Download Key Plate Tectonics Terminology (earthquakes and volcanoes)

Key Plate Tectonics Terminology (earthquakes
and volcanoes)
Acid Lava Thick viscous lava which flows short distances
Basic Lava Thin , runny lava which can flow long distances
Caldera: A large, circular depression in a volcanic terrain, typically originating in collapse,
explosion, or erosion.
Cinder cone: A steep, conical hill built up about a volcanic vent and composed of coarse
pyroclasts expelled from the vent by escaping gases.
Composite Volcano Steep sided cone with layers of ash and lava
Collision Boundary This is where two plates move together (usually Continental plate)
Conservative Boundary Some pairs of plates slide past each other along transform faults.
Core The centre of the earth
Crater The mouth of the volcano
Crust The thin layer of the earth's surface
Earthquake A shaking of the earth's crust
Epicentre The point within the earth's crust where the earthquake occurred
Fault: A planar or gently curved fracture in the Earth's crust across which there has been
relative displacement.
Focus The point on the earth's surface directly above the epicentre
Fold Mountains Mountains formed by the earth's movements
Igneous rock: A rock formed by congealing rapidly or slowly from a molten state.
Intrusion: An igneous rock body that has forced its way in a molten state into
surrounding country rock.
Intrusive rock: Igneous rock that is interpreted as a former intrusion from its crosscutting contacts, chilled margins, or other field relations.
Joint: A large and relatively planar fracture in a rock across which there is no relative
displacement of the two sides.
Laccolith: A sill-like igneous intrusion that forces apart two strata and forms a round,
lens-shaped body many times wider than it is thick.
Lahar: A mudflow of unconsolidated volcanic ash, dust, breccia, and boulders mixed with
rain or the water of a lake displaced by a lava flow.
Lava The name given to liquid magma when it reaches the surface of the earth
Magma: Molten rock material that forms igneous rocks upon cooling. Magma that
reaches the surface is referred to as lava.
Magma chamber: A magma-filled cavity within the lithosphere.
Magnitude: A measure of earthquake size, determined by taking the common logarithm
base 10) of the largest ground motion observed during the arrival of a P-wave or seismic
surface wave and applying a standard correction for distance to the epicenter.
Mantle: The main bulk of the Earth, between the crust and core, ranging from depths of
about 40 to 3480 kilometers. It is composed of dense mafic silicates and divided into
concentric layers by phase changes that are caused by the increase in pressure with
depth.
P-wave: The primary or fastest wave traveling away from a seismic event through the
solid rock, and consisting of a train of compressions and dilations of the material.
Richter Scale This measures the strength of the earthquake
Sea-floor spreading: The mechanism by which new sea floor crust is created at ridges in
divergence zones and adjacent plates are moved apart to make room. This process may
continue at 0.5 to 10 centimeters/year through many geologic periods.
Shield Volcano A gentle sided volcano with a wide base made up of basic lava
Subduction zone: A dipping planar zone descending away from a trench and defined by
high seismicity, interpreted as the shear zone between a sinking oceanic plate and an
overriding plate.
S-wave: The secondary seismic wave, traveling slower than the P-wave, and consisting of
elastic vibrations transverse to the direction of travel. It cannot penetrate a liquid.
Tectonic Plate A huge section of the earth's crust
Constructive Boundary Where two plates move apart
Tsunami Huge tidal waves that are caused by submarine earthquakes
Vent The opening through which the lava flows in a volcano
Volcanic ash: A volcanic sediment of rock fragments, usually glass, less than 2 millimeters
in diameter that is formed when escaping gases force out a fine spray of magma
Volcanic bomb: A pyroclastic rock fragment that shows the effects of cooling in flight in
its streamlined or "bread-crust" surface.
Volcanic cone: The deposit of lava and pyroclastic materials that has settled close to the
volcano's central vent.
Volcanic dome: A rounded accumulation around a volcanic vent of congealed lava too
viscous to flow away quickly; hence usually rhyolite lava.
Volcano A cone shaped mountain created by lava and ash being erupted from the earth