Volcano Vocabulary

An active volcano is one that erupts regularly.

A dormant volcano is one that has not erupted for many years, although there is still some activity deep inside.

An extinct volcano has ceased to be active.

A volcanic eruption is when hot rocks and lava burst from a volcano.

Geysers are springs that throw boiling water high in the air. They are caused by volcanic heat warming trapped ground water.

Earthquake Vocabulary

   Crust - the top layer of the earth, which consists of solid rock. Both the continental crust (land masses) and oceanic crust (the land beneath the ocean) belong to the crust.

   Epicenter - the point directly above the focus or source of the earthquake.

   Fault - a break or separation in rock, usually between two or more tectonic plates.

   Focus - the source of the earthquake inside the earth, where the rock first begins to break.

   Lithosphere - the uppermost layer of the earth, which consists of all solid rock. It includes both the crust and the upper mantle.

   Magnitude - the amount of energy released from the earthquake. The size of the seismic waves at the epicenter, which can be determined by the size of the wavy lines on the seismogram.

   Mantle - the layer beneath the crust. The upper mantle is solid rock; the lower mantle is molten rock.

   Mercalli Scale - a subjective measure of the strength of an earthquake. It measures the degree of intensity.

   Richter Scale - an objective measure of the strength of an earthquake. It measures the degree of magnitude.

   Seismic Waves - vibrations that move through the earth in a way similar to waves moving in water. They can travel through solids and liquids.

   Seismogram - written recording of the earth's vibrations, produced by a seismograph.

   Seismograph - instrument that plots the intensity of earthquake waves on a roll of specially marked graph paper.

   Seismologist - scientist who studies earthquakes.

Plate Tectonic Vocabulary

Collision Fault: Two plates moving toward each other resulting in both plates pushing upwards.

Converging boundary: Place where two plates moving from different directions meet head-on. Both collision and subduction faults are types of a converging boundary.

Continental drift: The Idea that continents move from one part of Earth to another.

Convection: Movement of a fluid because of density differences.

Diverging boundary: Place where two plates of lithosphere are moving apart and new lithosphere is formed.

Mid-ocean Ridge: Long chain of underwater mountains.

Normal Fault: A fault where the rocks above the fault move down.

Pangaea: Name of the hypothetical great continent thought to have split into the landmasses known today; a word coined by meteorologist Alfred Wegener from the Greek pan and gaie, meaning "all" and "land".

Plate: Large moving section of lithosphere that contains continents and seafloor.

Plate tectonics: Theory that solid plates move on top of the putty like asthenosphere.

Reverse fault: A fault where the rocks above the fault move up.

Rift: Deep valley which runs down the middle of a mid-ocean ridge.

Seafloor spreading: Theory that seafloor crust forms at mid-ocean ridges and then spreads in opposite directions.

Shield cone: Volcanic mountain with a broad base and gently sloping sides, made from lava flows.

Sliding boundary: Place where two plates meet and slide past each other. Also known as a transform fault.

Strike-slip fault: Fault where the rocks on either side of the fault break and slide past each other.

Subduction: Pushing of the edge of one plate below the edge of another.

Transform Fault: Place where two plates meet and slide past each other. Also known as a sliding boundary.

Geologic History Vocabulary

Geologic time scale – record of Earth’s history from the beginning to the present.

Eon – longest time frame in the geologic time scale.  Measured in billions of years.

Era – second longest time unit, measured in 100 millions of years.

Period – third longest time unit, measured in 10’s of millions of years.

Epoch – unit of time measured in millions of years.

Uniformitarianism – principle that states the processes that are forming the Earth now, were occurring throughout geologic time.

Original horizontality – principle that states that sediment is deposited in a horizontal position.

Superposition – states that if undisturbed, the youngest layers of rock are on top and the layers get older as you go down.

Unconformity – a gap in the rock record

Correlation – matching rock outcrops from different regions.

Radioactive decay – emission of radioactive particles from a radioactive substance.

Half-life – period of time it takes for one-half of a radioactive substance to decay.

Fossil – remains or evidence of a once living organism.