AEROSOLS - Particles suspended in a gaseous medium. There are fears that when they find their way to the upper atmosphere they can cause chemical reactions which destroy the ozone layer, allowing more of the Sun's ultraviolet radiation to reach the Earth's surface. Small aerosols (less than 2µm in diameter) also have the effect of increasing the planet's albedo, or reflectivity. This means less of the sun's energy reaches the atmosphere, causing the phenomenon known as Global Cooling.
ALBEDO - A measure of the reflecting power of an object. If the object has a high albedo then it reflects a lot of light.
ASH - fine pyroclastic fragments equal to or less than 4 millimeters in diameter. During volcanic eruptions, these very fine fragments render the eruption columns a characteristic deep brown to lead gray color.
ERUPTION - the ejection of volcanic materials (lava, pyroclastics, and volcanic gases) onto the earth's surface. It is usually a violent phenomenon, although an eruption may be relatively calm.
ERUPTION CLOUD - a gaseous cloud of volcanic ash and other pyroclastic fragments that is formed by a volcanic explosion.
ERUPTION COLUMN - the initial form that an eruption cloud takes at the time of explosion. It is also known as a vertical ash column.
LAVA - the red-hot molten rock materials violently or quietly extruded by a volcano. Lava is the term applied to magma when it finally reaches the earth's surface.
MAGMA - naturally occurring mobile molten rock materials, generated within the earth.
PYROCLASTIC - an adjective used to describe rock materials formed by fragmentation as a result of volcanic action. One of the most dangerous aspects of a volcanic eruption is Pyroclastic Flow.
PYROCLASTIC FLOW - a turbulent flowing mass of ejected fragmental volcanic materials mixed with hot gases and moving downslope at high speed (about 60 kph or more). Pyroclastic flow may result from the collapse of tall eruption columns or from spillover of ejected materials from erupting vents.
T.O.M.S. (Total Ozone Mapping Spectrometer) - A satellite which provides images of Sulphur Dioxide levels in the Earth's atmosphere.
VENT - the opening of the earth's surface through which volcanic materials are extruded.
VOLCANIC GASES - Mainly Hydrochloric Acid (HCl), Sulphur Dioxide (SO2) and Water Vapour (H2O), although proportions vary between volcanoes and other minerals may be present. As the volcanic cloud cools the Hydrochloric Acid and Water Vapour fall to the ground as precipitation.
VOLCANOES - Vents or fissures in the earth's surface through which magma rises from the earth's interior and erupts lava, gases, and pyroclastic material. Many volcanoes have cones consisting of ash, pyroclastic deposits, and lava. Volcanic cones are often topped by craters, created by volcanic explosians. Volcanoes frequently occur along the boundaries of tectonic plates.
This site was created by Chris Garrett (cg6145@bris.ac.uk)
Last updated 2nd April 1997