• Aviation Colour Codes: Description of the Volcanic Alert Levels used by International Civil Aviation. 

Volcanic Alert Levels vary across the world


In the event of a volcanic crisis, there often is worldwide interest in status of the volcano, as represented by hazard alert levels for volcanoes, but with the exception of colour codes for aviation, currently there is no standardised international volcano alert levels system.  This is due to:

  • Wide variation in the behaviour of individual volcanoes and in monitoring capabilities, and
  • the different needs of populations, including different languages and symbolism of colours or alert levels. 

National volcano observatories have developed alert level protocols that are regionally variable and differ significantly in detail.


Caution about use of Volcanic Alert Levels

Organizations with interest in natural hazards are strongly cautioned against posting global volcano hazard alerts or eruption "forecasts" from amateur or other groups that do not originate from volcano observatories or regional agencies with both responsibility for and familiarity with those volcanoes.  Posting of hazard alert levels can have major public safety and economic implications, and should not be done lightly.  The data needed to provide alert levels come from onsite and remote monitoring instrumentation and are best evaluated by staff of regional volcano observatories who are the most familiar with activity at their volcanoes.  The responsible observatories and organizations are listed on this World Organization of Volcano Observatory (WOVO) website, and hazard administrators and others are directed to these organizations for information on current volcano alert levels.

Currently, there is no WOVO-endorsed source of worldwide Volcanic Alert Levels, with the exception of aviation colour codes. For those seeking a near real-time overview of current reported activity that incorporates the direct observatory sources in our WOVO directory, we recommend the Weekly Activity Reports compiled by the Smithsonian Institution's Global Volcanism Program (GVP) and the U.S. Geological Survey (please see the link in the menu to the left).  The GVP also produces quality-controlled, longer-term monthly summaries of volcanic activity and a catalog of the world's volcanoes and their eruptive histories.

Aviation Colour Codes

Numerous instances of aircraft flying into volcanic ash clouds have demonstrated the life-threatening and costly damages that can be sustained; consequently, civilian aviation authorities and the airline industry actively strive to avoid any aircraft encounter with airborne ash. To help aircraft avoid ash clouds, a universal volcanic alert level system for aviation has been developed as part of the International Airways Volcano Watch, a universal warning system co-ordinated by the International Civil Aviation Organization, a UN specialist agency. This system uses four colour codes. A universal system is especially suitable for the aviation sector because pilots, dispatchers, and air-traffic controller planning or executing flights over broad regions of the globe quickly need to ascertain the status of numerous volcanoes in multiple countries and determine if continued attention, re-routing, or extra fuel is warranted.

The colour codes reflect conditions at or near a volcano and are not intended to pertain to hazards posed downwind by the drifting ash - all discernible ash clouds are assumed to be highly hazardous and should be avoided. Furthermore, users must be aware that the aviation colour code should not be extrapolated to represent the hazards posed on the ground, which might be quite different.

Not all observatories currently provide information in this format, but where they do, the aviation colour code is currently defined as below (from http://www.icao.int/icaonet/dcs/9766/9766_cons_en.pdf ). A previous version that contained a specific reference to FL250 (25,000ft) was superseded in 2007.


Volcano is in normal, non-eruptive state.
or, after a change from a higher level:
Volcanic activity considered to have ceased, and volcano reverted to its normal, non-eruptive state.


Volcano is experiencing signs of elevated unrest above known background levels.
or, after a change from higher level:
Volcanic activity has decreased significantly but continues to be closely monitored for possible renewed increase.


Volcano is exhibiting heightened unrest with increased likelihood of eruption.
Volcanic eruption is underway with no or minor ash emission.
[specify ash-plume height if possible]


Eruption is forecast to be imminent with significant emission of ash into the atmosphere likely.
Eruption is underway with significant emission of ash into the atmosphere.
[specify ash-plume height if possible]


Volcano Observatory Notice for Aviation (VONA)

ICAO also is considering the use of a new structured message to deliver hazard information from Volcano Observatories to air-traffic controllers, dispatchers, pilots, and aviation meteorologists in a clear, concise, and easily used format. A prototype message format has been developed called a Volcano Observatory Notice for Aviation (VONA). This can be issued by an Observatory when the aviation colour code at a volcano is changed (up or down) or within a colour-code level when an ash-producing event or other significant change in volcanic behaviour occurs. The VONA would be sent (faxed or emailed) by the Volcano Observatory to the pertinent Area Control Centre, Meteorological Watch Office, and Volcanic Ash Advisory Centre. Its structured format is intended to help non-volcanologists in these offices more easily understand and use the volcanological information. The Alaska Volcano Observatory is in the process of testing the VONA in the United States, and ICAO is in consultation with the International Union of Geodesy and Geophysics (which sponsors WOVO) to progress things. WOVO will report on the further development and recommended use of the VONA.

Suggested format for a Volcano Observatory Notice for Aviation (VONA) for issuance by a Volcano Observatory when an aviation color code is changed (up or down) or within a colour-code level when an ash-producing event or other significant change in volcanic behaviour occurs:

(2) Issued: Universal (Z) date and time (YYYYMMDD/HHMMZ).
(3) Volcano: Name and number (per Smithsonian database at
(4) Current Aviation Colour Code:
(5) Previous Aviation Colour Code:
(6) Source: Name of Volcano Observatory (volcanological agency)
(7) Notice Number: Unique number with year
(8) Volcano Location: Latitude, longitude (in NOTAM format)
(9) Area: Regional descriptor (e.g., Cook Inlet, Alaska, USA)
(10) Summit Elevation: nnnn M (nnnn FT)
(11) Volcanic Activity Summary: Concise statement that describes activity at
the volcano. If known, specify time of onset and duration of eruptive activity.
(12) Volcanic Cloud Height: Best estimate of ash-cloud top in nnnn M (nnnnn
FT) above summit or AMSL (specify which). Give source of height data (ground
observer, pilot report, radar, etc.). "NIL" if no ash cloud is produced.
"NIL" if no ash cloud produced.
(13) Other Volcanic Cloud information: Brief summary of relevant cloud
characteristics such as colour of cloud, shape of cloud, direction of
movement, etc. Specify if cloud height is obscured or suspected to be higher
than what can be observed clearly. "NIL" if no ash cloud produced.
(14) Remarks: Optional. Brief comments on related topics such as monitoring
data, observatory actions, volcano's probable future activity (if
understood), etc.
(15) Contacts: Names, phone numbers (voice and fax), email addresses
(16) Next Notice: "Will be issued when conditions at the volcano warrant
changing the aviation colour code or when a significant volcanic event occurs
within the current colour code." Or, indicate if final notice for an event.


Cost recovery for Volcano Observatories for services to aviation

(added to this page April 2010)

The first version of a new guide to State Volcano Observatories about cost recovery from aviation with the warning system for volcanic clouds (the International Aviation Volcano Watch) has been put together and published on the WOVO site. Thanks to all the authors! We welcome feedback on this document - your comments will go to version 2.

At this stage the document is in English. Discussions are underway about creating a Spanish translation, which is seen as the first most useful translation to do.