Magma contains dissolved gases that are released into the atmosphere during eruptions. In addition, geothermal systems such as Sulphur Springs also emit large amounts of gases. Areas of cold spring activity also release dangerous gases into the atmosphere. The most common gases in volcanic areas are water vapour (H2O), carbon dioxide (CO2) and sulphur dioxide (SO2) with smaller amounts of hydrogen sulphide (H2S), carbon monoxide (CO), hydrogen chloride (HCl) and hydrogen fluoride (HF). SO2, CO, CO2 and H2S are present in toxic amounts close to the vent of an erupting volcano and may be emitted from fumaroles. Further away from the vent these gases can become dissolved in atmospheric clouds to produce acid rain and mist which affect human and animal eyes and respiratory systems and corrode metal building materials. One of the most common volcanic gases, carbon dioxide (CO2) is extremely dangerous as breathing air with greater than about 20% CO2 can cause almost instantaneous death. As it is heavier than air, CO2 tends to accumulate in hollows in the ground, displacing the breathable air. Since it is invisible and has no taste or smell, people and animals are unable to notice that it is there and may suffocate. People have died in this way at the Boiling Lake in the Valley of Desolation in Dominica and livestock have been found dead in low-lying areas near cold soufrière in Saint Lucia