Volcanoes

Volcanoes, based on their frequency of eruption or volcanism, are referred to as either active, dormant, or extinct. Active volcanoes have a history of volcanism and are likely to erupt again, while extinct ones are not capable of eruption at all as they have no magma source. "Dormant" volcanoes have not erupted in a long time – generally accepted as since the start of the Holocene, about 12,000 years ago – but may erupt again. However, dormant volcanoes are technically considered to be seismically "active". These categories are not entirely uniform; they may overlap for certain examples. Large eruptions can affect atmospheric temperature as ash and droplets of sulfuric acid obscure the Sun and cool Earth's troposphere. Historically, large volcanic eruptions have been followed by volcanic winters which have caused catastrophic famines.