Page 19 - Fundamentals of Physical Volcanology
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xviii GLOSSARY
maria (singular: mare) The latin name for the p waves Primary waves, compressive waves
dark areas on the Moon, consisting of floods of spreading out from an earthquake focus into the
basaltic lava filling very large impact craters. surrounding rocks. These waves travel faster
mass extinction A biological event in which than any other type of seismic waves.
large numbers of species die out in a geologically pahoehoe A type of lava where the surface is
relatively short space of time. smoothly folded into a series of ripples called
mass flux The mass of magma passing though a ropes.
volcanic system every second. pahoehoe toe A small lava flow unit consisting
meteoric Generally, description of any phe- entirely of pahoehoe lava extending for a short
nomenon associated with the atmosphere. In distance from a larger flow unit.
volcanology, applied to near-surface water that partial melting The process in which part of a
has collected as a result of rain or snow. mass of rock melts, the liquid still containing the
mid-ocean ridge The ridge formed along a con- mineral grains that have not yet melted.
structive tectonic plate margin by the accumula- perched lava pond A lava flow that has spread
tion of lavas erupted onto the ocean floor. out sideways so that it has a similar width to
mush column A zone within the crust where its length. The shape is sometimes controlled
magma passes through so often that the host by pre-existing topography but can be self-
rocks are partly molten. generated by a suitable combination of eruption
negatively buoyant Description of material that rate and very shallow ground slope.
is denser than the material surrounding it, so that peridotite A type of rock rich in olivine, found in
it will tend to sink through its surroundings. the Earth’s mantle.
neutral buoyancy level Any location above or petrology The general term for the study of all
below ground where volcanic materials have the aspects of rocks.
same density as their surroundings. phoenix cloud Alternative term for a co-
Newtonian Description of a fluid with the ignimbrite cloud.
property that any change in applied stress pro- phreatomagmatic Description of an eruption
duces a directly proportional change in rate of involving interaction between magma and sur-
deformation. face, near-surface or ground water.
nonNewtonian Description of a fluid in which phreato-Plinian Description of a sustained ex-
the rate of deformation is not directly propor- plosive eruption in which magma interacts with
tional to a change in the applied stress. surface or ground water, generally resulting in
normally graded Description of a pyroclastic more fragmentation of the magma than in a
deposit in which the grain size increases down- Plinian eruption.
ward in the deposit. pillow A lava flow lobe that is approximately as
nova (plural: novae) A type of tectonic structure wide as it is thick, produced by a low lava extru-
on Venus in which fractures radiate out from a sion rate under water.
central zone. pillow lava A lava flow consisting of a pile of
nuclear winter A prolonged period of cooling pillows.
when heat reaching the surface from the Sun plastic Description of a fluid that is capable of de-
is greatly reduced by dust in the atmosphere forming smoothly in response to an applied stress.
thrown up from the explosion of a large number plastic viscosity The property of a non-
of nuclear weapons. Newtonian fluid expressing the ratio between a
nuée ardente French for “burning cloud,” one of change in applied stress and a corresponding
the possible names for a pyroclastic surge. change in rate of deformation.
ophiolite A body of rock consisting of the subsur- plate One of a series of sections of the Earth’s
face part of an old spreading center now uplifted lithosphere behaving as a rigid solid.
and exposed at the Earth’s surface by tectonic plate tectonics The term applied to our current
forces. understanding of the structure of the Earth’s