The main gas emitted by volcanoes is water vapour. Which is followed by carbon dioxide,which is a gas causing green-house effect, so its emission into the stratosphere is likely to lead to the temperature increase. Another gas emitted is sulfur dioxide, its products reflect the sun rays preventing them from reaching the earth and cause significant temperature falls. Other harmful effects include the destruction of the ozone layer and the pollution of the atmosphere. The gases emitted by volcanoes can also harm people, animals and plants directly. This is especially relevant for the regions in the immediate vicinity of the epicenter. The damage to human health can vary from insignificant to major and in some cases can even cause lethal outcome. Such gases as sulfur dioxide and hydrogen chloride are poisonous and can harm eyes, mucus and the respiratory system. If carbon dioxide, is emitted in big amounts and gathered in places with little ventilation, can lead to asphyxiation and death. Carbon dioxide in soil also harms plants. In areas around active volcanoes forests have been noticed to die out. .
Some of the gases, after undergoing certain chemical reactions, remain in the troposphere and others, reacting with water, fall down as acid rain. While these acid compounds are still in the atmosphere they can damage airplanes causing metal corrosion. The article discusses the effects of the eruption of the supervolcano of Toba in Sumatra. This eruption took place about 73,000 years ago. According to the research, its effects were tremendous and nearly led to the extinction of humans. The main effect was a drastic change of climate with the average temperature decreasing by about sixteen degrees centigrade. This happened because the ash from the eruption and the sulfuric acid formed from the emitted sulfur prevented the sun rays from reaching the Earth in sufficient amounts. What followed was an ice-age that lasted for approximately 1,800 years.
