Volcanic ash and your health

Published 19 October 2026

Volcanic ash is not smoke: it is crushed rock and glass, and it needs different care. Here is what it does, how to protect yourself, and how Kabut reports it.

Ash is not smoke

Haze from fires is made of burning: soot, tar droplets and gases from plants and peat. Volcanic ash is made of rock. An explosive eruption shatters magma and the rock around the vent into fragments, and the finest of them are tiny pieces of volcanic glass with sharp, jagged edges. Ash does not dissolve in water, it can be carried hundreds of kilometres by the wind, and when it falls it settles as grit on everything.

Kabut keeps the two apart on purpose. On the map fire detections and the smoke they make are drawn in ember orange, while ash advisories are violet and volcanoes a brighter violet, so a plume over Java never reads as a fire front.

Indonesia has more active volcanoes than almost any other country, and several erupt often enough that ash is a regular event for the people near them: Merapi near Yogyakarta, Semeru in East Java, Sinabung in North Sumatra, Lewotobi Laki-laki on Flores and Ruang off North Sulawesi among them.

What it does to the body

For most people a light ashfall is an irritant rather than a danger, but it is an unpleasant one:

Eyes. Grit causes itching, redness and a scratchy feeling. Do not rub; rinse with clean water. People who wear contact lenses may be better off with glasses while ash is falling.
Nose, throat and airways. Fine ash causes coughing, a sore throat and irritation. People with asthma or other lung conditions often feel it more, and should keep their reliever inhalers close.
Skin. Some people get mild irritation; washing it off is usually enough.

The finest ash is in the same size range as the PM2.5 that Kabut reports, so a heavy ashfall can push a city's reading up as well. Seek care for breathing difficulty, chest pain or dizziness, as you would during heavy haze.

Protecting yourself

Stay indoors while ash is falling, with windows and doors shut.
Wear a respirator outside. An N95 or equivalent, fitted properly, filters fine ash the way it filters smoke; Masks for haze covers fit. A cloth mask is better than nothing against coarse grit, but does little against the fine fraction.
Wet ash before sweeping it. Dry sweeping lifts the finest particles back into the air. Damp it down lightly first, and wear a mask while cleaning.
Drive slowly or not at all. Ash cuts visibility and makes roads slippery, especially once it is wet.

Water and roofs

Protect water supplies. Cover water tanks and storage containers, and if you collect rainwater, disconnect the downpipes before ash falls so it does not wash into the tank.
Watch the roof. Ash is heavy, and wet ash much heavier. A thick layer can damage gutters and weak roofs. Clearing a roof is dangerous: ash is slippery, and falls from roofs cause injuries after ashfalls. Do it only if it is safe, with someone else present, or leave it to people equipped for it.

How Kabut reports volcanoes and ash

Two separate facts, from two separate sources, and neither implies the other.

Erupting comes from the Smithsonian Institution's Global Volcanism Program, which records whether a volcano's eruption is continuing.
Ash advisory comes from SIGMETs, warnings to aircraft published through the NOAA Aviation Weather Center. They describe where an ash cloud is, how high it reaches and which way it is moving.

A volcano can be erupting with nothing in the air, and ash can still be in the air after an eruption has paused, so the Volcano tab never counts volcanoes with an advisory as erupting.

For a city, Kabut decides one thing: whether it is under an ash cloud, whether one is heading toward it, or only whether one is nearby. It calls a cloud "heading your way" only within 300 km, so a volcano on the other side of the archipelago cannot claim ash is coming for you. Kabut does not estimate when ash will arrive. An advisory gives one direction at one height, which is not enough to promise a time. Methodology has the full detail.

Official alerts come from PVMBG

Kabut does not show the official volcano alert levels — Normal, Waspada, Siaga and Awas — because PVMBG, Indonesia's volcanology agency, publishes no public data feed for them. Check them at magma.esdm.go.id, and always follow instructions from local authorities, especially exclusion zones around a volcano. Those zones exist because of hazards far worse than ash: pyroclastic flows and lahars travel fast and give little warning.

This is general information, not medical advice.