolved load (for rivers); by saltation, suspension and surface creep (for wind); by basal and internal ice flow (for glaciers).
  • Deposition — settling of transported material where transport energy decreases (e.g., floodplains, deltas, alluvial fans, beaches, moraines).

Controls on geomorphic processes: rock type and structure, climate (temperature and rainfall), slope/relief, vegetation and land use, time, drainage/network pattern, base level (sea level). These factors determine rates (e.g., denudation rates) and the dominant processes in a region.

Dynamic balance and landscape evolution: Landscapes evolve toward an equilibrium form under prevailing conditions (e.g., graded river profile). Disturbances (tectonics, climate change, human activity) shift this balance, accelerating erosion or deposition and creating new landforms over time.

Why it matters: Understanding geomorphic processes helps explain flood risk, soil erosion, landslide hazard, coastal change, river management, and guides sustainable land-use planning.

Definition: Endogenic (internal) processes are forces and movements originating within the Earth that change the shape, elevation and structure of the crust. They are driven by internal heat (mantle convection, radioactive decay) and produce deformation (folding, faulting), volcanism and seismic activity.

Main causes / driving mechanisms:

• Plate tectonics: relative motion of lithospheric plates (convergence, divergence, transform).
• Mantle convection: slow circulation of mantle material that carries heat and moves plates.
• Density contrasts and buoyancy (isostasy): crust floats on denser mantle and uplifts or subsides to restore equilibrium.
• Gravitational forces such as slab pull and ridge push.

Primary types of endogenic processes:

• Diastrophism (crustal deformation): Folding (anticlines, synclines) and faulting (normal, reverse/thrust, strike-slip) during compressional, extensional or shear stresses. Produces mountain ranges, basins and fault scarps.
• Orogeny and epeirogeny: Orogeny = mountain building by plate collision and folding; epeirogeny = broad, gentle uplift or subsidence of large crustal areas (continental warping).
• Volcanism and plutonism: Movement of magma to form volcanoes, lava flows, pyroclastic deposits and intrusive bodies (dikes, sills, batholiths).
• Seismicity (earthquakes): Sudden release of strain energy along faults, producing seismic waves that deform the surface and can trigger secondary processes (landslides, tsunamis).

Effects on landforms: Creation of mountain ranges (Himalaya), rift valleys (East African Rift), oceanic ridges (mid-Atlantic Ridge), volcanic islands (Iceland, Japan) and transform features (San Andreas Fault). Endogenic uplift exposes rocks to erosion which then shapes further landscapes.

Time scales: Endogenic processes operate over a broad range: instantaneous (earthquakes, eruptions), short to medium (decades to millions of years for uplift, volcanism), long (tens to hundreds of millions of years for major orogeny and plate reorganization).

Link to other geomorphic processes: Endogenic processes build relief and create conditions (elevation, slope, fractures) that allow exogenic (external) processes—weathering, erosion, transport and deposition—to modify the landscape further.

Important concept — Isostasy (buoyant equilibrium): Crustal blocks float on the denser mantle; when weight is added (ice sheets, sediments) the crust subsides, and when weight is removed (erosion, melting), the crust rebounds (isostatic uplift). This balances mass vertically over geological time.

Definition: Weathering is the in‑situ breakdown and decomposition of rocks and minerals at or near Earth’s surface by physical, chemical and biological processes. It produces regolith, soil and loose rock fragments without removal by transport (that is erosion).

Types of weathering:

• Physical (mechanical) weathering: Disintegration of rock into smaller pieces without chemical change. Major processes: frost action (freeze‑thaw), thermal expansion and contraction, exfoliation (sheeting), salt crystallisation, pressure release and abrasion. Prominent in cold climates with frequent freeze–thaw or in deserts with large diurnal temperature range.
• Chemical weathering: Decomposition of minerals by chemical reactions with water and gases. Important processes: carbonation (dissolution by carbonic acid), hydrolysis (conversion of feldspars to clays), oxidation (iron minerals rusting), hydration and solution. Dominant in warm, humid climates.
• Biological weathering: Both mechanical and chemical effects produced by plants, animals and microbes: root growth pries cracks open; organisms produce organic acids that accelerate chemical breakdown; burrowing animals and human activity increase rock exposure.

Factors controlling weathering:

• Climate (temperature and precipitation): warm and wet → faster chemical weathering; freeze–thaw frequent → strong physical weathering.
• Rock type and mineral composition: carbonate rocks and mafic minerals weather more easily than resistant quartz.
• Surface area and fracturing: greater surface area (thin fragments, joints, cracks) → faster weathering.
• Time: longer exposure → greater degree of weathering.
• Vegetation, slope, drainage and topography.

Products of weathering: Regolith, soil horizons (A, B, C), saprolite, clay minerals, dissolved ions in groundwater and rivers; characteristic landforms such as tors, residual hills and rounded boulders (spheroidal weathering).

Weathering vs Erosion: Weathering is the in‑place breakdown of rock. Erosion is the removal and transport of weathered material by water, wind, ice or gravity.

Significance: Essential for soil formation, controls landscape evolution by preparing material for transport, influences slope stability, supplies ions to rivers and oceans and affects human infrastructure (rock decay, foundation weakening).

Typical classroom/field observations:

• Cracked and rounded boulders showing exfoliation and spheroidal weathering.
• Limestone caves and karst features produced by carbonation.
• Soil profile development on bedrock with clay accumulation in the B horizon.
• Broken rock fragments near cliff bases from physical weathering and rockfalls.

Definition: Mass wasting (or mass movement) is the downslope movement of rock, soil, regolith and vegetation under the direct influence of gravity. It occurs when driving forces (mainly gravity) exceed resisting forces (cohesion, internal friction, and friction at the base).

Causes and controls:

• Slope angle: Steeper slopes increase the component of gravity driving movement.
• Rock/soil properties: Weak, weathered, fractured or unconsolidated materials are more susceptible.
• Water: Increases weight, reduces cohesion and increases pore water pressure, which lowers shear strength.
• Vegetation: Roots bind soil and increase slope stability; removal increases risk.
• Triggers: Intense rainfall, rapid snowmelt, earthquakes, volcanic activity, undercutting by rivers or human excavation.

Classification (common scheme): Mass movements are classified by the type of material and the mode of movement:

• Falls: Very rapid free-fall of rock or debris (rockfall).
• Topples: Forward rotation and movement of a block about a pivot point.
• Slides (translational/rotational): Material moves along one or more surfaces. A slump is a rotational slide of coherent material along a curved surface.
• Flows: Material behaves like a viscous fluid (earthflow, debris flow, mudflow). Often rapid and can travel long distances.
• Creep: Very slow downslope movement of soil/rock, often indicated by tilted trees, fences or walls.
• Solifluction: Slow flow in permafrost or seasonally frozen ground where thawed surface layer moves over frozen subsoil.

Processes / mechanics (simple view): Consider a block of weight W on a slope of angle θ. The weight produces two components: the driving (parallel) force W·sinθ and the normal (perpendicular) force W·cosθ. Stability depends on shear strength of the material (cohesion c and internal friction φ) vs driving shear stress. When driving shear stress exceeds shear strength, movement occurs.

Impacts: Destruction of infrastructure (roads, houses, dams), loss of life, landscape modification, sedimentation of rivers and reservoirs, interruption of transport and utilities.

Mitigation and management: Slope grading/benching, drainage to reduce pore pressure, retaining walls and buttresses, rock bolts and nets, revegetation, land-use zoning and early-warning monitoring (inclinometers, piezometers, rainfall thresholds).

Definition: Fluvial processes are the actions of running water (rivers and streams) that shape the land by eroding, transporting and depositing sediments. They are a major agent of landscape change in areas with surface runoff.

Main components

• Erosion: The removal of material from the river channel and banks. Principal types:
  • Hydraulic action (force of water)
  • Abrasion (scraping by transported particles)
  • Attrition (particles collide and break)
  • Solution/corrosion (chemical dissolution)
• Transportation: Movement of sediment in three forms:
  • Bed load (rolling, sliding, saltation of larger particles)
  • Suspended load (fine silt and clay carried within the water)
  • Dissolved load (ions in solution)
• Deposition: When river velocity falls and it loses competence/capacity, it deposits material forming features like floodplains, levees, point bars, alluvial fans and deltas.

Processes controlling fluvial action

• Gradient or slope of the channel (steeper = more erosion)
• Discharge (volume of water flowing per unit time)
• Load size, amount and type (bed, suspended, dissolved)
• Channel roughness and shape
• Base level (ultimate base level = sea level) and tectonics
• Climate, vegetation and human activity (land use, dams, deforestation)

Stages of river development (classical model)

• Youth: Steep gradient, vertical erosion dominant, V-shaped valleys, interlocking spurs, waterfalls and rapids.
• Maturity: Reduced gradient, lateral erosion starts, wider valleys, meanders begin to form.
• Old age: Low gradient, extensive lateral erosion and deposition, wide floodplains, ox-bow lakes, levees, and large deltas.

Important landforms produced by fluvial processes

• Erosional: V-shaped valleys, gorges, waterfalls, potholes, river cliffs.
• Depositional: Meanders and ox-bow lakes, point bars, floodplains, levees, alluvial fans (at mountain fronts), deltas (at river mouths).

Concepts: Competence, Capacity, Stream Power

• Competence: Maximum particle size a stream can carry (depends mainly on velocity).
• Capacity: Total quantity of sediment a stream can transport (depends on discharge and competence).
• Stream power: Rate at which a river does work on its bed and banks (influences erosion and transport).

Summary: Fluvial processes are dynamic and interlinked: higher slope and discharge increase erosive force, producing characteristic erosional landforms in upland/youthful reaches; downstream, reduced slope and increased discharge promote transportation and deposition that build floodplains, deltas and other depositional features. Human activities (dams, channelisation, deforestation) strongly modify natural fluvial behaviour.

Overview: Glacial processes are the set of physical actions performed by glaciers that reshape Earth's surface. Glaciers erode, transport and deposit material, producing characteristic landforms at regional and local scales. These processes depend on glacier type, slope, temperature regime and availability of debris.

Major categories of glacial processes

• Erosion – Removal of bedrock and sediments by moving ice. Main mechanisms:
  • Plucking (quarrying): Freeze–thaw at the glacier base and sides breaks blocks of rock which are lifted and carried away by the ice.
  • Abrasion: Rock fragments embedded in the ice grind the bedrock like sandpaper, producing striations and rock flour.
• Transportation – Movement of debris by ice or meltwater. Modes:
  • Supraglacial (on the surface), englacial (within the ice), and subglacial (at the bed).
  • Meltwater streams transport and sort material in outwash plains.
• Deposition – When ice melts or slows, it drops its load, forming depositional features such as moraines (lateral, medial, terminal), drumlins, eskers, kames and outwash plains.

Glacier movement (dynamics)

• Internal deformation: Ice flows plastically (creep) under its own weight; deformation increases with depth and shear stress.
• Basal sliding: The whole glacier slides over its bed when meltwater lubricates the bed or when the bed is saturated; more common in temperate glaciers.
• Surging: Short-lived episodes of rapid flow due to changes in basal conditions or water pressure.

Zones of a glacier: Zone of accumulation (higher elevations where snowfall adds mass) and zone of ablation (lower elevations where melting, sublimation and calving remove mass). The altitude where annual accumulation equals ablation is the equilibrium line (ELA).

Key landforms produced by glacial processes

• Erosional: Cirques (corries), arêtes, horns, U-shaped valleys, hanging valleys, truncated spurs, fjords.
• Depositional: Moraines (lateral, medial, terminal), drumlins, eskers, kames, outwash plains, till sheets.

Importance: Glacial processes influence landscape evolution, create fertile outwash plains, shape drainage patterns, and are indicators of climate change through mass-balance variations.

Definition: Aeolian (wind) processes are geomorphic actions by which wind erodes, transports and deposits sediment. They are dominant in arid, semi-arid and coastal environments where vegetation is sparse and loose sediment is available.

Main processes:

• Erosion
  • Deflation – removal of loose fine particles (dust and silt) by the wind; produces features like blowouts and desert pavements.
  • Abrasion – mechanical wearing of rock surfaces by wind-driven sand acting like sandpaper; produces polished surfaces, ventifacts and yardangs.
• Transport (modes)
  • Suspension – very fine particles (clay, silt) carried long distances within the air column (dust storms, long-range dust transport).
  • Saltation – the common mode for sand-sized grains: particles are lifted briefly and follow short ballistic hops, striking the surface and ejecting other grains.
  • Creep (surface creep) – larger particles roll or slide along the ground pushed by wind or impacted by saltating grains.
• Deposition – occurs where wind velocity falls below the carrying capacity; results in dune formation, sand sheets and loess accumulation.

Typical Aeolian landforms:

• Dunes – barchan (crescentic), transverse, longitudinal (seif), parabolic, star dunes depending on wind regime and sand supply.
• Loess – thick deposits of wind-blown silt forming fertile upland plains (e.g., Chinese Loess Plateau).
• Yardangs – streamlined wind-sculpted ridges oriented with prevailing wind.
• Ventifacts – isolated, faceted rocks polished by abrasion.
• Desert pavements – closely packed surface of coarse pebbles left after deflation removes fines.

Controls on aeolian activity: wind velocity and variability, sediment grain size and availability, moisture and vegetation, surface roughness, and topography.

Significance and impacts: soil erosion and loss of fertility, formation of economically important deposits (loess), hazards from dust storms (health, transport disruption), and long-distance nutrient transport (e.g., Sahara dust to the Amazon).

Measurement and conceptual tools: Hjulström diagram (relates particle size to erosion/transport/deposition velocities), wind speed profiles (logarithmic with height), and empirical transport equations (e.g., Bagnold).

Overview
Coastal and marine processes are the physical actions (waves, tides, currents, winds and sea-level changes) that shape coastlines. They include erosion, transportation and deposition of sediments and create characteristic coastal landforms such as cliffs, wave-cut platforms, beaches, spits, bars, estuaries and tidal flats.

Wave formation and motion
Waves are generated mainly by wind blowing over the sea surface. A wave is a transfer of energy through water: particles move in nearly circular orbits. Key wave parameters are height (H), wavelength (L), period (T) and frequency (f). In deep water the orbital motion is circular; in shallow water or near the shore orbits flatten and waves break when the water depth becomes about 1.3 times the wave height.

Types of waves

• Constructive waves — low height, long wavelength, weak backwash; deposit material and build beaches.
• Destructive waves — high height, short wavelength, strong backwash; erode the coast and steepen the beach.

Wave processes causing erosion

• Hydraulic action — force of water entering cracks, compressing air and fracturing rock.
• Abrasion/attrition — rock fragments and sand grind surfaces and each other.
• Solution/corrosion — chemical dissolution of soluble minerals by seawater.
• Wave pounding — repeated impact of waves weakening rock.

Deposition and sediment transport
Where wave energy falls, sediments settle to form beaches, spits, bars and barrier islands. Longshore drift (or littoral drift) moves sediment along the shore when waves strike at an angle; longshore currents carry suspended material parallel to the coast. Where the shoreline geometry or river mouth traps sediment, depositional features develop.

Tides
Tides are periodic rise and fall of sea level caused by gravitational interaction between the Earth, Moon and Sun. Most coasts experience semi-diurnal tides (two high and two low each lunar day ≈ 24 h 50 min). Spring tides (new/full moon) have the greatest tidal range; neap tides (first/third quarter) have the smallest. Tidal range controls the extent of intertidal zones, estuary dynamics and tidal flats.

Currents
Ocean currents are persistent water movements driven by wind, density differences and tides. Nearshore currents include longshore currents (driven by oblique waves) and rip currents (strong seaward jets). Offshore currents redistribute heat and sediments at larger scales.

Coastal landforms (brief)

• Erosional — cliffs, wave-cut platforms, sea caves, arches, stacks.
• Depositional — beaches, spits, tombolos, barrier islands, sand bars, lagoons and deltas/estuaries.

Human interactions & management
Human activity (harbour construction, groynes, sea walls, sand nourishment) alters natural processes and may cause erosion or accretion elsewhere. Sustainable management requires understanding sediment budgets, wave climate and sea-level rise.

Key concepts to remember

• Wave energy concentrates on headlands (causing erosion) and disperses in bays (encouraging deposition) by refraction.
• Longshore drift transports material alongshore; depositional features form where transport is interrupted.
• Tidal amplitude and local coastal shape determine how tides affect shoreline processes.

Groundwater — definition and origin
Groundwater is the water that occupies the pore spaces and fractures of subsurface rocks and sediments. It originates from rainfall and surface water that infiltrates the ground (recharge) and is stored in subsurface zones until it returns to the surface via springs, wells or discharge to rivers and oceans.

Storage and flow

• Porosity — the percentage of void space in a rock or sediment that can store water (e.g., sand has high porosity; massive granite has low porosity).
• Permeability — the ability of a material to transmit water; depends on pore connectivity and fractures.
• Zones — unsaturated (vadose) zone above the water table containing air and some water; capillary fringe just above the saturated zone; saturated (phreatic) zone where all pores are filled with water.
• Water table — the surface separating the unsaturated and saturated zones; its shape reflects topography and recharge/discharge conditions.
• Aquifers — rock or sediment units that store and transmit usable groundwater. Types: unconfined (open to the surface), confined (bounded by impermeable layers and under pressure), and semi-confined.

Groundwater movement
Groundwater moves slowly from high hydraulic head to low hydraulic head along hydraulic gradients. Flow rate is controlled by hydraulic conductivity (K) and the gradient.

Sources and outlets
Recharge: precipitation, seepage from rivers, infiltration from irrigation. Discharge: springs, baseflow to rivers, pumping from wells, seepage to sea.

Importance and problems
Groundwater is a major fresh water resource for drinking, irrigation and industry. Problems include over-extraction (lowering of water table, subsidence), contamination (nitrate, pesticides, industrial waste), and saltwater intrusion in coastal aquifers.

Karst processes — definition
Karst describes landscapes and subsurface features formed primarily by the chemical dissolution of soluble rocks (mainly limestone — calcium carbonate, dolomite, gypsum). Karstification is driven by slightly acidic water that reacts with carbonate minerals.

Chemistry of karstification (simplified)
CO2 from air and soil dissolves in rainwater to form weak carbonic acid. This acid reacts with calcite in limestone:

CO2 + H2O ⇌ H2CO3
CaCO3 (calcite) + H2CO3 → Ca2+ + 2 HCO3−

When groundwater loses CO2 (degassing) or conditions change, calcium carbonate can precipitate to form speleothems (stalactites and stalagmites):

Ca2+ + 2 HCO3− → CaCO3 (solid) + CO2 + H2O

Karst landforms (surface and subsurface)

• Sinkholes (dolines) — circular depressions formed by collapse or solution of surface limestone.
• Disappearing (losing) streams — surface streams that flow into swallow holes and continue underground.
• Caves and caverns — underground voids formed by dissolution; may contain speleothems (stalactites hang from ceilings; stalagmites rise from floors).
• Limestone pavements — flat, jointed exposed rock with clints (blocks) and grikes (fissures).
• Poljes — large flat-floored depressions subject to seasonal flooding.
• Karst towers — steep isolated hills (prominent in tropical karst regions like Guilin, China).

Controls on karstification

• Rock solubility and purity (pure, well-jointed carbonate rocks karstify fastest).
• Climate — humid and temperate to tropical climates with abundant vegetation and soil CO2 are favourable.
• Vegetation and soil — produce CO2 that increases acidity of infiltrating water.
• Time — karst features develop over long periods.
• Structural controls — joints, bedding planes and faults guide water flow and enlargement.

Interactions between groundwater and karst
Karst aquifers are highly productive but vulnerable: they transmit water rapidly through conduits (high permeability but variable storage), so contaminants can travel quickly and springs can be strong and variable. Groundwater flow in karst is a mix of diffuse flow through pores and fast conduit flow.

Examples of human and environmental significance

• Water supply: karst springs can be important drinking-water sources (but require careful protection).
• Hazards: collapse sinkholes can damage infrastructure; contamination can spread rapidly.
• Tourism and science: caves and speleothems are important for tourism and paleoclimate records.

Summary
Groundwater and karst processes are linked: infiltration and groundwater chemistry drive dissolution of soluble rocks to create karst landscapes and underground drainage systems. Understanding porosity, permeability, hydraulic head and karst hydrogeology is essential for sustainable groundwater management and hazard mitigation.

Denudation is the overall process by which the Earth's surface is worn away and lowered by the combined action of weathering, mass wasting (mass movement) and erosion by agents (running water, glacier, wind, waves, and groundwater). It reduces relief and transports rock and soil material from one place to another.

Key components of denudation

• Weathering – in-situ breakdown of rock to regolith and soil (mechanical, chemical, biological).
• Mass wasting – downslope movement of rock and soil under gravity (falls, slides, slumps, creep).
• Erosion – detachment and removal of material by an agent (rivers, glaciers, wind, waves).
• Transportation – movement of sediment (by flow, ice, wind).
• Deposition – settling of transported material when the transporting energy falls.

Gradation (also called leveling) describes the set of processes by which the landscape is reduced toward an equilibrium form. Gradation includes erosion, transportation and deposition acting together to produce gentler slopes and an overall lowering of relief. Classic geomorphology often describes stages of landscape evolution: youthful (steep slopes, deep incision), mature (well developed drainage, rounded relief), and old (low relief, peneplain).

Graded stream – a stream is called graded when its slope, discharge and sediment load are in dynamic equilibrium: it has just enough slope and energy to transport the incoming sediment without net aggradation or degradation, forming a smooth concave longitudinal profile.

Base level is the lowest level to which a land surface can be eroded. There are two main kinds:

• Ultimate/base level of erosion – sea level (the absolute lowest). Rivers cannot erode below the sea level over long term.
• Local base levels – lakes, resistant rock ledges, sea cliffs, or a larger river into which a tributary flows; these act as temporary limits to erosion and control local profiles.

Relationship between these concepts

• Denudation processes operate continuously; gradation describes their long-term tendency to produce lower, smoother topography.
• Base level controls the longitudinal profile of rivers; a fall in base level causes rejuvenation (renewed incision), while a rise causes aggradation (sediment build-up).
• Dynamic equilibrium: landscapes and rivers fluctuate around conditions in which uplift, climate, and base level balance denudational lowering.

Factors controlling denudation and gradation – climate (rainfall, temperature), lithology (rock strength, joints), slope and relief, vegetation cover, time (landscape age), tectonic uplift/subsidence, and human activity (deforestation, mining, damming).

Measurement and rates – denudation may be estimated by sediment yield of rivers, cosmogenic radionuclide dating, or comparing volume loss over mapped areas. Rates are commonly given as mm/ka (millimetres per thousand years) or mm/yr.

Practical implications – understanding denudation and base level is essential for floodplain management, soil conservation, reservoir siltation estimates, coastal protection and interpreting landscape history (e.g., river terraces, marine terraces, canyons).

Definition: Factors controlling geomorphic processes are the physical, chemical, biological and temporal conditions that determine how fast and in what manner the Earth's surface is weathered, eroded, transported and deposited.

Major groups of controlling factors

• Internal (Endogenic) factors
  • Tectonics and uplift: Active uplift creates steep slopes and high relief, increasing potential energy and rates of erosion (e.g., young mountain belts).
  • Rock structure and lithology: Rock type, joints, bedding, foliation and faulting control weaknesses where weathering and erosion act (e.g., folded sedimentary rocks produce differential erosion).
• External (Exogenic) factors
  • Climate: Temperature and precipitation determine the dominant processes (chemical weathering in warm, humid climates; freeze–thaw in cold climates; intensity of fluvial erosion in high-rainfall regions).
  • Relief and slope angle: Steeper slopes favor mass wasting and rapid runoff; gentle slopes favor deposition and soil formation.
  • Vegetation and land cover: Roots stabilize soil and slow erosion; removal of vegetation accelerates erosion and landslides.
  • Drainage characteristics and discharge: Stream flow (volume and velocity) determines erosive power, transport capacity and deposition patterns.
  • Base level (sea level for coasts and rivers' lowest level): Changes in base level control whether rivers incise or deposit; sea-level rise/fall influences coastal erosion and sedimentation.
  • Time: Duration of exposure affects the degree of weathering and landscape evolution; long periods produce mature landforms.
  • Human activity: Deforestation, mining, dams and urbanization alter sediment supply, runoff and stability.

How these factors control specific geomorphic processes

• Weathering: Controlled mainly by climate (temperature, moisture), rock composition (mineral solubility, grain size, porosity), and time. Example: chemical weathering more intense in tropical climates; freeze–thaw in mountains.
• Mass wasting (slope failure): Controlled by slope angle, water content, rock/soil cohesion, vegetation, and triggers such as earthquakes or heavy rain. Saturation reduces shear strength and promotes slides.
• Fluvial erosion & transport: Controlled by discharge (Q), velocity (v), channel slope (S), sediment size and load. Greater velocity and discharge increase competence and capacity.
• Deposition: Occurs where velocity falls (reduced slope, channel widening, meeting standing water). Particle size and settling velocity determine sorting.

Conceptual links (summary): Rock properties + structure set where processes act; climate and vegetation determine process intensity and type; relief/slope and tectonics set available potential energy; drainage and discharge determine transport; time and human actions modify the system.

Overview

Human activities alter natural geomorphic processes (weathering, mass wasting, erosion, transportation and deposition) by changing surface cover, drainage, sediment supply, groundwater regimes and coastal dynamics. These alterations accelerate or reduce rates of landscape change, often producing unintended environmental problems such as increased erosion, sedimentation, flooding, coastal retreat and subsidence.

Main mechanisms by which humans affect geomorphic processes

• Vegetation removal: Deforestation, overgrazing and land clearing reduce root reinforcement and interception, increase rainfall impact on soil, lower infiltration and increase surface runoff and soil erosion.
• Land-use change and urbanization: Converting permeable surfaces to impermeable ones (roads, buildings) increases runoff volume and peak discharge, shortens lag time, and increases channel erosion and flood risk.
• Agriculture and tillage: Disturbs soil structure, increases erodibility and sediment yield; irrigation can change groundwater levels and cause salinization.
• Mining and quarrying: Remove material and vegetation, create overburden dumps and loose slopes susceptible to erosion and mass movement.
• River engineering (dams, levees, channelization): Dams trap sediment, starving downstream reaches and coasts of sediment (causing erosion); levees confine flow and increase downstream flood peaks; channelization increases flow velocity and incision.
• Groundwater extraction and fluid withdrawal: Causes land subsidence, changes pore pressure and slope stability, and alters baseflow in rivers.
• Coastal structures and sand mining: Sea walls, groynes and ports interrupt alongshore sediment transport, causing local erosion and accretion; sand mining reduces beach/dune resilience.

Consequences for geomorphology

• Increased soil erosion and sediment yield: Higher rates of sheet, rill and gully erosion; more sediment delivered to rivers and reservoirs, reducing storage capacity.
• Altered river morphology: Channel incision or aggradation, bank collapse, changed planform (meander migration) and floodplain modification.
• Enhanced mass wasting: Slope failures and landslides triggered by vegetation removal, excavation and changes in groundwater.
• Coastal change and retreat: Reduced sediment supply from rivers (after damming) accelerates shoreline retreat; coastal protection structures transfer erosion downcoast.
• Ground subsidence: Due to compaction from groundwater or hydrocarbon extraction and loading from urban infrastructure.

Management and mitigation

Measures include reforestation and afforestation, terracing and contour farming, check dams and silt traps, sustainable mining practices, controlled urban drainage (permeable pavements, retention basins), regulated groundwater extraction, and soft-engineered coastal protection (beach nourishment, dune restoration).

What are conceptual models and theories?

In geomorphology, conceptual models and theories are simplified, generalized representations that explain how landforms are created, modified and destroyed by geomorphic processes. Models can be verbal, graphical or mathematical. Theories are broader frameworks that link processes, rates and forms to produce testable predictions about landscape evolution.

Types and roles

• Analogue/Conceptual models: simplified diagrams or narratives (for example, Davisian cycle of erosion) used to visualise stages and relationships.
• Mathematical models: equations that express relationships between variables (for example, stream power law).
• Numerical and physical models: lab or computer simulations that reproduce process behaviour under controlled conditions.

Major classical theories

• Davisian cycle of erosion (William Morris Davis): A genetic model describing landscape evolution through three idealized stages — youth, maturity and old age — driven by uplift followed by denudation. It emphasises time-sequenced change from rugged relief to a peneplain.
• Penck's theory of slope development (Walther Penck): Emphasises simultaneous uplift and denudation. Key idea is slope retreat and the tendency of slopes to evolve in parallel as the base level lowers or uplift continues.
• Uniformitarianism vs Catastrophism: Uniformitarianism states that present-day processes operating at similar rates explain past landforms; catastrophism allows for rare, high-magnitude events to produce major geomorphic change.

Modern concepts

• Equilibrium concepts: Landscapes tend towards steady or dynamic equilibrium where process rates balance (for example, sediment supply equals transport capacity). Types include steady-state (constant form), dynamic equilibrium (form fluctuates around a mean) and threshold behaviour (sudden adjustment when forcing exceeds a threshold).
• Graded river concept: A river reaches a graded state when slope, discharge and sediment load are in balance so the long profile is smoothly concave and does not tend to aggrade or degrade over long periods.
• Thresholds and non-linear responses: Many geomorphic systems show little change until a forcing (rainfall, uplift, base-level fall) crosses a threshold, producing rapid adjustments such as landslides or channel incision.

Strengths and limitations

• Models simplify complex reality to make processes understandable and testable. They are useful teaching tools and starting points for field interpretation.
• Limitations include over-simplification (e.g., Davisian stages rarely occur exactly as described), regional variability, and ignoring episodic events or human impacts. Modern geomorphology combines classical models with quantitative data and process-based experiments.

How to use these models in the field

• Use Davis or Penck as hypotheses: compare observed valley shapes, slope forms and drainage patterns with model predictions.
• Look for evidence of equilibrium: concave longitudinal profiles, channel adjustments after floods, matched sediment supply and transport.
• Search for threshold responses: recent landslides, rapid incision, or aggradation linked to climate or land-use changes.

Overview

Methods of study and measurement in geomorphology combine field observation, remote sensing, geophysical techniques, laboratory analyses and quantitative/mathematical tools to describe landforms, determine processes, measure rates (erosion, uplift, sediment transport) and date events. Together these methods allow geomorphologists to map form, understand process, and produce numeric indices for comparison.

Main approaches

• Field mapping and observation: systematic mapping of landforms, lithology, structures and soil/sediment profiles; use of topographic maps and compass/clinometer for slope angles. Field mapping gives ground-truth for remote data.
• Remote sensing and aerial photography: satellite images and aerial photos show spatial patterns (river meanders, coastal change, landslides). Multispectral images reveal vegetation/sediment differences and change detection over time.
• Topographic maps and DEMs (Digital Elevation Models): used to create contour profiles, slope maps, aspect maps and to compute morphometric indices (drainage density, relief ratio, hypsometric curve).
• GPS and surveying: precise horizontal and vertical positions for measuring uplift/subsidence, channel migration and long-term landscape change.
• Hydrological measurement: discharge (Q) by area–velocity methods, sediment load sampling, hydrographs to study river response to rainfall.
• Geophysical techniques: seismic refraction/reflection, ground-penetrating radar (GPR), electrical resistivity and magnetics to image subsurface structures, buried channels, and bedrock topography.
• Laboratory and sediment analyses: grain-size analysis, mineralogy, heavy-mineral and geochemical fingerprinting to interpret transport history and provenance.
• Dating methods: radiocarbon (14C), optically stimulated luminescence (OSL), cosmogenic nuclide dating to assign ages to terraces, deposits and surfaces and to compute rates (e.g., uplift or incision rates).
• Experimental and monitoring tools: erosion pins, sediment traps, flumes, inclinometer stations, and automated sensors (rainfall, water level) for continuous measurement.
• GIS and quantitative morphometry: computing indices (drainage density, bifurcation ratio, hypsometric integral, slope, concavity) and spatial analysis (buffering, overlay, change detection).

Integration and interpretation

Best practice combines multiple methods: remote sensing for broad pattern recognition, field checks for validation, DEM-based morphometry for quantitative indices, geophysics for subsurface structure, and dating for rates/timing. Quantitative indices are interpreted together (e.g., high drainage density + steep slopes may indicate high runoff/erodibility).

Commonly measured variables: elevation, slope angle, profile concavity, channel length, stream order, basin area, stream discharge, sediment concentration, rock/soil properties, age of deposits.