Volcanicity | Geography Optional for UPSC (Notes) PDF Download

A volcano is a vent or opening through which molten lava, ash, gases, and other materials from the Earth's interior are released. The majority of volcanoes are found at convergent and divergent plate boundaries, while some are located within plate interiors and connected to hot spots.

Types of Volcanic Eruptions

• Icelandic eruptions are characterized by fissures that allow basaltic lava to flow out in large quantities. This type of eruption is generally non-violent and results in the formation of plateaus. Examples include the Columbia River Basalt Group in the United States and the Deccan Plateau in India.
• Hawaiian eruptions can involve fissures, craters, or calderas, and typically produce small lava domes from which lava and gases are released. These eruptions are characterized by fire fountains and relatively low amounts of gas emissions.
• Strombolian eruptions create stratovolcanoes, where the lava flows out and solidifies in layers. These eruptions involve rhythmic to continuous explosions caused by the intermittent release of gas. Additionally, they can eject clots of lava, which result in the formation of bombs and scoria.
• Vulcanian eruptions also form stratovolcanoes, but their associated lava is more viscous. The eruptions can be more violent due to the formation of a solid crust over the vent, leading to a buildup of gas pressure. These eruptions typically involve the ejection of bombs, pumice, and ash, followed by lava flows from the top or flank of the volcano.
• Vesuvian eruptions are extremely violent and involve the explosive release of gas-charged magma from a stratovolcano vent. These eruptions usually occur after a period of relative calm and involve the ejection of lava in an explosive spray, accompanied by gas clouds that can reach great heights and deposit tephra.
• Plinian eruptions are a more intense form of Vesuvian eruptions, characterized by the rapid upward movement of gas clouds that can extend for several miles. These clouds are typically narrow at the base and expand outward at higher elevations, but they generally contain low amounts of tephra.
• Pelean eruptions result from high-viscosity lava and delayed explosiveness. The conduit of a stratovolcano can become blocked by a dome or plug, with gas escaping through lateral openings or by the destruction or uplift of the plug.
• Katmaian eruptions are a variant of Pelean eruptions, characterized by the massive release of fluidized ash flows and widespread explosive tephra. These eruptions commonly produce ignimbrites and can also lead to the formation of hot springs and fumaroles.

Classification of Volcanoes

On the basis of material erupted:

1. Basalt cone: basalt cones are very rare. They are low rather than high because of the fluidity of basaltic lava.
   • Ex- Rangitoto (New Zealand) and Skjaldbreit (Iceland) are the most suitable examples.
2. Basalt dome: basalt domes are flat domes formed by fluid basalt lava. They are less in height and broad.
   • Hawaiian volcanoes are the best example.
3. Ash and cinder cones: these are high volcanoes formed by high viscous lava. Ash and cinder cones are built where eruptions are the explosive type with predominance of pyroclastic material. The growth of an ash or cinder cone begins around a crater.
4. Composite or Strato cone: they are formed by alternate sheets of lava and pyroclastic material. It is formed by alternate periods of explosive and quiet eruptions. Most of the largest volcanoes of the world fall under this category.
   • Mt Fujiyama of Japan, Vesuvian of Italy, Cotapaxi, and Chimborazo of Equador are good examples.

On the basis of periodicity

1. Active volcanoes: volcanoes that constantly eject lava, gases, ash, cinder, etc. are known as active volcanoes. There are about 600 active volcanoes in the world, most of them being around the pacific “ring of fire”.
   • The Stromboli volcano erupts so much fire that it has been termed as the lighthouse of the Mediterranean.
2. Dormant volcano: A volcano that has not erupted for a long time but still has the probability of eruption is called a dormant volcano. Mt Kilimanjaro is one such volcano.
3. Extinct volcano: a volcano that functioned in a long geological past but is no longer active is called an extinct volcano. They are only the remnants of the volcanoes. In many of the cases crater, lakes are formed by filling of water into craters.
   • Aconcagua of Andes is a typical example of an extinct volcano.

Volcanic Mountains

These mountains are made of volcanoes (made of material ejected from fissures in the earth’s crust)

The material includes:

• Molten lava
• Volcanic bombs
• Cinders
• Ashes
• Dust and liquid mud

These materials fell around the vent in successive layers, building up a characteristic volcanic cone.
These mountains are often called as mountains of accumulation.

Example:

• Mt. Fuji (Japan)
• Mt. Merapi (Sumatra)
• Mt. Mayon (Philippines)
• Mt. Agung (Bali)
• Mt. Cotopaxi (Ecuador)

Plateaux

Elevated upland with extensive leveled surfaces and usually descend steeply to the surrounding lowland.

• Also known as Tablelands
• Most highlands are subject to the erosional process and so, plateaux are no exception.
• According to the mode of formation and physical appearance, the plateau is of 3 types – Tectonic, Volcanic, and Dissected.

Tectonic Plateaux

• As the name suggests they are formed because of Movements inside the earth which sometimes caused uplifting of leveled land.
• They have uniform altitude and considerable size.
• Example – Deccan plateau (India)
  • Meseta of central Iberia (tilted tectonic plateau)
  • Harz of Germany (faulted)

Intermontane Plateaux

• Plateaus enclosed by fold mountains (Intermontane means situated between mountains)
• Example – Tibet plateau between Himalayas and Kunlun
• The intermontane plateaus are some of the most extensive and highest plateaux in the world.

Volcanic Plateaux

• Similar to the volcanic mountains, the volcanic plateau formed from the solidification successive layers deposited by basaltic lava which comes from inside the earth.
• Also known as lava plateau
• Example-
  • Antrim plateau of Northern Ireland
  • The northwestern part of Deccan plateau
  • Columbia – Snake plateau

Dissected Plateaux

• As the name dissected suggests, they are as a result of weathering and erosion by running water, ice and winds
• Weathering and erosion and gradually worn down and made surfaces irregular
• In Humid highland, stream and sometimes glaciation cut deep narrow valleys in the plateau which are dissected plateaux
• Example – Scottish Highlands
• In drier countries, vertical corrosion by rivers and abrasion by winds will dissect the plateau into steep-sided tabular masses termed mesas and buttes, intersected by deep canyons. This is a common feature of arid and semi-arid areas, e.g. in the south-western USA
• Mineral-rich – Mot plateau are mineral-rich
• Example-
  • African plateau – Gold, Diamond, copper, manganese, and chromium
  • Brazilian plateau – Iron and Manganese
  • Deccan plateau – Manganese, Coal, and Iron
  • Western Australia plateau – Gold and Iron

Landforms Associated with Vulcanic Activities

Volcanic activity affect Earth’s landforms. Solid, liquid or gaseous materials may find their way to the surface from some deep-seated reservoir beneath. For example – Geyser and springs, volcanic eruption, sometimes gas sources are found. Molten magma is a mobile rock. It mostly enters weak portions of the crust.

The resultant landforms depend on many factors like –

• Strength and fluidity of the magma
• Types of cracks, faults, and joints penetrated by magma
• The manner in which magma escapes to the surface.

Intrusive landforms – Magma while thrusting its way up to the surface may cool and solidify within the crust as plutonic rocks.

Extrusive landforms – Magmas that reach the surface and solidify, form extrusive landforms.

Rocks formed by either plutonic or volcanic activity are called igneous rocks.

Landforms of Igneous Intrusions

Sill-

• Sill: Intrusion of molten magma horizontally along the bedding planes of sedimentary rocks.
• Denudation of overlying sedimentary strata in sill exposes the intrusion which looks like bold escarpment (a steep slope or cliff, such as one which marks the edge of a range of hills)
• Example – Great whin sill of NE England

Dyke-

• Dyke – intrusion of molten magma vertically
• Denudation results – Upstanding walls or shallow trenches
• Example-
  • Cleveland Dyke of Yorkshire, England
  • Isles of Mall and Arran in Scotland
  • Quartzite dyke, North of Kuala Lumpur

Liths – igneous intrusions on a larger scale
Various types of liths – Laccolith, Lopolith, Phacolith, Batholith. All of them took place differently in the Earth’s crust and solidified within the upper layers of the crust.

Laccolith

• Large blister or igneous mound with a dome-shaped upper surface and a level base fed by a pipe-like conduit from below.
• Shape similarity – Dome
• Example – Henry mountains, Utah, USA

Lopolith

• A large igneous intrusion which is lenticular in shape with a depressed central region.
• Shape similarity – Saucer
• Example – Bushveld lopolith of Transvaal, South Africa

Phacolith

• Igneous rocks occupying the crest of an anticline or the bottom of a syncline and fed by a conduit which is below it.
• Shape similarity – Lens
• Example – Corndon hill in Shropshire, England

Batholith

• A very large igneous intrusion extending to an unknown depth in the earth’s crust.
• Shape similarity – irregular shape
• Example-
  • Wicklow Mountains of Ireland
  • Uplands of Britanny, France
  • Main Range of West Malaysia
• The orientation of Batholith –
  • It is believed that large masses of magma that were going up came into contact with country rock and metamorphosed them.
  • These metamorphosed rocks with solidified magma gave rise to extensive Batholiths.

Origin of Volcanoes

• We have read those volcanic activities are associated with crustal disturbances and mostly takes place where the crust has a weak portion because of faulting or folding.
• As we go deep inside crust temperature increases (1°F increase with 65 feet) and so we can expect the interior of the earth in the semi-molten state which could consist of solid, liquid, and gaseous material, collectively called as magma.
• Gases like – carbon dioxide, sulphurated hydrogen, and small proportions of Nitrogen chlorine, and other volatile substances charged magma heavily.
• Gases and vapor increase the mobility and explosiveness of Lava.

Types of lava

• Basaltic lava
• Acidic lava

All volcanoes pass through Active, Dormant, and Extinct stages but we are not sure about when they will be extinct. Example – Mt. Vesuvius and Mt. Krakatau. Both known as extinct but erupted violently.

Extrusive Landforms

• Nature and composition of Lava and ejected materials which reach the surface of the earth.
• As we have already read that basic lava is very fluid and it flows for long distances resulting in extensive lava plains.
• Example – our Deccan plateau has formed in a similar way & Snake basin, USA.
• Basalt plateau example – NW Deccan and also found in Iceland.

Volcanic Cones

• Highly fluid lava (i.e. Basic lava) forms lava domes or Shield volcanoes (with gently rising slopes and Broad, flattened tops)
• Example – Hawain volcano (best-developed lava domes)
• Mauna Loa
• Kilauea (steep-walled caldera with lava pit of Halemaumau)

Cinder Cone

• Less fluid lavas (i.e. acid lava) forms – Ash and cinder cones (with large central craters and steep slopes)
• They are small volcanoes (not greater than 1000 feet height)
• Example – Mt. Nuovo (near Naples) & Mt. Paricutin (Mexico)
• They form – Lava tongue, lava dammed lakes, lava bridges, lava tunnels

What comes out from the vent of the Volcano and what they do?

• Fine particles (Volcanic dust) are shot high in the sky. They can travel worldwide before coming to earth.
• They came down in the form of “Black Snow” and can bury houses or people.
• Pyroclasts – coarser fragmental rocks which include lapilli (rock fragments ejected from a volcano), scoria (basaltic lava ejected as fragments from a volcano, typically with a frothy texture), pumice and volcanic bombs.

Composite Cones

• Most volcanoes have this kind of cone.
• Built by – Several eruptions of lava, ashes and other volcanic materials (come out through conduit from the main conduit from magma chamber/reservoir) which forms a lot of layers and increases the height.
• From the main conduit subsidiary pipes or dykes reach the surface as a feeder to parasitic cones (like water pipelines in our house from a main big pipeline). From these subsidiary pipes, lava comes out to the sides of the cone.
• Example –
  • Mt. Etna (Sicily)
  • Mt. Stromboli (Lighthouse of Mediterranean)
  • Mt. Vesuvius
  • Mt. Fuji
  • Mt. Popocatepetl
  • Mt. Chimborazo

Caldera Cone

Crater formation – during an eruption the material from the top of the cone is blown off or collapses into vent widening the orifice into a large crater.

• Greatly enlarged depressions are called Calderas
• These are the result of violent eruptions accompanied by the subsidence of much of the volcano into the magma beneath.
• Water may collect in the crater or the caldera-forming crater or Caldera lakes e.g. Lake Toba in Sumatra.

Some Volcanic Eruptions

Mt. Vesuvius

• A somma-stratovolcano located on the Gulf of Naples in Campania, Italy
• Vesuvius has erupted many times since and is the only volcano on the European mainland to have erupted within the last hundred years.
• Today, it is regarded as one of the most dangerous volcanoes in the world because of the population of 3,000,000 people living nearby.
• Vesuvius was formed as a result of the collision of two tectonic plates, the African and the Eurasian. The former was subducted beneath the latter, deeper into the earth.

Mt. Krakatau

• A volcanic island situated in the Sunda Strait between the islands of Java and Sumatra in the Indonesian province of Lampung.
• The most notable eruptions of Krakatoa culminated in a series of massive explosions over August 26–27, 1883, which were among the most violent volcanic events in recorded history.
• The 1883 eruption ejected approximately 25 km3 (6 cubic miles) of rock (OMG)
• After remaining dormant for almost half a century, an eruption m 1927 pushed up a cinder cone from the submarine floor.
• This new volcanic island was named Anak Krakatau, meaning ‘the child of Mt. Krakatau’.

Mt. Pelee

• A semi-active volcano at the northern end of Martinique, an island in the Lesser Antilles island arc of the Caribbean.
• Its volcanic cone is composed of layers of volcanic ash and hardened lava.
• The volcano is currently in a dormant state.
• Erupted white-hot lava and super-heated steam.

Kilauea-Hawaii

• Kilauea is Hawaii’s most active volcano and parts of it have been continuously erupting since January 3, 1983. But the last major volcanic eruption at Kilauea was in 2014 and lasted for several months.

Mount Etna-Italy

• Europe’s biggest active volcano, Mount Etna-erupted recently.

The Distribution of Volcanoes in The World

• Volcanoes are mostly located in intensely folded or faulted regions
• Active volcanoes – 500
• Dormant and extinct volcanoes – 1000s
• Occurrence – Coastal mountain ranges, off-shore islands and in the midst of oceans, but there are few in the interiors of continents.

Pacific Region

• Greatest concentration – circum pacific region (Pacific ring of fire) – Includes 2/3rd world’s volcanoes.
• The western pacific – chain starts from the Aleutian Islands, Japan extending in the south up to the Philippines, Indonesia (Java and Sumatra particularly), pacific islands of Solomon, New Hebrides, Tease and North Island, New Zealand.
• Eastern pacific – Starting from Andes to Central America (particularly Guatemala, Costa Rica and Nicaragua), Mexico and right up to Alaska.

Atlantic

• Few volcanoes
• Many dormant or extinct
• Example – Madeira, Ascension, St. Helena, Cape Verda Island. and Canary Island
  • Active – Iceland and Azores

Mediterranean

• In alpine – folds – Vesuvius, Etna, Stromboli, and the Aegean Islands

Asia

• Mt. Ararat (recall with “are rat” or “Airavat” (Indra’s elephant name))
• Mt. Elbrus (elbows or eyebrows)
• It’s interesting and surprising that the Himalayas have no active volcanoes.

Africa

• Mt. Kilimanjaro and Mt. Kenya (east African rift valley – extinct)
• Mt. Cameroon – an only active volcano of west Africa.
• Madagascar – some volcano cones but not active volcanoes
• West Indian islands – Mt. Pelee and St. Vincent (violent explosion in recent times)
• Lesser Antilles – made of volcanic islands
• Interior volcanoes in continents – rare.

Most Recent Volcanic Eruptions

• Stromboli – Italy
• Dukono – Indonesia
• Ibu – Indonesia
• Sangeang Api – Indonesia
• Krakatau – Indonesia
• Merapi – Indonesia
• Kerinci – Indonesia
• Karangetang – Indonesia
• Barren Island – Andaman and Nicobar, India
• Sinabung – Indonesia
• Semeru volcano – Indonesia’s East Java province

Geysers and Hot Springs

Geysers

• Fountains of hot water and superheated steam.
• It can sprout up to the height of 150 feet from under the earth.

How do geysers work?

• Water near the volcanic or thermal region is heated beyond the boiling point.
• The jet of water emitted with the explosion and it is triggered or cause any gases which seep out from heated rocks

Where they are found?

• Mostly in 3 areas –
  • Iceland
  • New Zealand – Rotorua district of North Island
  • USA – Yellowstone Park (old faithful – world’s best-known geyser)

Hot Spring

• It can be found anywhere on the Earth where water is sinked deep enough beneath the surface to be heated by interior forces.
• Rises without any explosion (in geyser explosion is there)
• Contains – dissolved minerals
• Uses – dissolved minerals, heat house, swimming pools, and domestic purposes.
• Locations – Honduras, Canada, Chile, Hungary, Iceland, Israel, Japan, New Zealand, Fiji, and the United State

Semeru Volcano

• Semeru – also known as “The Great Mountain” – is the highest volcano in Java and one of the most active.
• It previously erupted in December 2019.
• Indonesia, with the maximum number of active volcanoes in the world, is prone to seismic upheaval due to its location on the Pacific’s Ring of Fire.
• Semeru volcano is also part of the Island arcs formed by the subduction of the Indo-Australian plate below Sunda Plate (part of Eurasian Plate). The trench formed here is called the Sunda trench whose major section is the Java Trench.

Mt Merapi

• Merapi (Mountain of Fire) is the most active of Indonesia’s 130 active volcanoes.
• It rises to 2,911 meters and has steep slopes with dense vegetation on its lower sides.
• It is located near the center of the island of Java and Indonesia’s cultural capital, Yogyakarta.
• Mt Merapi’s last significant eruption was in 2010. At that time, more than 300 people were killed and some 2,80,000 residents were forced to evacuate the surrounding areas.

Conclusion

Volcanic eruptions and their resulting landforms significantly impact the Earth's surface. Various types of eruptions, such as Icelandic, Hawaiian, Strombolian, Vulcanian, Vesuvian, Plinian, Pelean, and Katmaian, create diverse landforms like plateaus, volcanic mountains, and plains. The composition of lava and the manner in which it escapes the Earth's crust determines the formation of intrusive and extrusive landforms. Furthermore, volcanic activities are associated with crustal disturbances, which mostly take place in the weak portions of the crust due to faulting or folding. As such, understanding volcanic eruptions, their types, and the landforms they create is crucial for comprehending the Earth's geological processes and landscape evolution.

Frequently Asked Questions (FAQs) of Volcanicity

What are the different types of volcanic eruptions?

There are several types of volcanic eruptions, including Icelandic, Hawaiian, Strombolian, Vulcanian, Vesuvian, Plinian, Pelean, and Katmaian eruptions. These eruptions differ in the level of violence, the type of lava produced, and the resulting landforms created.

How are volcanoes classified based on the material erupted and periodicity?

Volcanoes are classified into basalt cones, basalt domes, ash and cinder cones, and composite or strato cones based on the material erupted. They can also be classified as active, dormant, or extinct based on their periodicity.

What are some examples of volcanic mountains and plateaux?

Examples of volcanic mountains include Mt. Fuji (Japan), Mt. Merapi (Sumatra), Mt. Mayon (Philippines), Mt. Agung (Bali), and Mt. Cotopaxi (Ecuador). Examples of volcanic plateaux include the Antrim plateau of Northern Ireland, the northwestern part of the Deccan plateau, and the Columbia-Snake plateau.

What are the different types of plains and their formation?

Plains can be classified into structural, depositional, and erosional plains based on their formation. Structural plains are formed due to the Earth's crustal movements, while depositional plains are created by the deposition of materials brought by various agents of transportation. Erosional plains are formed as a result of weathering and erosion by running water, ice, and winds.

What are the different types of landforms associated with volcanic activities?

Volcanic activities can result in both intrusive and extrusive landforms. Intrusive landforms include sills, dykes, and various types of liths (laccoliths, lopoliths, phacoliths, and batholiths). Extrusive landforms include volcanic cones, lava domes, ash and cinder cones, and composite cones.