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Volcanoes do not always have the classic cone shape, like shield volcanoes or stratovolcanoes: sometimes they can also not have a volcanic edifice but rather one long fracture in the Earth’s crust from which lava flows. In this case we speak of linear volcanoes and can often be observed along the mid-ocean ridges.
Shield volcanoes and stratovolcanoes are also called central volcanoes, in the sense that they are fed by a tip duct which culminates in a central apparatusLinear volcanoes, on the other hand, are equipped with a series of ducts that run along large fractures, or rather from a system of fractureswhich affect the earth’s crust and which propagate to great depths. And it is from these fractures that the magma rises! This type of volcano is typical of mid-ocean ridgeswhere oceanic crust is continuously generated, but this phenomenon can also occur on land.
Linear volcanoes can emit enormous amounts of magma in a geologically short period of timewhich is usually not very viscous (therefore poor in silica and very fluid) so it will tend to flow sideways very easily. In continental environments, when we have this type of volcanic activity, the magma that comes out of these large fractures covers enormous areas, giving rise to enormous expanses of lava rock: the so-called basaltic plateaus. Almost always a plateau is composed of a series of lava flows, therefore an overlapping of multiple levels, also originating from numerous eruptions that have followed one another over time. So in other words a basaltic plateau is nothing other than the product of a series of eruptions of linear volcanoes.
It must be said that this type of volcanism was extremely frequent in all continents in past times: in India, South America, South Africa, Russia… in each of these cases there was a series of fracture systems from which an enormous quantity of magma flowed out, forming the basaltic plateaus that we can see today. Consider that one of the most famous plateaus, that of Deccanoccupies most of peninsular India. A similar situation exists in Parana Basin – between southern Brazil, Argentina and Paraguay – The Columbia Plateau in the USA and the Drakensberg in South Africa.
