Volcanic eruptions are natural events that can release volcanic ash, gases, rock fragments, lava and steam into the atmosphere. Among these hazards, volcanic ash and volcanic gases can travel beyond the immediate eruption area and affect people who may not be directly exposed to lava or the volcano itself.

Breathing volcanic ash and gases can irritate the eyes and respiratory system. At sufficiently high concentrations, some volcanic gases can cause severe breathing problems, unconsciousness and even death. People with asthma, chronic lung disease, heart disease, young children and older adults may be particularly vulnerable.

WHAT ARE VOLCANIC ASH AND VOLCANIC GAS?

1. VOLCANIC ASH

Volcanic ash is made up of extremely small particles of pulverised rock, minerals and volcanic material produced during an eruption.

Despite its name, volcanic ash is not ordinary ash from a fire. It can be hard, abrasive and sometimes corrosive. Fine particles can become airborne and be inhaled into the respiratory system. Some volcanic ash may also contain crystalline silica, which can be harmful to the lungs.

Volcanic ash can:

Irritate the nose and throat
Trigger coughing
Cause breathing difficulties
Irritate the eyes
Worsen asthma
Reduce visibility
Contaminate water and food
Damage machinery and vehicles
Accumulate on roofs and potentially contribute to structural collapse

2. VOLCANIC GASES

Volcanoes can release several gases during eruptions and periods of volcanic activity.

Important volcanic gases include:

Sulfur dioxide (SO₂)
Carbon dioxide (CO₂)
Hydrogen sulfide (H₂S)
Hydrogen chloride (HCl)
Hydrogen fluoride (HF)
Carbon monoxide (CO)
Water vapour

The amounts and combinations of gases vary from one volcano and eruption to another.

Some volcanic gases can be particularly dangerous because they may be colourless or difficult to detect without specialised equipment.

WHAT IS VOLCANIC SMOG OR "VOG"?

Another important volcanic air-pollution phenomenon is known as vog, short for volcanic smog.

Vog can form when volcanic gases, particularly sulfur dioxide, react with oxygen, moisture and sunlight in the atmosphere, producing fine acidic aerosol particles.

These particles can travel with the wind and affect air quality in areas some distance from the volcano.

Vog may cause:

Watery eyes
Sore throat
Headache
Coughing
Breathing difficulties
Chest discomfort
Worsening asthma symptoms
General tiredness

WHAT CAUSES VOLCANIC ASH AND GAS?

1. VOLCANIC ERUPTIONS

The primary source is an active volcanic eruption.

When pressure and gases build inside a volcano, magma and volcanic material can be expelled through the volcanic vent.

Explosive eruptions can send ash and gases high into the atmosphere.

2. MAGMA-GAS INTERACTIONS

Magma contains dissolved gases. As magma rises toward the surface, pressure decreases and gases can escape.

These gases can contribute to volcanic emissions even before a major eruption occurs.

3. LAVA FLOWS

Lava can release gases as it reaches the surface.

Even when an eruption does not produce a large explosive ash cloud, volcanic gases can still create air-quality problems.

4. VOLCANIC ACTIVITY AFTER AN ERUPTION

Volcanic hazards do not necessarily disappear immediately after an eruption.

Ash may remain on the ground and become airborne again because of:

Wind
Vehicles
Human activity
Construction
Cleaning activities

Volcanic gases may also continue to be released from active volcanic areas.

WHY ARE VOLCANIC ASH AND GASES DANGEROUS?

The danger depends on several factors, including:

The type of volcanic material
Concentration of ash or gases
Duration of exposure
Distance from the volcano
Wind direction
Weather conditions
Individual health conditions

A person close to a volcanic eruption may face much higher concentrations than someone farther away.

Heavy gases such as carbon dioxide and hydrogen sulfide can also accumulate in low-lying or poorly ventilated areas, creating potentially dangerous conditions.

HEALTH EFFECTS OF VOLCANIC ASH

1. EYE IRRITATION

Volcanic ash can irritate the eyes because the particles can be abrasive.

Possible symptoms include:

Red eyes
Watery eyes
Burning sensation
Itching
Eye pain
Increased sensitivity

Larger or sharp particles can potentially scratch the surface of the eye.

2. NOSE AND THROAT IRRITATION

Inhaling ash can irritate the upper respiratory tract.

A person may experience:

Sneezing
Runny nose
Nasal irritation
Dry throat
Sore throat
Burning sensation in the throat

3. COUGHING

Coughing is one of the common responses to inhaled volcanic ash and gases.

The cough may be:

Dry
Persistent
Irritating
Accompanied by phlegm
Worse after prolonged exposure

4. WHEEZING

Fine particles and volcanic gases can irritate and narrow the airways.

This may result in wheezing, particularly among people with asthma or other respiratory conditions.

5. SHORTNESS OF BREATH

Higher exposure can result in difficulty breathing.

A person may feel:

Unable to breathe comfortably
Tightness in the chest
Breathlessness while walking
Difficulty taking a deep breath

Severe exposure to volcanic gases can cause serious respiratory distress.

HEALTH EFFECTS OF VOLCANIC GASES

Different gases can affect the body in different ways.

SULFUR DIOXIDE (SO₂)

Sulfur dioxide is an important volcanic gas that can irritate:

Eyes
Nose
Throat
Airways

It can cause breathing difficulties and may worsen asthma and other respiratory diseases.

CARBON DIOXIDE (CO₂)

Carbon dioxide is normally present in the atmosphere, but extremely high concentrations can be dangerous.

Because CO₂ is heavier than air, it can accumulate in low-lying or poorly ventilated areas.

Very high concentrations can lead to:

Headache
Dizziness
Confusion
Loss of consciousness
Suffocation

HYDROGEN SULFIDE (H₂S)

Hydrogen sulfide is another volcanic gas that can be hazardous at high concentrations.

Exposure can cause symptoms such as:

Eye irritation
Headache
Dizziness
Breathing difficulties

Very high concentrations can be life-threatening.

HYDROGEN FLUORIDE (HF)

Hydrogen fluoride can be released by some volcanic eruptions.

It can irritate the respiratory tract and can contaminate ash and the surrounding environment.

The risks vary significantly according to the eruption and local conditions.

VOLCANIC ASH AND ASTHMA

People with asthma can be especially sensitive to volcanic ash and gases.

Exposure may trigger:

Coughing
Wheezing
Chest tightness
Shortness of breath
Asthma attacks

People with asthma should follow their prescribed asthma action plan and reduce exposure as much as possible during volcanic air-pollution events.

WHO IS MOST AT RISK?

Although volcanic ash and gases can affect anyone, some people may be more vulnerable.

These include:

Children and babies

Their respiratory systems are still developing.

Older adults

Older people may have a higher likelihood of underlying respiratory or cardiovascular conditions.

People with asthma

Volcanic ash and sulfur dioxide can aggravate asthma symptoms.

People with chronic lung disease

People with COPD, emphysema or other chronic respiratory illnesses may experience worsening symptoms.

People with heart disease

Air pollution and respiratory stress can place additional strain on people with cardiovascular conditions.

Pregnant women

Pregnant women should follow official health and evacuation advice during volcanic emergencies.

CDC specifically identifies children, older adults and people with respiratory conditions as groups that may experience greater problems from volcanic ash exposure.

OTHER DANGERS CAUSED BY VOLCANIC ASH

The danger is not limited to human health.

1. REDUCED VISIBILITY

Ash and volcanic smog can significantly reduce visibility.

This can increase the risk of:

Road accidents
Aviation problems
Difficulty navigating outdoors

Vog can also reduce visibility for road, air and marine transportation.

2. WATER CONTAMINATION

Volcanic ash and chemicals can contaminate water supplies.

People should follow local authorities' instructions regarding drinking-water safety after an eruption.

3. ROOF COLLAPSE

A thick layer of wet volcanic ash can become extremely heavy.

Large accumulations on roofs can damage buildings or contribute to roof collapse.

4. DAMAGE TO VEHICLES AND MACHINERY

Volcanic ash can be abrasive and can enter engines and mechanical systems.

Driving through heavy ashfall can stir ash back into the air and increase exposure.

It can also clog vehicle engines and cause mechanical problems.

HOW TO PROTECT YOURSELF FROM VOLCANIC ASH AND GAS

1. FOLLOW OFFICIAL WARNINGS

This is the most important step.

Follow instructions from:

Local authorities
Emergency services
Disaster-management agencies
Health authorities
Volcanic monitoring agencies

If an evacuation order is issued, leave the area according to official instructions.

2. STAY INDOORS WHEN ADVISED

If ash is falling and authorities advise sheltering indoors:

Close windows
Close doors
Close other openings
Keep outside air from entering unnecessarily
Avoid unnecessary outdoor activities

CDC recommends keeping windows and doors closed to reduce exposure to ash and gases.

3. USE A PROPER RESPIRATOR

If you must go outside during ashfall, a properly fitted NIOSH-approved N95 respirator can reduce inhalation of volcanic ash particles.

However, an important distinction is necessary:

An N95 respirator filters particles but does not filter toxic gases and vapours.

Therefore, wearing an N95 does not make it safe to enter an area containing dangerous concentrations of volcanic gas. The safest approach is to avoid the contaminated area and follow evacuation or shelter instructions.

4. PROTECT YOUR EYES

Wear protective goggles when ash is present, particularly during outdoor activities or cleanup.

Avoid rubbing your eyes if ash gets into them.

5. COVER YOUR SKIN

Wear:

Long-sleeved clothing
Long trousers
Closed footwear

This can help reduce skin irritation from ash and volcanic material.

6. AVOID LOW-LYING AREAS

During volcanic activity, avoid low-lying areas when instructed by authorities because some volcanic gases, particularly heavier gases, can accumulate there.

7. AVOID UNNECESSARY DRIVING

Driving during heavy ashfall can:

Reduce visibility
Increase accident risk
Stir ash into the air
Damage vehicle engines

If authorities advise against travelling, stay where you are or evacuate according to official instructions.

HOW TO CLEAN VOLCANIC ASH SAFELY

Volcanic ash should not simply be treated like ordinary household dust.

When cleaning:

Wear an appropriate respirator.
Wear protective goggles.
Cover exposed skin.
Avoid unnecessary exposure.
Follow local cleanup instructions.
Be careful on roofs because ash can make surfaces slippery.
Be aware that accumulated ash can be extremely heavy.

If ash has accumulated heavily on a roof, professional assistance may be safer than attempting to clean it yourself.

WHAT SHOULD YOU DO IF YOU EXPERIENCE SYMPTOMS?

If you develop eye, nose or throat irritation while exposed to volcanic gases or fumes, move away from the contaminated area immediately.

Symptoms caused by gas exposure may improve when exposure stops. If symptoms persist, seek medical attention.

For people with asthma or chronic respiratory disease, follow the treatment plan provided by their healthcare professional.

WHEN IS IT AN EMERGENCY?

Seek emergency medical attention if someone develops:

Severe difficulty breathing
Severe shortness of breath
Rapid or difficult breathing
Severe dizziness
Confusion
Loss of consciousness
Severe chest symptoms
Bluish lips or skin
Symptoms that rapidly worsen

Very high concentrations of some volcanic gases can cause unconsciousness and death.

PREPARING BEFORE A VOLCANIC ERUPTION

People living near active volcanoes should prepare before an eruption occurs.

A basic emergency kit can include:

Drinking water
Emergency food
Essential medications
First-aid supplies
Flashlight
Extra batteries
Battery-powered radio
N95 respirators
Protective goggles
Sturdy shoes
Important documents

It is also useful to know:

Evacuation routes
Emergency shelters
Local warning systems
Where family members should meet
Which authorities provide official updates

CDC recommends preparing both an evacuation plan and a sheltering plan before an eruption.

VOLCANIC ASH VS VOLCANIC GAS

Hazard	Main concern	Possible effects
Volcanic ash	Fine particles entering the respiratory system	Coughing, throat irritation, breathing problems, eye irritation
Sulfur dioxide	Irritation of airways	Coughing, wheezing, breathing difficulties
Carbon dioxide	Accumulation in low areas	Dizziness, unconsciousness, suffocation
Hydrogen sulfide	Toxic gas exposure	Eye/respiratory irritation, dizziness, severe toxicity at high concentrations
Vog	Fine acidic volcanic aerosols	Eye irritation, sore throat, coughing, breathing difficulties

The exact risks depend on the volcano, eruption, concentration, weather and distance from the source.

FINAL THOUGHTS

Volcanic eruptions can create hazards far beyond lava and falling rocks. Volcanic ash, sulfur dioxide and other volcanic gases can seriously affect air quality and human health.

Short-term exposure can cause eye irritation, coughing, sore throat, headaches, wheezing and breathing difficulties, while high concentrations of certain gases can cause severe respiratory distress, unconsciousness and death. People with asthma, chronic lung disease, heart conditions, young children and older adults may be particularly vulnerable.

The most effective protection is to avoid exposure. Follow official warnings, evacuate when instructed, stay indoors when advised, keep ash outside the home, use a properly fitted N95 respirator when exposure to ash cannot be avoided, protect the eyes and skin, and seek medical attention when significant symptoms occur.

Most importantly, never assume that an area is safe simply because you cannot see or smell volcanic gas. Some volcanic gases can be invisible or difficult to detect, making official warnings and evacuation instructions particularly important.

Disclaimer: This article is intended for general health and safety education. It does not replace instructions from local disaster-management authorities or professional medical advice. During an actual volcanic eruption, always prioritise official evacuation and emergency instructions.

15 September

THE DANGERS OF VOLCANIC ASH AND VOLCANIC GAS: CAUSES, HEALTH EFFECTS AND HOW TO PROTECT YOURSELF