BharatNotes
Introduction
Geomorphology is the scientific study of the origin and evolution of landforms on the Earth's surface. The term derives from the Greek words geo (earth), morphe (form), and logos (study). Landforms are shaped by the interplay of endogenetic processes (tectonic forces originating within the Earth — volcanism, folding, faulting, uplift) and exogenetic processes (forces operating on the Earth's surface — weathering, erosion, deposition by running water, glaciers, wind, and waves).
This chapter covers the rock cycle, weathering, mass movement, and the major categories of erosional and depositional landforms — fluvial, glacial, aeolian, marine, and karst — along with the theoretical models of Davis and Penck.
Rocks and the Rock Cycle
Rocks are naturally occurring solid aggregates of minerals. They are classified into three types based on their mode of formation:
Types of Rocks
| Type | Formation Process | Examples | Characteristics |
|---|---|---|---|
| Igneous | Solidification of molten magma or lava | Granite (intrusive/plutonic), Basalt (extrusive/volcanic), Gabbro, Obsidian | Primary rocks; crystalline; no fossils; hard and resistant |
| Sedimentary | Compaction and cementation of sediments deposited by water, wind, or ice | Sandstone, Limestone, Shale, Conglomerate, Coal | Layered (stratified); contain fossils; cover ~75% of Earth's surface area but only ~5% of crust by volume |
| Metamorphic | Transformation of existing rocks under heat and pressure | Marble (from limestone), Slate (from shale), Quartzite (from sandstone), Gneiss (from granite) | Foliated or non-foliated; harder and denser than parent rock |
The Rock Cycle
The rock cycle describes the continuous transformation of rocks from one type to another:
- Igneous rocks are formed when magma cools and solidifies (either below the surface as plutonic rocks or on the surface as volcanic rocks).
- Igneous rocks are broken down by weathering and erosion, and the sediments are transported and deposited to form sedimentary rocks through compaction and cementation.
- When sedimentary or igneous rocks are subjected to intense heat and pressure (metamorphism), they become metamorphic rocks.
- Any rock type can be melted back into magma, restarting the cycle.
- Metamorphic rocks can also be weathered to form sedimentary rocks, and igneous rocks can directly metamorphose without first becoming sedimentary.
The rock cycle is not linear — any rock type can transform into any other, depending on the geological conditions.
Weathering
Weathering is the in-situ breakdown and decomposition of rocks and minerals at or near the Earth's surface through physical, chemical, and biological processes. Unlike erosion, weathering does not involve the transport of material — the broken-down material remains in place.
Physical (Mechanical) Weathering
Physical weathering disintegrates rock into smaller fragments without altering its chemical composition.
| Process | Mechanism | Regions |
|---|---|---|
| Frost weathering (freeze-thaw) | Water enters cracks, freezes and expands (by ~9%), widening the crack. Repeated cycles shatter the rock. | Cold and high-altitude regions (Himalayas, Arctic) |
| Thermal expansion and contraction | Daily heating and cooling causes differential expansion of minerals, leading to exfoliation (peeling of outer layers) and granular disintegration | Hot deserts (Sahara, Thar) |
| Exfoliation (unloading) | When overlying rock is removed (by erosion), underlying rock expands upward, causing concentric sheets to peel off — creating exfoliation domes | Granite landscapes (e.g., Half Dome, Yosemite) |
| Salt crystallization | Saline water enters pores; as it evaporates, salt crystals grow and exert pressure, breaking the rock | Coastal and arid regions |
| Pressure release | Deep-seated rocks formed under high pressure crack when they are exposed at the surface and pressure is relieved | Mountain regions |
Chemical Weathering
Chemical weathering involves the decomposition of rock through chemical reactions that alter its mineral composition.
| Process | Reaction | Example |
|---|---|---|
| Oxidation | Minerals react with oxygen, forming oxides. Iron-bearing minerals turn reddish-brown (rust). | Laterite soils in tropical regions |
| Hydration | Minerals absorb water into their crystal structure, causing expansion and weakening. | Feldspar absorbs water; anhydrite becomes gypsum |
| Hydrolysis | Minerals react with water (H+ and OH- ions) to form new minerals. | Feldspar + water = clay minerals (kaolinite) |
| Carbonation | CO2 dissolves in rainwater to form carbonic acid (H2CO3), which dissolves carbonate rocks. | Limestone dissolving to form karst features |
| Solution | Minerals dissolve directly in water. | Rock salt (halite), gypsum dissolving in water |
Note: Chemical weathering is most intense in hot and humid climates (tropical regions) because both heat and moisture accelerate chemical reactions.
Biological Weathering
Living organisms contribute to both physical and chemical weathering:
- Plant roots grow into cracks and widen them (physical).
- Burrowing animals (earthworms, rodents, rabbits) loosen and mix soil material.
- Lichens and mosses produce organic acids that dissolve rock surfaces (chemical).
- Bacteria decompose organic matter, producing acids that aid chemical weathering.
Mass Movement (Mass Wasting)
Mass movement is the downslope transfer of rock, regolith (loose surface material), and soil under the direct influence of gravity — without the primary involvement of a transporting agent like water, wind, or ice.
Types of Mass Movement
| Type | Speed | Material | Mechanism |
|---|---|---|---|
| Creep | Very slow (mm to cm per year) | Soil and regolith | Gradual downslope movement; often unnoticed; tilted fences and walls are indicators |
| Solifluction | Slow | Water-saturated soil | Common in periglacial regions; thawed active layer flows over frozen permafrost |
| Earthflow | Moderate | Clay-rich, water-saturated material | Material flows as a viscous mass; common on moderate slopes |
| Mudflow | Fast | Water-saturated mud and debris | Rapid flow of mud down steep channels; common in volcanic and semi-arid regions (lahars on volcanoes) |
| Landslide (translational) | Fast to very fast | Rock and debris | Material slides along a planar surface (bedding plane or fault) |
| Landslide (rotational/slump) | Fast | Coherent block of rock/soil | Material rotates along a curved slip surface; leaves a concave scar |
| Rockfall | Very fast | Individual rocks and boulders | Free-falling rock fragments from steep cliffs; common in mountains |
| Avalanche | Extremely fast | Snow, ice, rock, debris | Massive, rapid flow of snow/ice mixed with debris; highly destructive |
Factors Influencing Mass Movement
- Slope gradient — steeper slopes are more susceptible
- Water content — saturation reduces friction and adds weight
- Vegetation — roots bind soil; deforestation increases risk
- Rock structure — weak planes, joints, faults
- Seismic activity — earthquakes trigger landslides
- Human activity — road construction, mining, deforestation
Fluvial Landforms (Running Water)
Rivers are the most significant agent of erosion and deposition on the Earth's surface. Fluvial landforms are divided into erosional and depositional features, corresponding broadly to the upper, middle, and lower courses of a river.
Erosional Landforms
| Landform | Description | Location |
|---|---|---|
| V-shaped valley | Steep-sided, narrow valley cut by vertical erosion (downcutting) in the upper course | Mountainous regions; upper Ganga in Himalayas |
| Gorge | Very deep and narrow valley with near-vertical walls | Indus Gorge near Gilgit; Grand Canyon (Colorado River) |
| Canyon | A wider gorge, often in arid or semi-arid regions where lateral weathering is limited | Grand Canyon, USA |
| Waterfall | Water falling vertically over a resistant rock ledge, with a softer rock below that erodes faster (undercutting) | Jog Falls (Sharavathi River, Karnataka); Niagara Falls |
| Plunge pool | A deep pool at the base of a waterfall, formed by the erosive force of falling water | At the foot of all major waterfalls |
| Pothole | Circular depressions in a rocky river bed, formed by the abrasive action of pebbles swirled by eddies | Common in upper courses |
| River terrace | Step-like flat surfaces on valley sides, formed when a river cuts down through its own floodplain deposits | Common in rejuvenated rivers |
| Incised/Entrenched meander | Deeply cut meanders formed when a meandering river on a plain is uplifted and starts downcutting again | Goosenecks of the San Juan River, Utah |
Depositional Landforms
| Landform | Description | Location |
|---|---|---|
| Alluvial fan | Fan-shaped deposit of sediment at the base of a mountain, where a fast-flowing stream suddenly enters a plain and loses velocity | Foot of Himalayas; Dehra Dun |
| Alluvial cone | Steeper and smaller than an alluvial fan | Narrow mountain valleys |
| Floodplain | Flat area adjacent to a river channel, built of alluvium deposited during floods | Indo-Gangetic Plain |
| Natural levee | Low ridges of sediment along both banks of a river, built up by repeated flooding | Mississippi River; Brahmaputra |
| Meander | Sinuous curves in the middle and lower course of a river, where erosion occurs on the outer bank (cut bank) and deposition on the inner bank (point bar) | All mature rivers |
| Oxbow lake | A crescent-shaped lake formed when a meander loop is cut off from the main channel | Common in floodplains |
| Delta | A triangular or fan-shaped deposit of sediment at the mouth of a river entering a calm body of water | Ganga-Brahmaputra delta (world's largest); Nile delta |
| Estuary | A funnel-shaped river mouth where the river meets the sea, with tidal influence; no delta formation due to strong tidal action | Narmada, Tapi estuaries |
Types of Deltas
| Type | Shape | Example |
|---|---|---|
| Arcuate (fan-shaped) | Triangular, curved outer margin | Nile, Ganga, Rhine |
| Bird's foot | Finger-like extensions projecting into the sea | Mississippi |
| Cuspate | Tooth-shaped, pointed projection | Tiber (Italy) |
| Estuarine | Delta formed inside an estuary | Seine (France) |
Glacial Landforms
Glaciers are large masses of ice that move slowly under their own weight. They are found in high-altitude mountain regions (alpine/valley glaciers) and polar regions (continental ice sheets). Glaciers erode through plucking (freezing and pulling away rock fragments) and abrasion (scratching the bedrock with embedded debris).
Erosional Landforms
| Landform | Description |
|---|---|
| Cirque (corrie/cwm) | An armchair-shaped hollow on a mountainside, formed at the head of a glacier by freeze-thaw weathering and plucking. When filled with water after the glacier retreats, it becomes a tarn (cirque lake). |
| Arete | A narrow, knife-edge ridge formed between two adjacent cirques eroding back-to-back. |
| Horn (pyramidal peak) | A sharp, pointed peak formed when three or more cirques erode backward toward the same summit. Example: Matterhorn (Switzerland). |
| U-shaped valley (glacial trough) | A wide, flat-floored valley with steep sides, carved by a valley glacier deepening and widening an existing V-shaped valley. |
| Hanging valley | A tributary valley left "hanging" above the main glacial trough because the tributary glacier was smaller and could not erode as deeply. Waterfalls often cascade from hanging valleys. |
| Fjord | A deeply eroded U-shaped valley that has been flooded by the sea after the glacier retreated. Found in Norway, New Zealand, Chile. |
| Roche moutonnee | An asymmetrical rock mound — smooth and gentle on the upstream side (abrasion) and steep and jagged on the downstream side (plucking). |
| Glacial striations | Parallel scratches on bedrock, caused by rock fragments embedded in the base of a moving glacier. |
Depositional Landforms
| Landform | Description |
|---|---|
| Moraine | Accumulation of debris (till) deposited by a glacier. Types: lateral (along valley sides), medial (where two glaciers merge), terminal/end (at the snout), ground (spread over the valley floor). |
| Drumlin | An elongated, oval-shaped mound of glacial till, streamlined in the direction of ice movement. Steep end (stoss) faces upstream; gentle slope (lee) faces downstream. Often found in swarms ("basket of eggs" topography). |
| Esker | A long, narrow, winding ridge of sand and gravel deposited by meltwater streams flowing within or beneath a glacier. |
| Kame | An irregular mound of sand and gravel deposited at the margin of a glacier by meltwater. |
| Outwash plain (sandur) | A flat plain of stratified sand and gravel deposited by meltwater streams beyond the terminal moraine. |
| Erratic | A boulder transported far from its source by a glacier and deposited in an area of different rock type. |
| Kettle lake | A depression formed when a block of ice embedded in glacial deposits melts, leaving a hole that fills with water. |
Aeolian Landforms (Wind)
Wind is an effective agent of erosion, transportation, and deposition in arid and semi-arid regions where vegetation is sparse and loose sand is abundant.
Erosional Landforms
| Landform | Description |
|---|---|
| Mushroom rock (pedestal rock) | A rock pillar with a wider top and narrower base, formed because sand-laden wind erodes more effectively near the ground (within 1-2 metres). |
| Yardang | An elongated ridge carved by wind abrasion, aligned parallel to the prevailing wind direction. Made of softer rock; harder layers form ridges. |
| Ventifact | A rock sculpted and faceted by windblown sand, with flat, polished surfaces. |
| Deflation hollow (blowout) | A depression created when wind removes loose sand and fine material from the surface. |
| Inselberg | An isolated steep-sided residual hill rising abruptly from a flat desert plain. Ayers Rock (Uluru) in Australia is an example. |
| Desert pavement (reg/hamada) | A surface layer of closely packed pebbles and stones left behind after wind removes finer material. |
| Zeugen | Tabular blocks of rock with a resistant cap of harder rock protecting softer rock underneath; wind erodes the softer layers, creating furrows. |
Depositional Landforms — Sand Dunes
| Dune Type | Shape | Wind Condition |
|---|---|---|
| Barchan | Crescent-shaped; horns point downwind | Moderate wind; limited sand supply |
| Transverse dune | Long ridges perpendicular to the wind | Abundant sand; consistent wind direction |
| Seif (longitudinal) dune | Long, narrow ridges parallel to the wind direction | Strong, consistent winds |
| Star dune | Multi-armed star shape; arms radiating from a central peak | Variable wind directions |
| Parabolic dune | U-shaped; horns point upwind (opposite of barchan) | Partially vegetated surfaces; coastal areas |
Loess
Loess is a deposit of fine-grained, wind-blown silt. Unlike sand, loess is transported over long distances by wind and deposited far from deserts. The loess plateau of China (deposited from the Gobi Desert) is the most extensive example, covering over 6,00,000 sq km with deposits up to 335 metres thick.
Marine (Coastal) Landforms
Waves, tides, and currents are the primary agents shaping coastal landforms.
Erosional Landforms
| Landform | Description |
|---|---|
| Sea cliff | A steep rock face formed by wave erosion undercutting the base of a coastline. |
| Wave-cut platform (shore platform) | A gently sloping rocky surface at the base of a retreating cliff, exposed at low tide. |
| Sea cave | A hollow carved into a cliff by wave action exploiting a zone of weakness (fault or joint). |
| Sea arch | Formed when two caves on opposite sides of a headland erode through to meet. |
| Sea stack | A pillar of rock left standing after the roof of a sea arch collapses. Example: Old Man of Hoy, Scotland. |
| Sea stump | A stack further eroded and reduced to a low remnant. |
| Geo (inlet) | A narrow, deep inlet formed when waves erode along a fault or joint. |
Depositional Landforms
| Landform | Description |
|---|---|
| Beach | An accumulation of sand, shingle, or pebbles deposited by waves along the shore. |
| Spit | A narrow ridge of sand or shingle extending from the mainland into the sea, formed by longshore drift. Example: Spurn Point, UK. |
| Tombolo | A sand bar connecting an island to the mainland. |
| Bar | A ridge of sand or shingle across a bay or river mouth, formed by deposition. |
| Lagoon | A shallow body of water separated from the sea by a bar or spit. Example: Chilika Lake (Odisha), Vembanad Lake (Kerala). |
| Barrier island | A long, narrow island of sand parallel to the coastline, separated from the mainland by a lagoon. |
Karst Topography
Karst topography develops in regions underlain by soluble rocks — primarily limestone, but also dolomite, gypsum, and rock salt — where chemical weathering (carbonation and solution) dominates.
Erosional Features
| Feature | Description |
|---|---|
| Sinkholes (dolines) | Circular depressions formed by solution weathering or collapse of underground cavities. |
| Swallow hole (ponor) | A point where a surface stream disappears underground through a sinkhole. |
| Uvala | A larger depression formed by the merging of several sinkholes. |
| Polje | A large, flat-floored enclosed depression in karst terrain, often several kilometres across. |
| Karren (lapiez) | Grooves, channels, and furrows dissolved into exposed limestone surfaces. |
| Disappearing stream | A river that flows into a swallow hole and continues underground. |
Depositional Features (Inside Caves)
| Feature | Description |
|---|---|
| Stalactite | A tapering column hanging from the roof of a cave, formed by dripping water depositing calcium carbonate. |
| Stalagmite | A tapering column rising from the floor of a cave, formed by water dripping from above. |
| Pillar (column) | Formed when a stalactite and a stalagmite meet and fuse. |
| Dripstone | A general term for all cave deposits formed by dripping water. |
Major Karst Regions
- Karst region — Dinaric Alps (Slovenia/Croatia) — the type locality from which the term "karst" derives
- Guilin karst — Southern China — tower karst with dramatic pillars
- Mammoth Cave — Kentucky, USA — world's longest cave system (over 680 km mapped)
- India — Meghalaya (Mawsmai, Krem Liat Prah — India's longest cave at ~34.8 km); Madhya Pradesh (Pachmarhi); Chhattisgarh (Kutumsar Cave)
Theories of Landform Development
Davis's Cycle of Erosion (Geographical Cycle)
William Morris Davis (1850-1934), an American geographer, proposed the Geographical Cycle (or Normal Cycle of Erosion) between 1884 and 1934. He postulated that landforms evolve through a sequence analogous to the life stages of a living organism — youth, maturity, and old age.
Davis's three controlling factors: Structure (rock type and geological arrangement), Process (erosion agents), and Stage (time elapsed since uplift).
| Stage | River | Valley | Landscape |
|---|---|---|---|
| Youth | Steep gradient; fast flow; vigorous vertical erosion (downcutting) | Deep, narrow, V-shaped valleys; waterfalls and rapids | High relief; flat interfluves; streams are few and far between |
| Maturity | Graded profile developing; lateral erosion begins | Wider valleys; floodplains form; meanders appear | Maximum relief (difference between ridge tops and valley floors); well-integrated drainage network |
| Old Age | Very low gradient; slow flow; deposition dominates | Broad, flat valleys; extensive floodplains; oxbow lakes | Low, rolling landscape called a peneplain (almost-plain); residual hills called monadnocks rise above the general level |
Rejuvenation: If the land is uplifted again during or after the old stage, the cycle restarts — rivers gain renewed energy and begin downcutting again, producing features like incised meanders, raised beaches, and river terraces.
Criticism of Davis:
- Assumes a single rapid uplift followed by a long period of stability — geologically unrealistic
- Treats landform evolution as time-dependent rather than process-dependent
- Ignores the role of climate, assuming only a "normal" (temperate, humid) cycle
- Too descriptive and qualitative; lacks mathematical rigour
Penck's Morphological Analysis
Walther Penck (1888-1923), a German geomorphologist, rejected Davis's time-dependent sequential model and instead proposed a process-based approach called morphological analysis. He argued that landform characteristics at any point reflect the ratio between the rate of uplift (endogenetic forces) and the rate of erosion (exogenetic forces).
| Phase | German Term | Rate of Uplift vs. Erosion | Slope Form | Landscape |
|---|---|---|---|---|
| Waxing development | Aufsteigende Entwicklung | Uplift exceeds erosion (accelerating uplift) | Convex slopes | Relief increases; steep V-shaped valleys |
| Uniform development | Gleichformige Entwicklung | Uplift equals erosion | Straight (rectilinear) slopes | Relief is maintained; equilibrium between tectonic and erosive forces |
| Waning development | Absteigende Entwicklung | Erosion exceeds uplift (decelerating uplift) | Concave slopes | Relief decreases; valleys widen; landscape flattens to an endrumpf (Penck's equivalent of peneplain) |
Key differences from Davis:
- Penck rejects the idea of a single uplift; uplift is continuous and variable in rate
- Slope form (convex, straight, concave) indicates the tectonic condition of the region
- Focus is on the relationship between tectonic forces and erosion, not on time or stage
- Penck's model is more dynamic and process-oriented
Criticism of Penck:
- Difficult to apply in practice — determining the exact ratio of uplift to erosion is complex
- His work was published posthumously and edited by his father (Albrecht Penck), leading to some ambiguity
- Underestimates the role of climate and rock type
Exam Strategy
For Prelims: Focus on identification of landforms from descriptions or diagrams. Common questions test the difference between cirque and canyon, stalactite and stalagmite, barchan and seif dune, spit and tombolo. The tables in this chapter are designed for quick revision.
For Mains GS-I: Questions on geomorphology are typically diagram-based or comparative. Examples: "Discuss the major erosional and depositional landforms associated with glacial activity" or "Compare and contrast the theories of Davis and Penck." Always supplement your answer with a labeled diagram.
Common Mains questions:
- Explain the rock cycle with the help of a neat diagram.
- Discuss the erosional and depositional landforms associated with wind action in desert regions.
- Compare the cycle of erosion models of Davis and Penck. Which model is more applicable to the Indian landscape?
- Describe the formation of karst topography and name major karst regions in India.
- How do marine processes create and modify coastal landforms? Illustrate with examples.
Last updated: 28 March 2026
