Maarg Manthan · Topic 3.22

Karst Depositional Landforms: Stalactites, Stalagmites, Pillars

Geography › Geomorphic Processes and Landform Evolution · Topic 3.22

Karst depositional landforms are the mineral formations built inside limestone caves by dripping and flowing water. When water rich in dissolved calcium bicarbonate reaches the air of a cave, it loses carbon dioxide and leaves behind a thin film of calcite. Over thousands of years this builds stalactites, which hang from the roof, stalagmites, which rise from the floor, and pillars (columns), where the two meet. Together these cave deposits are called speleothems, and also include flowstone, curtains and helictites.

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

At a Glance

Stalactite Hangs from the cave roof
Stalagmite Rises from the cave floor
Pillar Joined stalactite and stalagmite
Mineral Calcite (calcium carbonate)
Indian caves Borra, Belum, Meghalaya
Exam link UPSC Prelims, Geography: Geomorphic Processes and Landform Evolution

Where Does It Fit?

This topic completes the study of groundwater landforms by describing what is built inside caves, after the previous topic described what is dissolved away. It ends the run of topics on soluble rocks before those on glaciers and coasts. Previous topic: gypsum Process Solution by carbonic acid Sinkhole Depression where rock dissolves or collapses Doline and uvala…">Karst (Groundwater) Topography: Sinkholes, Dolines, Uvalas. Next topic: Glacial Erosional Landforms: Cirques, Tarns, Horns, Arêtes, Glacial Troughs/Fiords.

What Are the Underground Features: Caves, Stalactites and Stalagmites?

Underground water dissolves the rock along joints and creates passages and chambers, which form caves. When water rich in dissolved calcium carbonate drips from the cave roof, part of the carbon dioxide escapes and calcite is deposited. Three kinds of cave deposits, called speleothems, result:

Stalactites: icicle-like formations hanging from the roof of the cave.
Stalagmites: columns growing upward from the floor, formed by drips from above.
Pillars or columns: a stalactite and stalagmite that meet and join.

The longest cave system in the world is the Mammoth Cave system in Kentucky, USA, which has over 650 km of surveyed passages. India’s well-known limestone caves include the Borra Caves in the Araku Valley of Andhra Pradesh, Belum Caves in Kurnool, one of the longest caves in the plains of peninsular India, Mawsmai and Krem Liat Prah in Meghalaya, Gupt Godavari in Chitrakoot, and the Sahastradhara and Robber’s Cave near Dehradun. The Meghalaya caves are among the longest in the subcontinent. Karst is also important for water: the aquifers of limestone are a major source of groundwater, though they are vulnerable to pollution, since water moves rapidly through channels without filtration.

How Do Cave Deposits Form?

Solution above: rainwater with carbon dioxide dissolves limestone as it moves down through cracks, forming calcium bicarbonate in solution.
Drip into a cave: a drop hangs from the roof of a cave, where the air has less carbon dioxide.
Precipitation: the drop loses carbon dioxide and some water evaporates, so calcite is left behind as a thin ring at the roof. The reaction is the reverse of the one that dissolved the rock.
Growth: successive drops add rings, forming a hollow tube and then a cone, the stalactite. The drop that falls to the floor deposits more calcite, which builds a stalagmite below it.
Joining: if they meet, they form a pillar or column.

Growth is very slow, usually fractions of a millimetre to a few millimetres a year, so large formations are thousands of years old.

What Are the Main Cave Deposits?

Formation	Description	Remark
Stalactite	Icicle-like cone hanging from the roof	Remember: ‘c’ for ceiling
Stalagmite	Mound or cone rising from the floor	Remember: ‘g’ for ground; usually thicker and blunter
Pillar (column)	Stalactite and stalagmite joined	Supports the roof
Flowstone	Sheet of calcite deposited by water flowing down walls or floors	Looks like a frozen waterfall
Curtain (drapery)	Thin, wavy sheet hanging from a sloping roof	Often translucent
Helictite	Twisted, branching formation that defies gravity	Made by capillary forces
Travertine and tufa	Calcite deposits at springs and in streams on the surface	Pamukkale terraces in Turkey, Mammoth Hot Springs in the USA

Where Are Famous Caves, and What Are Their Uses and Risks?

India: the Borra Caves in the Ananthagiri hills of the Araku Valley in Andhra Pradesh, among the largest in the country, with stalactites and stalagmites; the Belum Caves in Andhra Pradesh, among the longest in the plains of India; the Krem caves of Meghalaya; Kutumsar and Kailash caves in Chhattisgarh; and the Dehradun caves.
World: Carlsbad Caverns in New Mexico, USA; Postojna Cave in Slovenia; Mammoth Cave in Kentucky, USA; Son Doong in Vietnam, among the largest known cave passages.
Uses: tourism, scientific records, because speleothems preserve layers that reveal past climate and rainfall, and habitats for specialised cave animals such as bats and blind fish.
Risks: breaking of formations, light and crowds which promote algae growth, and pollution of drip water.

The solution features that make caves are in Karst (Groundwater) Topography: Sinkholes, Dolines, Uvalas, and the carbonation process behind them in Weathering: Chemical, Physical/Mechanical and Biological Processes. As an analytical point, cave deposits form a natural archive, and protecting them is therefore a matter of both heritage and science.

Why Is This Topic Important?

Terms Stalactite versus stalagmite is asked
Process Reverse of carbonation
Archive Palaeoclimate record

What Came Next?

The next topic describes the erosional landforms of glaciers. Next topic: Glacial Erosional Landforms: Cirques, Tarns, Horns, Arêtes, Glacial Troughs/Fiords.

Key People and Terms

Stalactite Cave deposit hanging from the roof
Stalagmite Cave deposit rising from the floor
Pillar Joined stalactite and stalagmite
Speleothem Any cave mineral deposit
Flowstone Calcite sheet on cave surfaces
Travertine Calcite deposit at springs

Exam Corner

Points to Remember

Stalactite = ceiling; stalagmite = ground.
They are made of calcite.
A pillar is formed when they meet.
Growth is millimetres a year or less.
Borra Caves lie in the Araku Valley.

Do Not Confuse With

Stalactite and stalagmite Hanging versus rising
Karst erosional and depositional forms Dissolving versus building
Travertine and flowstone Surface spring deposit versus cave sheet

Memory Hook

Ceiling drips a stalactite, ground builds stalagmite; meet in the middle, pillar’s right.

Mains Angle

Questions ask for the process and Indian examples. These points add depth.

Process Precipitation of calcite
Archive Climate records
Conservation Protecting caves

A Question You May Face

An original practice question, not a past paper question.

“Explain how stalactites, stalagmites and pillars are formed in limestone caves.”

How to Answer

Solution Water dissolves limestone.
Deposition Calcite drips out.
Forms Stalactite, stalagmite, pillar.
Importance Heritage and climate record.

GS Relevance

Prelims: stalactites, stalagmites and pillars, how they form, Indian caves. GS Paper 1: groundwater landforms.

Frequently Asked Questions

What is the difference between stalactites and stalagmites?

Stalactites are icicle-shaped deposits of calcite that hang from the roof of a cave, formed by dripping water. Stalagmites are columns that grow upward from the floor beneath the drips. When they meet, they form a pillar or column.

How is a stalactite formed?

A stalactite forms when water containing dissolved calcium bicarbonate seeps through the roof of a limestone cave. The drop loses carbon dioxide and some water, and leaves behind a small ring of calcite. Over thousands of years, repeated drops build an icicle-like cone that hangs from the roof.

What is a pillar in a cave?

A pillar, or column, is a cave formation created when a stalactite growing down from the roof and a stalagmite growing up from the floor meet and join. It forms a continuous column of calcite that seems to support the roof of the cave.

What is a speleothem?

A speleothem is any mineral formation built inside a cave by flowing or dripping water. The calcite forms include stalactites, stalagmites, pillars, flowstone, curtains and helictites. Speleothems preserve layers that scientists use to reconstruct past climate, rainfall and vegetation.

Where are the Borra Caves?

The Borra Caves are in the Ananthagiri hills of the Araku Valley in the Alluri Sitharama Raju district of Andhra Pradesh, near Visakhapatnam. They are among the largest caves in India, with stalactite and stalagmite formations in limestone, and are a major tourist attraction.

PYQ Practice — Statement Analysis

1 Stalactites grow upward from the floor of a cave.

False

Stalactites hang from the roof; stalagmites rise from the floor.

2 A stalagmite grows downward from the roof of a cave.

False

It grows upward from the floor.

3 Stalactites and stalagmites are made mainly of calcite.

True

They are precipitated from groundwater.

4 A pillar forms when a stalactite and stalagmite join.