Volcano Alert Levels and Aviation Color Codes, Explained

When a volcano makes the news, you'll hear it described two ways at once — maybe "raised to Watch" and "aviation code Orange." They sound like the same thing said twice. They aren't. They're two separate warning systems built for two completely different groups of people, and knowing which is which tells you a lot about what's actually happening.

You can see currently restless volcanoes on the LEV map with the Volcanoes layer switched on. Each one carries its current alert status, drawn from official volcano observatories.

Two systems, two audiences

The confusion is understandable, because most active volcanoes carry both a ground alert level and an aviation color code, and they don't always match.

The ground alert level is for people who live and work near the volcano. In the system used by the US Geological Survey and mirrored widely, it has four steps:

• Normal — the volcano is in its typical, non-eruptive background state.
• Advisory — signs of elevated unrest above background.
• Watch — heightened unrest with increased potential for eruption, or a minor eruption underway.
• Warning — a hazardous eruption is imminent, underway, or expected.

The aviation color code is for pilots and airlines, and it cares about one thing only: ash in the sky.

• Green — normal, non-eruptive.
• Yellow — elevated unrest, or returning to normal after activity.
• Orange — heightened unrest with increased eruption potential, or an eruption with little or no ash.
• Red — eruption imminent or underway with significant ash emission likely.

A volcano in a remote area might sit at aviation Red (it's erupting ash into busy flight corridors) while its ground threat is modest because nobody lives nearby. The reverse happens too. That's the whole reason for two scales.

Why aviation gets its own warning

It seems odd that planes get a dedicated volcano warning system — until you understand what volcanic ash does to a jet. Ash isn't soft soot; it's pulverized rock and volcanic glass. Pulled into a jet engine, it melts in the heat of combustion, then re-freezes onto the turbine, which can choke the engine into a mid-air flameout. It also scours windscreens opaque and clogs the sensors pilots rely on.

The hard part: ash is nearly invisible to the naked eye at altitude and doesn't reliably show up on the weather radar that planes use for storms. So a separate, satellite-fed early-warning system is the only way to keep aircraft clear of it. This is also why volcanic eruptions can ground flights across an entire region — when the satellite imagery shows an ash cloud drifting across a flight corridor, airlines reroute long before any pilot could spot it.

How the alert level is decided

A volcano usually announces itself before it erupts. Scientists watch for a cluster of warning signs: swarms of tiny earthquakes as magma forces its way upward (which is why volcano monitoring and earthquake tracking go hand in hand), the ground physically swelling or tilting, shifts in the gases venting from the summit, and rising heat visible from orbit. When several of these trend upward together, the observatory raises the level. When they calm, it lowers it again.

Reading it on the map

On the live map, switching on the Volcanoes layer shows the ones currently flagged, each tagged with its status. Pair it with the smoke and ash satellite layer during an eruption and you can watch the plume itself drift downwind — the same fusion view that makes wildfire smoke trackable.

The bottom line

Two scales, two audiences. The ground alert level (Normal → Warning) tells you how worried to be on the ground; the aviation color code (Green → Red) is a pilot's ash warning. When they disagree, that gap is telling you exactly where the danger lies — underfoot, or overhead in the flight paths.