Besides human activities, volcanoes also introduce significant quantities of potentially harmful chemical compounds into the environment, mainly in the forms of gases and particles. As exemplified by volcanic events of massive proportions, the impacts can be profound and global. Such eruptions are capable of injecting millions of tonnes of sulphur dioxide gas into the stratosphere (more than ten miles above us) within short periods of time. There, the sulphur dioxide is oxidised to form a cloud of sulphuric acid droplets (or aerosols), which work to alter interactions between the atmosphere and sun, and so affect the Earth’s climate.
Less violent eruptions that are mainly restricted to the troposphere (the lowest layer of the Earth's atmosphere) are much less likely to alter global climate. However, their regional environmental effects can be equally severe. One of the greatest environmental disasters of the last 250 years was triggered by an Icelandic fissure eruption. Over 8 months in 1783-4, enormous emissions of sulphur dioxide, hydrogen chloride and hydrogen fluoride were disgorged and a volcanic pollutant cloud formed over the island. The cloud, often referred to as a dry acid fog, also fumigated many parts of Europe, causing damage to vegetation and public health problems. In Iceland alone, an estimated 10,000 people died, due mainly to a famine that took hold after the country's food and drinking water supplies were contaminated by fluorine.
Poisonous gases also are released continuously or semi-continuously into the environment by non-erupting volcanoes. For example, Mount Etna in Sicily emits 3,000 tons of sulphur dioxide on an average day, which is equivalent to the UK's total industrial emissions. Up to 10,000 tons of sulphur dioxide can be released during episodes of intense activity. Non-eruptive plumes can disrupt ecosystems, cause crop failures and adversely affect public health around areas in the immediate vicinity of a volcano. In Nicaragua, emissions from the Masaya volcano have completely destroyed coffee plantations that once thrived in the fertile volcanic soil. Only the occasional ruined building, slowly corroding away by the action of volcanic acid gases and rain, now punctuates the desolated landscape. Yet, most of the local population has no choice but to stay put and wait for the volcano to shut off.
The effects, or potential effects, of active volcanoes on the environment and on public health is an important issue, given the large number of communities, including megacities, that exist and keep growing around and upon active and dormant volcanoes. One estimate is that around half a billion people live within 100 km of an historically active volcano, mostly in densely populated cities.
At York, we are adopting a multidisciplinary approach to investigate the atmospheric, environmental and health hazards posed by volcanic activity. In particular, we are studying how gas and particles evolve in volcanic plumes, how different types of soils respond to volcanic acid inputs and how tropical vegetation is affected by volcanic gases. The long-term goal is to identify best practice in volcanic pollution risk assessment and management.