Villagers walk in the grounds of a temple as Mount Agung erupts behind them. – Reuters photo
KRAKATOA’S eruption in 1893 is well documented as its explosion ejected volcanic ash to a height of 32,000 metres.
Such atmospheric pollution saw a decrease in solar radiation received on the earth’s surface by up to 20 per cent and a sequence of the coldest and wettest years followed in Europe.
Britain recorded many of its wettest and coldest summers ever. All this coincided with the time of that volcano’s massive eruption of ash into the stratosphere and upper atmosphere.
In 2010, the Icelandic volcano, Eyjafjallajokull, erupted driving ash upwards to 8,000 metres in the atmosphere, from April to June, causing massive disruptions to air traffic. I well remember being redirected, whilst on a flight from KLIA to London Heathrow, to Charles De Gaulle airport in Paris. The plane and all passengers sat on the tarmac there for nearly two hours until London airport reopened. This explosive volcanic eruption was so high that its silica rich ash-clouds reached even into the jet stream, thus disrupting aircraft movements.
Today, our greatest concern should be for the people of Bali, who are living under the clouds of the second highest peak in Indonesia, Mount Agung. This volcano currently peaks at 3,142 metres above mean sea level.
The bigger picture
Locally known as Gunung Agung or ‘Great Mountain’, this stratovolcano has featured highly in the international media in the last six months. Situated just off the Eastern tip of Java, it is in a region of tectonic plate activity where the slowly converging Eurasian and Indo-Australian plates meet. This is an oversimplification of tectonic plate movements, for many are fractured into smaller plates moved by molten magmatic intrusions from deep below the Earth’s crust, in the Mantle-layer.
Mount Agung’s last eruption was in March 1963, when volcanic ash was emitted to a height of 4,000 metres above the summit. In May that year, the column of ash, on a second eruption, lifted dust particles to 10,000 metres into the atmosphere. These dramatic events saw intense devastation, particularly west of the summit where ash and other pyroclastic material settled up to 12km away. Red hot lava spilled over the crater walls for up to 7km, moving at 60km per hour downslope with the eventual collapse of the crater’s rim.
For the Balinese it was a devastating and horrific scenario. Over 75,000 people were evacuated; 1,500 persons and as many, if not more, animals died from this eruption. Because of heavy rainfall, the landed ash turned to mud causing ‘lahars’ or mudflows, which slid down the volcano’s slopes to engulf villages. This is recorded as a ‘Plinian’ style eruption with nuees ardentes (glowing clouds in the sky), containing sulphurous gases. It was explosive.
Mount Agung in 2017
In early August, earthquakes were recorded in the immediate vicinity of the volcano with increasing intensity in the following weeks. In September, these intensified together with more audible rumblings, leading 130,000 people to evacuate their homes for sports centres and community buildings. At this time, there were over 800 earthquakes a day but by the end of October there was a significant fall in the volcano’s activity.
Early November saw a revitalisation in volcanic activity with an ash cloud up to 3,800 metres, and another 29,000 people were housed away from the evacuation zone. On Nov 25, a huge surge of deep-seated magma within the crater spewed out ash upward to a height of 4,000 metres.
This ash plume drifted in a southern direction because of the prevailing winds. The following day, yet another blast came from the volcano and drifting south and south eastwards towards the international airport of Ngurah Rai, near Denpasar.
On Nov 27, the height of the volcanic plume reached upwards to a height of over 9,000 metres and 59,000 passengers were stranded before the airport was reopened on Nov 29.
On Red Alert
Globally, there are nine international Volcanic Ash Advisory Centres (VAAC). Darwin, Australia, is one of these that advises airports in the Southeast Asia region as to the toxic fumes of volcanoes and the chances that silica ejected volcanic ash may crystallise into glass onto an airliner’s jet turbines.
On Nov 26, the alert level for the volcano reached Grade 4 on the Volcanic Explosive Index (VEI). This index was devised by USA geologists, in 1982, following the super-volcanic eruption of Mount St Helens, in Washington State, two years previously.
The index is on a logarithmic scale from 1 to 8 with each number on the scale 10 times more potent than the previous one. The scale is based upon how much volcanic matter is ejected, to what height in the atmosphere and how long a particular blast is likely to last. On Nov 28, the number of evacuees from Mount Agung rose to 39,000 relocated in 225 centres. The following day the airport was reopened.
What next?
A volcano is not unlike a bottle of fizzy lemonade. When its cap is on the gases are contained, but unscrew the cap and an explosion may occur. At the time of writing, Mount Agung is classified, in volcanologist’s terms, as being in a phreatic state, producing ash, sulphurous gases, and steam.
Any minute it may move into a phreomagmatic state with outpourings of lava from its vast crater, which is 900 metres wide and 200 metres deep with the capacity to contain 60 million cubic metres of lava. Once this cauldron is filled, the lava will rapidly spill over the rim in a blocky form, with sudden avalanches burying all and sundry in its path.
Already its new lava dome has developed within its old crater rim. In the first week of December, the ash plume looked like the mushroom shaped plume of an atomic blast and reached 2,000 metres up into the atmosphere.
There are still 40,000 villagers living precariously, inside the exclusion zone on this mountain, facing the constant fear of the loss of their houses, fields, livestock and their own lives. The volcano meanwhile continues to swell, like the inflation of a balloon until it reaches a state of entropy.
On Christmas Eve, Mount Agung began erupting again with as clouds reaching 2.5km. On Thursday, Mount Agung continued erupting with volcanic ash being shot up as high as 1km.
Waiting game
The economic effects of these eruptions are being felt locally in agricultural production and in the tourist trade. Honeymooner’s dreams have been dashed and a normal December to January tourist boom from European and Australian visitors has received setbacks with many countries issuing warnings to potential visitors. Much will depend on the wind directions and the intensity of the rainfall.
Rest assured visitors, all pilots are briefed before departure, for short and long haul flights, of the atmospheric conditions at different altitudes on their proposed routes. The information on Balinese volcanic ash is provided by VAAC in Darwin in order to keep aircraft in this area clear of volcanic ash.
The world’s largest supercomputer was this year installed at the UK’s Meteorological Office in Exeter. This cost approximately RM490 million, covering the size of several football pitches and processing 16 quadrillion calculations per second.
Recently, I attended a lecture given by Rob Varley, CEO of this governmental organisation and 1st vice-president of the World Meteorological Organisation. His theme was simply, ‘Putting scientific knowledge into action!’ His office provides essential information daily to governmental services worldwide on the present and near future state of the atmosphere to include recent satellite imagery and measurements of the height and content of volcanic plumes.
In hindsight, preventative action certainly speaks louder than words. While we still, with bated breath, await Gunung Agung’s supervolcanic blast, we know that Indonesia and other adjoining nations have emergency plans and rescue organisations on standby. I, for one, will never ever again moan about my flight being grounded because of volcanic ash pollution in the upper atmosphere. I still dream of visiting Bali sooner rather than later.