Volcanic Emissions: Understanding Air Pollutants From Volcanoes

Volcanic eruptions can have a significant impact on air quality, releasing harmful gases and particles into the atmosphere. These emissions can lead to serious health hazards and even influence climate change. While human activities remain the primary driver of climate change, volcanoes can also contribute to rising greenhouse gas emissions, particularly through the release of carbon dioxide (CO2) and sulphur dioxide (SO2). This paragraph will explore the air pollutants that originate from volcanic activity and their potential consequences for the environment and human health.

Volcanic ash and lava bombs can extend miles away from the volcano

Volcanic eruptions release a variety of gases and particles into the atmosphere, including volcanic ash and lava bombs, which can travel far distances from the volcano. The distribution of these particles depends on the size of the eruption and the debris. The bigger the eruption, the further the debris will travel.

Volcanic ash is created when magma is fragmented into tiny glass shards, along with shattered rocks and minerals. These particles are propelled into the air at astounding rates and can reach very high altitudes. The settling rate of the ash is between 10-1 to 10-3 m/s, according to Stokes Law. The ash produced during an eruption can be a telltale sign of the eruption and can help identify the specific volcano when found far from the source. The shape and composition of the glass shards, as well as the mineralogy of the ash, can be analysed to determine its origin.

The distance that volcanic ash can travel varies depending on the size and intensity of the eruption. During a large eruption, ash can be spread over a wide area, covering nearby regions and even reaching distant locations. For example, the 1883 Krakatau eruption released ash that fell on Singapore, located 840 km away, and Cocos (Keeling) Island, 1155 km away. The ash from this eruption spread around the equator in 13 days and reached higher latitudes after three months, causing vivid red sunset afterglows that were visible in New York, Poughkeepsie, and New Haven.

Lava bombs are another type of particle released during volcanic eruptions. These bombs are formed from magma or lava and are named according to their shape, which is determined by the fluidity of the magma. Ribbon or cylindrical bombs, for example, form from highly to moderately fluid magma and have a circular or flattened cross-section. Lava bombs can cause damage through impact or subsequent fire damage, and they may occasionally explode due to internal gas pressure as they cool. The Kilauea volcano in Hawaii is known for its lava bombs, with a basketball-sized bomb injuring 23 people on a tour boat in 2018.

The dispersal of volcanic ash and lava bombs can have significant impacts on the environment and human populations. The ash and lava bombs can travel miles away from the volcano, affecting areas downwind from the eruption. The United States Geological Survey has stated that "At Kilauea Volcano, the recent effusive eruption of about 0.0005 km3/day (500,000 m3) of basalt magma releases about 2,000 tonnes of SO2 into the lower troposphere. Downwind from the vent, acid rain and air pollution are persistent health problems when the volcano is erupting." Therefore, it is crucial for volcanologists and atmospheric scientists to study the distribution of these particles to minimise the potential risks to human health and the environment.

Volcanic gases like sulphur dioxide can cause global cooling

Volcanic eruptions are a significant source of air pollution. They inject vast amounts of volcanic gas, aerosol droplets, and ash into the atmosphere. While the ash falls relatively quickly and has little lasting impact, the gases and aerosols can spread quickly and expansively, causing global cooling.

Volcanic gases, such as sulphur dioxide (SO2), are released in massive quantities during volcanic eruptions. SO2 is the most abundant chemically active gas emitted by volcanoes. It is readily oxidized to sulphuric acid within weeks. While SO2 has a direct cooling effect, its conversion to sulphuric acid is the most significant contributor to global cooling.

The sulphuric acid condenses rapidly in the stratosphere to form fine sulphate aerosol droplets. These aerosols can remain suspended in the atmosphere, reflecting and scattering sunlight back into space. This reduces the amount of solar radiation reaching the Earth's surface, leading to a cooling effect. The 1991 eruption of Mount Pinatubo in the Philippines, for example, released about 20 million tons of SO2, causing detectable global cooling of the lower atmosphere.

The magnitude of the cooling effect depends on the amount of SO2 emitted and the altitude it reaches. Major volcanic eruptions, like that of Mount Pinatubo, can inject SO2 into the stratosphere, where it has a more significant impact on climate. The aerosols formed from SO2 can spread globally, reflecting and scattering sunlight, resulting in a cooling effect that can last for several years.

Volcanic activity has been linked to periods of global cooling throughout history. For instance, the 8.2 ka event, approximately 8,175 years ago, was marked by a rapid temperature drop of at least 3.3°C in less than two decades. This cooling event is attributed to a decrease in volcanic activity, demonstrating the role of volcanic gases in climate regulation.

Volcanic carbon dioxide is a greenhouse gas that promotes global warming

Volcanic eruptions release carbon dioxide and other gases into the atmosphere. While volcanic eruptions do contribute to an increase in atmospheric carbon dioxide, human activities release far more carbon dioxide than volcanoes. For instance, human activities release an amount of carbon dioxide equivalent to a Mount St. Helens-sized eruption every 2.5 hours. Nevertheless, volcanic carbon dioxide is a greenhouse gas that has the potential to promote global warming.

Volcanoes emit carbon dioxide in two ways: during eruptions and through underground magma. Carbon dioxide from subterranean magma is released through vents, porous rocks and soils, and water that feeds volcanic lakes and hot springs. Much of the carbon dioxide released by volcanoes is emitted by the degassing of subterranean magma when the volcano is not erupting.

During major explosive eruptions, huge amounts of volcanic gas, aerosol droplets, and ash are injected into the stratosphere. While the injected ash falls rapidly from the stratosphere and has little impact on climate change, volcanic gases like sulfur dioxide can cause global cooling. In contrast, volcanic carbon dioxide, a greenhouse gas, has the potential to promote global warming. The most significant climate impacts from volcanic injections into the stratosphere come from the conversion of sulfur dioxide to sulfuric acid, which forms fine sulfate aerosols. These aerosols increase the reflection of radiation from the Sun back into space, cooling the Earth's lower atmosphere or troposphere.

While volcanic carbon dioxide has the potential to promote global warming, it is important to note that the impact of human activities on the carbon cycle far exceeds that of volcanoes. Human activities, such as burning fossil fuels, deforestation, and cement production, have added more than 2,000 billion metric tons of carbon dioxide to the atmosphere since the start of the Industrial Revolution. In 2010, human activities were responsible for a projected 35 billion metric tons of carbon dioxide emissions, which is about 80 to 270 times larger than annual global volcanic carbon dioxide emissions. Furthermore, while large volcanic eruptions are rare and only occur globally about once a decade, human carbon dioxide emissions are ceaseless and increasing annually.

Hydrogen fluoride ash particulates can settle on grass and be consumed by livestock

Volcanic eruptions are a significant source of air pollution. During major eruptions, huge amounts of volcanic gases, aerosol droplets, and ash are injected into the Earth's stratosphere. While the injected ash falls rapidly from the stratosphere and has little impact on climate change, volcanic gases, such as sulfur dioxide, can cause global cooling. Additionally, volcanic carbon dioxide, a greenhouse gas, has the potential to contribute to global warming.

One specific pollutant released during volcanic eruptions is hydrogen fluoride. When hydrogen fluoride ash particulates settle on the ground, they can coat grass and other vegetation. Cattle and other livestock may then consume this ash-coated grass, absorbing fluorine into their bodies. This accumulation of fluoride in their teeth and bones can damage their health and productivity. In some cases, fluorine poisoning and death can occur in livestock that graze on grass contaminated with high concentrations of fluoride.

The effects of volcanic ashfall on agricultural crops and livestock can vary depending on several factors. These include the thickness and type of ash, the growing conditions of the crops, the timing and intensity of rainfall, and the condition of the pasture and animals before the ashfall. It is challenging to predict the exact consequences and costs of ash damage, especially for large explosive eruptions or a series of smaller eruptions over an extended period.

To mitigate the potential hazards of volcanic ashfall, it may be advisable to sample and analyze ash or ash-coated vegetation. This analysis can help determine the presence of harmful substances, such as soluble fluoride, and guide decisions to protect livestock and crops. By improving our understanding of the effects of volcanic ash on agriculture, farmers and governments can implement more effective measures to reduce the damaging consequences of volcanic eruptions on the agricultural sector.

Volcanic activity may contribute to the melting of ice caps in Antarctica

Volcanic activity has been a source of fascination and concern for scientists and the general public alike. Beyond the immediate danger to nearby communities, volcanoes also contribute to air pollution and climate change. During eruptions, volcanoes release large amounts of volcanic gas, aerosol droplets, and ash into the atmosphere. These emissions can have both cooling and warming effects on the planet, influencing global temperatures.

Volcanoes emit a range of pollutants, including sulphur dioxide, hydrogen fluoride, hydrogen chloride, and carbon dioxide. Sulphur dioxide, for instance, can lead to the formation of acid rain, which poses a persistent health hazard to nearby communities. Similarly, hydrogen fluoride released from volcanic eruptions can impair the surrounding biosphere, including flora and fauna.

While the impact of volcanic activity on the Antarctic ice caps is complex and subject to ongoing scientific investigation, there is evidence to suggest that it may play a role in the melting process. The West Antarctic Ice Sheet, in particular, has been the focus of research due to the presence of subglacial volcanoes and geothermal heating. It is believed that geothermal heating from these volcanoes contributes to the melting of the ice sheet's base, providing subglacial meltwater that lubricates ice streams and facilitates faster ice flow.

However, it is important to note that the extent and rate of melting attributed to volcanic activity in Antarctica are not well understood. While volcanoes likely contribute to some degree of melting, especially in specific regions, other factors such as changes in ocean currents and seawater temperatures are also considered significant contributors. Additionally, according to a 2024 NASA-led study, the overall Antarctic ice sheet is gaining mass annually, as observed using ICESat.

Furthermore, the potential for a feedback loop between melting ice and volcanic activity has been proposed. As ice melts, it could awaken dormant volcanoes in Antarctica, triggering further volcanic activity. This hypothesis underscores the dynamic and interconnected nature of the Earth's systems and the ongoing scientific efforts to enhance our understanding of these complex processes.

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