Made Nagi / EPA
The eruption of Mount Agung on the island of Bali in Indonesia has emitted a huge plume of volcanic ash over the region, reaching more than 9km up into the atmosphere. This has disrupted flights over Bali and nearby islands. With the Aviation Colour Code listed as red (the most dangerous), air passengers are once again being stranded, just as many were following the 2010 Eyjafjallajökull eruption in Iceland, or during the Puyehue-Cordón eruption in Chile the following year.
The volcano is still erupting. This means it could become even more explosive – and as such flying nearby remains a risk. In addition, volcanic ash disruption is strongly influenced by wind direction and speed – so the evolving situation still needs to be carefully monitored by the local meteorological offices, and also the Darwin Volcanic Ash Advisory Centre that issues various ash warnings to the aviation sector.
The threat posed by a particular volcano’s ash depends on what it is made of, as no two eruptions are exactly alike. Volcanic ash consists of fragments of pulverised rocks, minerals and volcanic glass (silica) that varies dependent on the chemical composition of the magma.
Once this glass is sucked into jet engines, it is heated up and can accumulate as resolidified ash on the turbines, resulting in engine failure. The higher the concentration and density of glass, the more problematic the ash will be, although even fine ash has electrostatic charge that can lead to electrical failure.
Ash ahoy. Made Nagi / EPA
Therefore even at low concentrations, where the ash is barely visible to the naked eye (if at all), it can still pose significant threats and damage to aircraft. Ash also causes significant abrasion to the plane and its windows, while disrupting communications and damaging sensitive equipment.
Mt Agung has previously emitted sulphur-rich gases. Following its most recent major eruption in 1963, its emissions may have led to significant atmospheric cooling of 0.3℃ in average northern hemisphere temperatures. High levels of sulphur dioxide and carbon dioxide can also generate discomfort for aircraft passengers, leading to irritations to the eyes, nose, throat and increased airway resistance – as well as corroding the aircraft. Therefore these gas emissions pose a real risk to passenger comfort, as well as cooling of the tropical troposphere.