eventual partial meltdowns and fires in other reactors, which resulted in the
release of radioactivity directly into the atmosphere. More than 200,000
residents were evacuated from affected areas putting the disaster on par with
the 1986 Chernobyl nuclear reactor explosion.VOLCANOES
Volcanoes are divided into four main categories: active, inactive, dormant, and
extinct. Active volcanoes produce magma (melted rock) at the surface with the
majority of volcanoes (approximately 95%) occurring at subduction zones and
mid-oceanic ridges. Transfer of heat often happens at convergent boundaries,
where tectonic plates are crashing together. As the denser tectonic plate
subducts, or sinks below the less-dense tectonic plate at these convergent
boundaries, hot rock from below can intrude into the cooler plate above. This
process transfers heat and creates magma which can then rise to the surface.
Over millions of years, the magma in this type of subduction zone can create a
series of active volcanoes known as a volcanic arc. The remaining 5% of active
volcanoes occur at hot spots, areas where plumes of magma come close to the
surface.
Active volcanoes may produce ejecta (lava rock and/or ash), molten lava,
and gases such as steam (H 2 O), carbon dioxide, hydrogen chloride, and sulfur
dioxide (SO 2 ). Sulfur dioxide is more effective than ash particles in cooling the
climate by combining with water vapor to form sulfuric acid aerosols, which
form a haze of tiny droplets that reflect solar radiation. In 1992, the year after the
Mt. Pinatubo eruption, the effect of stratospheric sulfate particles decreased the
average global temperature by as much as 1°F (0.5°C) by decreasing the amount
of sunlight reaching Earth. The particles settle out of the atmosphere usually
within two years and contribute to acid rain.