Page 14 - Fundamentals of Physical Volcanology

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Glossary

'a'a A type of lava having a very rough surface andesite A rock type of intermediate silica
texture. content, commonly associated with subduction
absolute temperature The thermodynamic tem- zones.
perature of a substance, measured on a scale arachnoids Tectonic structures up to many hun-
where zero corresponds to the molecules form- dreds of kilometers in diameter, with complex
ing the substance having no motion. The unit central parts and radiating fracture systems, seen
of absolute temperature is the Kelvin (K); the in the crust of Venus. The name suggests that
Kelvin has the same size as the degree Celsius they look like spiders.
(ºC) and 0K corresponds to –273.15ºC. ash cluster A collection of ash particles loosely
accidentally breached An accidentally breached held together by moisture, ice, or electrostatic
lava flow is one in which an overflow or breakout forces.
from the main channel occurs when the channel ash pellet A collection of ash particles strongly
is blocked by material breaking off its walls. held together by moisture, ice, or electrostatic
accretionary lapilli Small (between 4 and 32 mm forces.
in diameter) rounded particles formed by the basalt A rock type with a low silica content, com-
accretion of large numbers of smaller particles monly associated with ocean floor spreading.
in a volcanic eruption plume. The small particles basaltic andesite A rock type of low to interme-

may be held together by water, ice, or electro- diate silica content.
static forces. base surge A cloud of hot gas and entrained parti-
acidity spikes Localized high concentrations of cles flowing out close to the ground from the site
sulfuric acid found at certain depths in ice cores of a volcanic (or nuclear) explosion.
drilled in polar regions. These correspond to the billion Used in this book in its American con-
9
deposition of snow soon after volcanic eruptions text to mean the number 10 , i.e., one thousand
which released large amounts of sulfate aerosols million.
into the atmosphere. Bingham plastic A liquid that has not only a
active continental margin The edge of a con- viscous resistance to deformation and flow, but
tinental land mass at which one of the plate- also a finite strength that must be overcome by
tectonic processes of subduction or faulting is any applied force before any flow takes place.
taking place. block lava A type of viscous lava in which the
aerosols Small droplets of water in the atmo- surface fractures into large blocks.
sphere in which volatile species, especially sulfur block-and-ash flow deposit A mixture of coarse
dioxide, are dissolved. and fine pyroclasts. deposited from a pyroclastic
air drag The force exerted on a particle moving density current.
through the atmosphere as a result of the friction bulk modulus The property of a material express-
between the surface of the particle and the air. ing the way the density changes with pressure.