Bali volcano: What does Mount Agung's likely eruption mean for travellers?

The volcanic alert level on the Indonesian island of Bali has been raised to the maximum, level four, as Mount Agung appears to be on the point of a major eruption.

With the airport closed, tens of thousands of tourists are stranded on the island. Many more are due to travel to Bali over the next few weeks; the island is a popular destination at Christmas and New Year.

Simon Calder provides answers to the key travel questions.

Mount Agung, in the east of the island, became more active in September. Magma, made up of molten rock as well as gases and fluids, has been moving up through the volcano. Starting on 21 November, plumes of steam and ash began to emerge from Mount Agung, reaching a mile into the sky. Now it appears that a full-scale eruption is imminent. Indonesia’s National Disaster Management Authority has raised the alert level to its highest, 4.

Communities close to the volcano are being moved, to try to avoid a repeat of the tragedy in 1963: last time Mount Agung erupted, around 1,600 islanders died.

Around 330,000 British nationals visit Indonesia every year, many of them heading to Bali – though Abta, the travel association, said: “There will only be a relatively small number of UK holidaymakers on the island at this time of year.

The main tourist areas, Kuta and Seminyak, are around 40 miles from Mount Agung, while the cultural hub of Ubud is about 25 miles away. The Foreign Office says: “Monitor local media reports, follow the advice of the local authorities and stay outside of the exclusion zone.” Australia’s foreign ministry says: “Past eruptions of Mount Agung have shown this volcano’s potential to cause significant impacts to the island of Bali, including the potential for widespread ash fall outside the declared danger area surrounding the volcano.”

Many holidaymakers will want to leave the island, but its only international airport, Denpasar, is closed until at least 7am, local time, on Tuesday morning. Many flights to and from Lombok airport, on the adjacent island, have also been cancelled. With dozens of flights grounded, thousands of tourists are stranded, and the numbers are growing with each cancellation.

When services re-start, priority will be given to people already booked on those departures rather than those whose flights have been cancelled.

Anyone booked on KLM’s daily departure to Amsterdam has to be looked after by the airline; under European passenger rights’ rules, EU carriers must provide accommodation and meals until they can fly you out.

Most travellers, however, are on South East Asian and Australian airlines, which have no such obligations. Tourists booked on a proper package holiday can ask their tour operator to provide care. Independent travellers may be able to get some recompense from their travel insurers. The Association of British Insurers said: "Check your travel insurance for the scope of any cover provided against cancellation and disruption caused by a volcanic eruption."

Some standard policies cover volcanic ash disruption, but many do not. For example, with Columbus "Ash Cloud Cover" is an optional extra. The firm says: "No claims arising as a result of volcanic ash are eligible without this upgrade." Note that anyone who took out the insurance policy after Mount Agung started rumbling may have their claim rejected.

The complete shutdown of the skies in 2010 after the Icelandic volcano erupted was seen as excessive: tens of thousands of flights were cancelled; eight million individual journeys were disrupted and airlines collectively lost around half a billion pounds. But the International Civil Aviation Organization (ICAO) spells out the dangers succinctly: “Volcanic ash consists mostly of sharp-edged, hard glass particles and pulverized rock. It is very abrasive and, being largely composed of siliceous materials, has a melting temperature below the operating temperature of modern turbine engines at cruise thrust.

”A volcanic ash cloud may be accompanied by gaseous solutions of sulphur dioxide (which when combined with water create sulphuric acid), chlorine (which when combined with water create hydrochloric acid) and other chemicals which are corrosive to the airframe and are hazardous to health.

“Given these facts, it is self evident that volcanic ash in the atmosphere may pose a serious hazard to aircraft in flight. Thus, aircraft should avoid volcanic ash encounters.”

In 1982, a British Airways Boeing 747 inadvertently flew through a plume of volcanic ash over Indonesia, on a flight from Kuala Lumpur to Perth, and all four engines shut down at 37,000 feet. Eventually an engine was restarted and the aircraft landed safely.

The Darwin Volcanic Ash Advisory Centre in northern Australia, which is responsible for advising aircraft in the region, issued a red alert warning of continuous volcanic ash to 30,000 feet. There are also reports of volcanic ash on the ground at Denpasar airport.

The fastest track between Singapore and Kuala Lumpur to Sydney goes directly over Bali, therefore potentially affecting UK travellers to Australia. In practice the chosen route will depend on a range of factors, notably predicted wind speeds. But even if an ash cloud starts to form, airlines could tolerate a diversion of up to 500 miles without too much trouble. Flights on 27 November were typically delayed by a few minutes.

Singapore Airlines, which carries many British travellers to and from Bali, is allowing anyone with bookings between now and 4 December to request a refund, or to postpone their trip to a future date up to the end of January 2018.

The airline says that passengers requesting refunds should not contact the call centre immediately because of high call volumes.

If you have booked through an agent, then your contract is with them, and they will need to make changes on your behalf.

Anyone who chooses a new destination should be able to switch travel insurance can usually be transferred to cover the new location.

At present airlines and holiday companies are unlikely to offer alternatives: they are dealing with imminent departures and waiting to see what happens with Mount Agung over the next week or two. Unless and until the Foreign Office warns against travel to Bali, there is no legal obligation for tour operators to provide refunds or alternative holidays.