chapter 10 earthquakes and plate boundaries

Richter scale

A scale that rates an earthquake's magnitude based on the size of its seismic waves; logarithmic base 10 scale

Volcanic rock

Igneous rock cooled from lava, or from volcanic dust and ash.

Fault

A break or crack in the earth's crust

GPS

A system that determines the precise global position of something on Earth through a system of satellites, tracking stations, and receivers.

Vector

A quantity that has magnitude and direction

Scalar

A physical quantity that has magnitude only (no direction)

Plate boundary

the place where two plates meet

Oceanic Crust

the portion of Earth's crust that is usually below the oceans and not associated with continental areas, thinner and higher in density that continental crust and basaltic rather than granitic in composition

Continental Crust

the relatively thick part of the earth's crust that forms the large landmasses. It is generally less dense and more granitic than basaltic in composition

Convergent boundary

A plate boundary where two plates move toward each other

Transform boundary

The boundary between tectonic plates that are sliding past each other horizontally

Divergent boundary

The boundary between two tectonic plates that are moving away from each other

Metamorphic rock

A type of rock that forms from an existing rock that is changed by heat, pressure, or chemical reactions.

Igneous rock

a type of rock that forms from the cooling of molten lava on the surface or molten magma below the surface

Extrusive

a type of igneous rock that generally contains small crystals and forms when lava cools quickly on Earth's surface.

Intrusive

a type of igneous rock that generally contains large crystals and forms when magma cools slowly beneath Earth's surface.

Tectonic plates

a block of lithosphere that consists of the crust and the rigid, outermost part of the mantle; lithospheric plates

Mercalli scale

developed to rate earthquakes according to the level of damage at a given place; Roman numerals I-XII

Moment magnitude scale

A scale that rates earthquakes by estimating the total energy released by an earthquake; logarithmic scale of base 10

Subduction

A more dense tectonic plate going under another plate into the mantle at a convergent boundary

Landform

a natural feature of the earth's surface.

Trench

extremely deep areas in the ocean that are created by a subducting plate

Volcanoes

an opening in the Earth's crust through which molten lava, ash, and gases are ejected; commonly (but not always) made near convergent and divergent plate boundaries

Mountains

Formed by two continental plates colliding and forcing each other upwards.

Rift valley

A deep valley that forms where two plates move apart

Ocean rise

fast-spreading, gentle slopes due to fast divergent spreading

Mid ocean ridge

An undersea mountain chain where new ocean floor is produced; a divergent plate boundary.

Sea floor spreading

The process by which molten material adds new oceanic crust to the ocean floor at a divergent boundary

Volcanic island arc

a chain of volcanic islands generally located a few hundred kilometers from a trench where there is active subduction of one oceanic plate beneath another

Radiometric Dating

the process of measuring the absolute age of geologic material by measuring the concentrations of radioactive isotopes and their decay (daughter) products

Isotope

Atoms of the same element that have different numbers of neutrons

Unstable Isotope

An isotope in which the nucleus is likely to break apart at random times

Radioactive Decay

A spontaneous process in which unstable nuclei lose energy by emitting radiation

Parent Isotope

the isotope that undergoes radioactive decay

Daughter Isotope

the stable isotope produced by the radioactive decay of the parent isotope

Half-life

length of time required for half of the radioactive (parent) atoms in a sample to decay (into daughter atoms)

Mass Number

the sum of the number of neutrons and protons in an atomic nucleus