Volcanology

The volcanology or vulcanology is the science which studies the volcanic phenomena, their products and their settings in place : Volcano S, Geyser S, Fumerolle S, volcanic eruptions, magma S, Lava S, Tephra S, etc

A volcanologist or vulcanologist is the scientist specialist in this discipline related on the Géophysique, the Sismologie and the Géologie of which it is a speciality.

History of volcanology

See also: History of volcanology

The history of vulcanology is, like the majority of the others stories of the natural science, marked by three great stages. A superstitious stage where the beliefs and the Mythe S religious dominate largely over knowledge then a scientific contribution which seeks to reconcile the observations and the beliefs and finally a scientific knowledge of the phenomenon which starts only at the 18th century by William Hamilton, later thus that the others Natural science. Lastly, in 1912, with the theory of the Plate tectonics of Alfred Wegener, the mechanisms, which not only cause the eruptions but also the earthquakes, start to be included/understood.

Objective

See also: volcanologic Prediction

The objectives of this science are to include/understand the origin and the operation of the volcanos and the comparable phenomena in order to establish a diagnosis (for one given period) on the risks and the dangers incurred by the populations and the human activities. The studies and research initially proceed on the ground in order to carry out collections of information in the form of observations, measurements and samplings and in the second time in laboratory in order to analyze and to interpret the data and the samples.

The volcanologists, helped by progress in Metrology, then will carry out a census of the volcanos and the development of a classification according to the éruptif  type;: hawaïen, Strombolian, Vulcanian, Pelean, plinien and surtseyen. They will also establish the link between Geyser S, Fumerolle S, Solfatare S, etc and Volcan S and will explain their operations. Various geological formations will be also explained by volcanicity and their installation will be the subject of many recherches : Dyke S, Neck S, run Lava, Ignimbrite, Pozzolana, Guyot S, Atoll S, etc

Measuring instruments and observations

Various measuring instruments elaborate or were borrowed from other disciplines in order to obtain reliable data on operation of the Volcan S and in particular the prediction of the volcanic eruptions. The event starting an volcanic eruption is the arrival of magma in the magmatic Chambre which will cause its setting under pressure. This setting under pressure is accompanied by a swelling by the volcano dù to the dilation of the rocks and the push of the magma on the walls. This swelling of the volcano will generate microphone Séisme S, an increase in the slope of the slopes of the volcano, an increase in the diameter of the crater or summit Caldeira. The arrival of the magma in the magmatic room will cause as for him the degasification of the tank and could be located like a thermic anomaly using a infra-red thermometer or a Pyromètre.

The Sismographe S make it possible to the volcanologists to detect the microseisms caused by the setting under pressure of the magmatic room. The seismographs can also detect the Trémor  : right before an volcanic eruption, the increase of the magma in the volcanic chimney generates a continuous and weak vibration volcano. This trémor constitutes a reliable tool thus making it possible to announce the imminence of an eruption.

The Inclinometer or the Accéléromètre measures as for them the variations of slope of the volcano until a precision of one per million. They are placed at various places on the slopes of the volcano at the time of a phase of rest. The setting under pressure of the magmatic room causes a swelling of the volcano which sees the slope of its slopes being accentuated. Following the volcanic eruption, the pressure in the magmatic room drops what decreases the slope of the slopes of the volcanos. Thus the volcanologist can envisage the beginning and the nearest end of an eruption when the inclinometers indicate a variation of the slope of the volcano.

The Altimètre plays a part additional to the inclinometer. Also placed on the slopes of the volcano, it will indicate the increases and the reductions in Altitude to the wire of swellings and deflations of the volcano.

The interferometer makes it possible to measure the distance between two points thanks to a Laser. The measuring device and the reflectors being placed on both sides crater or of a Caldeira, they make it possible to indicate an increase or a reduction in the size of the crater or will caldeira, sign which the volcano inflates or according to the pressure in the magmatic Chambre deflates.

Sampling makes it possible to determine the type and the eruptive past of the volcano according to nature, the proportion and the composition of the Lave S, the Tephra S and gases. The resumption of the gas emission by a volcano or the variations in their compositions can constitute an index determining in the imminence and the characteristics (eruptive standard, power, etc) of an eruption. The volcanologists also proceed to statements of temperature of gases and lava in fusion thanks to a Pyromètre.

At the time of an volcanic eruption, the volcanologists on the spot can proceed to various measurements, observations and échantillonnages : taking away of liquid lava, gas, of will tephras, observation of the course of the eruption (height of the volcanic plume, number and power of the explosions, the fountains of lava, speed and temperature of lava flow, etc),…

The volcanologist also takes topographic measurements using Théodolite S and geological (taking away of rock) with an aim of drawing up a chart and a history of the volcanic risks in the neighborhoods of the Volcan.

Analyzes and interpretations

The analyzes are in general made in the volcanologic Observatoire of the studied volcano when it has one of them.

The measurements taken using the instruments are deciphered, compared with the past of the volcano and between the volcanos, etc while the samples undergo chemical series of measure and analyzes , crystallographic, Physique S, geochemical,…

The summary of the results and their stepping thus makes it possible to carry out diagrams, cartographies, etc making it possible to establish a history of the volcano and to evaluate the eruptive risk for one more or less long period.

At the time of the forecast of an eruption, the volcanologists help themselves of various taken measurements. If one or more of the factors of the volcano varies (composition of gases, slope of the volcano, seismicity, etc), it is perhaps the sign which an eruption prepares.

Petrography and mineralogy

Two great types of volcanic rocks constitute 95% of the Lave S and Tephra S emitted by the Volcan s : the Basalt S and the Andesite S.

These two rocks in majority are made of crystals of Silice, Feldspath S and Pyroxène mingled with a volcanic Verre which did not have time to completely crystallize because of the increase and the brutal cooling of the magma. The Obsidienne for example is made only of one volcanic glass. The Basalt, resulting from the magmatism of Not hot and dorsal, results from the fusion partial of the coat by decompression on the level of the dorsals. The origin of the magma coming from the hot spots is still prone to debate. It is a fluid lava because it is relatively low in gas and silica (approximately 45%). The Andesite, resulting from the magmatism of Subduction, results as for it from fusion partial of the coat by hydration on the level of the pits of subduction. The andesites are pastier because they are richer in gas and Silice (approximately 55%). The Viscosité of a magma is dependant on its silica content because it is this mineral which determines the number of possible connections with the Oxygène  : the more one magma contains silica, the more viscous it is and the more the volcanic eruption will have an explosive tendency.

The Carbonatite is a very rare lava made up in majority of carbonate of Calcium (Calcite), of carbonate of Magnésium (Dolomite), of carbonate of Fer and Magnésium (sidéro - Magnésite) or of sodium carbonate. Very fluid, comprising only very few Silica (less than 1%), of not very high temperature (500 to 550°C), it is black when it is emitted but bleached in contact with the air once cooled (a few hours) because its minerals react with ambient moisture. Only the Ol Doinyo Lengaï currently emits carbonatites.

Volcanos of the Decade

The Années 1990 were declared “Decade international for the reduction of the natural disasters” by the the United Nations. The IAVCEI (for International Association off Volcanology and Chemistry off the Earth' S Interior literally International association of the volcanology and the chemistry of the interior of the Earth ) then decided to draw up a list of Volcan S likely credits or recently credits and, according to their eruptive past and their proximity with populated zones, to produce great volcanic catastrophes. The goal of this list made up of sixteen volcanos (“Decade volcanoes” in English) is to promote their study and the sensitizing of the populations on their subject in order to prevent any human risk.

The sixteen volcanos are:

The increased attention related to these volcanos in particular allowed some succès :

  • deviation of a casting of Lava on the Etna in 1992 avoiding the destruction of habitations  thus; ;
  • better comprehension of the history of the Galeras   ;
  • better comprehension of the implication of water in the eruptions of the Taal   ;
  • adaptation of the legislation in the case of new construction to the accesses of the Mount Rainier   ;
  • reduction of the thickening of the dwellings in the Caldeira of Taal  ;
  • development of a plan of evacuation of the agglomeration of Naples.

But the scientists and the authorities also met important problèmes :

  • the failure of the management of the eruption of the Mount Unzen with the death of 43 people including three volcanologists in 1991   ;
  • the death of six volcanologists and three tourists in the crater of Galeras during an eruption not envisaged in 1993. The volcanologists, who had not envisaged the excursion on the volcano, took part in a conference of volcanology in the town of Pasto   ;
  • impossibility of approaching the Santa Maria/Santiaguito because of the civil war in Guatemala until in 1996, date of the signature of a Cease-fire   ;
  • overflow of the genocide of Rwanda to the Zaire and destabilization of the mode of Mobutu Sese Seko with the first and the second war of Congo, preventing from approaching the Nyiragongo starting from 1996   ;
  • limited appropriations granted to these studies.

Famous volcanologists

See too

Related articles

External bonds

  • volcanic Risk management in France
  • Site of the BRGM
  • Site of European Volcanologique Association
  • USGS - Forecast of the lahars
  • European volcanologic Company

Sources

  • Measurements and raised of ground
  • History of the volcanology of the XVIIe century at the beginning of the XXe century
  • magmatic Rocks
  • Volcanos of the Decade on the site of the USGS

References

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