What each volcano alert level actually means

When an observatory announces that a volcano has moved to “watch”, most people take away two things: something changed, and it sounds bad. What almost nobody knows is which specific decision belongs to that step, or why the same volcano sometimes carries two different colour labels on the same day.

The four steps on the ground

The USGS uses a four-level scale for the hazards that affect people living around a volcano.

Level	What is happening	What it means for you
Normal	Typical background activity, no sign of change	Know your route and your hazard map
Advisory	Activity above known background, or easing down from a higher level	Check bag, fuel and contacts
Watch	Escalating unrest with increased eruption potential, or an eruption underway with limited hazards	Bag ready, plan agreed, follow the notices
Warning	Hazardous eruption imminent, underway or suspected, with significant threats	Leave as local authorities direct

The aviation scale runs separately, and it is not talking to you

In parallel, the same volcano carries an aviation colour code — green, yellow, orange, red — describing ash in the atmosphere. It exists because volcanic ash melts inside jet engines and can shut them down, so airlines need their own signal.

The two scales often move together, but not always. A volcano can sit at aviation orange because of an ash plume heading toward a flight corridor while the ground level stays at watch, because none of it is falling on towns.

If you read a notice and see two labels, look at the one that matches your situation: on the ground, the alert level; in the air, the colour.

What to do at each step

At normal. This is when you do the boring work: find your volcano’s hazard map, learn whether your house sits in a valley draining it, and agree where the family meets if phones are down.

At advisory. Check what you should already have. Fuel tank above half, bag packed, medication counted, respirators in the house. Nobody needs to sleep elsewhere yet.

At watch. This is where decisions get made with a clear head, because there is still time. Anyone with limited mobility, a late pregnancy or dependence on powered medical equipment should leave at this step rather than the next: at the next one the roads are already full.

At warning. You do what local authorities say, by the route they name. This is not the moment to be deciding anything.

Where to see your volcano’s level

Observatories publish the level of every monitored volcano and update it with each notice. The ZonaProtec monitor shows the current level of USGS-monitored volcanoes near the point you search, with its aviation code and a link to the observatory notice that issued it.