Maarg Manthan · Topic 2.6

Relationship Between Rocks and Landforms

Geography › Geology – Minerals and Rocks · Topic 2.6

The kind of rock beneath a surface decides much about its landforms. Hard, resistant rocks such as granite and quartzite stand out as hills and ridges, while soft rocks such as shale and clay are worn into valleys and lowlands, a process called differential erosion. Limestone dissolves to make karst, basalt makes plateaus, sandstone makes cliffs and mesas, and the structure of the rocks, such as dip, folds and joints, controls the shape of ridges, drainage and slopes.

5 min read · UPSC Prelims · Geography · Geology – Minerals and Rocks

At a Glance

Main idea Rock type and structure shape the landscape
Process Differential erosion
Hard rocks Granite, quartzite: hills and ridges
Soluble rocks Limestone: karst
Indian examples Aravalli ridges, Deccan Traps, Bhedaghat marble gorge
Exam link UPSC Prelims, Geography: Geology – Minerals and Rocks

Where Does It Fit?

This topic links rocks to the surface features studied in the macro on geomorphic processes. It shows that landforms depend on both the type of rock and the agents of change such as water, wind and ice. Previous topic: Rocks as Aggregates of Minerals; Petrology. Next topic: Black soil From basalt (Deccan Traps) Red soil From granite and gneiss…">Relationship Between Rocks and Soils.

How Does Rock Resistance Control Relief?

In short: weak rocks are lowered faster than strong ones, so the hard rocks are left standing high.

Rock	Behaviour	Typical landform	Example
Granite and gneiss	Hard but jointed; weathers into rounded forms	Domes, tors, boulder-strewn inselbergs	Hampi in Karnataka, the Chota Nagpur hills
Basalt	Hard but breaks along cooling joints	Flat-topped plateaus and steps; columnar joints	Deccan Traps, Giant’s Causeway
Quartzite	Very hard, resistant to weathering	Long, sharp ridges	Aravalli ridges, the Delhi Ridge
Sandstone	Porous, moderately hard	Cliffs, mesas, buttes, canyons	Vindhyan scarps, Monument Valley
Limestone	Dissolved by weak acids	Caves, sinkholes, karst plateaus	Chhattisgarh caves, Krem caves of Meghalaya
Marble	Soft but fine-grained	Narrow gorges	Bhedaghat on the Narmada
Shale and clay	Soft, easily eroded	Valleys and lowlands	Valleys between hard ridges

How Does Rock Structure Matter?

Horizontal layers: a resistant cap over soft layers gives flat-topped mesas and buttes with steep sides, as in the American Southwest.
Gently tilted layers: give a one-sided ridge called a cuesta, with a gentle dip slope and a steep scarp.
Steeply tilted layers: give sharp, nearly symmetrical ridges called hogbacks.
Folds: the folded mountains of the Himalaya and Alps have ridges and valleys that follow the folds.
Faults: produce straight scarps and rift valleys, as in Endogenic Processes: Diastrophism, Orogenic and Epeirogenic Processes.
Joints: cracks that let water in and shape drainage patterns, rock steps and gorges.

How Does the Climate Interact with the Rock?

The same rock gives different landforms in different climates. Limestone makes caves and sinkholes in humid regions, but stands as steep cliffs in deserts. Granite weathers into deep clay-rich soil in the humid tropics, but into bare domes and boulders in dry regions. Water, wind and ice work on the rocks in different ways, as seen in Exogenic Processes: Denudation, Weathering, Mass Movements, Erosion, Transportation, Deposition and Weathering: Chemical, Physical/Mechanical and Biological Processes. The permeability of the rock also matters: porous rocks like sandstone take in rainfall and have few streams, while impermeable rocks like clay give dense drainage.

Rock also affects human use of land. Hard rock gives good foundations and building stone, but is costly to excavate for roads and tunnels. Limestone regions have scarce surface water, because rain sinks underground, and sinkholes can damage buildings. Weak shales slide easily on slopes and are a common cause of landslides in the hills. Basalt plateaus weather to fertile black soil, which has supported cotton farming in the Deccan for centuries, and granite hills have long been quarried for stone.

What Are Some Indian Examples?

Peninsular shield: ancient granites and gneisses form the rolling plateau with inselbergs and domes.
Aravalli range: old folded quartzite and schist ridges, now worn low.
Deccan Traps: basalt lava layers give a stepped plateau, and weather into black cotton soil.
Marble Rocks at Bhedaghat: the Narmada cuts a narrow gorge through marble and dolomite near Jabalpur.
Karst: limestone caves of Meghalaya, Chhattisgarh and Andhra Pradesh, including the Borra Caves.
Himalaya: young folded sedimentary and metamorphic rocks, steep and prone to landslides.

The Himalaya, being young, steep and made of folded and fractured rock under heavy rain, shows how structure and climate together drive frequent landslides. As an analytical point, geologists read the rocks to explain the landscape, and planners use the same knowledge to site roads, dams and towns. The link of rocks with soil is in Relationship Between Rocks and Soils.

Why Is This Topic Important?

Concept Explains relief differences
Examples Indian landforms asked
Planning Siting dams and roads

What Came Next?

The next topic explains how rocks, in turn, give rise to the soils on which life depends. Next topic: Relationship Between Rocks and Soils.

Key People and Terms

Differential erosion Unequal wearing of rocks
Inselberg Isolated hill left by erosion
Mesa Flat-topped hill with steep sides
Cuesta One-sided ridge
Joint Crack in rock without movement
Karst Limestone landscape of caves and sinkholes

Exam Corner

Points to Remember

Hard rocks form ridges; soft rocks form valleys.
Limestone forms karst.
Deccan Traps are basalt plateaus.
Bhedaghat gorge is cut through marble.
Aravalli ridges are made of quartzite.

Do Not Confuse With

Mesa and butte Large flat-topped hill versus a smaller remnant
Cuesta and hogback Gentle tilt versus steep tilt
Joint and fault Crack without displacement versus crack with movement

Memory Hook

Hard stands, soft bends; lime dissolves, basalt steps.

Mains Angle

Questions ask for examples of structural and lithological control. These points add depth.

Lithology Rock resistance
Structure Dip, folds, joints
Climate Same rock, different forms

A Question You May Face

An original practice question, not a past paper question.

“Explain how the nature of rocks controls the development of landforms, with examples from India.”

How to Answer

Principle Differential erosion.
Rocks Granite, basalt, limestone.
Structure Dip, folds, joints.
Examples Aravalli, Deccan, Bhedaghat.

GS Relevance

Prelims: rocks and landforms, examples such as Deccan basalt, Aravalli quartzite and marble gorges. GS Paper 1: geomorphology.

Frequently Asked Questions

How do rocks influence landforms?

The resistance, solubility and structure of rocks determine how they respond to weathering and erosion. Hard rocks such as quartzite stand out as ridges, soft rocks like shale form valleys, limestone dissolves into karst features, and basalt forms plateaus, so the same agents produce different landforms on different rocks.

What is differential erosion?

Differential erosion is the unequal wearing away of rocks of different hardness by the same agents of erosion. Weak rocks are lowered faster, leaving more resistant rocks standing as hills, ridges, mesas and cliffs. It is the main reason why rock type controls the shape of the landscape.

Which rock forms the Deccan Plateau?

The northwestern part of the Deccan Plateau is made of basalt lava flows called the Deccan Traps, formed by fissure eruptions about 66 million years ago. The layered basalt gives a stepped, flat-topped landscape, and weathers into the black cotton soil, also known as regur.

Why does limestone form caves and sinkholes?

Limestone is made of calcite, which dissolves in rainwater containing carbon dioxide because the water forms weak carbonic acid. Over time, the water enlarges cracks into caves and sinkholes, giving the landscape called karst. Such features are common in humid regions with thick limestone.

What is a mesa?

A mesa is a flat-topped hill with steep sides, formed where a layer of resistant rock caps softer layers beneath it. As the softer rocks around are eroded, the cap rock remains as a table-like hill. A smaller remnant of a mesa is called a butte.

PYQ Practice — Statement Analysis

1 Limestone regions often develop karst landforms.

True

Limestone dissolves in weak acid.

2 Soft rocks usually form ridges while hard rocks form valleys.

False

Hard rocks form ridges.

3 The Aravalli ridges are composed largely of quartzite.