Dangers des émissions de gaz volcaniques

"The world is not more volcanically active; we are just more aware of volcanism" writes Denison University Associate Professor of Geosciences Erik Klemetti. Indeed, we have the impression that volcanic eruptions have been increasing in recent years, but in fact, they are still as frequent but are more publicized. It is also true that the capacity to monitor volcanoes has increased with new technologies, and the interest in volcanoes is much more widespread.

Volcanoes in the world

Today's volcanoes

There are about 10,000 volcanoes on Earth, 1,500 are active and nearly a dozen erupt every day. Some active ones require constant monitoring to protect surrounding nature and nearby houses. 10% of the active volcanoes are located in the United States.

Active volcanoes graphic @Statista, Smithsonian Institution Global Volcanism Program

  • Kilauea volcano on the island of Hawaii in the United States: it has been erupting since January 5, 2023, and is in a closed area of the Hawaii Volcanoes National Park. Volcanic gases are the main danger for the population, consisting of water vapor, carbon dioxide, and sulfur dioxide mixture. "We have measured a sulfur dioxide emission rate reaching about 4,000 tons per day on January 8, 2023," said the USGS (United States Geological Survey). The instability of the crater that can make the earth shake has caused the closure of the area to the public since 2008.
  • The Cotopaxi volcano in central Ecuador: is considered the most dangerous volcano in the world. Active since 2015, it woke up in October 2022. It is highly monitored today because it generates fumaroles up to 2 km above the crater. Volcanologists have also seen ash fall in several localities around the volcano.

Different types of volcanoes

Following the geographical location and the chemistry behind the molten activity, we can distinguish several types of volcanic eruptions. They do not all have the same consequences on the population and the environment.

Volcanic gas emissions Mount Pinatubo

  • Explosive eruptions: the gas is captured in the rock of the volcano in fusion. That makes the pressure rise until it is released violently, creating explosions of lava and various volcanic emissions (i.e., Mount Pinatubo in 1991)
  • Effusive eruptions: when the magma becomes less sticky, it releases gas, and the magma flows down the slopes of the volcano (i.e., the Kilauea volcano of Hawaii in 2018)
  • Fissural eruptions (can be included in effusive eruptions): huge fissures already present all around the volcano open up, causing large quantities of fluid lava to gush out over several kilometers in length (i.e., Grindavik volcano in Iceland in August 2022)


For the less initiated, we found it interesting to indicate some definitions to understand better the subject of volcanoes.

Stromboli volcano eruption @source Sipa-Press

Smoke: gases enclosed in the magma that escape at the surface of an active volcano.

Magma: molten rock located several kilometers deep under the Earth in what we call "magma chambers". It is composed of dissolved gases, liquids, and solid elements, such as crystals. As long as it remains underground, it is known as "plutonic rock".

Caldera: a vast, almost circular volcanic crater with a flat bottom, limited by cliffs, and with a diameter greater than 2 km. The origin of calderas is different from the craters' one.

Pyroclastic flow or flow: flow located at the base of a glowing cloud and rising little from the ground. It is a dense aerosol composed of volcanic gases and particles of various sizes, ranging from volcanic ash to boulders, larger than a house.

Slag: solid residue formed from lava that has cooled and fragmented.

Halogenides: toxic acids formed with the combination of metals with chlorine, fluorine, bromine, and iodine.

CAMS (Copernicus Atmosphere Services Monitoring): a monitoring service providing information on air pollution, solar energy, greenhouse gases, and climate around the world

Volcanic gas emissions

In 1815, Mount Tambora in Indonesia created a caldera 6 km in diameter and 1000m deep; boiling of ashes mixed with gases bubbled up 45 km into the sky; when it fell back, pyroclastic flows hit the Earth and killed more than 10,000 people. Ashes and gases that went into the atmosphere darkened the sun's light and increased the reflectivity of the Earth, resulting in a lack of summer. The eruption killed on itself more than 10,000 people, but the aftermath caused nearly 80,000 people to die from starvation and disease brought by the gases in the atmosphere.

Mount Tambora eruption


Magma is composed of dissolved gases (sulfur dioxide, carbon dioxide, hydrogen sulfide, and halides), the driving force behind volcanic eruptions. As the magma rises to the surface, the pressure decreases, and the volcano releases with strength the gases into the atmosphere.

The carbon dioxide emitted by volcanoes, between 180 and 440 million tons per year, is colorless and odorless, so it is difficult to detect the gas. Therefore gas detectors can be set up in areas with active volcanoes to prevent and anticipate people's protection. Researchers can also be fitted with portable gas detectors when in direct contact with volcanic emissions.Even if this gas dissolves to tiny concentrations, CO2, once cooled, becomes heavier than air. So it can move to low-lying zones where we can find high concentrations.

Intense SO2 emissions are as harmful to humans as to the environment because they can turn into acid rain which will pollute the air terribly.

Hydrogen sulfide is the most recognizable gas because of its unpleasant smell. This gas specification helps anyone who comes into contact with H2S to protect oneself's mucous membranes.

Hydrogen halides, composed of fluorine, chlorine, and bromine halogens, are extremely hazardous toxic acids. They dissolve rapidly in water or the atmosphere and can cause acid precipitation.

Climate and environmental issues

Volcan Bromo en Indonesie source volcanofoundation.org

We don't realize it because volcanoes are all around the world, but they play a significant role in changing the climate. When they erupt, they release into the atmosphere ashes, metals, and also large quantities of gases and particles (or aerosols) that will change the climate for the duration of the eruption locally or in a larger area following the eruption power. These effects are variable according to the strength of the volcano and its geographical position. Thus volcanoes located in tropical territories can generate volcanic emissions that will spread all over the world. For example, the eruption of Mount Pinatubo in 1991 caused quantities of particles and gases to gush out at more than 20 km high, which circled the earth for three weeks, causing a global meteorological change.

" The impact of large volcanic eruptions on our climate [...] is due to the emission of particles, mainly fine ashes and sulfates, which effectively disperse the solar radiation" explains Santiago Arellano. Thus, the sun's rays pass through a dust filter that reduces the power of the star. Thus, the stronger the eruptions, the higher the emissions and the less the sun's rays will reach the earth's surface. We have already observed a decrease of 0.5°C due to the eruption of a volcano.

On the other hand, small eruptions cause emissions that remain at low altitudes. Thus they are more easily swept away by precipitation and do not remain in the atmosphere. They have no impact on the climate.

Some researchers are studying the possibility that global warming has a reverse impact and could be the origin of the multiplication of volcanic eruptions. We can take as an example the melting of glaciers under which are located volcanoes that are not active today, but which could be when these blocks disappear. This could also be the case for volcanoes located at altitudes where their ice cap is likely to disappear and thus make volcanic landslides appear.

Scientist measuring the concentration of volcanic emissions

As previously mentioned, the emission of sulfur dioxide can turn into acid rain which can be disastrous for the environment. Indeed, the combination H2O (water) + O2 (oxygen) + SO2 (sulfur dioxide) = H2SO4 (sulfuric acid) results in a devastating acid for the land and crops. Farmers are torn between enjoying the fertile soil that is volcanic land and having their crops destroyed by an eruption of lava, ashes, and gases.

Hazards for population

It is essential to monitor the presence of volcanic emissions that can be the source of degraded air quality and thus cause harm to public health and industries such as aviation (the first sector affected by emissions of volcanic gases in the atmosphere). The monitoring program called Copernicus (CAMS) gets thus aims to monitor the atmosphere by observing the movement and behavior of sulfur dioxide (SO2) present in volcanic emissions during eruptions. 

Monitoring of Cumbre Vieja La Palma

CAMS could detect poor air quality in North Africa, Europe, above the Atlantic Ocean, and the Caribbean during the Cumbre Vieja volcano eruption in La Palma in December 2021, which generated a lot of sulfate aerosols in the air. The CAMS service uses observations established by satellites to monitor SO2 flux and combines this data with global-level information to predict air quality composition over five days. Some sensitive individuals may be affected even with low- levels of toxic gases in the air.

Despite non-explosive lava effluvia, viscerally erupting volcanoes will release many gases that are really hazardous to humans: sulfur dioxide, carbon dioxide, hydrogen sulfide, and halides. The gases will reach the population depending on the geographical position of the volcano and the weather conditions.

A CO2 gas level of 3% is already a significant danger for the inhabitants, who may experience serious health problems such as headaches, dizziness, accelerated heart rate, and shortness of breath. Above 15% CO2 can cause unconsciousness and death.

Sulfur dioxide is a very irritating gas for the skin, respiratory tract, eyes, nose, and mouth. Therefore a researcher should equip himself with a portable single-gas detector dedicated to SO2, like the Dräger Pac 6500. It is a suitable complement to respiratory protection to detect at least the concentration level of the gas and thus anticipate any contact.

volcanic gas emissions move in the air

Whatever the gas concentration is, hydrogen sulfide is highly toxic to the respiratory tract, causing severe irritation. If exposure to the gas is long-term,  lung failure, unconsciousness, or cardiac arrest may occur.

Hydrogen halides cover the ash particles emitted and cause pollution of drinking water, agricultural fields, or mountain pastures.

Delayed risks can appear with the diffusion of the gas which moves. Thus the volcano in the Canary Islands that woke up in September 2021 brought a large cloud of toxic gases that led a village to confine itself for a few hours three months after the beginning of its eruption.

Collaboration of professions

Climatologists and volcanologists work closely together to ensure protection by detecting and exchanging the information and analysis they do. 

Volcanologists want to track the rate and scale of gas, lava, or ash emissions, to determine the physical state of the volcano and predict its activity. Meteorologists are interested in tracking volcanic plumes, to better understand the circulation patterns and interaction of volcanoes with the atmosphere”, explains a researcher. “Climatologists want to know where, how high and how much certain gases are emitted, in order to quantify climate forcing. Aeronautical authorities aim to locate volcanic ash plumes, in order to alert pilots and avoid accidents.

Climatologists and volcanologists collaborate-source www.lmv.uca.fr

The tools used by volcanologists are not devices designed for monitoring volcanoes but have other objectives established in their design (for example, devices that monitor the ozone layer) that allow them to make analyses and predictions. For example, they can use colorimetric tubes to analyze the concentration rate of a gas at the edge of a crater of an active volcano.

Discovering a volcano: choose the right equipment

On an active but not exploding volcano, fumaroles escape. Composed of toxic gases, it is essential to wear a mask when at the top of this type of volcano. The fumaroles are composed of water vapor (non harmful and majority component), sulfur dioxide and hydrogen sulfide. You can wear a gas detector (Ventis Pro) to be alerted quickly and evacuate the area quickly.

To explore a volcano, you need a protection that is resistant to heat, gases and all kinds of visible or invisible fumes. High hiking boots are a solid base to walk without being worried by obstacles and difficult access paths, littered with debris of all kinds. Windbreaker, fleece, cap or hat, and scarf are essential complements to basic protection.

Yves Moussalam volcanologue au service du climat © Stefan Walter

If you are going to visit an explosive volcano, it is necessary to have a dust mask because the ash particles, however small, are very harmful. The GVS Elipse 3 mask will be a perfect addition to your equipment. Complete your outfit with a hard helmet to protect you from possible slag that could fly and hit you.

To optimize your safety, we recommend that you wear large, tightly closed goggles to fully enjoy the show while protecting your eyes from particles in the atmosphere. This is why you can choose the GVS Elispe Integra mask.

To protect yourself during an excursion near a volcano that releases a lot of sulfurous gas, it is essential to wear a full face gas mask with an ABEK-P filter that filters acidic gases in particular. For asthmatics, take this type of filter no matter what volcano you discover.

Most of the gases emanating from volcanoes are irritating, so it is necessary to bring clothing that covers the whole body. A humidified scarf will protect your respiratory tracts in case of unexpected gas emissions if you are not equipped with masks.

When climbing on the slopes, you may need to use your hands. That's why it's important to have garden gloves that are resistant to existing corrosive products.

We have seen the relationship that can exist between climate change and volcanic eruptions reciprocally. Unesco observers predict that within 30 years, the Mediterranean will experience a tsunami due to volcanic activity on the seabed. "From underwater exploration to the prevention of populations, the organization is multiplying measures to face the danger".