Mitigating the Effects of Volcanic Eruptions

As the late Kofi Annan aptly put it,” Communities will always face natural hazards, but today’s disasters are often generated by, or at least exacerbated by human activities.” Volcanoes are no different; poor land-use planning, inadequate preparation and communication as well as public mistrust can intensify the potentially catastrophic effects that result from volcanic eruptions. In 1990 it was estimated that 9% (455 x 106 people ) of the population lived within 100km of active volcanoes [1]. Some do this for the minerals (such as for sulphur on Mt Ijen, East Java), the cheap, clean geothermal energy and tourism (Iceland) or even the fertile soils for agriculture (Mt Nyiragongo, DRC). Some simply have no choice. Either way, the risks to life, property, society and the economy need to be carefully managed and reduced wherever possible.

Risk is often pseudo-mathematically written as Hazard X Value X Vulnerability ÷ Capacity. Thus risk can be reduced by lowering the hazard threat, the value of people and property in the hazard zone (as well as their vulnerability), whilst at the same time expanding the coping capacity. Cities, due to high population densities and their innate interdependencies of infrastructures, people and resources, are at a particularly high risk. Developing countries with uncontrollable urbanisation are having to infringe on marginalised land, or expand to coastal areas where volcanoes are more prevalent and the effects of volcanogenic tsunamis are more severe. Risk management is critical, as although there can be instantaneous impacts (within hours of eruption), almost two-thirds of all fatalities occur more than a month after eruptions begin [2]. People grow accustomed to prolonged events as seen in Montserrat where the first fatalities occurred 23 months after the eruption began in July 1995. Risk management, be it mitigatory or preventative can curtail potential devastation.

The idea that risks can be overcome by technological and scientific invention (the dominant approach) is fading in popularity as losses continue to rise and people become increasingly sceptical of what ‘experts’ have to say. Instead, bottom-up policies that reduce marginalisation and improve socio-economic standings are being used to educate and train people – after all, we cannot simply stop an eruption from occurring. It is important that when deciding on what measures to enact, that the costs of implementing measures are contrasted against the potential benefits of the efforts. Premature evacuation for example, or evacuation for a minor event, may cost the economy hundreds of thousands of dollars (equivalent) and cause a greater loss of life in the process than if the population had been told to stay put with acceptable risk. Acceptable risk is an interesting concept, exemplified by the UK’s Health and Safety Executive. It gives an annualised individual risk of death where different hazards can be relatively compared: the boundary between ‘Broadly Acceptable’ and ‘Tolerable’ lies at 1:1,000,000; whilst the boundary between ‘Tolerable’ and ‘Unacceptable’ is 1:10,000 for the general public. This kind of measure is particularly important in aiding the communication rift between the scientific and policy-making worlds, which without checks and balances could result in economic failure, social upheaval or on the other end of the spectrum – mass casualties. Volcanologists at the Rabaul Volcano Observatory (New Britain, Papua New Guinea) and local authorities co-ordinated extremely well providing clear advice to the public through their four defined levels of unrest. In 1983/1984, with the situation only at ‘Stage 2’, evacuations were not carried out, helping to sustain economic activity and prevent disruption to the community, whilst at the same time keeping the public ‘on-side’ for future events. This showed its worth when in 1994 evacuations were needed as a few days later, the eruption grew in intensity and magnitude, causing severe destruction of infrastructure. With orderly plans in place of who, how, when and where to evacuate people, many lives were saved and an impressively small number (5) died whilst fleeing.

By failing to prepare, you are preparing to fail

Benjamin Franklin

Feeding into this, topographic maps and models of Pyroclastic Density Current (PDCs) Flows, Lava Flows and Lahars are critical in this evacuation process. Using event trees, the probabilities of say a Lahar reaching a radius of 15km in the North-Eastern quadrant can be calculated. In Montserrat, this probability is a calculated average from the team of scientists who have different weightings depending on how accurate and experienced they are in predicting potential ranges of events. These may then feed into traffic light systems such as in Mexico, which give localised warnings. This aids the routes and locations where people take refuge, as plans must constantly adapt to the ever-evolving situation and signals (seismic, geodetic and geochemical) that the volcano in question is giving off.

Thus, the importance of planning and preparation cannot be underestimated. Much like fire drills in office complexes and earthquake drills in Japan, evacuation plans and drills for volcanic disasters are crucial to keeping populations safe, often in the millions in Naples’ case. Boundary maps, although problematic as they can lull residents into false senses of security or reduce the land value of a property on ‘the wrong side of the line’, are a useful starting point in long-term preparation, in conjunction with the use of models. Micro-scale solutions such as slanted roofs can reduce the crushing weight of falling ash. Having emergency infrastructures such as sirens, generators, radios for communication between authorities, secure water pathways to avoid contamination by fluoride, and food rations are important long-term preparatory measures to improve the efficiency of recovery operations and reduce death tolls. The volcanic observatory in Montserrat even has a PDC-proof bunker so that crucial work can continue even in the worst situations. Preparation across generations is vital, a lesson that was leant from the eruption of Nevado del Ruíz, Colombia where many residents didn’t know about the dangers that shadowed them from kilometres above. This is why school children in Portici have been encouraged to do drawings, even make productions on the 1631 subplinian eruption of Vesuvius that all but destroyed the municipality. These children talk to their parents and when they grow up, with their children, helping to remind everyone of the very real dangers that could emerge from the Campi Flegrei system.

Learning from history is crucial but at the same time flawed. Many volcanoes haven’t erupted in recorded activity, some volcanoes are even thought to just be passive mountains before it is too late such as Mt Lamington, Papua New Guinea. Furthermore, just because there aren’t stratigraphic records for PDC flows at a certain distance from the volcano, this absence doesn’t mean they never reached that far. Instead, as PDC deposits are often thin and unconsolidated, they are prone to erosion and thus records may simply be ‘erased’. Predictions and models that rely on probabilities often have to be made on global magnitude-frequency curves for that type of volcano as there simply isn’t enough data. As no two volcanoes are identical, significant errors can arise. However, history is still important and hard engineering can indeed help in this regard. Dams and levees can be built on known flow paths above vulnerable towns and villages. In 1986, exsolving CO2 from Lake Nyos, Cameroon flowed downhill (CO2 is denser than air) and asphyxiated 1800 people. On the result of this tragedy, Lake Nyos (and neighbouring Monoun) now house some floating siphon systems that help to gradually and safely ‘de-gas’ the lakes and prevent more, unnecessary loss of life. Thus reflection on history is an important, albeit flawed mechanism to improve preparation and mitigate against the effects of volcanoes.

Not only is local cooperation and communication vital, but so too is international preparation. The International Civil Aviation Organisation, for example, created the International Airways Volcano Organisation which works in collaboration with the World Meteorological Organisation amongst others. This helps to mitigate the effects of airborne ash particulate which can end up in the engines of civil aviation planes, as a patchwork of 9 large airspaces are covered by different Volcanic Ash Advisory Centres. Similar processes are required for monitoring the potential widespread effects of volcanogenic tsunamis akin to those of Mt Tambora and more infamously yet, Krakatau. Exchange programmes such as where scientists from Goma, Congo receive training in Hawai’i, and ‘floating-volcanologists’ who temporarily migrate to areas in need of assistance, all are just stepping stones in the right direction to minimising risk on a global scale. There are significant worldwide disparities in funding and equipment availability, especially when governments have to weigh up the opportunity costs of monitoring a potentially dangerous volcano with the very real situation of a starving population.

Long-term and short-term measures to mitigate the potential devastation that volcanoes can bring are crucial. Even small and inexpensive ideas such as hanging a bedsheet over the front door to show that you have evacuated, play an unquantifiably important role in minimising catastrophes. As Benjamin Franklin famously put it “By failing to prepare, you are preparing to fail”.


  1. Small, C., and Naumann, T., 2001, The global distribution of human population and recent volcanism, Environ. Haz. 3, 93-109
  2. Simkin, T., Siebert, L., and Blong, R., 2001, Volcano fatalities – lessons from the historical record, Science, 291, 255

(Featured Image: © Jasper Sodha)