The very word volcano comes from the Roman Vulcan , then called Vulcanus. He was actually a figure from Greek mythology that the Romans adopted. Lava was then associated with the molten iron that flew out of the works of Hephaestus, the Greek god of fire and metalworking. What the ancients could never understand was why volcanoes exist, where the lava comes from, and, perhaps most unsettlingly, that they don't only exist on our planet.
Why do volcanoes exist?
Different layers of planet Earth
Volcanoes (like earthquakes) are closely related to the internal structure of our planet . The Earth has a solid central core, measured by seismic data, with a radius of 1220 km. The outer layer of the core is semi-solid, extending to a radius of 3400 km. Beyond this lies the mantle, where lava is found. The mantle can be divided into two parts: the lower mantle, which extends from a depth of 700 km to 2885 km, and the upper mantle, which extends from 700 km to the crust, with an average thickness of 50 km.
Although it may not seem so at first glance, the Earth's crust is made up of large plates called tectonic or lithospheric plates. This means that the crust is not completely uniform. The plates float on the basaltic mantle , from which lava originates; this phenomenon is called continental drift.
The different plates that exist, as well as the direction of the pressure they receive (Source: Wikipedia)
This type of drift contains fissures , which are most noticeable at sea level. Enormous mountain ranges of volcanoes cross the ocean floors; these are the mid-ocean ridges. These enormous mountain ranges are, in turn, formed by enormous fissure volcanoes. Along these fissures, which are many thousands of kilometers long, material from the mantle is constantly being uplifted . This material slides in two longitudinal bands, continuously generating new crust. There are places where the boundaries between tectonic plates are on land, not in the oceans, and it is there that volcanoes originate. These are the narrowest areas of the Earth's crust , where tectonic plates meet.
How do volcanoes originate?
The Earth's crust is also regularly destroyed in areas called subduction zones . As we've mentioned, tectonic plates aren't literally "stuck together." This means there are areas where some plates sink beneath others and merge with the mantle. These plate boundaries experience immense pressure, resulting in significant seismic instability, which manifests as earthquakes and volcanic eruptions.
San Andreas Fault, California, United States
Mid-ocean ridges are the most unstable zones . Exceptionally, some of these violent volcanoes located on the ocean floor can erupt above sea level. They form islands of intense volcanic activity, such as Iceland. The most unstable zones are those where one tectonic plate overrides another, or even where they slide past each other laterally, such as the famous San Andreas Fault in the United States. This fault is easily recognizable due to the deep discontinuities in the ground. Because of the high seismic activity, scientists predict a major earthquake in this area, nicknamed the Big One.
Parts of a volcano
Differentiation of the parts of a volcano
- Magmatic chamber: It corresponds to the inner zone of the earth's crust, where the magma is found. This is where magma builds up under pressure before rising to the surface. It is usually between 1 and 10 kilometers deep.
- Chimney: The conduit through which the magma that rises in the eruptions, the lava, comes out. After the eruption, it is plugged with cold rocks, that is, with the solidification of the magma that has been there.
- Volcanic cone: It is the truncated cone formation that arises around the crater. It is formed by the accumulation of materials produced and emitted by the eruptions.
- Secondary volcanic cone: Formation of a small auxiliary chimney through which the magma comes out.
- Crater: It is the hole through which the magma comes out towards the earth's surface. Depending on the volcano, its dimensions and shapes will be very different. It can be shaped like an inverted funnel or cone, and measure from a few meters to kilometers.
- Domes: It is the accumulation of very viscous lava derived from magma that, when cooled over the eruptive mouth itself, can plug it.
- Geyser: They are like small volcanoes, but made of boiling water vapor. Very typical in areas like Iceland.
- Skunks: Cold fumaroles that give off carbon dioxide.
- Fumaroles: Emission of gases from lava in craters.
- Vent: It corresponds to the weak point of the earth's crust where the magma has been able to rise from the chamber to reach the surface.
- Solfataras: Emissions of water vapor together with hydrogen sulfide.
- Volcano Types
The temperature, the type of material, the viscosity and the elements dissolved in the magma all together create the type of eruption, the volcano. Together with the amount of volatile products that accompany it, we can differentiate the following types:
Strombolian Volcano
ParicutÃn volcano, Mexico
It originates from an alternation of erupting materials . These layers form a stratified cone of fluid lava and solid material. The lava is fluid, emitting abundant and violent gases, along with projections of bombs, lapilli, and scoria. Because the gases escape easily, it does not produce ash or pulverized material. When the lava overflows the crater rim, it flows down the slopes and ravines, without covering a large area , unlike in Hawaiian-type volcanoes.
Hawaiian Volcano
Kilauea, the most famous Hawaiian-type volcano
Like Strombolian lava, this type is quite fluid. It does not produce explosive gas emissions. In this case, when the lava overflows the crater rim, it flows easily down the volcano's slopes, covering large areas and traveling great distances . Volcanoes of this type have gentle slopes, and when some lava debris is carried by the wind, it forms crystalline threads.
Vulcanian volcano
Vulcanian volcano
Named after the volcano Vulcanus, this type of eruption, with its steep, inclined cones, is characterized by its intense gas emissions . The lava released is viscous and solidifies rapidly. These eruptions are very powerful and pulverize the lava. They produce a large amount of ash, which, when ejected into the air, is accompanied by other fragmented materials. The magma that reaches the surface, the lava, solidifies quickly, but the escaping gases break and crack its surface, making it very rough and irregular.
Peleano Volcano
Mont Pelée, Martinique island, France
In this type of volcano, the lava from its eruptions is especially viscous and solidifies rapidly . It can completely block the crater, forming a kind of dome or spire. This creates immense pressure as the gases are unable to escape, resulting in a massive explosion that either lifts the dome or destroys the upper part of the slope.
An example of a Pelean volcano is the colossal eruption of Mount Pelée on May 8, 1902. The extraordinary force of the accumulated gases, mixed with ash, shattered the volcano's walls as they succumbed to such immense pressure. The eruption affected the city of St. Pierre on the French island of Martinique, resulting in 29.933 deaths due to the resulting pyroclastic flow.
Phreatomagmatic Volcano
Surtsey Island, Iceland. Arising from a phreatic eruption. Photo by Erling Ólafsson
Phreatomagmatic volcanoes are found in shallow waters , referred to as shallow waters by the International Hydrographic Organization. They typically have a crater lake and sometimes form atolls, oceanic coral islands. The volcano's own energy is amplified by the expansion of rapidly heated water vapor, resulting in extraordinarily violent eruptions . They do not usually produce lava flows or rock extrusions.
Pliniano volcano
Teide, Canary Islands, Spain
In this type of volcano, which differs from a typical volcanic eruption, the gas pressure is very strong, producing violent eruptions. It also forms pyroclastic flows that, upon cooling, generate ashfall. These eruptions can even bury entire cities.
In addition, it is also characterized by the alternation of pyroclastic eruptions with eruptions of lava flows. This gives rise to an overlap in strata, which causes these volcanoes to have very large dimensions. A good example of this, we have it in Teide.
Now that we have seen what a volcano is, it should be noted that they do not only exist on our planet. This phenomenon is one of those that our planet Earth also has in common with other planets in the solar system and throughout the universe. For all that magma contained within that one day under pressure explodes out. Wherever we look, we can see similarities, with our planet, and even with ourselves. And it is that "we all have a volcano inside: we keep so many things that, one day, we take them all out at once", Benjamin Griss.
Do you know which volcanoes are active?
