Ash travels with the wind, and wet ash is far heavier than people expect. Here is what ashfall does to a building and what to check.
Lava flows follow the ground and stay near the volcano. Ash does not. It goes up, gets into the wind, and lands wherever the wind takes it, sometimes tens or hundreds of kilometres away.
That is why the distance on a hazard report is only half the ashfall story.
Not soft. Volcanic ash is finely fragmented rock and glass. It is abrasive, it is slightly acidic when wet, and it does not dissolve or blow away the way ordinary dust does.
Dry ash is heavier than most people assume. Wet ash is much heavier still, because it absorbs water and compacts. That combination, ashfall followed by rain, is the one that collapses roofs.
Roofs. Accumulated ash is a load the roof was probably not designed to carry, especially light metal roofing on long spans. Collapse is the main cause of injury from ashfall.
Gutters and drains. Ash washes off the roof and blocks everything downstream, which turns into water damage.
Water supply. Open tanks and catchment systems get contaminated. Ash-laden water clogs filters and damages pumps.
Machinery and electronics. Abrasive fine particles get into aircon units, generators, pumps, and vehicles.
Health. Fine particles are a respiratory hazard, and the recommendation to stay indoors and wear a proper mask comes from the health authorities, not from us.
Agriculture. Crops are smothered and livestock is affected by ingesting ash with feed.
A hazard report gives the distance from your exact coordinates to the nearest mapped volcano. See the volcanic proximity brief.
That is a fixed, factual input and it is genuinely useful for the near-field hazards: pyroclastic flow, ballistic projectiles, and lahar in the channels draining the volcano.
For ashfall it is a weaker guide, because the controlling variable is wind direction on the day, not distance. The Taal eruption in January 2020 put ash across a wide area of southern Luzon, well beyond the immediate surroundings, and it did so because of where the wind was blowing.
PHIVOLCS is the authority on alert levels, danger zones, and ashfall advisories. Check them directly for any property near a volcano; a screening reports a distance, not a status.
Before anything happens:
During ashfall:
After, and this is the important one:
PHIVOLCS is the authority on volcanoes: alert levels, danger zones, ashfall advisories, and evacuation. A hazard screening reports the distance from your point to the nearest mapped volcano and terrain-based layers around it. It does not forecast ashfall, model wind, or assess a roof. That last one is a licensed structural engineer's job and it is the one that keeps a house standing.
CheckHazard does not replace a professional geotechnical or engineering survey.