VOLCANOES: Volcano is an opening or vent through which molten lava, ash, gases, etc. comes out from the earth’s interior. Most of the volcanoes are concentrated at convergent and divergent plate boundaries but others, located in the interior of plates are associated with hot spots.
Types of Volcanic eruptions:
- Icelandic: it flows as a fissure eruption. The lava is basaltic and has less viscosity. It flows quietly and in large quantities forming plateaus. There is no violent activity or cone formation. ex. Columbia (USA), Deccan plateau (India), etc.
- Hawaiian: there can be fissure, crater or caldera eruptions. It forms small domes from which mobile lava and gases erupt. It produces fire fountains and only a minor amount of gases.
- Stambolian: they form stratocones, i.e. lava comes out and solidifies in a layered structure. They have rhythmic to continuous explosions resulting from spasmodic gas escape. Sometimes clots of lava are ejected producing bombs and scoria. It can have periodic more intense activity with the outpouring of lava.
- Vulcanian: they are also stratocone volcanoes. The associated lavas are more viscous. Sometimes the lava solidifies over the vent forming a crust resulting in gas pressure buildup leading to violent explosions. After a long quiet period eruption occurs ejecting bomb, pumice, and ash. Lava flows from the top of the flank after the main explosive eruption. Dark ash-laden clouds, convoluted, cauliflower-shaped, rises to moderate heights more or less vertical depositing tephra along the flanks of the volcano.
- Vesuvian: it throws extremely violent explosive gas-charged magma from stratocone vent. The eruption occurs after a long period of quiet or mild activity. Vent tends to be emptied to a considerable depth. The lava erupts in explosive spray and the gas cloud reaches a great height and deposits tephra.
- Pilian: it is a more violent form of visuvian eruption. The last major phase is the uprush of gas that carries clouds rapidly upward in vertical columns for miles. It is narrow at the base but expands outward at upper elevations. But the clouds are generally low in tephra.
- Pelean: it results from high viscosity lava and delayed explosiveness. The conduit of stratovolcano usually gets blocked by dome or plug, some gas escapes from lateral opening or by destruction or uplift of the plug.
- Katmaian: it is a variant of Pelean eruption characterized by massive outpourings of fluidized ash flows accompanied by widespread explosive tephra. Ignimbrites are common end products. Also hot springs and fumaroles are formed.
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 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.
These mountains are made of volcanoes (made of material ejected from fissures in the earth’s crust)
The material includes:
- Molten lava
- Volcanic bombs
- 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.
- Mt. Fuji (Japan)
- Mt. Merapi (Sumatra)
- Mt. Mayon (Philippines)
- Mt. Agung (Bali)
- Mt. Cotopaxi (Ecuador)
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.
- 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)
- 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.
- 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
- Antrim plateau of Northern Ireland
- The northwestern part of Deccan plateau
- Columbia – Snake plateau
- 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
- 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
TYPES OF PLAINS
A plain can be –
- Level or undulation
- Rises up to 100 feet above sea level
These are the best land in a country and intensively cultivated and populated.
Economic importance of a plain increases if a river also passes through it.
- Indo – Gangetic plains
- Mississippi plain
- Yangtze plain
Some most extensive temperate plains are grasslands like Russian steppes, North American Prairies and Argentina Pampas.
On the basis of their formation 3 types – Structural, depositional and erosional plains.
- Structurally depressed areas of the world
- Most extensive natural lowlands
- Because they are formed from the horizontally bedded rocks they are relatively undisturbed by the crustal movements of the earth.
- Example –
- Great plains of the Russian platform
- Great plains of USA
- Central lowlands of Australia
- The deposition name itself suggests that these plains are formed by the deposition of materials brought by various agents of transportation.
- Rise towards adjacent highlands
- Their fertility and economic development depend on types of sediments that are deposited by transportation.
- Active erosion(by the river) in the upper course results in the large quantities of alluvium brought down to the lower course and deposited to form extensive alluvial plains, flood plains, and deltaic plains.
- These are most productive in agriculture.
- Example – Mile delta of Egypt (Rice and cotton) & Ganges delta (Rice and Jute).
LANDFORMS ASSOCIATED WITH VULCANIC ACTIVITIES
Vulcanic activities 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 eruptions, 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: 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 – intrusion of molten magma vertically
- Denudation results – Upstanding walls or shallow trenches
- 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.
- 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
- A large igneous intrusion which is lenticular in shape with a depressed central region.
- Shape similarity – Saucer
- Example – Bushveld lopolith of Transvaal, South Africa
- 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
- A very large igneous intrusion extending to an unknown depth in the earth’s crust.
- Shape similarity – irregular shape
- 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
There are 3 types of volcanoes – Active, Dormant and Extinct.
- Active – frequent eruption or eruption within the recent time
- Dormant – can erupt in future
- Extinct – have all the features of the volcano but not erupted in historic times.
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.
- 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.
- 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)
- 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.
- 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
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
- 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.
- 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’.
- 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 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.
- 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.
- 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.
- Few volcanoes
- Many dormant or extinct
- Example – Madeira, Ascension, St. Helena, Cape Verda Island. and Canary Island
- Active – Iceland and Azores
- In alpine – folds – Vesuvius, Etna, Stromboli, and the Aegean Islands
- 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.
- 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
- Semeru – Indonesia
- Sangeang Api – Indonesia
- Krakatau – Indonesia
- Merapi – Indonesia
- Kerinci – Indonesia
- Karangetang – Indonesia
- Barren Island – Andaman and Nicobar, India
- Sinabung – Indonesia
GEYSERS AND HOT SPRINGS
- 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 –
- New Zealand – Rotorua district of North Island
- USA – Yellowstone Park (old faithful – world’s best-known geyser)
- 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