Sulphur plume, Anak Krakatau

Volcanic hazards: Sulphur Dioxide

If you are planning on entering an active volcanic region it is important to know about the dangers that have the potential to affect you. A major hazard at some active volcanoes is sulphur dioxide (SO2). This gas is naturally emitted by active volcanoes, it’s concentration can fluctuate without warning and hence pose a danger to tourists and scientists. In this blog post we will look into the symptoms of SO2 poisoning and what you should do if you or a member of your team start to experience any of these.

Sulphur plume, Anak Krakatau
Potentially dangerous sulphurous plume emitted from Anak Krakatau. Credit: S.wanmer 2014

Sulphur Dioxide (SO2)

SO2 is an invisible gas commonly emitted by volcanoes. Often it cannot be seen but if it is present in high enough concentrations it can start to trigger symptoms within humans which can be lethal if not noticed and mitigated straight away.

How can you detect the presence of an invisible, yet poisonous gas? First of all you will probably smell it! SO2 has a strong ‘eggy’ smell that can usually be noticed at even low concentrations [1]. Detecting the smell of rotten eggs around a volcano tells you that you are being exposed to SO2 but does not mean that the levels are high enough to cause you any harm. Other symptoms of SO2 exposure may develop and alert you to more dangerous levels of SO2 exposure:

  1. Coughing due to irritation of the throat lining by Sulphuric acid, which forms when SO2 comes into contact with fluids. A high level of irritation within the airways can begin to restrict breathing, particularly in persons who experience asthma or are generally unfit. If breathing becomes difficult then it is important to evacuate.
  2. Stinging, irritated eyes. Very high levels of Sulphur exposure can begin to damage your eye sight, but it is unlikely that levels will reach high enough for this without other symptoms becoming alarmingly apparent beforehand.
  3. Skin irritation, redness or blistering. If you have any skin exposed then the sulphurous gases may react with the moisture on your skin causing irritation or a slight burning sensation. At higher concentrations redness and blistering can also occur. When skin irritation happens it is important to thoroughly clean your skin and your clothes, when you return from your adventure, to wash away the irritating sulphur and its acids.

If you have not been exposed to sulphur before then it is possible that you will be more sensitive to its effects than someone who has been exposed before. It is possible to build up a tolerance to the sulphurous gases and their effects over time with multiple periods of exposure. For example people work at sulphur mines where they can be exposed to very high levels of sulphur during mining, yet they can have minimal symptoms! Although, the effects of long term sulphur exposure aren’t well known, so it may be possible that a persons general health could be affected in the future even if there are no immediate symptoms.

People will all react differently when exposed to varying levels of sulphurous gases. Some people may be very sensitive and experience scary symptoms early on. It is important to listen to the concerns of all team members who you may be with, or to be acutely aware of your own reactions to the environment if alone. Children have a larger lung surface area and will therefore likely receive a larger dose of SO2 than any adults.  It is important that adults realise this and make sure they can evacuate in sufficient time for their children and not base evacuation on their level of symptoms, even if they are highly sensitive to SO2.

When you visit an active volcano it may be possible to see plumes of gas being emitted, if the wind patterns of the area are well known then it may be possible to climb a volcano upwind so as not to be exposed to dangerous levels of gas. If the wind patterns are unpredictable it is better to not attempt a summit hike. If you get caught in the middle of a dense cloud of volcanic gases and it is not possible to evacuate quickly then there is a real potential for suffocation. Many poisonous volcanic gases are denser than air and will hug the ground, therefore they can be hard to escape if you stand in their path. It is possible for the gases to be channelled along valleys and troughs within the volcanic surface, if you find yourself here and need to escape it might be best to climb any nearby ridge to escape the gases. If caught in any other situation look for the quickest route out of the plume, particularly if the gases are thick enough to see the cloud. In many cases it will be best to move down away from the source of the gases. In some cases it may be advisable to wear protective clothing and carry breathing apparatus or gas masks.

There have been several cases, particularly of unknowing tourists, becoming lethally poisoned by SO2 at volcanoes around the world. I hope that this post will help you to identify any potential dangers so that you can remain safe whilst visiting active volcanoes anywhere in the world.


[1] All health hazards associated with sulphuric gases, including symptoms and treatment:

Leave a Reply

Your email address will not be published. Required fields are marked *