Volcanic ashfall

In an explosive volcanic eruption, rock is torn apart and blasted high into the atmosphere as a cloud of very fine particles. This volcanic ash consists of tiny, angular pieces of rock, minerals and volcanic glass. It is fine enough to be inhaled, hard enough to scratch eyes, paint and machinery, and it does not dissolve in water.

The wind often carries the ash cloud far away from the volcano, sometimes hundreds of kilometres. That is why places that cannot even see the volcano can be affected by ashfall. There, ash is then usually the main hazard: for health, for traffic, for the water supply and for buildings.

When ash gets wet, it soaks up water and becomes considerably heavier. A layer of ash that seems harmless when dry can overload flat or weak roofs after a rain shower. Ash also clogs filters, gutters and drains and can turn into a concrete-like mass in the sewers.

Protection during ashfall follows three simple principles: keep the particles out, do not stir them up, and recognise loads early. As soon as a warning comes, put masks, goggles, water and food for a few days ready, cover sensitive electronics and bring animals and vehicles under a roof. Cover or disconnect rainwater tanks and follow the water utility's instructions.

During the ashfall, stay indoors. Close windows and doors, switch off ventilation and air-conditioning or set them to recirculation, and seal draughts with damp cloths. If you have to go out, wear a well-fitting FFP2 or N95 mask, close-fitting goggles and long clothing. Wear glasses instead of contact lenses, because ash grains under a lens can scratch the cornea. Stay outdoors as briefly as possible.

When cleaning up, dampen the ash lightly before pushing it together, and collect it in strong bags. Do not dry sweep, or you will stir up the finest particles again. Do not wash it into the drains either, and dispose of it as the municipality instructs. A simple cloth over your mouth is not enough protection.

Near the volcano there are far greater dangers than ash: lava, glowing hot clouds of gas and rock that race down slopes at great speed, and mudflows of ash and water. In such hazard zones there is only one rule: follow evacuation orders immediately and do not enter closed zones. In danger, call the local emergency number (112 in the EU).

People with asthma or other respiratory diseases are particularly at risk during ashfall. They should stay indoors and keep their prescribed medication at hand; if short of breath, get medical help. Children and older people should also keep their exposure to ash as low as possible.

Do not climb onto a roof without fall protection – ash is slippery, and a fall can end badly. Thick layers of ash on flat or weak roofs should be removed by professionals or with fall protection, especially before forecast rain. If there are signs of overloading, leave the building. Driving on ash is like driving on snow: slippery, with poor visibility. Only drive if absolutely necessary, slowly and with lights on.

In 2010 the eruption of the Icelandic volcano Eyjafjallajökull showed how far ash can reach: across large parts of Europe, air traffic was restricted for days, because ash can be dangerous to aircraft engines. Anyone travelling to volcanically active areas should therefore expect closed airports and roads, follow the travel advice of their foreign ministry and the local authorities, and plan supplies for delays.

The International Volcanic Health Hazard Network, a network of experts, publishes guidance for the public. Among other things, it recommends staying indoors, using well-fitting particle masks and dampening ash before removing it. The specific instructions, however, always come from the local authority, because every eruption is different.

A common misconception is that volcanic ash is harmless dust you can just blow or sweep away. Doing exactly that puts the finest particles, the ones of most concern to health, back into the air. Working slowly, damply and with protection is more laborious, but it protects lungs, eyes and equipment.