Reading VAAC alerts as a flyer

Why ash grounds aircraft

Volcanic ash is glass shards and mineral fragments. When ingested into a jet engine at cruise temperatures (around 1,400 °C), the glass melts in the combustor and re-solidifies on the cooler turbine blades, glassing them shut. The engine can flame out. The 1982 British Airways Flight 9 incident (a 747 over Indonesia that lost all four engines in a Galunggung ash plume, glided 25,000 feet, then restarted engines below the ash layer) is the textbook event. The 1989 KLM 867 over Mount Redoubt Alaska is similar.

Ash also abrades the fuselage, blocks pitot tubes (airspeed sensors), and damages avionics. Even minor ash exposure can require expensive engine inspection.

Aviation regulators therefore route aircraft around ash plumes. When ash plumes are extensive and persistent, large regions of airspace close, sometimes for days. The 2010 Eyjafjallajökull eruption closed European airspace for 6 days; an estimated 10 million travellers were stranded.

The nine VAACs

ICAO designates nine Volcanic Ash Advisory Centers, each responsible for monitoring a defined region. Each VAAC issues Volcanic Ash Advisories (VAAs) in plain English plus Significant Meteorological (SIGMET) bulletins that aviation uses operationally.

• London VAAC: Iceland, North Atlantic Europe. The most-tested VAAC after the 2010 Eyjafjallajökull event.
• Washington VAAC: Eastern Caribbean, parts of Central and North America east of the Rockies.
• Anchorage VAAC: Alaska, Aleutian Islands. Frequently busy (Aleutian volcanoes erupt often along the Anchorage-to-Asia great circle routes).
• Tokyo VAAC: Japan and Korean Peninsula, parts of the Western Pacific.
• Darwin VAAC: Indonesia, Papua New Guinea, northern Australia. Probably the busiest VAAC by volume, given Indonesia’s 130+ active volcanoes.
• Wellington VAAC: New Zealand and Southwest Pacific.
• Buenos Aires VAAC: Southern South America (Chile, Argentina, Patagonia).
• Toulouse VAAC: Africa, the Atlantic and Mediterranean fringes.
• Montréal VAAC: Canada.

Each VAAC publishes bulletins on a defined web feed; some have dedicated apps. For travellers, the practical interface is via airlines (who consult VAACs operationally), the flight-tracking apps (FlightAware, FlightRadar24), and the relevant national weather service.

Aviation colour codes

ICAO uses a four-colour aviation code for volcanic activity:

• Green: volcano is in normal, non-eruptive state.
• Yellow: volcano shows signs of elevated unrest above background level.
• Orange: volcano is exhibiting heightened or escalating unrest with increased potential of eruption.
• Red: eruption is imminent or underway with significant ash emission into the atmosphere.

These map roughly to the country-specific volcano alert ladders. Red is when aviation impact begins.

What the alert actually triggers

• Airspace closures: when an ash plume is detected at flight altitudes, the relevant FIR (Flight Information Region) closes affected blocks of airspace. Aircraft route around or hold; flights are cancelled or diverted.
• Airport closures: ashfall on an airport grounds operations until cleared. The 2011 Puyehue-Cordón Caulle eruption closed Bariloche airport for weeks and affected Buenos Aires intermittently. Anchorage closures from Aleutian eruptions are routine.
• Cancellation cascades: aircraft and crew are positioned hub-and-spoke; one regional closure cascades globally. The 2010 Eyjafjallajökull closure rippled to Asia and North America within hours.
• Engine inspection: aircraft that have transited near plumes require post-flight inspection; individual aircraft out of service for hours to days.

The rebooking decision

When you are caught in a VAAC-driven flight disruption, the practical decisions:

• Watch the airline app, not the news: airlines update operationally as VAAC bulletins refresh. Push notifications via the airline app outpace news cycles.
• Rebooking priority: the longer you wait, the further back you are in the queue. The first 6 hours of a disruption are usually rebookable; after that, the seats fill.
• Alternative routings: consider rail or bus for short-distance recovery (e.g. Heathrow to Frankfurt by Eurostar via Brussels if a UK-Germany route closes). In the 2010 European closure, many travellers rode buses across Europe to reach onward connections.
• Hotel and meal allowances: under EU Regulation 261/2004, EU departing or arriving flights cancelled for extraordinary circumstances still oblige the airline to provide meals, accommodation, and rebooking at no extra cost. Most other jurisdictions less generous; check your airline’s policy.
• Insurance trigger: travel-disruption insurance varies on volcanic-ash coverage. Many policies after 2010 explicitly include or exclude it. Check before you fly.
• Stay near the airport: if rebooked within 48 hours, do not commit to multi-day excursions far from the airport. Conditions can clear faster than expected.
• Family check-in: agree before any trip how often you check in during disruption; satellite SMS options if cell networks saturate.

Reference disruption events

• 2010 Eyjafjallajökull (Iceland): European airspace closed 14 to 20 April. Around 10 million travellers stranded. IATA loss estimate USD 1.7 billion. The event drove a fundamental reconsideration of ash-tolerance limits.
• 2011 Grímsvötn (Iceland): smaller disruption, mostly Northern Europe.
• 2011 Puyehue-Cordón Caulle (Chile): ash circled the Southern Hemisphere; Australian and New Zealand airports closed multiple times; Patagonia tourism impact for months.
• 2015 Calbuco (Chile): similar Southern Hemisphere effects; Bariloche and Buenos Aires disruptions.
• 2017-2018 Volcán de Fuego (Guatemala): ash impact on Guatemala City airport; regional cancellations.
• 2018 Kilauea (Hawaii): localised disruption to Hilo and Kona airports.
• 2021 Cumbre Vieja (Canary Islands): La Palma airport closures for weeks.
• 2022 Hunga Tonga (Tonga): South Pacific disruption; the eruption also produced a pressure-wave tsunami.
• 2023 Mount Marapi (Indonesia): Padang airport disruption.
• 2023 to 2026 Reykjanes Peninsula sequence (Iceland): multiple eruptions, mostly low-explosivity, with limited aviation disruption thanks to the basaltic effusive character. Major airport remained operational.

Country brief

• Iceland: London VAAC; 2010 reference event; 2021-2026 Reykjanes sequence largely effusive with minimal aviation impact.
• Indonesia: Darwin VAAC; busiest region; PVMBG aviation colour codes published on MAGMA Indonesia app.
• Philippines: Darwin VAAC plus PHIVOLCS; Mayon, Taal, Pinatubo aviation impacts.
• Japan: Tokyo VAAC; Sakurajima continuous ash; Mt Fuji dormant.
• Chile: Buenos Aires VAAC; Patagonia eruption disruption recurring; SERNAGEOMIN.
• Italy: Toulouse VAAC; Etna continuous activity; Catania airport closures recurring; Stromboli.
• United States: Anchorage VAAC (Aleutians) and Washington VAAC (continental).
• Costa Rica: Washington VAAC; San José airport sometimes affected by Poás and Turrialba.
• Mexico: Washington VAAC; Popocatépetl produces routine ash to Mexico City airspace; CENAPRED publishes Spanish-language alerts.

One more time

Ash is fatal to jet engines, so airspace closes around plumes and airports close under ashfall. Nine VAACs cover the world; most travellers interact with the system via airline apps and FlightAware. The colour codes (green/yellow/orange/red) map to the country volcano alert ladders. When caught in a disruption, watch the airline app, rebook fast, know your EU 261 rights if applicable, consider rail recovery, and stay near the airport. The Field Manual’s volcanic eruption guide covers the ground-hazard side; this guide is the aviation-disruption companion.