A volcano is nothing but a rupture on the planet which allows gases, lava, and volcanic ash to escape from the chamber of magma below the surface. The Earth is made up of 17 major and rigid tectonic plates that float over its mantle layer that is hotter and softer. This is the main reason why volcanoes occur on the surface of our planet. These are usually found at the points where the tectonic plates either diverge or converge. The volcanoes in the Mid-Atlantic Ridge are examples of volcanoes formed by divergent tectonic plates. The volcanoes in the Pacific Ring of Fire are caused by convergent tectonic plates that are coming together. It has also been found that volcanoes can be formed at places where the crust’s interior plates are stretching or thinning. Such volcanoes are found in the East African Rift, Wells Gray-Clearwater volcanic, field and Rio Grande Rift in North America. Such volcanism falls under the umbrella of “plate hypothesis” volcanism. There are also many volcanoes away from plate boundaries known as mantle plumes. These are the “hotspots” like Hawaii, which are caused due to the upwelling diapirs with magma coming from the core-mantle boundary. They arise from about 3,000 km deep below the earth. In areas where two tectonic plates slide past each other, the occurrence of volcanoes is not see usually. Know about Volcanoes for Kids from the report given below!
The origin of the word “Volcano” can be traced back to the name of Vulcano, which is a volcanic island in the Aeolian Islands in Italy. The name of the island is derived from Vulcan, who is the God of Fire as per Roman mythology. The study of volcanoes is a science in itself, known by the name Volcanology or Vulcanology.
A number of hazards can be posed by erupting volcanoes. This is seen not only in the immediate vicinity of the volcanoes. Volcanic ash is found to be a threat to aircrafts where the particles may get melted by the high temperature. These particles alter the shape of turbines by adhering to them. This disrupts its operation. Ash and droplets of sulphuric acid can obscure the sun and lower the temperature of the Earth’s atmosphere. This cools down the troposphere. Moreover, they also absorb the heat that is radiated up from the Earth and warm the upper atmosphere or the stratosphere. Such volcanic winters have caused catastrophic famines in the course of Earth’s history.
On hearing the name volcano, the first perception is of a conical mountain that spews lava and poisonous gases via a crater found on its summit. But, this is just one kind of volcano. There are many other types as well. Some volcanoes are found to have rugged peaks that are formed by lava domes instead of the usual summit crater. There are other types that have landscape features like plateaus. The vent for spewing lava, ash, and gases can be developed at any place on the landform. This could give rise to smaller cones. An example of this type is found in Hawaii. Then there are ice volcanoes called cryovolcanoes, which are found mainly on some moons of Jupiter, Saturn, and Neptune. Mud volcanoes are generally not associated with any known magmatic activity. The temperatures found on mud volcanoes are generally lower than that of the igneous volcanoes. An exception is on cases when the mud volcano is a vent of any igneous volcano. Other commonly found types are Shield volcanoes, Fissure vents, Lava domes, Volcanic cones or cinder cones, Cryptodomes, Stratovolcanoes or Composite volcanoes, Submarine volcanoes, Supervolcanoes, and Subglacial volcanoes.
Volcanoes are usually classified by their frequency of eruption in to Active, Dormant or Inactive, and Extinct. Active volcanoes are the ones that erupt regularly. But, there is no hard and fast rule to define a volcano as active as the lifespan of volcanoes can range from a few months to over a million years. A volcano is considered to be erupting or likely to erupt if the volcano is currently erupting or showing significant new gas emissions, unusual earthquakes or any other such signs of unrest. A volcano is considered active if it has erupted in the last 10,000 years. Most of the volcanoes in this category are found around the Pacific Ring of Fire. The most active volcanoes on Earth as per 2013 are Kilauea or the famous Hawaiian volcano which has been continuously erupting since 1983 to form the longest lava lake, Mount Etna and Stromboli in the Mediterranean region that have been in continuous eruption, and Mount Yasur in Vanuatu that that has been erupting continuously for over 800 years. There are several other active volcanoes also.
Volcanoes are classified as extinct if they are unlikely to erupt again due to no magma supply any more. A few examples of extinct volcanoes are a number of volcanoes in the Hawaiian-Emperor Seamount chain in the Pacific Ocean, Zuidwal, Hohentweil, and the Shiprock volcanoes in the Netherlands. The Edinburgh Castle in Scotland is located atop an extinct volcano.
The distinction between extinct and dormant volcanoes is quite difficult. A volcano is considered extinct if there are no written records of its activity. There are volcanoes that remain dormant for a very long time like the Yellowstone and Toba, which remained inactive for 700,000 years and 380,000 years respectively. Vesuvius was inactive till it erupted in AD 79 to destroy famous towns in Roman history. Pinatubo was inconspicuous till it erupted in 1991. Same was the case with the Soufriere Hills volcano on Montserrat Island and the Fourpeaked Mountain in Alaska.
There are over 1500 active volcanoes on the surface of the Earth. 80 or more volcanoes have been discovered under the oceans. The liquid rock inside a volcano is known as Magma. The magma that flows out of a volcano is termed as lava. As it flows out, fresh lava glows red hot to white hot. Lava is known to be a poor conductor of heat. As such, it cools slowly. Lava slows down as it flows and then thickens.
Volcanoes can also be classified according to the composition of the material erupted, or the lava. This affects the shape of the volcano. Felsic lavas contain over 63% of silica, and are highly viscous. Intermediate lavas contain 52 to 63% of silica. Such “andesitic” volcanoes are found above subduction zones, like the Mount Merapi in Indonesia. Mafic lava contains 45% to 52% of silica, and higher percentages of magnesium and iron or basaltic. They are less viscous and usually hotter. Ultramafic lava is the last classification with less than 45% silica. They are also called komatiites and are very rare. They are the hottest lavas and quite fluid in texture.
Interesting Facts about Volcanoes
The largest active volcano on Earth is the Mauna Loa in Hawaii. Here, coffee is grown in the volcanic soils. It is even taller that Mount Everest from its base below the sea level to the summit. Its height is 13,677 feet above the sea level.
Encircling the basin of the Pacific Ocean is the Pacific Ring of Fire. It is an area of frequent volcanic eruptions with 452 volcanoes. Over 50% of the active and dormant volcanoes in the world are situated here. About 81% of the world’s largest earthquakes and 90% of the world’s earthquakes happen here.
Some of the most famous volcanic eruptions of modern times are that of Mount Pinatubo in 1991, Novarupta in 1912, Mount St Helens in 1980, and Mount Krakatoa in 1883.
The biggest known volcano in the whole of the solar system is on Mars. It is the Olympus Mons that is 600 kilometres or 373 miles wide, and 21 kilometres or 13 miles high.
Lo, which is one of Jupiter’s moons, is the object with the most number of volcanic activities in the solar system. It is covered in volcanoes, and the surface is constantly changing due to this fact.
Volcanoes are also found on the ocean floor and also under icecaps, like the volcanoes seen in Iceland.
The most common volcanic gases are water vapour, sulphur dioxide, carbon dioxide, hydrogen fluoride, hydrogen chloride, and hydrogen sulphide.
The ash coming out of volcanic eruptions can be sent high in to the air to a height of over 30 kilometres or 17 miles above the Earth’s surface.
Large volcanic eruptions can drop the average temperatures on Earth by around half of a degree by reflecting the radiation from the sun. The last century has seen several examples of this process.
Pumice is a unique igneous rock that has the ability to float in water. It is a volcanic rock that can also be used as an abrasive. It finds use in salons for removing dry skin in pedicures. It is light in colour and contains lots of air bubbles due to the trapped gases among fragile volcanic glass and minerals. It is light and porous, and formed during highly explosive eruptions from all types of magma like andesite, dacite, basalt, and rhyolite.
Lahar is a type of mudflow or debris flow that contains rocky debris, pyroclastic material, and water. It flows down from the volcano and along a river valley usually. Its consistency and the cement like properties make it very dangerous. It is in liquid form as it moves, but once it stops it solidifies. It can cause large destruction.
A pyroclastic flow contains fluidized mixture of semi-solid fragments, and hot gases that are expanding. It flows along the sides of the volcano and is heavier than air. These emulsions move like a snow avalanche, but they are too hot, move at hurricane like speeds, and contain highly toxic gases. Pyroclastic flows are considered to be the most dangerous of all kinds of volcanic phenomena.
A mountain that spews hot lava out of it is known as a volcano. Pressure build up below the Earth’s crust causes the formation of these volcanoes and shoots hot matter out of it, which can be highly dangerous.