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Volcano activity and types of eruptions

Volcano can be classified between those that are active and those that are off according to a time-dated eruption. Volcanic activity in a region can last for entire geological periods and periods of inactivity can be very long.

When the pressures that occur inside the earth’s crust are very large and there is a considerable increase in temperature, a magma originates, a viscous fluid hundreds of degrees. The composition of that magma abounds with water vapor and other gases.

If this molten mass remains a long time in the interior of the Earth it leads to cooling and forms plutonic rocks. But if it ascends and can locate a weak point of the crust, a crack, it can reach the surface and originate a volcano, which will form volcanic rocks.

Composition of the Earth

Magma is an extremely hot liquid and semi-liquid rock located beneath the Earth’s surface. The Earth has a layered structure consisting of the inner core,the  outer core,the  mantle,  and the  crust. Much of the planet’s mantle is made up of magma that moves in the form of currents.

This magma can pass through holes or cracks in the crust, causing a volcanic eruption. When magma flows or erupts on the Earth’s surface, it is called lava. Therefore, in the eruption gases escape into the atmosphere and a liquid fraction called lava remains.

Eruption phases of volcanoes

Although there are several types of volcanic eruptions, we can say that the eruption of a volcano such as Cumbre Vieja on the Island of La Palma is carried out in three phases:

  1. Initial phase.  It begins with the emission of gases through the crater and can be accompanied by Earth tremors. In La Palma there was a swarm of small earthquakes a few days before and during this initial phase.
  2. Proximal phase. We can say that on September 22, 2021 we have reached this phase in the Cumbre Vieja volcano. It is a phase in which there is an outflow of increasingly abundant and violent gases. The explosions expel volcanic ash and slag, which accumulate around the crater, forming the volcanic cone. The ground cracks and lava arise, which, like a river, slips down the slope of the cone, forming a river of fire that follows the slope of the place.
  3. Terminal phase. Explosions and emissions are spaced out and decreased until the volcanoes go to rest and shut down. It is a phase in which gases such as fumaroles, geysers, etc. are mainly emitted.

Now, we can say that we are in phase two and there is no scheduled date for the Cumbre Vieja volcano to begin to extinguish. Everything will depend on the measurements made by geologists at the site to be able to understand how long this eruption will last.

Types of volcanic eruptions

The modality of volcanic eruptions depends on the content and pressure of the gases. In turn, they depend on the viscosity and solidification rate of the lava. In general, the high viscosity and gas content increases the explosiveness of an eruption and its violence, and therefore the amount of pyroclastic material (from the Greek Greek πῦρ pyr ‘fire‘ and κλαστός klastós ‘broken‘).

Throughout history the same volcano can suffer different types of volcanic eruptions, although the normal sequence is always the outflow of gases, followed by pyroclastic materials and finally, lava, having sporadic explosions that keep the crater open.

Classification of volcanoes

The most classic classification of volcanoes is due to the French A. Lacroix of the early twentieth century. It must be said that today it is no longer used as a reference. Lacroix recognized four main types and named them Hawaiian, Strombolian (from Sicily), Vulcanian (from Sicily) and Pelean (from Martinique).

  1. Hawaiian. The lava is fluid, forming extensive castings from which gases are slowly released, giving rise to very gentle slope cones. In the crater a lava lake is formed, from which occasional explosion jets emerge, although they spew little ash. This fluid lava can reach quite a bit of speed as seen in the following video.

2. Strombolian or mixed. These days we have heard a lot that the type of volcanic eruption that occurs at the Cumbre Vieja volcano is Strombolian. The lava of the crater is less fluid, the gases escape causing sporadic explosions, more or less violent, projecting pyroclastic materials into the atmosphere that alternate with lava emissions. In addition to the Cumbre Vieja volcano, the Strómboli volcano, which gives its name to this type of volcano, is an example. The activity of this volcano is practically permanent, it is not the best place to live on the planet.

The following 30-minute BBC video is an example of their activity.

3. Vulcanian or explosive. The lava is not very fluid, solidifies very quickly at the point of emission forming a crust that is destroyed in subsequent eruptions. The gases are released in violent explosions, separated by long periods of rest. Its name comes from the island Vulcano  in Sicily.

4. Vesubian or explosive. Similar to the previous one, but with more violent eruptions. A long rest occurs that creates a lava plug in the chimney and a violent outflow of molten magma occurs forming incandescent clouds. Its name comes from the volcano  Vesuvius  that completely destroyed the city of  Pompeii. The following video is a recreation of what could have happened in that explosion of the Vesuvius volcano.

Live video of the Cumbre Vieja volcano

Radio Televisión de Canarias offers a live video of the eruption that can be followed at this link https://youtu.be/sFEZACRRJBk.  

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