Under Taal volcano’s ash


Volcanic ash and agriculture don’t mix. In early January, the Philippines’s Taal volcano, one of the world’s most dangerous, suddenly erupted, causing significant damage to crops and brutally depriving local people of their livelihood. Pierre Delmelle and Noa Ligot (Earth and Life Institute) travelled there to assess the losses and pursue full-scale experiments. Ultimately, their research aims to make recommendations for farmers and local authorities.

12 January 2020. Taal volcano, located on the island of Luzon in the Philippines, erupts. Less than a month later, Pierre Delmelle, professor in the Faculty of Bioengineering and member of the Earth and Life Institute, and PhD student Noa Ligot, board a plane. Destination: agricultural land around Taal volcano. ‘I’m captivated by the close relationships between agriculture and volcanoes,’ Prof. Delmelle says. ‘It’s a very dynamic interface. In active volcanic regions, agriculture is a major sector of economic activity because the soils formed on ash deposits are often fertile. Ironically, the ash responsible for its fertility can also lead to its destruction.’ In recent years, Prof. Delmelle has been interested in family farming on the flanks of Ecuador’s recently active volcanoes, Tungurahua and Cotopaxi. Then Taal, one of the world’s most dangerous volcanoes, erupted.

Rarely studied subject

In the Philippines, Prof. Delmelle had a specific objective: to document the impact of volcanic ash on crops. ‘Agriculture plays a central role in the definition of volcanic risk,’ he explains, ‘because the fertile lands surrounding volcanoes are high-density population areas. Globally, around one billion people are potentially subject to volcanic risk. The impacts of an eruption on agriculture have direct and harmful repercussions on the livelihoods and well-being of farming communities, but the resumption of agriculture after the eruption will also allow them to recover. Agriculture is therefore an essential element to consider in reducing the risk of disasters linked to volcanic activity, but the subject is rarely studied..”

Deposits on crops

Our UCLouvain duo wanted to help overcome this lack of knowledge by spending ten days in the area affected by Taal’s eruption. ‘We met the village communities in order to collect information on the effects of ash fall on crops,’ Prof. Delmelle says. ‘The farmers took us to their fields and we encouraged them to show us the damage. By cross-checking the information they gave us, a first picture of the situation could be drawn.’ Prof. Delmelle and Ms Ligot saw the damage to corn, cassava, tomato, and pineapple crops. During an explosive eruption, a volcano sends a plume of gas and ash into the atmosphere. Wind disperses the material and causes ash deposits. ‘In the areas most affected by Taal’s eruption, deposits accumulated several tens of centimetres,’ Prof. Delmelle says. The vegetation suffers under the weight of the ash, which sticks to leaves, sometimes causing collapse. Otherwise, leaves covered in ash no longer receive enough light to carry out photosynthesis. It appears that even if the deposit is thin, ash salts can ‘burn’ the foliage and lead to plant death. This reaction has not yet been elucidated.

Wider damage

Fields directly exposed to Taal’s ash fall were ravaged. Sheds, churches, homes and livestock shelters collapsed due to the rapid accumulation of ash on roofs. The ash was saturated with water, which greatly increased its weight (see box). Even mango trees in the prime of life collapsed. There were no human casualties, but more than 200,000 people within a radius of 14 km were evacuated, abandoning livestock, crops, and personal property. Further away from the volcano, eruption impacts are less apparent but nevertheless very real. ‘Crops suffered damage which resulted in partial or total crop loss. Fruits and vegetables covered with only a thin layer of ash were unsellable. This is a total loss for farmers, and they won’t receive any compensation.

Initial observations

After delimiting the area affected by ash fall, Prof. Delmelle and Ms Ligot systematically identified the impacts, taking photos of crops, measuring ash thickness, compiling farmer explanations, and taking samples. With the help of farmers and local authorities, they made an initial estimate of the expected yield loss for each type of crop. In order to establish a spatial distribution of the impacts, the information was entered into a geographic information system. On site, certain trends already appeared. ‘We found big differences depending on crop type, plant growth stage, and farmer actions immediately after the eruption (watering or shaking the plants). We also observed an encrustation of ash, probably linked to the high water content initially present in the deposit. The leaf is then literally trapped by this volcanic cement and condemned to die."

High salt content

Back in Belgium, our two scientists hastened to analyse their samples, before the coronavirus crisis slowed them down. The first discovery concerns the salts in the ash. ‘In some samples,’ Prof. Delmelle says, ‘the concentration of salts rich in sulphur is extremely high. This would explain why, far from the volcano, we still observe significant impacts on crops despite the deposit’s thinness.

Continue research both here and there

As soon as possible, the duo will return to the laboratory to continue analysis. In the meantime, Ms Ligot and Prof. Delmelle are starting a full-scale experiment using the facilities of Marbaix farm, a UCLouvain centre for agronomic experiments, where they planted potatoes and corn. In a few weeks, they will simulate a volcanic eruption by spreading on the crops half a tonne of ash they brought from a lava stone quarry in Germany. They will then monitor crop response to better quantify the effects of ash deposits on growth and production. ‘And the project doesn’t stop there,’ Prof. Delmelle says. ‘We’ve just received funding from ARES [the Wallonia-Brussels Federation’s Academy for Research and Higher Education] and Belgian Development Cooperation to deploy a synergy project in the Taal region. With a Belgian NGO and its Filipino partner, we’ll continue our collaboration with local farmers. The idea is to set up a network to monitor the longer-term impacts on agriculture of Taal’s eruption. Just like at the Marbaix farm, with the farmers’ help we’ll simulate an ash fall on crops, but this time under the environmental conditions of the Philippines. We hope to collect new data that will help to better quantify ash impacts.” 

Making recommendations

Several motivations drive all this research. ‘First, we want to broaden the field of knowledge in an area that is still too little explored,’ Prof. Delmelle explains. ‘At the same time, we’re developing a model that would predict the yield loss of a given crop based on plant development stage and ash characteristics. By combining this model with volcanic plume dispersion simulations, we hope to make recommendations to farmers and local authorities so that they prioritise certain crop types in risk areas.’ The primary objective is to identify, with local actors, strategies that can reduce the risk of disaster for agrarian populations subject to volcanic hazards.


Taal close-up

Taal is a Filipino volcano in the south of the island of Luzon, some 60 km south of the capital Manila. It’s one of the planet’s most active volcanoes. Since 1572, Taal has erupted approximately 40 times.

In the heart of a caldera

The peculiarity of this volcano is that its eruptive centre is located in the middle of a large caldera (~ 15 x 20 km) filled by a deep lake, Lake Taal. A caldera is a circular or elliptical depression at least two kilometres in diameter, which was formed by an explosive eruption involving huge volumes of magma, that is, molten rock. Taal is particularly dangerous because the meeting of magma and water increases the eruption’s explosiveness and allows the formation of base surges. These are turbulent flows highly charged with gas and fragmented magma which are projected at very high speed radially from the volcano. This type of phenomenon is responsible for lacustrine tsunamis that devastated the banks of Lake Taal.

An overpopulated area

LTaal is one of the planet’s most dangerous volcanoes. With a density of around 2,000 inhabitants per km², the Taal region is one of the most densely populated in the world. Agriculture is omnipresent and volcanic risk is particularly high.

12 January 2020

Taal’s eruption on 12 January 2020 was sudden, surprising residents, who were going about their business when the first ash fell. The volcano’s activity is closely monitored by the Philippine Institute of Volcanology and Seismology. Warning signs had been observed in the months before the eruption. However, the huge body of water surrounding the volcano greatly complicates the interpretation of geophysical and geochemical signals, and no one could have predicted the eruption. It in fact involved only a small volume of magma; most expelled material was old rock blasted out by the explosion of a large hydrothermal aquifer overheated during the ascent of a pocket of fresh magma within the volcanic structure.

Lauranne Garitte


Coup d’œil sur la bio de Pierre Delmelle

Pierre Delmelle earned a master’s degree in chemical engineering and agricultural industry from UCLouvain in 1991. His PhD at the Université Libre de Bruxelles (1995) focused on the geochemistry of hydrothermal fluids associated with active volcanoes in Indonesia and the Philippines. After several postdoctoral residencies in Japan, Canada, and Belgium, he was a lecturer for six years at York University in England. Returning to UCLouvain in 2011, he has been a professor in the Faculty of Bioengineering and a member of the Earth and Life Institute. His research focuses on the impact of volcanic eruptions on the environment and agriculture. He and his team invest in interdisciplinary projects that aim to generate knowledge, methods, and tools that can help reduce the vulnerability and increase the resilience of agrarian populations subject to volcanic hazards. He currently concentrates on Ecuador and the Philippines.

Published on July 16, 2020