Fumerolles: what is it?

Fumaroles are small plumes of gas or vapors of volcanic origin escaping from the ground through cracks, vents or vents. They are associated with zones of volcanism active. We thus speak of superficial paravolcanic manifestations. Fumaroles can therefore be associated with the degassing of wash recent or to vapors sneaking along fractures in the subsoil, directly above a still hot magmatic reservoir. Thus, it is not uncommon to observe fumaroles at the level of craters of volcanoes asleep for several decades, even centuries. It all depends on gradient geothermal energy in the region and speed cooling of the magmatic system.

Temperature and chemical composition of fumaroles

The chemical composition of fumaroles as well as their temperature are very variable. The temperature can thus reach 300 ° C, or even more than 1,000 ° C. The gas exhaust speed can also be very high, greater than 150 m / s. The gases emitted by the vents are generally composed of a large part of water vapor, associated with carbon dioxide (CO₂), sulfur, of the’hydrogen sulfide… The latter gas being particularly toxic, theinhalation vapors from fumaroles can be very dangerous.

Depending on the temperatures and the composition of the gas plumes, there are two types of fumaroles:

• so-called “dry” fumaroles, the temperature of which varies between 500 and 1,000 ° C, and which are rich in dihydrogen (H₂), sulfur dioxide (SO₂), in fluorine (F) and in chlorine (Cl);
• the fumaroles say ” acids “, Whose temperature varies between 300 and 500 ° C and which are rich in water vapor (H₂O), carbon dioxide (CO₂), hydrogen (H₂), sulfur dioxide (SO₂), hydrogen sulfide (H₂S) and in hydrogen chloride (HCl).

Depending on the chemical composition of fumaroles, certain elements, in particular ores such as copper, the iron and sulfur, can be deposited quickly on contact withair, at the vents. Deposits, especially sulfur, can be very important and are the object, as in the case of certain volcanoes in Indonesia, of an intense exploitation. The Kawah Ijen volcano thus produces 12 tonnes of sulfur per day. This ore is used in particular for the manufacture of fertilizers, tires, paper or evenmatches.

An indicator of the underlying magmatic activity

It goes without saying that the greater the magmatic activity of the zone, the higher the temperature of the fumaroles and the greater theepisode of sulfur compounds is important. In this sense, fumaroles are therefore generally intensely monitored by scientists. Analysis of their composition indeed gives a lot of information on the activity of the volcanic system underlying. Changes in the amount of CO₂ and sulfur would in particular make it possible to predict the occurrence of an eruption.

The most famous fumarole sites are of course Iceland, but also the Vulcano volcano in Italy, the Dallol hydrothermal field in Ethiopia, Yellowstone National Park in the United States, the island of Hawaii, Indonesia …