Maarg Manthan · Topic 4.8

Effects of Volcanoes

Geography › Mountains, Volcanoes, Earthquakes and Tsunami · Topic 4.8

Volcanoes affect the Earth in both harmful and beneficial ways. Eruptions cause deaths from pyroclastic flows, ash fall, lahars and gases, destroy property, disrupt air travel and can cool the global climate for a year or two. Over the long term they build islands and fertile soils, supply minerals, geothermal energy and building stone, and shaped the early atmosphere and oceans.

5 min read · UPSC Prelims · Geography · Mountains, Volcanoes, Earthquakes and Tsunami

At a Glance

Direct hazards Lava, pyroclastic flows, ash, gases, lahars
Indirect hazards Tsunamis, famine, flight disruption
Climate Sulphur aerosols cool the Earth
Benefits Fertile soil, minerals, geothermal energy, new land
Management Monitoring, hazard maps, evacuation
Exam link UPSC Prelims, Geography: Mountains, Volcanoes, Earthquakes and Tsunami

Where Does It Fit?

This is the eighth topic of the category on mountains, volcanoes, earthquakes and tsunami. The previous topic showed where volcanoes occur, and this one considers what they do to people and the planet. The next topic begins the study of earthquakes. Previous topic: Distribution of Volcanoes and Earthquakes – Ring of Fire. Next topic: Earthquakes – Causes, Focus and Richter Scale.

What Are the Hazards of Volcanoes?

In short: volcanoes kill mainly through fast-moving ash flows, gases and mudflows, not through slow lava.

Hazard	What happens	Example
Pyroclastic flows	Hot clouds of gas and ash, over 100 km an hour, that burn everything in their path	Mont Pelée 1902 destroyed St Pierre; Vesuvius 79 CE
Ash fall	Ash buries land, collapses roofs, damages crops and engines, harms health	Pinatubo 1991; Eyjafjallajokull 2010 grounded air traffic
Lahars	Mudflows of ash and water down river valleys	Nevado del Ruiz 1985 killed about 23,000 people in Armero
Lava flows	Slow flows that destroy property, seldom kill	Kilauea 2018; Mount Etna
Volcanic gases	Carbon dioxide, sulphur dioxide and hydrogen sulphide are toxic	Lake Nyos, Cameroon, 1986 carbon dioxide release
Tsunamis	From eruptions, collapse of a flank or caldera	Krakatoa 1883; Hunga Tonga 2022

Types of eruption that produce these hazards are in Types of Volcanic Eruptions.

How Do Volcanoes Affect Climate?

Among the effects of volcanoes, the one with the widest reach is global cooling. Big explosive eruptions inject sulphur dioxide into the stratosphere, where it becomes tiny droplets of sulphuric acid, aerosols, that reflect sunlight and cool the Earth’s surface. The cooling can last for one to three years. After the Tambora eruption in 1815, the summer of 1816 was so cold in Europe and North America that it was called the year without a summer, with crop failures. The Pinatubo eruption in 1991 cooled the global average temperature by about 0.5 degree Celsius over the next year or two. Aerosols also damage the ozone layer temporarily. Over geological time, huge eruptions, such as the Deccan Traps and the Siberian Traps, have been linked to climate change and mass extinctions, and the carbon dioxide emitted contributes to long-term greenhouse warming, though human emissions today are far greater than the annual volcanic output.

What Are the Benefits of Volcanoes?

Fertile soils: weathered volcanic ash and basalt give nutrient-rich soils; the black soil of the Deccan, derived from the Traps, is a famous example, and Java and Hawaii have rich farmland around volcanoes.
New land: volcanic islands such as Hawaii, Iceland and Surtsey have been built from the sea floor.
Minerals: magma carries metals such as copper, gold, silver and diamonds from kimberlite pipes; sulphur, pumice, perlite and building stone are also volcanic products.
Geothermal energy: hot rocks provide heat and power; Iceland meets much of its heating and a large share of its electricity from geothermal sources, as in Hotspots, Mantle Plumes, Geysers and Hot Springs.
Atmosphere and oceans: early volcanic outgassing is believed to have supplied water vapour and gases that formed the oceans and atmosphere.
Tourism and science: volcanic landscapes attract tourists and provide knowledge of the interior of the Earth.

How Are Volcanic Risks Managed?

Volcanic risk is managed by a combination of monitoring and planning. Monitoring uses seismometers, GPS, satellites and gas sensors to detect warning signs, while hazard maps show areas at risk from flows and lahars. Authorities set alert levels, create exclusion zones, carry out evacuation drills and plan for ash fall, including the closing of airspace using volcanic ash advisory centres. Communities need clear warning and local knowledge, since many eruptions have followed years of calm. India’s National Disaster Management Authority covers volcanic hazards in the Andaman and Nicobar Islands only in a limited way, since the country has only one active volcano. As an analytical point, the death toll from volcanoes has fallen in recent decades because of monitoring, but the number of people living near volcanoes has grown, so the exposed population is rising even as the risk to each person falls.

Why Is This Topic Important?

Dual nature Benefits and hazards both asked
Climate Link to aerosols and cooling
Disaster Management and preparedness

What Came Next?

The next topic describes the causes of earthquakes, focus and the Richter scale. Next topic: Earthquakes – Causes, Focus and Richter Scale.

Key People and Terms

Lahar Volcanic mudflow
Pyroclastic flow Fast hot cloud of ash
Aerosol Fine droplets in the air
Kimberlite Rock that carries diamonds
Outgassing Release of gases from the interior
Ashfall Deposition of volcanic ash

Exam Corner

Points to Remember

Pyroclastic flows are the deadliest hazard.
Lahars are volcanic mudflows.
Eruptions can cool the climate through aerosols.
Volcanic soils are fertile.
Iceland uses geothermal power widely.

Do Not Confuse With

Lava flow and pyroclastic flow Slow molten rock versus fast hot ash cloud
Lahar and tsunami Mudflow versus sea wave
Ash and aerosol Solid particles versus fine droplets

Memory Hook

Fire, ash and mud destroy; soil, land and heat restore.

Mains Angle

Questions ask for hazards and benefits. These points add depth.

Hazards Flows, ash, gases, mud
Climate Short-term cooling
Benefits Soil, minerals, energy

A Question You May Face

An original practice question, not a past paper question.

“Discuss the effects of volcanic eruptions on people, climate and the environment.”

How to Answer

Hazards Direct and indirect.
Climate Aerosols.
Benefits Soil and energy.
Management Monitoring.

GS Relevance

Prelims: volcanic hazards and benefits. GS Paper 1: effects of volcanoes; GS Paper 3: disaster management.

Frequently Asked Questions

What are the main hazards of volcanic eruptions?

The main hazards are pyroclastic flows, which are hot fast clouds of gas and ash, ash fall, lahars or volcanic mudflows, lava flows, toxic gases and tsunamis. Pyroclastic flows and lahars have caused the largest numbers of deaths in many eruptions.

How do volcanic eruptions affect climate?

Large explosive eruptions inject sulphur dioxide into the stratosphere, forming aerosols that reflect sunlight and cool the Earth for one to three years. Tambora in 1815 caused the year without a summer, and Pinatubo in 1991 cooled the planet by about 0.5 degree Celsius.

What is a lahar?

A lahar is a fast-moving mudflow of volcanic ash, rock fragments and water that rushes down river valleys on the slopes of a volcano. It can be triggered by rain or by the melting of snow and ice, and it killed about 23,000 people at Armero in 1985.

What are the benefits of volcanoes?

Volcanoes give fertile soils from weathered ash and basalt, build new islands and land, bring up minerals such as copper, gold and diamonds, and supply geothermal energy. They also helped to form the oceans and atmosphere through outgassing in the early history of the Earth.

How are volcanic hazards managed?

Volcanic hazards are managed by monitoring with seismometers, GPS, satellites and gas sensors, by preparing hazard maps and alert levels, creating exclusion zones and evacuating people in time, and by planning for ash fall, including warnings to aviation.

PYQ Practice — Statement Analysis

1 Volcanic eruptions can cause a temporary fall in global temperature.

True

Aerosols reflect sunlight.

2 A lahar is a flow of molten lava.

False

It is a volcanic mudflow.

3 The black soil of the Deccan is derived from volcanic basalt.