Volcanic Eruptions

When volcanoes are inactive, people can underestimate the risk, especially if they do not know about volcanic hazards. This increases vulnerability, especially in communities living on or near the volcano.

Volcanoes can have different styles of eruption. Some volcanoes generate pyroclastic flows, ballistic blocks and ash that can fall on communities, like at Fuego in Guatemala, Soufrière Hills, Montserrat and La Soufriere, St Vincent; others produce lava flows (for example, Hawaii). Sometimes mudflows (lahars) are generated when magmatic heat thaws ice, as happened in Colombia with the eruption of Nevado del Ruiz. Other times, mudflows occur when heavy rain mobilizes volcanic sediment on the volcano’s slopes. The most common effects on health caused by volcanic eruptions include traumatic injuries, burns, suffocation, skin irritation, eye injuries and conjunctivitis, respiratory problems, and even death.

Volcanic emissions (ash and gas) may impact food and water supplies as well as affecting livestock and domestic animals, crops and the environment. They may also impact basic services (water, transport, communications) and access to health services. The accumulation of ash on roofs can cause damage or collapse of buildings, both immediately and after the event, during the cleaning-up phase. Accidents, with multiple injuries, due to roof collapse are common.

Health facilities can be destroyed, or their operation compromised, restricting access to basic services.  To minimize disruption, preparedness for an eruption should involve set up of monitoring, knowledge of the different eruptive scenarios, permanent communication with technical authorities, alert systems, advanced preparations, and trained and properly equipped personnel.

Local authorities and the responsible civil and technical protection entities are fundamental partners in providing advice on the type of eruption that is expected, which allows preparation for an appropriate response and prevention of damage and losses.

Key facts

Types of eruptive events

The only effective preventative measure in case of an explosion is early evacuation from areas close to the volcano. The local health services and the population should receive updated information from the authorities on the areas at risk of impact from ballistics and blasts and the probability of explosion. Health risks are traumas, skin burns and lacerations by volcanic rock.
These flows of extremely hot ash, rocks and gas (sometimes called glowing avalanches or nuée ardente, and pyroclastic density currents) are generated during explosive eruptions or collapses of lava domes. The flows may travel for tens of kilometres, with superheated surges sometimes leaving the confines of river valleys down which they usually travel. They can cause death and injury through trauma, massive skin and lung burns, and asphyxiation. There may also be secondary impacts such as building and forest fires. In Saint Pierre, Martinique, 30,000 people died in 1902. The only preventive measure is early evacuation. Widespread, airborne dispersion of cool ash usually accompanies the flows.
During an explosive eruption, large plumes of ash may travel in the atmosphere for many tens, hundreds or even thousands of kilometres, raining ash on the land below. Ashfall may, therefore, affect many thousands of people. Accumulated ash can be heavy, especially when it is wet, putting strain on roofs, which may collapse. Fresh ash can be acidic and abrasive, damaging infrastructure, vehicles and household items. Short -term exposure to ash may cause eye, skin and throat irritation in otherwise healthy people. People with existing respiratory disease may experience aggravation of their symptoms (e.g., people with asthma, bronchitis and COPD). It is still unknown if long-term exposure to volcanic ash can cause respiratory disease.
Rainfall and melting ice (from magmatic heat) can mobilise ash and blocks on the volcano’s slopes, causing mudflows (lahars). Eruptions under glaciers can also cause floods. The mudflow following the eruption of Nevado del Ruiz in Colombia claimed the lives of 23,000 people in the city of Armero in 1985. Injury and death are caused by trauma, lacerations and drowning/suffocation. Evacuation from the at-risk areas (mainly river valleys and flood plains) is the best preventative measure.
Magmatic eruptions create lava flows which may trigger fires. The route of these flows is predictable and their emplacement relatively slow. Preventive measures include limited evacuation.
Volcanoes emit gases such as SO2, CO, CO2, H2S and HF, some of which accumulate in low areas and are easily inhaled, causing asphyxia and constriction of the respiratory tract. Preventive measures include evacuation, respiratory protection equipment for geologists and rescue teams.
Fact sheet

Volcanic ash is not ash at all. It is pulverized rock. A one-inch layer of dry ash weighs ten pounds per square foot as it lands. It often contains small pieces of light, expanded lava called pumice. Fresh volcanic ash may be harsh, acid, gritty, glassy, smelly, and thoroughly unpleasant. Although gases are usually too diluted to constitute a danger to a healthy person, the combination of acidic gas and ash which may be present within a few miles of the eruption could cause lung damage to small infants, elderly and susceptible, or those already suffering from severe respiratory illnesses.

  • A heavy ashfall blots out light. Sudden heavy demand for electric light may cause power supplies to burn out or fail.
  • Ash clogs water courses, sewers, sewage plants and machinery of all kinds.
  • Ash drifts onto roadways, cartways and runways like snow, but resembles soft sand.
  • Fine ash may be slippery.
  • The weight of ash may cause roofs to collapse.
  • In case of moderate or abundant ashfall, especially fine particles, bronchial asthma, and other chronic respiratory conditions may be aggravated, in children as well as in adults.
  • Death is highly improbable, although it could occur in persons with serious symptoms if they do not protect themselves from the ashes.
  • Ash particles are abrasive and can also cause abrasions in the cornea.
  • Follow the recommendations of the emergency authorities.
  • Do not panic, stay calm – for healthy people ash is more bothersome than hazardous to your health but you should minimize exposure to ash.
  • Stay indoors until the heavy ash is settled. 
  • If caught outside, stay covered and seek shelter.
  • While outside, use a mask, if available, or a handkerchief/cloth and protect the eyes, the skin, and cover the head.
  • Use the phone only if it is essential.
  • Use your radio for information on the ashfall.
  • Follow the recommendations of the emergency authorities.
  • You should minimize exposure to ash, staying indoors as much as possible.
  • Seek health care if chest or respiratory symptoms develop.
  • The most effective protection is to use a lightweight high efficiency mask (such as an N95 mask) or a common surgical mask.
  • Ensure a good fit of the mask to the face by adjusting nose clips and straps.
  • Use the same mask until it is visibly soiled or damaged.
  • Protect the eyes, the skin, and cover the head.
  • Remove contact lenses and use glasses when possible.
  • Minimize ash from entering the home:
  • Close doors and windows and seal off the chimney opening.
  • Place wet towels at the bottom of doors and other places where there are drafts.
  • Minimize use of forced air heaters, air conditioners, or clothes dryers. 
  • Do not operate fans.
  • Protect your water source from ash contamination. If the water has an acid taste or smell, use bottled water.
  • Remove ash from fruits and vegetables by washing them thoroughly.
  • Use a battery-operated radio for information.

People should know that breathing ash could be harmful and protection is advised for everybody. For the general population that must leave their homes for short periods, any type of common surgical mask should be efficient. Ensure a good fit of the mask to the face by adjusting nose clips and straps. Two types of population should be considered for special respiratory protection advice:

  • People who work outside and are heavily exposed to ash (e.g. cleaning crews, emergency and rescue teams, police).
  • People who are more vulnerable to ash particles (e.g. serious medical conditions, asthma sufferers, children, elderly).





 Inhalation of fine ash (<10 microns in diameter)

 Asthma, exacerbation of pre-existing lung disease

Laboratory test for particle size; Wear high-efficiency masks; Protect homes/offices from ash infiltration

Inhalation of siliceous dust (presence of crystalline silica, e.g., cristobalite, quartz)

Risk of Silicosis, if exposure heavy and continuous (years): an outdoor occupational hazard 

Laboratory tests for crystalline silica, respiratory protective equipment


Ingestion of water contaminated with fluoride, possibly also heavy metals

Gastrointestinal upset, even death in vulnerable (chronic sick)

Laboratory tests for leachable toxic elements; avoid surface waters for drinking supplies (i.e., use well water)

Ingestion of contaminated food (as above), including milk

As above

Laboratory tests for bioavailability of toxic elements; Observe health of foraging animals, laboratory analyses of milk

 Ocular and Skin

Foreign bodies in eyes

Conjunctivitis, corneal abrasions

Goggles for heavily exposed (e.g., outdoor workers)

Acid rain


Eye and skin irritation; Possible toxic contamination Laboratory tests for bioavailability of toxic elements; Observe health of foraging animals, laboratory analyses of milk
Ash exposure Skin irritation

Wear clothes that cover the skin



Roof collapse and falls from roofs


Prevent build-up of ash; exercise care if in danger of falling from a roof

Automobile accidents (slippery roads and poor visibility)


Traffic control

Aircraft engine damage


Radar warning of an eruption 

Radio and TV interference

Unable to receive warnings

Pre-eruption: advisory leaflets to all homes

Electricity outages (moist ash on horizontal insulators)

Breakdown of public utilities, home heating, etc.

Cover insulators or organize emergency repair crews

Poor visibility

Cessation of emergency transport; stranded homes and travelers; trauma

Designate emergency shelters

Baxter, Peter J. "Preventive Health Measures in Volcanic Eruptions." American Journal of Public Health 76 (1986) Supplement: 84-90