Maarg Manthan · Topic 3.4

Volcanoes: Types (Shield, Composite, Caldera, Flood Basalt, Mid-Ocean Ridge)

Geography › Geomorphic Processes and Landform Evolution · Topic 3.4

A volcano is an opening in the Earth's crust through which magma, gases and ash escape to the surface. The main types are shield volcanoes, built of fluid basaltic lava with gentle slopes; composite (strato) volcanoes, steep cones of alternating lava and ash with explosive eruptions; calderas, large basins left after a volcano collapses; flood basalts, huge lava plateaus from fissure eruptions; and mid-ocean ridge volcanoes, where new oceanic crust is made along the sea floor.

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

At a Glance

Shield Broad, fluid basalt; Mauna Loa
Composite Steep, explosive; Mount Fuji
Caldera Collapse basin; Krakatoa, Toba
Flood basalt Fissure plateau; Deccan Traps
Mid-ocean ridge Sea-floor spreading; Iceland on the ridge
Exam link UPSC Prelims, Geography: Geomorphic Processes and Landform Evolution

Where Does It Fit?

This topic follows the study of earthquakes and begins the part of the macro on volcanoes. It names the main kinds of volcano, while lava, landforms, geysers and distribution are taken up in the topics that follow. Previous topic: Distribution of Earthquakes and Earthquake Observatories. Next topic: Types of Lava: Andesitic (Acidic) and Basaltic (Basic) Lava.

What Is Volcanism?

In short: volcanism is the movement of molten rock from inside the Earth to the surface, where it erupts.

A volcano is a vent or fissure in the crust through which hot material from the interior is thrown out. Material that is molten rock beneath the surface is magma, and once it reaches the surface it is called lava. Alongside lava come gases, mainly water vapour with carbon dioxide, sulphur dioxide and hydrogen sulphide, and solid fragments called pyroclastic material, which range from fine ash to large volcanic bombs. The opening through which these emerge is the vent, and the bowl-shaped depression at the top is the crater. A volcano is called an active volcano if it has erupted in recent times and may erupt again, dormant if they are quiet but may erupt, and extinct if they are not expected to erupt. About 50 to 70 volcanoes erupt each year, and roughly 1,300 are considered potentially active on land.

What Are Extrusive Volcanic Landforms?

In short: extrusive landforms are built on the surface by lava and ash.

Landform	Features	Examples
Shield volcano	Broad, gentle dome built by very fluid basaltic lava; the largest volcanoes	Mauna Loa and Mauna Kea in Hawaii, Kilauea
Composite (strato) volcano	Steep cone built of alternating layers of lava and ash; explosive eruptions; acidic or intermediate lava	Mount Fuji, Mount Mayon, Vesuvius, Mount St Helens
Cinder cone	Small, steep cone made of ash and cinders around a vent	Paricutin in Mexico
Caldera	Huge basin formed when a volcano collapses after emptying its magma chamber, or is blown apart	Krakatoa, Toba in Sumatra, Crater Lake in the USA
Lava plateau (flood basalt)	Vast sheets of basalt from fissure eruptions	Deccan Traps in India, Columbia Plateau in the USA
Lava dome	Mound of thick lava piled over the vent	Mount St Helens dome

A caldera that fills with water becomes a crater lake. The Deccan Traps cover about 500,000 sq km in Maharashtra, Gujarat, Madhya Pradesh and Karnataka, and are described in Plate Tectonics: Major and Minor Lithospheric Plates. Mauna Loa in Hawaii is the largest active volcano on Earth by volume, and Mauna Kea, measured from its base on the sea floor, is taller than Everest. Barren Island in the Andaman Sea is India’s only confirmed active volcano.

How Do the Shield and Composite Volcanoes Differ?

Feature	Shield	Composite
Lava	Basic, fluid	Intermediate or acidic, viscous
Shape	Broad with gentle slopes	Steep, conical
Eruption	Quiet, effusive	Explosive
Materials	Mostly lava	Lava layers with ash and cinders
Setting	Hotspots and ridges	Subduction zones

What Are Mid-Ocean Ridge Volcanoes?

The largest volcanic system on Earth lies mostly unseen beneath the oceans. Along the mid-ocean ridges, plates move apart and basaltic magma rises from the mantle to fill the gap, building new oceanic crust. The system runs for about 65,000 km. Eruptions here are quiet, produce pillow-shaped lava that cools quickly in sea water, and are fed by fissures, not by a single cone. Most of the lava of the Earth erupts on the ridges, but unseen. In a few places the ridge rises above sea level, as in Iceland, where the Mid-Atlantic Ridge crosses a hotspot. Hot water vents called black smokers, with unusual life forms, are found here, as is described in Minor Relief Features: Mid-Oceanic Ridges, Seamounts, Submarine Canyons, Guyots, Atolls.

Which Are the Main Types of Eruption?

Type	Named after	Character	Example
Hawaiian	Hawaii	Quiet outpouring of very fluid basalt; lava fountains and lava lakes; shield volcanoes	Kilauea, Mauna Loa
Strombolian	Stromboli, Italy	Regular, moderate bursts of glowing lava fragments; persistent	Stromboli
Vulcanian	Vulcano, Italy	Short, explosive blasts that break a plug of hard lava, with thick ash clouds	Sakurajima, Soufriere Hills
Vesuvian and Plinian	Vesuvius and Pliny the Younger	Extremely violent; a tall column of gas and ash rises into the stratosphere, then collapses into pyroclastic flows	Vesuvius 79 CE, Krakatoa 1883, Pinatubo 1991
Peléan	Mont Pelée, Martinique	Dome collapse that sends glowing avalanches (nuées ardentes) down the slope	Mont Pelée 1902
Surtseyan and Phreatomagmatic	Surtsey, Iceland	Magma meets water; steam-driven explosions of ash and steam	Surtsey 1963, Hunga Tonga 2022
Fissure (Icelandic)	Iceland	Lava erupts along a long crack and floods wide areas	Laki 1783, Reykjanes eruptions, Deccan Traps

How Do the Types Compare?

Type	Lava and magma	Shape	Eruption	Setting
Shield	Basaltic, fluid	Broad dome	Quiet	Hotspots, ridges
Composite	Andesitic or rhyolitic, viscous	Steep cone	Explosive	Subduction zones
Caldera	Often silica-rich	Large basin	Cataclysmic, then collapse	After large eruptions
Flood basalt	Basaltic	Plateau of stacked flows	Fissure eruptions over a long time	Hotspots, rifting
Mid-ocean ridge	Basaltic	Linear ridge	Quiet, underwater	Divergent boundaries

The types of lava are explained in Types of Lava: Andesitic (Acidic) and Basaltic (Basic) Lava, and the distribution of volcanoes in Distribution of Volcanoes: Pacific Ring of Fire, Mediterranean Volcanism.

Why Is This Topic Important?

Classification Types and examples are asked
Link Plate boundary settings
India Deccan Traps and Barren Island

What Came Next?

The next topic compares the two main types of lava, andesitic (acidic) and basaltic (basic). Next topic: Types of Lava: Andesitic (Acidic) and Basaltic (Basic) Lava.

Key People and Terms

Shield volcano Broad, gently sloping volcano
Composite volcano Steep cone of lava and ash
Caldera Collapse basin of a volcano
Flood basalt Huge sheets of fissure lava
Pillow lava Rounded lava formed underwater
Cinder cone Small cone of ash and cinders

Exam Corner

Points to Remember

Shield volcanoes have gentle slopes.
Composite volcanoes are explosive.
Krakatoa and Toba are calderas.
The Deccan Traps are a flood basalt province.
Mid-ocean ridges make the most lava on Earth.

Do Not Confuse With

Shield and composite volcanoes Broad and quiet versus steep and explosive
Crater and caldera Small vent bowl versus a large collapse basin
Lava plateau and shield volcano Fissure sheets versus a central dome

Memory Hook

Shield is broad and gentle, composite is steep and mental; caldera caves in, flood basalt spreads thin.

Mains Angle

Questions ask for the types, their causes and global examples. These points add depth.

Magma type Controls shape
Setting Plate boundaries and hotspots
Hazard Explosive versus effusive

A Question You May Face

An original practice question, not a past paper question.

“Describe the different types of volcanoes and explain how the nature of lava and tectonic setting decide their form.”

How to Answer

List Five main types.
Link Lava viscosity and shape.
Setting Plates and hotspots.
Examples World and India.

GS Relevance

Prelims: types of volcanoes with examples, differences between shield and composite volcanoes. GS Paper 1: volcanism and landforms.

Frequently Asked Questions

What are extrusive volcanic landforms?

Extrusive volcanic landforms are those built on the surface by lava and ash erupting from a vent or fissure. They include shield volcanoes, composite volcanoes, cinder cones, lava domes, calderas and lava plateaus such as the Deccan Traps.

What is a caldera?

A caldera is a very large basin-shaped depression formed when a volcano collapses after its magma chamber empties or is blown apart in a huge eruption. It may fill with water to form a crater lake, as at Crater Lake in the United States.

What are the main types of volcanic eruptions?

The main types are Hawaiian, a quiet flow of fluid basalt; Strombolian, regular moderate bursts; Vulcanian, short explosive blasts; Plinian, the most violent with tall ash columns; Peléan, with glowing avalanches from collapsing domes; and fissure eruptions along long cracks.

What is a fissure eruption?

A fissure eruption is one in which lava erupts along a long crack in the crust instead of from a single vent. It can spread vast sheets of basalt over wide areas, as in Iceland, and formed the huge lava plateaus such as the Deccan Traps.

What is a mid-ocean ridge volcano?

A mid-ocean ridge volcano is part of the long chain of submarine volcanoes where tectonic plates move apart and basaltic magma rises to build new oceanic crust. The eruptions are quiet and mostly unseen, but they produce more lava than all other volcanoes, and sometimes the ridge rises above the sea, as in Iceland.

PYQ Practice — Statement Analysis

1 Shield volcanoes are built by fluid basaltic lava.

True

They have gentle slopes.

2 The Deccan Traps are an example of a lava plateau.

True

They formed from fissure eruptions.

3 Hawaiian eruptions are the most violent type of eruption.

False

They are quiet and effusive.

4 A fissure eruption comes from a single central vent.