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Volcanoes UPSC and APSC

  1. A volcano is a geological feature characterized by a fissure in the Earth's crust, serving as an outlet for the expulsion of various substances such as gases, molten rock elements (commonly known as lava), ash, and steam during the process of an eruption.

  2. Vents or apertures of this nature are found in regions of the Earth's crust characterized by comparatively weaker rock strata.

  3. Volcanic activity serves as an illustrative instance of an endogenic process.

  4. The formation of land shapes is contingent upon the level of explosiveness exhibited by a volcano.

  5. In cases when the volcano lacks explosiveness, a plateau may be generated, but an explosive volcano is more likely to result in the formation of a mountain.

Volcanoes UPSC and APSC
Volcanoes UPSC and APSC

The Distinction between Magma and Lava

Difference Magma and Lava
Difference Magma and Lava

  • The term "magma" is employed to refer to the molten rocks and associated substances observed within the Earth's interior.

  • The asthenosphere, which is a less rigid region inside the mantle, typically serves as the primary reservoir for magma generation.

  • Once magma reaches the Earth's surface through a volcanic vent, it is referred to as lava.

  • Hence, lava can be understood as the molten rock that emerges onto the Earth's surface, originating from the subsurface magma.

  • Volcanism refers to the geological phenomenon in which materials in solid, liquid, and gaseous states are discharged from the Earth's interior and ascend to the Earth's surface.

Types of Volcanoes

Types of Volcanoes
Types of Volcanoes

Shield Volcanoes

  • Methods for identification: The incline of the terrain is quite gentle, yet its expanse is considerable. They possess significant vertical as well as horizontal dimensions.

  • These volcanoes hold the distinction of being the largest in the world due to their extensive lava flows that extend across considerable distances. The Hawaiian volcanoes are widely recognized as prominent exemplars.

  • Shield volcanoes are characterized by gentle slopes and are primarily composed of solidified lava.

  • The aerial perspective of a shield volcano exhibits a resemblance to the shape of a warrior's shield, hence justifying its nomenclature.

  • The composition of these volcanoes primarily consists of basalt, a kind of lava characterized by its low viscosity, resulting in a very fluid eruption. Due to this rationale, the inclination of these volcanoes is not pronounced.

  • In general, these substances possess a minimal level of explosiveness. However, in the event that water infiltrates the vent, there is a potential for them to become explosive.

  • The forthcoming lava exhibits a fountain-like motion, expelling the cone-shaped material from the apex of the vent, subsequently evolving into a cinder cone.

Cinder Cone Volcanoes:

  • Cinders are a type of extrusive igneous rocks. A contemporary designation for cinder is Scoria.

  • Minor volcanic eruptions.

  • The composition of these volcanoes primarily comprises loose, granular cinders with a minimal presence of lava.

  • These geological formations exhibit pronounced vertical slopes and typically feature a small central cavity.

Composite Volcanoes:

  • The morphology of these structures is conical, characterized by relatively steep sides and occasional presence of tiny craters at their summits.

  • These types of volcanoes are referred to as "strato-" or composite volcanoes by volcanologists due to their composition, which includes alternating layers of solid lava flows and cinders or volcanic ash, resembling sand or gravel.

  • These entities are distinguished by the occurrence of eruptions involving lavas that are cooler and possess higher viscosity compared to basaltic lavas.

  • Frequently, these volcanoes give rise to eruptions characterized by explosive activity.

  • In addition to the emission of lava, substantial volumes of pyroclastic materials and ash are deposited onto the Earth's surface.

  • The aforementioned substance tends to aggregate in close proximity to the apertures of the vent, resulting in the development of stratified strata. Consequently, this phenomenon imparts a composite volcano-like appearance to the mountain.


  • These volcanoes are considered to be the most highly explosive among the several types seen on Earth.

  • Typically, volcanic eruptions exhibit such high levels of explosiveness that they result in a collapse of the volcanic structure, rather than facilitating the formation of towering edifices. The geological formations characterized by collapsed depressions are commonly referred to as calderas.

  • The presence of high levels of explosiveness suggests that the magma chamber associated with the phenomenon is of considerable size and located in close proximity.

  • A caldera can be distinguished from a crater based on its characteristics. Specifically, a caldera is a substantial depression resulting from the collapse of the Earth's surface following a significant volcanic eruption. In contrast, a crater is a smaller and more steep-sided volcanic depression that is formed by the excavation of material due to an eruptive plume.

Flood Basalt Provinces

  • These volcanoes exhibit the characteristic of emitting very fluid lava that has the ability to travel over considerable distances.

  • The Deccan Traps in India, which currently encompass a significant portion of the Maharashtra plateau, constitute a quite extensive flood basalt province.

Mid-Ocean Ridge Volcanoes

  • The presence of these volcanoes is observed in oceanic regions.

  • A comprehensive network of mid-ocean ridges, spanning over 70,000 kilometers, traverses throughout all the ocean basins.

  • The ridge's center region is characterized by a high frequency of volcanic eruptions.

Volcanic Landforms:

Volcanic Landforms:
Volcanic Landforms:

  1. The molten lava that is discharged during volcanic eruptions undergoes a process of cooling and solidification, ultimately transforming into igneous rocks.

  2. The process of cooling can occur either upon contact with the surface or internally within the object.

  3. Igneous rocks are categorized based on the specific region where the cooling of lava occurs.

  4. Volcanic igneous rocks, also known as extrusive igneous rocks, are a type of rock that forms from the solidification of magma on or near the Earth's surface.

Plutonic Igneous rocks (Intrusive igneous rocks):

  • The process of cooling occurs within the Earth's crust rather than on its surface. Examples of igneous rocks include granite, gabbro, and diorite. In accordance with their physical characteristics, intrusive igneous rocks can be categorized into many categories.

  1. Batholiths are voluminous masses of magmatic material that undergo cooling at significant depths, resulting in the formation of expansive domes. The aforementioned entities can be classified as granitic formations. Occasionally, they manifest on the terrestrial landscape as a result of denudation mechanisms that eliminate the superimposed substances.

  2. Laccoliths are substantial, dome-shaped intrusive formations characterized by a flat base and a conduit resembling a pipe that extends from beneath. The subterranean formation has a resemblance to a composite volcano structure. The geographical region known as the Karnataka Plateau is the subject of discussion.

  3. Lapoliths exhibit a saucer-shaped morphology, characterized by a concave curvature oriented towards the celestial sphere.

  4. Phacoliths are geological formations characterized by their undulating structure and distinct channel connecting them to a subsurface source.

  5. Sheets and sills refer to the almost horizontal bodies of intrusive igneous rocks. Thin layers are commonly referred to as sheets, whereas broad horizontal accumulations are known as sills.

  6. Dykes are geological formations that arise when molten lava emerges through fractures and fissures, afterwards solidifying in a nearly vertical orientation, resulting in the creation of wall-like structures. The Deccan Traps located in the Maharashtra region.

The spatial arrangement of volcanoes across the Earth's surface.

Most of the volcanoes in the world are found in three well defined belts:

  1. The Circum-Pacific Belt (The Pacific Ring of Fire).

  2. The Mid-World Mountain Belt.

  3. The African Rift Valley Belt.

Volcanic Activity - Key Observations:

  1. Volcanoes exhibit a strong association with areas characterized by pronounced folding and faulting.

  2. These organisms are found in proximity to coastal mountain ranges, as well as on islands and inside the mid-ocean regions.

  3. The interior regions of the continent typically exhibit a lack of their presence.

  4. The majority of active volcanoes are concentrated in the Pacific region, earning it the designation of the Pacific Ring of Fire.

Volcanic hazards

A volcanic hazard encompasses several volcanic processes that have the potential to jeopardize human lives, livelihoods, and infrastructure by posing a significant risk of harm. The vicinity of the volcano is susceptible to several dangers, including but not limited to lava flows, pyroclastic flows, lahars, jökulhlaups, and landslides or debris avalanches. Volcanic activity gives rise to several hazards that have the potential to impact regions located at considerable distances from the volcano. These hazards include the deposition of tephra or ash particles, the emission of gases, and the occurrence of tsunamis. The dangers associated with volcanic activity have the capacity to affect regions located several hundred or even thousands of kilometers away from the volcano. These hazards possess the ability to cause substantial consequences in terms of both public health and economic well-being (BGS, 2012).

Despite the inherent dangers associated with volcanoes, there exist numerous justifications for human habitation in close proximity to these geological formations. There exist potential emotional, sociological, and economic advantages. Understanding volcanic dangers is an essential measure for individuals residing in close proximity to volcanoes, as it enables them to effectively mitigate potential risks.

Tephra and ash falls

The nomenclature of volcanic materials is commonly based on the size of clasts, encompassing a wide spectrum ranging from meters to microns in dimensions. The term 'tephra' is commonly employed as a comprehensive designation for all fragments that are ejected during volcanic eruptions, irrespective of their size. Conversely, the term 'ash' specifically refers to particles that are smaller than 2 mm in diameter.

Tephra and ash falls UPSC
Tephra and ash falls UPSC

During the occurrence of a volcanic eruption, the majority of tephra particles are expected to descend and settle in the vicinity of the volcanic edifice. The presence of this phenomenon can impose a burden on the structural integrity of buildings' rooftops and hinder the visibility of road markings, so impeding the ease of driving. The deposition of tephra particles onto foliage has the potential to cause the entombment of plants or the removal of limbs from trees, so exerting a substantial influence on agricultural activities.

The particulate composition of volcanic ash allows for its efficient dispersion by wind currents, enabling it to travel significant distances ranging from hundreds to thousands of kilometers distant from the originating volcano. Additionally, it has the potential to be elevated to significant altitudes, occasionally even penetrating the stratospheric region. Volcanic ash comprises diminutive, jagged, angular shards of glass and other geological materials, and its abrasive properties render it capable of inflicting harm upon aircraft.


Active volcanoes have the capacity to release a range of gases before to, during, or following an eruption, which can pose local health risks and also possess the potential to impact the global climate. There exist five primary gases that present a potential hazard to human health:

The substances of interest in this discussion are carbon dioxide, hydrogen chloride, hydrogen fluoride, hydrogen sulphide, and sulphur dioxide.

Individuals may potentially encounter detrimental volcanic gases by inhalation or direct exposure to the skin and ocular surfaces. The health consequences span from moderate to severe, occasionally resulting in fatal outcomes. Following exposure, individuals may experience symptoms such as respiratory distress and pruritus.

Gas Volcanoes UPSC
Gas Volcanoes UPSC

The potential dangers posed by volcanic gases are heightened due to their invisible nature and ability to accumulate in low-lying areas surrounding an active volcano, owing to their higher density compared to the surrounding air. Elevated levels of volcanic gas can pose a potential health risk within aircraft cabins. Sulfur gases undergo a conversion process into sulfate aerosols, predominantly composed of sulfuric acid. In the event that these particles ascend to the stratosphere, they have the potential to persist for extended periods, hence inducing transient alterations in climate conditions.

Lava flows and lava domes

Lava flows refer to the expulsion of molten rock, known as magma, onto the outside surface of a volcanic structure. often, the occurrence of fatalities resulting directly from lava is infrequent due to its often sluggish flow, affording ample opportunity for timely evacuation of individuals. However, it is capable of causing destruction to any objects in its trajectory through a combination of burying, compression, and thermal effects. These volcanic eruptions are also linked to the release of volcanic gases and aerosols.

Lava Flows UPSC
Lava Flows UPSC

The viscosity of lava flows often exhibits a positive correlation with silica content, while displaying a negative correlation with temperature and water content. Basalts with low viscosity and high iron/magnesium content are considered to be the most fluid of the commonly observed lava varieties. These basalts are normally discharged at temperatures ranging from 1100 to 1200 degrees Celsius. They have the ability to traverse considerable distances. Andesites with high viscosity and silicon content exhibit much lower fluidity compared to basalt and are often erupted at temperatures ranging from 700 to 900°C. Short, thick flows or steep-sided lava domes are generated, exhibiting limited displacement from their respective volcanic sources. The velocity of lava flow varies depending on the composition of the lava, with high-silica, andesitic lavas often exhibiting rates of a few meters per hour, whereas fluid basalts can reach speeds of several kilometers per hour.

Lava domes are generated through the gradual extrusion of high-viscosity lava from a volcanic vent. Due to the elevated viscosity shown by the lava, its mobility is significantly limited, resulting in a restricted displacement from the volcanic vent. Consequently, a conical formation of molten rock, commonly referred to as a lava dome, accumulates in the vicinity. Lava domes provide a significant risk due to their inherent instability, which can lead to their collapse and subsequent generation of pyroclastic density currents.

Flood basalts

Flood basalts are a distinctive type of lava flow with unique characteristics. The occurrence of these volcanic eruptions is infrequent, and our comprehension of these phenomena is derived from the examination of previous eruptions observed in locations such as the Deccan Traps in India or the Siberian Traps. Volcanic eruptions of this magnitude have significant effects on extensive regions, spanning continental scales, with areas exceeding one million square kilometers. These eruptions can generate deposits with thicknesses reaching up to one kilometer and emit substantial quantities of gases. Consequently, they contribute to air pollution and can potentially influence the Earth's climate on a global scale.

There is a wealth of knowledge to be gained by studying flood basalts occurring in Iceland. The Holuhraun fissure eruption in 2014 attained dimensions comparable to those of flood basalt events. The current flood basalt in Iceland has surpassed the magnitude of the Laki eruption that occurred between 1783 and 1784. This historical event resulted in significant loss of life, with around 20% of the Icelandic population perishing due to the adverse effects of environmental degradation and starvation. It is quite probable that the aforementioned phenomenon also resulted in elevated mortality rates in other regions of Europe, mostly due to the dissemination of sulphur-containing gas and aerosols, which contribute to air pollution. Fortunately, occurrences of flood basalt eruptions are exceedingly few.

Pyroclastic flows

Pyroclastic flows are dynamic phenomena characterized by the rapid movement of high-temperature combinations of rock fragments and gases, known as "density currents," which traverse the Earth's surface with considerable velocity. When subjected to the force of gravity, the movement of pyroclastic flows typically follows downhill slopes, valleys, and lower elevations. However, it is worth noting that in certain instances, very forceful or energetic pyroclastic flows have been observed to exhibit anomalous behavior by defying the gravitational force and moving uphill. The temperature range of pyroclastic flows is from 100°C to 600°C. The usual velocity at which they traverse the slopes of the volcano is 110 kilometers per hour or greater.

Landslides and debris avalanches

Debris avalanches and landslides are often seen phenomena, however their occurrence does not necessarily stem from an active volcanic eruption or volcanic activity. Pyroclastic flows can be initiated due to a volcanic eruption or the collapse of a volcanic dome, especially in regions characterized by frequent heavy precipitation. Debris avalanches have a tendency to remain confined within valleys, allowing them to traverse considerable lengths that extend far beyond their initial origins. Mitigating the impact of debris avalanches is a formidable challenge due to their unpredictable occurrence, which can even manifest on inactive volcanic structures, resulting in extensive devastation across expansive regions. Once the process is set in motion, the evacuation of regions situated in the trajectory of debris avalanches becomes exceedingly challenging due to the remarkable velocity at which they propagate.


The term "lahar" originates from the Javanese language and refers to a specific form of mudflow resulting from the combination of volcanic materials and water, which can be either hot or cold. Lahars exhibit a wide range of velocities, spanning from velocities below 10 kilometers per hour to velocities in the order of tens of kilometers per hour. Glacial outburst floods can manifest as a consequence of volcanic eruptions involving ice or snow, leading to the generation of substantial quantities of meltwater. Alternatively, these floods can be initiated or set in motion by intense precipitation events. As these sediment-laden flows progress downstream, they have the potential to accumulate an increasing amount of unconsolidated material.

Viscous mudflows can consist of sediment comprising over 60% of their composition, with the remaining 40% being water, resulting in a viscosity akin to that of wet concrete. Mudflows that exhibit reduced viscosity and increased water content bear resemblance to intense torrential floods.


The term "Jökulhlaup" originates from the Icelandic language and is employed to denote a glacial outburst flood, which refers to the abrupt discharge of water from a lake situated beneath or in proximity to a glacier. One potential cause of a jökulhlaup event is the occurrence of a volcanic eruption beneath a glacier, which leads to the melting of the ice above or the destabilization of a dam composed of sediments from glacial moraine. The abrupt dismantling of the lake dam results in the discharge of a substantial quantity of water, leading to the occurrence of a 'megaflood' capable of causing the erosion and destruction of transportation infrastructure such as roads and bridges.


The term "tsunami" in the Japanese language is derived from the combination of the words "tsu" and "nami," which respectively translate to "harbor" and "wave." Tsunamis can arise as a consequence of several geological phenomena, encompassing seismic events such as earthquakes, as well as occurrences like landslides. While tsunamis are more infrequent, it is worth noting that volcanoes can also be a source of their occurrence. Indeed, historical records indicate that tsunamis have been responsible for the highest number of fatalities in relation to volcanic eruptions.

Tsunamis are generated through the displacement of water, whether it occurs in a lake or in the ocean. Volcanic phenomena can manifest through several methods, exemplified by the following instances:

A submarine eruption refers to the occurrence of volcanic activity beneath the surface of the ocean. It involves the release of magma, gases, and other volcanic materials into the water column. The collapse of part of a volcanic edifice refers to the failure or collapse of a section of a volcano's structure. This can occur due to various factors such as the weakening of the volcanic materials, gravitational forces, or the release of pressure from magma movement. The entrance of lahars or pyroclastic density currents into surrounding water refers to the flow of volcanic debris, such as mudflows (lahars) or hot ash and gas mixtures (pyroclastic density currents), into nearby bodies of water. This can happen when volcanic materials are mobilized by gravity or by the force of an eruption and subsequently enter waterways or the ocean.

Submarine eruptions have the potential to generate localized tsunamis, whereas extensive, explosive, pyroclastic density-forming eruptions can give rise to substantial tsunamis that impact entire continents, causing widespread devastation.

One instance that exemplifies such an occurrence is the eruption of Krakatau in 1883, which took place in Indonesia. Although there remains ongoing debate on the precise origin of the tsunamis, it is evident that the volcanic eruption generated substantial pyroclastic flows and resulted in the subsequent collapse of the volcano. A considerable number of tsunamis were generated, and among them, the most catastrophic event led to a loss of life exceeding 36,000 individuals. In a more recent occurrence, specifically in 2018, a further tsunami materialized as a consequence of volcanic activity inside the same complex. Anak Krakatau, sometimes referred to as the offspring of Krakatau, is a volcanic formation that has gradually developed over the course of the last century along the periphery of the Krakatau caldera, which was formed in 1883. In December 2018, an event occurred where roughly 50% of the volcano underwent a collapse, leading to the emergence of a tsunami that impacted a significant portion of the coastal areas around the Sunda Straits. Tragically, this event resulted in the loss of over 400 lives.


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