Maarg Manthan · Topic 3.15

Effects of Weathering: Exfoliation Domes and Tors

Geography › Geomorphic Processes and Landform Evolution · Topic 3.15

Weathering leaves its mark on the land in many forms. The best known are exfoliation domes, rounded hills of massive rock such as granite that peel off in curved sheets like the layers of an onion, and tors, free-standing piles of rounded boulders on a hill top, left when the weathered rock around them is stripped away. Other effects are regolith and soil, spheroidal boulders, honeycomb weathering, talus, laterite and bauxite crusts, and karst. The rock below is attacked first along joints.

5 min read · UPSC Prelims · Geography · Geomorphic Processes and Landform Evolution

At a Glance

Exfoliation dome Rounded rock hill that peels in sheets
Tor Stack of boulders on a hill
Cause Weathering along joints, then stripping
Rock Mostly massive granite
Indian examples Hampi, Ramanagara, Savandurga
Exam link UPSC Prelims, Geography: Geomorphic Processes and Landform Evolution

Where Does It Fit?

This topic follows the one on the processes of weathering and shows what they leave behind. It is the first of the landform topics in the macro, and it pairs with the next topic on mass movements, which move the weathered debris downhill. Previous topic: Weathering: Chemical, Physical/Mechanical and Biological Processes. Next topic: Mass Movements: Heave, Flow, Slide; Slow, Rapid and Landslide Categories.

What Is Exfoliation and How Do Exfoliation Domes Form?

In short: exfoliation is the peeling of curved sheets from the surface of a massive rock, and a dome is what is left.

Unloading: granite forms deep underground under great pressure. When erosion removes the cover, the pressure falls and the rock expands outward.
Sheeting: the rock cracks along joints parallel to the surface, in layers called sheets.
Peeling: heat, cold and water enter the cracks and the outer sheets flake and slide off.
Dome: the process rounds off the hill into a smooth dome with a few joints.

Examples of exfoliation domes include Stone Mountain in Georgia and Half Dome in Yosemite in the USA, and Sugarloaf Mountain in Rio de Janeiro, Brazil. In India, the granite domes of the Karnataka and Telangana plateau, and the hills around Bengaluru, show the same sheeting. Savandurga near Bengaluru is often cited as one of the largest monolithic hills in Asia. Exfoliation by frequent heating and cooling is also discussed under Weathering: Chemical, Physical/Mechanical and Biological Processes, though geologists now stress pressure release as the main cause.

What Are Tors and Inselbergs?

Landform	Description	How it forms	Examples
Tor	Piles or towers of rounded, jointed boulders on a hill or slope	Water attacks the rock along joints below the ground, rotting it into rounded cores in a stage called deep weathering. Then the loose material is stripped off and the cores are exposed	Dartmoor (England), Hampi (Karnataka), Matobo Hills (Zimbabwe), Joshua Tree (USA)
Inselberg or bornhardt	Isolated steep-sided rocky hill rising from a plain	A more resistant mass is left standing as the surrounding rock is worn down	Uluru (Australia), Sugarloaf (Brazil), granite hills of the Deccan
Spheroidal weathering	Rounded boulders or shells	Water attacks the corners and edges of jointed blocks, which are weathered faster than the faces	Boulders in granite and basalt
Honeycomb weathering (tafoni)	Small pits and hollows in rock faces	Salt crystals grow in pores and flake away the rock	Coasts and deserts

The boulder landscape at Hampi in Karnataka is a famed Indian example, where granite blocks balance on top of one another, a result of the two-stage process.

What Other Effects Does Weathering Have?

Regolith and soil: the cover of loose debris and soil on which plants grow, as in Black soil From basalt (Deccan Traps) Red soil From granite and gneiss…">Relationship Between Rocks and Soils.
Talus or scree: sloping piles of angular debris at the foot of cliffs, produced by frost wedging.
Caves and sinkholes: from solution of limestone.
Duricrusts: hard crusts of laterite, bauxite or calcrete, formed when weathering leaves iron, aluminium or lime near the surface.
Ore enrichment: deep weathering concentrates iron, manganese and aluminium ores, and is behind India’s bauxite and laterite deposits.
Damage to structures: acid rain and salt weathering damage buildings and monuments, such as the stonework of heritage sites.

As an analytical point, weathering is the first step in a chain that ends in new landforms and soils, and the form of a hill reveals the rock and climate that shaped it. The debris is moved by processes in Mass Movements: Heave, Flow, Slide; Slow, Rapid and Landslide Categories.

Climate decides which of these effects dominate. In hot deserts, rapid heating and cooling and salt growth give honeycomb pits, boulder fields and bare rock domes. In the humid tropics, deep chemical rotting gives thick regolith, rounded boulders and laterite crusts. In cold mountains, frost wedging produces sharp-edged blocks and long talus slopes. These regional contrasts are why the same granite looks different in the Thar, the Western Ghats and the high Himalaya.

Why Is This Topic Important?

Landforms Domes and tors are asked
India Peninsular granite landscape
Link Soils and ores

What Came Next?

The next topic describes mass movements: heave, flow and slide. Next topic: Mass Movements: Heave, Flow, Slide; Slow, Rapid and Landslide Categories.

Key People and Terms

Exfoliation Peeling of rock sheets
Tor Heap of boulders on a hill
Inselberg Isolated rocky hill
Sheeting Curved joints parallel to surface
Talus Debris slope below a cliff
Tafoni Honeycomb pits in rock

Exam Corner

Points to Remember

Exfoliation domes form mainly by pressure release.
Tors form in two stages: deep weathering, then stripping.
Hampi is a famous tor landscape.
Uluru is an inselberg.
Talus collects below cliffs.

Do Not Confuse With

Tor and inselberg Boulder pile on a hill versus a whole isolated hill
Exfoliation and unloading Result versus cause
Talus and scree Same debris slope; different names in use

Memory Hook

Onion peels on a dome; boulders balance, tor and Hampi are home.

Mains Angle

Questions ask for landforms made by weathering and Indian examples. These points add depth.

Process Unloading, sheeting, stripping
Forms Dome, tor, inselberg
India Peninsular granite

A Question You May Face

An original practice question, not a past paper question.

“Explain how exfoliation domes and tors are formed, with examples.”

How to Answer

Dome Unloading and sheeting.
Tor Two-stage process.
Examples World and India.
Other effects Soils and ores.

GS Relevance

Prelims: exfoliation domes, tors, inselbergs and Indian examples. GS Paper 1: landforms resulting from weathering.

Frequently Asked Questions

What is an exfoliation dome?

An exfoliation dome is a rounded, dome-shaped hill of massive rock, usually granite, from which curved sheets of rock peel off like the layers of an onion. It forms when erosion removes overlying rock, the pressure drops and the rock expands and cracks parallel to its surface.

What is a tor?

A tor is a free-standing pile or tower of rounded rock blocks on a hill top or slope. It forms in two stages: water first weathers jointed rock below the ground into rounded cores, and then the loose weathered material is stripped away, leaving the boulders exposed. Hampi in Karnataka is a well-known example.

What is an inselberg?

An inselberg, or bornhardt, is an isolated, steep-sided hill of resistant rock that rises abruptly from a plain. It is left behind as the surrounding rock is worn down by weathering and erosion. Uluru in Australia and some granite hills of the Deccan plateau are examples.

What is spheroidal weathering?

Spheroidal weathering is a process in which chemical weathering attacks the corners and edges of jointed blocks of rock more strongly than their faces, since they have more exposed surface. The blocks become rounded, producing boulders that may peel in concentric shells like an onion.

How does weathering help in forming mineral deposits?

Deep weathering in warm, humid climates leaches away silica and soluble minerals, leaving behind a concentrated residue. This process forms laterite and bauxite, the ore of aluminium, and enriches deposits of iron and manganese, so many ore bodies in India lie in weathered layers.

PYQ Practice — Statement Analysis

1 Exfoliation domes are mainly found in massive rocks such as granite.

True

They peel in sheets.

2 A tor is a deposit left by a glacier.

False

It is a weathering landform.

3 Hampi in Karnataka has a famous boulder landscape.