Active volcano
|
A volcano that has erupted within the past 10,000 years and/or is expected to erupt within the next 10,000 years. |
Amplitude
|
The maximum displacement from a zero value during one complete oscillation. |
Andesite
|
A dark volcanic rock with a silica content of about 60%. Andesite is the second most abundant volcanic rock in Earth's crust. |
Anomaly
|
A pronounced deviation from the accepted normal value or condition. |
Ash fall
|
A layer of volcanic ash that falls from an eruption plume. |
Asthenosphere
|
A soft layer of the Earth's upper mantle lying just below the lithosphere. |
Atmosphere
|
A layer of gases surrounding Earth. |
Atom
|
The smallest component of an element having the chemical properties of the element. Atoms consist of a nucleus containing combinations of neutrons and protons and one or more electrons bound to the nucleus by electrical attraction. |
Basalt
|
A dark volcanic rock with a silica content of 40 to 50%. Basalt makes up most of the ocean floor and is the most abundant volcanic rock in Earth's crust. |
Body waves
|
Seismic waves that travel through solid rock, including S waves and P waves. |
Caldera
|
A large bowl-shaped crater formed by explosive volcanic eruptions and/or by collapse of a volcano's surface material into the magma chamber. |
Calibrate
|
To determine, check, or rectify the graduation of any instrument or system giving quantitative measurements. |
CE
|
"Common Era" is the most commonly used year-numbering system worldwide. The years are equivalent to the Anno Domini (AD) system, which it replaces. |
Centrifugal force
|
The outward force that draws a rotating body away from the center of rotation. |
Cinder
|
Light pieces of lava, formed from magma that is ejected, cooled, fragmented in the air, and falls back down. Also called "scoria". |
Cinder cone volcano
|
A small, steep-sided volcano composed primarily of cinder. |
Compass
|
An instrument that detects magnetic polarity, used for determining directions by means of a freely rotating magnetized needle that indicates magnetic north. |
Composite volcano
|
A cone-shaped volcano built from layers of pyroclastic material and lava. (It is also called a Stratovolcano.) |
Compound
|
A pure substance composed of two or more elements whose composition is constant. |
Compression
|
Pushing together. |
Compression waves
|
Seismic waves that oscillate parallel to the direction in which the energy is traveling. Commonly called "P waves". |
Continent
|
One of Earth's main landmasses including, Europe, Asia, Africa, North America, South America, Australia, and Antarctica. |
Continental crust
|
The layer of rocks that forms the continents and the areas of shallow seabed close to their shores. |
Convection
|
The transfer of heat by the circulation or movement of the heated parts of a liquid or gas. |
Convective eruption column
|
A shaft of heat and particles rising up from an erupting volcano. |
Convergent
|
Colliding, coming together. |
Crater
|
A steep-sided, bowl-shaped hollow at the top of a volcano. |
Cretaceous
|
The geologic time period spanning roughly 145 to 65 million years ago. |
Cross section
|
A two-dimensional view of a three-dimensional object. A "slice" through an object. |
Crust
|
The thin, outermost layer of Earth, which comprises the continents and ocean floors. |
Deformation
|
Change in size or shape of an object resulting from an applied force. |
Devonian
|
The geologic time period spanning roughly 400 to 350 million years ago. |
Diffraction
|
The apparent bending, spreading out, or other changes in seismic wave direction. |
Displacement
|
The removal of one mass and replacement by another within a given space. |
Divergent
|
Separating, breaking apart. |
Dome
|
A mound of lava and other volcanic material that has built up around the vent of a volcano. |
Dormant volcano
|
An active volcano that is not currently erupting. |
Earthquake
|
Vibrations induced in Earth's crust by the abrupt rupture and rebound of rocks in which strain has been slowly accumulating. |
EDM
|
Electronic Distance Meter |
Elasticity
|
The property of a substance that enables it to change its length, volume, or shape in direct response to an applied force, and to recover its original form upon the removal of the force. A rubber band has elasticity. |
Emit
|
To release or discharge into the environment. |
Energy
|
The capacity to do work. |
Epicenter
|
The point on Earth's surface directly above the origin of disturbance that creates an earthquake. |
Erratic
|
Wandering, not fixed. |
Eruption
|
The ejection of material from a volcano or geyser. |
Extension
|
Pulling apart. |
Extinct volcano
|
A volcano that has not erupted in the past 10,000 years and is not expected to erupt within the next 10,000 years. |
Fault
|
A fracture along which pieces of Earth's crust move relative to one another. |
Fault trace
|
The line where a fault intersects Earth's surface, either on a horizontal plane or in vertical cross-section. |
Fissure
|
A crack through which magma erupts onto Earth's surface. |
Focus
|
The belowground point of origin of an earthquake. Also called a "hypocenter". |
Fold mountains
|
Mountains formed by folding of Earth's crust during the convergence of tectonic plates. |
Foot wall
|
The block of rock below the fault trace or fault plane. |
Force
|
An influence that causes a mass to accelerate. |
Foreshock
|
A relatively small earthquake that precedes a greater one by a few hours, days, or weeks and originates at or near the focus of the larger earthquake. |
Friction
|
Resistance generated by rubbing two surfaces together. |
Fumerole
|
A vent or opening in Earth's surface producing gas or steam. |
Glacier
|
A large mass of ice formed from many years of snow, which flows very slowly over land. |
Global positioning system
|
A space-based global navigation satellite system that provides reliable positioning, navigation, and timing services to worldwide users on a continuous basis. |
GPS
|
Abbreviation for global or geographic positioning system. |
Granite
|
A coarse-grained igneous rock composed chiefly of orthoclase, feldspars, and quartz, usually with lesser amounts of one or more other minerals, as mica, hornblende. |
Granitic
|
Composed chiefly of orthoclase, feldspars, and quartz, usually with lesser amounts of one or more other minerals, as mica, hornblende. |
Ground deformation
|
Change in shape of the ground surface caused by moving magma. |
Hanging wall
|
The block of rock above the fault trace or fault plane. |
Hot spot
|
An upwelling of magma from beneath Earth's crust, caused by a disturbance at the boundary between the solid mantle and the liquid outer core. |
Hydrophone
|
A device for locating sources of sound under water. |
Hydrous
|
Water-bearing. |
Hypocenter
|
The belowground point of origin of an earthquake. Also called a "focus". |
Hypothesis
|
A proposition set forth as an explanation for the occurrence of some specified group of phenomena, either as a provisional conjecture to guide investigation (working hypothesis) ,or accepted as highly probable in the light of established facts. |
Infrared radiation
|
Part of the electromagnetic spectrum with wavelengths longer than visible light and which correspond to temperature. |
Inner core
|
Earth's innermost, hottest portion, which consists of a solid metallic alloy. |
Instability
|
The quality or state of being unstable; a tendency to behave in an unpredictable, different, or erratic manner. |
Intensity
|
The amount of damage experienced at Earth's surface at a given location during an earthquake. |
Lag time
|
The time interval between one specified event and another. |
Lahar
|
A massive mudflow caused by a volcanic eruption. |
Landmass
|
A large, continuous area of land. |
Landslide
|
The downward falling or sliding of a mass of soil, detritus, or rock on or from a steep slope. |
Laterally
|
Proceeding from or directed to the side, moving parallel to. |
Latitude
|
A geographic coordinate that specifies the north-south position of a point on Earth's surface. |
Lava flow
|
Lava that has poured out of a vent and covers the land surface. |
Lava fountain
|
A fountain-like eruption of lava. |
Lithosphere
|
The solid outer shell of the earth, including Earth's crust and the solid outermost layer of the mantle. |
Logarithmic
|
A relationship between sequential numbers in which each number is multiplied by a specified number to equal the next number. The specified number for the Moment Magnitude Scale is 10. |
Longitude
|
A geographic coordinate that specifies the east-west position of a point on Earth's surface. |
Ma
|
Abbreviation for the Latin "mega annum", used in geologic chronology to denote "millions of years ago". |
Magma
|
Very hot molten rock, which is formed deep below ground by partial melting of Earth's crust and mantle. |
Magma chamber
|
A cavity deep below ground where rising magma collects before an eruption. |
Magnet
|
A body that attracts iron. |
Magnetic
|
Having the properties of a magnet. |
Magnetic reversal
|
Change from one polarity to the opposite polarity. |
Magnetic field
|
A region near a magnet in which a magnetic force acts on any other magnet. |
Magnetometer
|
An instrument for measuring the intensity of Earth's magnetic field. |
Magnitude
|
The amount of energy released during an earthquake. |
Mantle
|
The portion of Earth's interior between the crust and the core. |
Masonry
|
Work constructed by a mason, including stonework and concrete. |
Mercalli Intensity Scale
|
A 1 to 12 scale used to measure intensity of shaking experienced during an earthquake. |
Meteorologist
|
A scientist dealing with the atmosphere and its phenomena, including weather and climate. |
Microscopic
|
Able to be seen only with the aid of a microscope. |
Millennium
|
A period of one thousand years. Plural: millennia. |
Mineral
|
A class of naturally occurring substances of a definite chemical composition and crystalline structure, such quartz or feldspar. |
Minimum age
|
The youngest age a feature can be given the data presented. (The feature could be older.) |
Molecule
|
The smallest physical unit of an element or compound, consisting of one or more like atoms in an element and two or more different atoms in a compound. |
Moment Magnitude Scale
|
A logarithmic scale for measuring the energy released during an earthquake. The scale has no upper limit. |
Objective
|
Not influenced by personal feelings, interpretations, or prejudice; based on facts; unbiased. |
Oceanic
|
Occurring on or in the ocean. |
Oceanic crust
|
Part of Earth's lithosphere that surfaces in the ocean basins. |
Orbit
|
The curved path, usually elliptical, described by a planet, satellite, or spacecraft, around a celestial body, such as the earth or sun. |
Ordovician
|
The geologic time period spanning roughly 500 to 440 million years ago. |
Oscillation
|
A single fluctuation between maximum and minimum values of a wave that repeatedly and regularly fluctuates above and below some mean value. |
Outer core
|
A liquid layer about composed of iron and nickel which lies above Earth's solid inner core and below its mantle. |
P waves
|
Seismic waves that oscillate parallel to the direction in which the energy is travelling. Also called "Compression waves". |
Paleomagnetic
|
Magnetic polarization acquired by the minerals in a rock at the time the rock was deposited or solidified. |
Permian
|
The geologic time period spanning roughly 300 to 250 million years ago. |
Pillow lava
|
Lava in the form of a rounded, pillow-shaped mass, resulting from a subaqueous volcanic eruption. |
Pixel
|
A square area over which information is averaged. |
Plate tectonics
|
A theory in which the lithosphere is divided into a number of crustal plates, each of which moves on the plastic asthenosphere more or less independently to collide with, slide under, or move past adjacent plates. |
Plume
|
A concentrated cloud of gas or ash. |
Polarity
|
The positive or negative state in which a body reacts to a magnetic field. |
Progressive
|
Going forward or onward; proceeding step by step. |
Province
|
An administrative division or unit of a country. |
Pumice
|
Cinder with so many gas chambers, it can float on water. |
Pyroclastic flow
|
A cloud of superheated gas, ash, and rock that erupts from a volcano and travels quickly down slope. |
Pyroclastic flow deposit
|
A layer of ash and rock deposited by a pyroclastic flow. These can be many meters thick. |
Pyroclastic material
|
Volcanic debris formed by solidification of erupted lava in air, including volcanic dust, ash, cinders, and pieces of rock. |
Quaternary
|
Earth's current geologic period, covering the past 2.6 million years. Recent sediments from the period are generally not yet consolidated into rock. |
Radiation
|
The process in which energy is emitted as particles or waves. |
Recede
|
To go or move away; retreat; withdraw. |
Remote sensing
|
Monitoring conducted at some distance from the object of study. |
Richter magnitude scale
|
A logarithmic scale for measuring earthquake magnitude, developed in the 1930's. This scale is no longer in use. |
Rift valley
|
A portion of Earth's crust, bounded on at least two sides by faults, that has dropped downward in relation to adjacent crust; a "graben". |
Rupture
|
An offset or displacement of the ground surface that may occur as a result of an earthquake. |
S waves
|
Seismic waves that oscillate perpendicular to the direction in which the energy is travelling. Also called "Shear waves". |
Satellite
|
A device designed to be launched into orbit around Earth, another planet, or the sun. |
Satellite imagery
|
Photographs of Earth or other planets made by means of artificial satellites. |
Seismic activity
|
Underground movements including earthquakes and tremors. |
Seismic signature
|
The pattern or shape of a seismic signal recorded by a seismograph. |
Seismic waves
|
Waves of energy that travel through the ground and cause the shaking experienced during earthquakes. |
Seismograph
|
Scientific instruments that measure seismic activity. |
Seismologist
|
A scientist who studies of earthquakes and the propagation of elastic waves through Earth. |
Semi-solid
|
Having a somewhat firm consistency; more or less solid. |
Sensor
|
A mechanical device sensitive to light, temperature, radiation, or specific chemical compounds, that transmits a signal to a measuring or control instrument. |
Shakemap
|
A map of earthquake intensity generated from data collected from a network of seismographs, with interpolated intervening values. |
Shear waves
|
Seismic waves that oscillate perpendicular to the direction in which the energy is travelling. Commonly called "S waves". |
Shield volcano
|
A low, broad, gently sloping, dome-shaped volcano made up of many layers of basaltic lava that build up through repeated eruptions. |
Silica
|
A fundamental component of volcanic rocks, silica content is the most important factor determining magma viscosity. |
Silicone
|
A nonmetallic element occurring in minerals and rocks and constituting more than one fourth of Earth's crust. |
Silt
|
Soil particles with a grain size smaller than sand and larger than clay. |
Stratosphere
|
The layer of the atmosphere above the troposphere, approximately 16 to 48 km above Earth's surface. |
Stratovolcano
|
A cone-shaped volcano built from alternating layers of pyroclastic material and viscous andesitic lava. (It is also called a composite volcano.) |
Subduction
|
The process by which one tectonic plate is drawn down or overridden by another. |
Subduction zone
|
The region where one lithospheric plate descends beneath another plate and dives into the asthenosphere. |
Subjective
|
Existing in the mind; belonging to the observer rather than to what is being observed. |
Submersible
|
A ship capable of submerging and operating under water; submarine. |
Summit
|
The highest point of a mountain, a peak. |
Surface waves
|
High amplitude seismic waves that travel through the material at Earth's surface. |
Tectonic plate
|
A section of Earth's crust and lithosphere that moves above the asthenosphere. |
Tephra
|
Pieces of material produced by a volcanic eruption. Tephra can include ash, cinder, and volcanic bombs or blocks. |
Tertiary
|
The geologic time period spanning roughly 65 to 2.6 million years ago. |
Tiltometer
|
A scientific instrument used to measure changes in the slope of a volcano. |
Time interval
|
A defined span of time. |
Topography
|
Variations in surface elevation. |
Transform
|
Sliding past each other. |
Tremor
|
Low amplitude earthquake activity associated with the movement of magma. |
Triangulation
|
A technique for determining a location (e.g., an earthquake epicenter) by finding the intersection of three arcs. |
Triassic
|
The geologic time period spanning roughly 250 to 200 million years ago. |
Troposphere
|
The lowest layer of the Earth's atmosphere. |
Tsunami
|
A huge ocean wave generated by earthquakes or violent volcanic eruptions. |
Unconsolidated
|
Not yet hardened into rock, e.g. ocean, lake, or river sediments. |
USGS
|
United States Geological Survey. |
Vent
|
An opening in the surface of a volcano through which steam, gas, or lava can flow. |
Viscosity
|
A fluid's resistance to flow. The viscosity of magma is determined by its chemistry and temperature. |
Viscous
|
Having a relatively high resistance to flow; thick and sticky. |
Visible light
|
A small fraction of the radiation wavelength spectrum that we see as colors. |
Volcano
|
A cone that forms above and around a vent as erupted volcanic materials accumulate. |
Volcanologist
|
A scientist who studies volcanoes. |
Volcanology
|
The scientific study of volcanoes. |
Vulcan
|
The ancient Roman god of fire. |