Effusive Volcanoes

Volcanic eruptions can have significant consequences, including disruptions to aviation and, depending on the volume of gas emitted, significant public health and environmental impacts. This subsequently leads to a number of secondary impacts, including disruption to critical supply chains and economic impacts.

During major explosive eruptions huge amounts of volcanic gas, aerosol droplets and ash are injected into the stratosphere. In other systems, gases are emitted continuously into the atmosphere from soils, volcanic vents, fumaroles and hydrothermal deposits. The gradual release of gas acts as an irritant and may pose long-term health hazards.

Effusive Volcanoes

An effusive eruption is a volcanic eruption characterised by the outpouring of lava onto the ground, as opposed to the violent fragmentation of magma by explosive eruptions. Effusive eruptions are not violent eruptions; the eruptions occur when hot (1200°C), runny basalt magmas reaches the surface. Dissolved gases escape easily as the magma erupts and lava pours out onto the ground from a vent and spreads. Lava in this kind of eruption will be vary in thickness, length and width depending on where the eruption happens, the discharge rate and what kind of minerals make up the lava.

Gases in Volcanoes

The most abundant gas in these eruptions is water vapour, followed by carbon dioxide and sulphur dioxide. Secondary gases are also commonly emitted, including hydrogen sulphide, hydrogen, carbon monoxide, hydrogen chloride, hydrogen fluoride, and helium. The biggest potential hazards of these to humans, animals and agriculture is sulphur dioxide, carbon dioxide and hydrogen fluoride.

Effects of Sulphur Dioxide

Sulphur dioxide can lead to acid rain and air pollution downwind from a volcano. The effect of sulphur dioxide on people and the environment varies, depending on the amount of gas a volcano emits into the atmosphere. Sulphur dioxide is a colourless gas with a pungent odour that irritates skin, the tissues and mucous membranes of the eyes, nose, and throat. Sulphur dioxide chiefly affects upper respiratory tract and bronchi.

Effects of Carbon Dioxide

Volcanoes release more than 130 million tonnes of carbon dioxide into the atmosphere each year. This colourless, odourless gas doesn’t usually pose a direct hazard to life because it quickly dilutes to low concentrations whether it is released continuously from the ground or during eruptions. Emissions are most dangerous to people and animals when they can build up in confined spaces such as natural topographic depressions and building basements. Carbon dioxide gas is heavier than air and the gas can flow into low-lying areas; breathing air with more than 30% carbon dioxide can quickly induce unconsciousness and cause death.

Effects of Hydrogen Fluoride

Hydrogen fluoride is a colourless gas with a strong irritating odour. Absorption of fluoride from gas exposure is mainly through the respiratory tract. Its high water solubility means that absorption in the nose and upper respiratory tract is rapid. Vapours of hydrogen fluoride are a severe irritant to the eyes, mucous membranes and the upper respiratory tract and inhalation may cause ulcers of the upper respiratory tract. Short-term overexposure causes extreme irritation and burning of the skin and mucus membranes.