I was in Canada when the rumblings began. Like so many other Bali residents I became an amateur vulcanologist, obsessively checking daily seismic activity and monitoring the Facebook earth tremor updates. I filled my suitcase with N95 masks and goggles to bring back instead of the usual interesting groceries.

At time of writing we still don’t know when/whether Gunung Agung will erupt. According to the Oxford University Earth Sciences together with the Indonesian Volcanological Survey and the Earth Observatory of Singapore, it has been blowing its top for about 5,000 years at approximately 100 year          intervals. If it follows its pattern from 1963 there could be a slow lead-up to a small eruption, followed a few months later by a major bang, followed in another few months by another bang, then several months of grumbling and belching and lots of volcanic ash. Or not. No one really knows.

I’m back on the ground now and puzzling about how to ash-proof a house specifically designed for good ventilation. There’s no glass in my windows and much of the space is outdoors. My small bedroom the only place of sanctuary if there’s an ash dump. I try to imagine the large windows and vents all covered in plastic and unbleached cotton as I shelter there with three dogs, three hens, a parrot, two lovebirds, five pigeons and the turtles if I can catch them.

I’ve spent many hours researching volcanic ash and trying to find its positive aspects, which are very few. Pray hard that the winds will remain favourable for a very long time and blow most of it away over the sea. Because aside from a few minor commercial uses it’s just a bloody nuisance when it’s not downright dangerous and destructive.

First the good news.  Volcanic ash (tephra) can be added to soap as an exfoliant. It can be used as an abrasive in mechanics.  Very fine ash is used in some toothpaste and minus-200-mesh ash can be used for polishing plate glass. You could buy it on Alibaba for $1/kg but don’t rush; soon you can have all you want for free.  If you’re willing to wait a few hundreds of thousands of years, the ash may become bentonite clay.  Apparently, adding water to the clay gives it a negative electric charge, which in turn removes toxins from the body. So it makes a great face and body mask for your (by then) rather desiccated epidermis.

There can be agricultural benefits but I’ve had difficulty finding hard data.  Volcanic ash is rich in minerals but these can take months or years to leach out and nourish the soil. According to Ratih Nurruhliati, a Sundanese geologist who specialises in volcanoes, there are many variables.

“Tephra contains primary minerals which have an abundance of nutrients,” she told me. “Over time, chemical and biological weathering, the ashes will release the nutrients and the ash will increase its surface area, enabling it to hold more nutrients and water. In addition, volcanic ash has the capacity to sequester a high amount of carbon (taking carbon out of the atmosphere and fixing it in the soil).

“The breakdown of volcanic ash will differ from place to place.  If it rains right after the eruption, it can be quite rapid. It could take months or years depending on the weather conditions and the make-up of ash. I think in the case of the Galunggung (Java) eruption, after nine months of eruptions it was another six months before the farmers could start to plant.”

But even a few centimetres of tephra can be an agricultural disaster. The ash inhibits transpiration and photosynthesis in plants. Plant survival depends on ash thickness, ash chemistry, compaction of ash, amount of rainfall, duration of burial and the length of plant stalks at the time of ash fall.  The acidic nature of ash will lead to elevated soil sulfur levels and lowered soil pH, which can reduce the availability of essential minerals and alter the soil’s characteristics so that crops and plants will not survive. No plants, no livestock.

Land rehabilitation after ash fall depends on the ash deposit thickness and may require mixing the deposit with the buried soil or removing the ash and applying topsoil. Or the land might eventually recover on its own. After the 2014 eruption of Mount Sinabung in North Sumatra, some of the ashes were being colonised by lichens and grasses after three years.

“This natural phenomenon renews the soil, but it takes time for the ashes to weather,” says Dian Fiantis from the University of Andalas in Padang. “We need to work on solutions that will hasten the rate of soil formation.”

But if you happen to be a builder, volcanic ash is your friend.  The ancient Romans used it to make concrete walls and buildings that are still standing today.  They found that mixing finely ground volcanic pumice or ash with quicklime combined with sand and aggregate made a concrete that will even set underwater. The raw material probably came from the nearby volcano of Vesuvius.

The Greeks also used cement made with volcanic ash and some examples dating from the 6th or 7th century BC stillexist on Rhodes. A similar concrete was used by the ancient Egyptians when building the pyramids and the sphinx at Giza, and the Minoans also made cement using the ample supplies of volcanic ash and limestone found on Crete. So hopefully someone out there is figuring how to use tephra during the post-eruption reconstruction.  There will be lots of it.

Volcanic ash can have an impact on electricity, causing disruption to electric power supply systems at all levels of power generation, transformation, transmission and distribution.  See for the technical details. So be prepared in case the power goes out.  The same source explains how telecommunication and broadcast networks can be affected by volcanic ash,   so we may be looking at a period of withdrawal from our devices.

You don’t want to get it in your computer, air conditioner, car engine, water pumps or lungs either.  Ash particles of less than 10mm diameter suspended in the air are inhalable, and people exposed to ash falls have experienced respiratory discomfort, breathing difficulty, eye and skin irritation, and nose and throat symptoms.  Most of these effects are short-term and are not considered a significant health risk to those without pre-existing respiratory conditions. There have been no documented cases of silicosis developed from exposure to volcanic ash, but make sure you and your staff have N95 masks and goggles in case of an ash fall.

After reviewing countless papers by engineers, medics, historians and agronomists, I can confidently report that there is no lighter side to volcanic ash. Heaven knows I’ve looked for it.

For most people reading this, the eruption will be inconvenient. For the tens of thousands of families whose only home and assets are on that mountain, it will be devastating. If Gunung Agung does blow, and it seems likely, the government and NGOs will be finding ways to help them survive and move forward over the next year or so. We can all be part of this process.

Stay tuned, and pray for a fair wind.



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