The primary impact volcanoes have on the environment is the release of volcanic gases into the atmosphere. Volcanoes release around 130 million tons of carbon dioxide each year, as well as toxic pollutants like sulfur dioxide, hydrogen sulfide, hydrogen chloride and hydrogen fluoride. However, volcanoes can also have a positive impact on the environment because the lava and ash produced by an eruption contain valuable nutrients for the soil.
In addition to the danger volcanoes pose to local animals through the release of gas and pyroclastic material, their environmental impacts can be severe and long-lasting. The eruption of Krakatoa in 1883 created large tsunamis and threw enough ash and gas into the atmosphere to trigger short-term climate change. Global temperatures the following year were 2.2 degrees Fahrenheit below normal, and weather patterns were disrupted for five years. Particles in the atmosphere produced dark skies and vivid red sunsets in the years following the eruption, and some art historians suggest that the red sky in Edvard Munch's painting "The Scream" may have been inspired by the volcano's global effects.
When magma reaches the surface and hardens, it becomes a stone called tephra. Over time, tephra breaks down, releasing high levels of nutrients into the soil. Some of the most fertile areas on Earth are on the sites of ancient volcanic eruptions, allowing farmers to enjoy the legacy of geologic events long past.