Page 18 - Fundamentals of Physical Volcanology

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GLOSSARY xvii

island arc An arcuate group of volcanic islands lava tube The interior of a lava flow where the sur-
formed above a subduction zone at the edge of a face layers of the flow have ceased to move and
tectonic plate. thus form an insulating roof reducing heat loss
isopach A contour line on the map of a volcanic from lava still flowing beneath.
deposit joining places where the thickness of the levée The stationary edge of a lava flow.
deposit is the same. level of neutral buoyancy See “neutral buoy-
isopleth A contour line on the map of a volcanic ancy level.”
deposit joining places where the grain size of the linear rille A type of graben found on the Moon.
deposit is the same. liquidus The temperature at which a magma is
jökulhlaup The Icelandic word for a “glacier- completely molten.
burst,” the sudden release of a very large volume lithic clast A fragment of rock broken from the
of water that has accumulated under a glacier rocks through which a volcanic event has taken
as a result of melting caused by an eruption place and incorporated into the erupted volcanic
there. materials.
juvenile In volcanology, the word implies mater- lithosphere The outer part of a planet where the
ial that has come directly from the deep interior rocks behave as brittle solids, consisting of the
of the planet. crust and the upper part of the mantle.
kimberlite A rare type of mafic rock resulting lithostatic load The pressure at a given depth
from the eruption or intrusion of magma coming below the surface due to the weight of the over-
from unusually great depth in the mantle. Econ- lying layers of rock.
omically important because some kimberlites littoral cone A cone-shaped accumulation of
bring with them diamonds from the mantle. pyroclasts on land close to the ocean, built up by
kinetic energy The type of energy associated explosions when lava enters the water.
with the movement of material. maar A crater formed by an explosive interaction
komatiite A type of ultramafic magma forming between magma approaching the surface and
low-viscosity lava flows, common in early Earth surface or near-surface water.
history. magma Molten or partly molten rock beneath the
laccolith An intrusion of magma that has a rela- surface of a planet.
tively large vertical extent compared with its magma ocean A layer of molten rock on the
horizontal width. surface of a planet, formed when the outer layers

Large Igneous Province A region where large of the planet accumulate so fast that heat from
volumes of basaltic lava have been erupted – the impact of each added asteroid cannot be radi-
essentially a more general term for a region in ated away completely before the next impact
which a flood-basalt eruption has happened. happens.
lava breakout A place where lava breaks out from magma reservoir A long-lived body of magma
the edge of an existing lava flow deposit. beneath the surface that forms when new magma
lava dome A relatively thick and short lava flow from the mantle is added faster than the existing
deposit. magma body can cool.
lava flow An individual deposit of a discrete phase magmon A localized concentration of magma in
of an effusive eruption. the pore space of host rocks. The rocks deform
lava flow field A group of lava flow deposits to allow the magma concentration to pass
emplaced in successive phases of a prolonged through, so that it moves like a wave through the
eruption. host rocks.
lava fountain A jet of hot pyroclasts ejected from mantle plume A part of the mantle where buoy-
an explosive volcanic vent, rising to a significant ancy causes the mantle rocks to rise toward the
height, and then falling back to the surface. Also surface. Commonly the site of pressure-release
called a fire fountain. melting.