Table 1 Volcano level of alert colour codes for aviation (extracted from ICAO Doc 9766 (Second Edition), Table 4-4) (ICAO, 2004)

Green

Volcano is in normal, non-eruptive state.

or, after a change from a higher alert level:

Volcanic activity considered to have ceased, and volcano reverted to its normal, non-eruptive state.

Yellow

Volcano is experiencing signs of elevated unrest above known background levels.

or, after a change from a higher alert level:

Volcanic activity has decreased significantly but continues to be closely monitored for possible renewed increase.

Orange

Volcano is exhibiting heightened unrest with increased likelihood of eruption.

or

Volcanic eruption is underway with no or minor ash emission.

[specific ash-plume height if possible].

Red

Eruption is forecasted to be imminent with significant emission of ash into the atmosphere likely.

or

Eruption is underway with significant emission of ash into the atmosphere.

[specific ash-plume height if possible].