The eruption of La Palma is assuming an accelerated vulcanology course for the Spaniards, fortunately little accustomed to deal with volcanoes.
It has taught us, for example, to distinguish between an effusive or explosive eruption.
When he began to rugir on September 19, we knew that it was a ston-type eruption, but it is also having Hawaiian episodes and freatomagma pulses.
What does it mean?
How is the volcanic activity that is taking place on Canaria Island?
In the world there are currently around 1,500 active volcanoes, and each one is unique, although they share common features.
There are different classifications, the main ones take into account the form or structure of the volcano, or the characteristics of its eruption.
However, the Geologist Ramón Casillas Ruiz, Professor of Petrology and Geochemistry of the University of La Laguna, in Tenerife, considers more appropriate to talk about different types of volcanic activity than of volcano types.
As Francisco José Pérez Torrado explains, Vulcanologist at the University of Las Palmas de Gran Canaria, “What we know as dorsal (Rift in scientific terminology) of Old Summit is a volcanic megastructure composed of hundreds of volcanic cones aligned in a northern direction.
South”.
The scientist clarifies that the volcano that is being created in this eruptive event is not an old summit volcano and we must still assign a name: “As we have commented on several occasions within the scientific committee of the pevolca, we consider that the best thing is that
Be the inhabitants of the island who propose it. ”
In the classification by the type of volcanic activity, the main categories are the Plinian or Vesubian, the fight, the Vulcan, the Sungromol, the Hawaiian and the hydromagma.
According to Ramón Casilla Ruiz, the main factors that determine that an eruption occurs in one way or another are the viscosity of the magma (which is not the same as the density, with which it is often confused), the content of dissolved gases and
The ability of the magma to free them.
“Viscosity is the ability of a fluid to get moving and in the case of magma, it depends on its chemical composition, the temperature at which it is, of the dissolved gases and the proportion of crystals of minerals present
. At higher temperature, less viscosity; more dissolved gases, less viscosity. The fundamental factor is the chemical composition: the more silicon oxide (also called silica, SiO2) has, more viscous will be, “says this geologist.
“The other factor is the content of dissolved gases that magma has, which, in turn, depends on the pressure to which it is, and its ability to free themselves from them. If the magma is at little pressure, it dissolved few
Gases. It’s like what happens when you open a bottle of cava: If we remove the plug the pressure decreases and the gas is released, “he explains.
Another aspect that influences is the possibility that the magma comes in contact with water, which can be the water of the sea or the water present in an aquifer, ie a permeable rock body containing water in its pores and fissures.
“The problem is that if the magma, somehow already fragmented, interacts with water in certain proportions, an instantaneous vapor is produced that triggers a very large explosiveness (due to the expansion suffered by gases when passing from liquid phase to vapor phase
) That spray the magma. This expansion is, for example, that makes moving a steam machine, “compares.
It is characterized by explosive eruptions that alternate with short periods of calm.
“The magma is little viscous but with a lot of gas, when the gas bubbles detached, fragments of magma are released to the atmosphere (etymologically, fragments of fire) that fall around the emission point and when accumulating, form a
Cono, “says Ramón Casilla Ruiz.
These gases are releasing rhythmically, causing frequent explosions.
It receives its name from the Italian volcano Stómboli, located on the Sicilian Island of the same name.
This volcano has been permanently active for at least 2,000 years, with periods in which its activity intensifies and others in which it decreases.
In a Hawaiian eruption, the emission of very fluid lava predominates, with few gases that are released very easily.
They are eruptions that could be rated as calm because they do not usually be accompanied by explosions.
They are typical of Hawaii volcanoes.
One of the most active volcanoes on the planet is the Kilauea, who has just come back into eruption.
“We start from a little viscous magma, with little silica, it can be, for example, basaltic, very fluid and quite degassing. If you have few gases, when you go to the surface during an eruption – the magma happens to be named as lava-
as a supplier. This is how the lava is leaving one of the emission points of the palm volcano, about 1,150 degrees centigrade and very fluid, almost like water; it moves easily but as it cools, it increases
its viscosity and accelerates the solidification of the base, from the front and ceiling, while the interior of the laundry is kept more fluid and moving, thus dragging the base and the already solidified ceiling, which causes its fragmentation in numerous
Clastos, “explains Ramón Casilla Ruiz.
“In La Palma, three types of volcanic activity are being given simultaneously, more frequently stonbolk and Hawaiian and more sporadically, freatomagma,” says the geologist.
“Floratomagma activity occurs when Magma, already fragmented by degassing, comes into contact with water from an aquifer, which suffers from instantaneous vapor that triggers a very large explosiveness (due to the expansion suffered by gases when passing from liquid phase
A phase steam) that sprays the magma lava in very fine particles and columns of chiroclasts and water vapor are formed in the form of cauliflower and cypress “, details.
“The eruption we are observing on the island of La Palma is of a fussural type that is, it arises along a crack that opens on the ground. Different eruptive centers are emerging, but, little by little, some become inactive,
And there are two or three survivors left, around some of which builds the main volcanic cone. In the emission centers of this cone. The main eruptive mechanism is the stonbolian, although, over time, have had junior pulses
explosiveness that we know as hydromagmatics (or pararatomagma if the magma-water interaction in the duct is with groundwater, as is the case) “, coincides José Pérez Torrado, which is also part of the Geomorphology Research Group, Territory and Landscapes in Volcanic Regions
(Geovol).
According to this expert, “a stonbolian mechanism is relatively low explosiveness. From the main emitter center emerges the column of gases and pyroclasts that rises to the atmosphere. The fatter piroclasts (we know as bombs and slag) fall near the conduit
And when accumulating, they are forming the cone. At the base of it and in possible satellite bulbs that are being established is where the magma without fragment arises, forming the “rivers” of lava that we know technically as laundry. When there is hardly gas column
and explosive piroclast and we only have a fountain that feeds a lava, then we talk about Hawaiian, effusive or almost almost null explosive mechanisms. ”
“That alternates each other, or that both live, as it happens right now (we have a stonbolian mechanism in the main and Hawaiian cone crater at the satellite emitter center that has generated lava pouring that has traveled on top of the previous ones, for that reason
, thermally isolated, which has allowed him not to increase his viscosity during the flow and achieve greater distance arriving at the sea), it is very common in an eruptive process of these characteristics. As are the freatomagma pulses he has also had, “says Francisco
José Pérez Torrado.
Ultraplinian eruptions (more explosive than the so-called Plinian or Vesubiano) generate very violent explosions due to the high pressure of the gases in the magmatic chamber.
They form a great ash cloud that throughout history have come to bury cities, as happened with Pompeii and Herculano after the eruption in the year 79 of the Vesuvius Italian volcano.
“Very viscous magmas with many gases have the problem that it costs that the gases will be released. They are trapped in bubbles inside the magma, they expand and exert a great pressure on the walls of the bubbles as the magma ascends and loses pressure
. At a given moment, the gas gets breaking the walls of them and we had high pressure gas bubbles confined in the magma, a mass of magma particles in high-pressure gases that forms a high-speed eruptive jet
and that transports gases and piroclasts to several kilometers of height. Then form a large eruptive column constituted by gases, ash and pumice. From this column, the piroclasts fall by gravity, as if it were a snow, generating a rain of
Piroclasts or Plinian rain that can cover an entire area, with thicknesses of several meters “, says Ramón Casilla Ruiz.
“It is also possible that the eruptive jet collapse gravitatively and forms a mass of piroclasts that moves flush from the ground as a snow of snow, at a lot of temperature, and during its journey you can incorporate tree trunks, rocks, etc. those flows
Pyroclasts destroyed Pompeii and Herculaneo “, says Ramón Casilla Ruiz.
They are so called in honor of Plinio El Viejo, who died in that eruption when he was to investigate her, and that she was the uncle of Pliny the young man (who described them for the first time).
