Students

B

Bank-full stage The bank-full stage is the elevation of the water surface of a stream flowing at full channel capacity.

Barrier island A barrier island is a long, low-lying ridge of sand and gravel isolated from the mainland by shallow lagoons, bays, or marshes.

Basalt Basalt is a volcanic rock formed from partially melted mantle that migrates to Earth’s surface. The most abundant volcanic rock on Earth, it is denser, on average, than rocks of the continental crust because it contains more iron and magnesium.

Base level Base level is the elevation at which a river cannot flow farther or erode deeper into its bed.

Beach A beach is an accumulation of loose water-borne material (generally sand and pebbles but also boulders and shell fragments in places) deposited on the edge of a body of water—typically a gently sloping shore washed by waves or tides.

Beach drift Beach drift is the gradual movement of sediment in a zigzag pattern along the shore, caused by waves that come ashore obliquely.

Beach face The beach face is the flat ramp of sand leading down to the water’s edge at a beach.

Beach nourishment Beach nourishment is a soft stabilization method that brings in sand to create a new beach and bulk up the underwater slope of the beach face so as to develop at least a temporary positive sediment budget.

Bed A bed is an individual layer of sedimentary rock that can be distinguished from other layers.

Beneficiation Beneficiation is the process of crushing ore, separating minerals, and concentrating valuable minerals.

Berm A berm is a flat area of beach sediment composed of sand or gravel that is covered by water only during very high tides or large storms.

Berm A berm is a flat area of beach sediment composed of sand or gravel that is covered by water only during very high tides or large storms.

Bioavailable Bioavailable refers to the relationship between the amount of a substance an organism is exposed to and the amount the organism absorbs. The more of the substance retained by an organism as a result of a specific exposure, the more bioavailable the substance is.

Biodiversity Biodiversity refers to the full range of variability within the living world at all levels, including genomes, species, and ecosystems. The number of species in an area is commonly used as a measure of its biodiversity.

Biomagnification Biomagnification is the process whereby chemicals become more concentrated in individual organisms as they are passed up the food chain.

Biomass Biomass is essentially plant debris in all its various forms, including even household garbage and livestock manure.

Bioremediation Bioremediation is the technology that uses natural or enhanced microbial action in the soil to degrade contaminants.

Biosolids Biosolids are treated sewage sludge—the solid organic matter recovered from a sewage treatment process that can be used as fertilizer.

Biosphere The biosphere is made up of all the living things that inhabit Earth.

Body waves Body waves are seismic waves that travel through the interior of the Earth.

Braided channel A braided channel is a stream channel that frequently branches and rejoins around bars or islands of sediment.

Breakwater A breakwater is a barrier built in the water parallel to a coast to break the force of the waves and protect a harbor, anchorage, beach, or shore area.

Bulkhead A bulkhead is a vertical wall, typically constructed of timber, concrete, or steel, usually smaller than a seawall and not designed for high-wave-energy environments.

C

Caldera A caldera is a large circular-to-oblong depression that forms when magma chambers erupt their contents and the volcanic mountain above them collapses into the empty magma chamber.

Capacity A stream’s capacity is its ability to transport sediment, the maximum bed load and suspended load it can carry.

Cap and trade program A cap and trade program creates a financial incentive for emission reductions by assigning a cost to polluting. The rights to emit defined amounts of pollutants are bought and sold; those who pollute less than their allowed amount can make money by selling their right to release pollutants to others.

Carbon sequestration Carbon sequestration is the capturing and storing of CO₂ emitted by hydrocarbon burning.

Carrying capacity Carrying capacity is the number of people that Earth can support sustainably at a specified level of economic and social well-being (standard of living).

Channel A channel is the bed where a natural body of surface water is usually present and the main current normally flows.

Cinder cone A cinder cone is a conical hill formed by the accumulation of cinders and other ejected volcanic material, normally of basaltic or andesitic composition.

Clastic sedimentary rock A clastic sedimentary rock such as shale, sandstone, or conglomerate is formed from clastic sediment (sediment formed from rock fragments and mineral grains).

Clay Clay is a general term for a group of water-bearing aluminum silicate minerals having a layered structure. They commonly form from the hydrolysis of other silicate minerals.

Clean Air Act (CAA) The CAA is a federal statute to protect air quality in the United States; it regulates activities that have the potential to cause everything from acid rain to stratospheric ozone depletion and CO₂ emissions. The CAA authorizes national air quality standards and an emissions permitting system.

Clean Water Act (CWA) The CWA is a federal statute to protect surface water quality in the United States; it defines a variety of ways to reduce direct pollutant discharges into waterways, finance municipal wastewater treatment facilities, and manage polluted runoff.

Cleavage A cleavage is a weak plane in a mineral’s internal structure along which it will break.

Coal-Bed Methane (CBM) Coal-bed methane is methane that is generated and trapped in coal.

Cohesion Cohesion is the force created by attractions between grains of material that makes them stick together. Derived largely from electrical attractions between particles at the atomic level, it is affected by the amount of moisture present.

Comprehensive Environmental Response, Compensation, and Liability Act (CERCLA) CERCLA is a federal statute that authorizes the federal government to respond to releases of hazardous substances from closed and abandoned sites, provides ways to allocate liability for these releases, and establishes a trust fund (with tax revenues from the chemical and petroleum industries) to clean them up. Because of this funding capability, CERCLA is commonly called Superfund.

Compressibility Compressibility is a measure of how a soil compacts under applied forces, such as when a building is constructed upon it.

Cone of depression A cone of depression is a cone-shaped lowering of the upper surface of a body of groundwater around a well from which water is being withdrawn faster than it is replenished.

Confined aquifer A confined aquifer is an aquifer that is overlain by low-permeability material.

Consumptive use A consumptive use of water (such as evaporation, transpiration, incorporation into products or crops, or consumption by man or livestock) disperses water to other system reservoirs and causes depletion of the source.

Continental crust Continental crust is the outermost part of Earth’s geosphere that underlies the continents—it makes up Earth’s landmasses and their shallowly submerged edges. It is characterized by rocks that contain abundant silicon, oxygen, aluminum, potassium, and sodium.

Continental drift Continental drift is a general term for many aspects of a hypothesis, originally proposed by Wegener in 1912, that continents move relative to one another. Subsequent research established the theory of plate tectonics, which explains many of Wegener’s observations.

Continental margin A continental margin is the part of a continent, especially the submerged part (the continental rise, slope, and shelf), adjacent to oceanic crust.

Convergent plate boundary A convergent plate boundary is the boundary along which two tectonic plates move toward each other.

Core A core is a cylinder of solid rock cut by a drill and brought to the surface for geologic examination and sampling.

Creep Creep, a very slow type of earthflow, is a more or less continuous downslope movement of mineral, rock, and soil particles under the influence of gravity.

Crust The crust is the thin, outermost part of the geosphere. Continental crust, with an average thickness of about 35 km (22 mi), underlies the continents; oceanic crust, with an average thickness of about 7 km (4 mi), underlies the oceans.

Cryogenic distillation Cryogenic distillation is distillation at the very low temperatures at which gases become liquids and boil; it is used to separate individual gases such as nitrogen from the atmosphere.

Crystal A crystal is a homogeneous solid structure (a mineral grain) that often exhibits a regular geometric form and planar surfaces reflecting its orderly internal atomic structure.

Cutbank A cutbank is a steep bare slope formed by lateral erosion of a stream.

D

Debris flow A debris flow is a water-rich moving mass of rock fragments, soil, and mud, in which more than half the particles are larger than sand size.

Delta A delta is a deposit of sediment at the mouth of a stream where it enters a body of water such as a lake or the ocean.

Differentiation Differentiation is the process by which the composition of magma changes through the physical separation of early-crystallized minerals (as when they sink in a magma chamber).

Discharge Discharge is the rate of flow of surface water at a given moment, expressed as volume per unit of time.

Dissipative A dissipative use of a substance is one that leaves it dispersed and unrecoverable.

Distillation Distillation purifies water by heating it to drive off steam (which is pure freshwater) and then condensing the steam back into a liquid.

Divergent plate boundary A divergent plate boundary is the boundary along which two tectonic plates move away from each other.

Divide A divide is an area of high ground, such as a ridge or summit, marking the boundary between two adjacent watersheds.

Dome A dome is a steep-sided, rounded accumulation of lava extruded from a volcano to form a dome-shaped or bulbous mass of solidified lava above and around the vent.

Dredging Dredging is the removal of unwanted sediment by scooping it off the bottom or pumping it away as a thick slurry using a suction dredge.

Driving force The driving force of slope failure is the force of gravity, which pulls downward on surface materials.

Dune restoration Dune restoration is a soft stabilization tool that uses fencing, vegetation planting, and other methods to expand and stabilize dunes.

E

Earth systems The Earth systems are the four basic components of our planet: atmosphere, hydrosphere, geosphere, and biosphere.

Earthflow An earthflow is a debris flow composed of fine-grained material such as soil, sand, or silt.

Earthquake An earthquake is a vibration in the Earth caused by the release of elastic strain on a fault.

Earthquake cycle The earthquake cycle is the repeated generation of earthquakes by the buildup and release of elastic strain on a fault.

Eccentricity Eccentricity is the degree to which an orbit, such as Earth’s around the Sun, varies from a perfect circle.

Elastic rebound theory The elastic rebound theory states that movement along a fault is the result of an abrupt release of a progressively increasing elastic strain between the rock masses on either side of the fault.

Elastic strain Elastic strain is the change in shape or size of material caused by stress along a fault that can be reversed when stress is released.

Element An element is a pure chemical substance that cannot be broken down chemically into other substances. It is distinguished by its atomic number, the number of protons in the nucleus of its atoms.

Environment In environmental geology, the environment is very broadly defined to include all the physical and biological components involved in Earth systems interactions.

Environmental Impact Statement (EIS) An EIS is a document that must be publicly filed when the federal government takes a “major Federal action significantly affecting the quality of the human environment.” An EIS comprehensively examines the environmental and human impacts the action may have.

Eon An eon is the major interval of geologic time on the geologic time scale. Geologic time is divided into four eons.

Epicenter The epicenter is the point on the Earth’s surface that is directly above the focus of an earthquake.

Erosion Erosion is the transport of geosphere materials from one place to another by natural movements of water, wind, or ice (glaciers).

Estuary An estuary is a semi-enclosed coastal bay where freshwater from rivers mixes with seawater.

F

Fall A fall, the fastest mass movement, is characterized by the tumbling, rolling, or free fall of materials down a steep slope or cliff.

Fault A fault is a place where rock has broken and the blocks on opposite sides of the break have moved relative to each other.

Fault creep Fault creep is the slow and gradual movement along a fault that doesn’t cause significant earthquakes.

Fault trace A fault trace is a linear feature that marks the intersection of a fault plane with the ground surface.

Feedback mechanism A feedback mechanism is a response to a change in the climate system that either amplifies the change (positive feedback) or diminishes the change (negative feedback).

Feldspars Feldspars are a group of silicate minerals that contain silica, aluminum, potassium, sodium, and calcium.

Felsic Felsic is a compositional name for igneous rocks with abundant quartz and feldspar.

Ferromagnesium minerals Ferromagnesium minerals are silicate minerals that contain abundant iron or magnesium in their internal atomic structure.

Fissure A fissure is a volcanic opening at the Earth’s surface having the form of a long crack.

Flash flood A flash flood is a local and sudden flood of relatively great volume and short duration, generally resulting from brief but heavy rainfall over a relatively small area with steep slopes or the failure of an ice jam or constructed dam.

Flood basalt Flood basalt is a term applied to basaltic lavas that occur as vast accumulations of essentially horizontal flows erupted from fissures in rapid succession over large areas.

Flood crest Flood crest is the highest stage of a flood.

Flood frequency curve A flood frequency curve is a graphic illustration of annual flood discharges and their recurrence intervals.

Flooding Flooding is the covering of normally dry lands with water. It occurs along rivers when the discharge is so great that the water rises and overtops the river’s natural or artificial banks.

Floodplain A floodplain is a flat or nearly flat lowland bordering a stream that may be covered by its waters at flood stages.

Flotation Flotation is a process that separates sulfide mineral grains from a slurry by attaching them to specific types of bubbles.

Flow Flow is a general term for mass movements in which the material moves like a liquid, with particles in motion independently of each other.

Flux Flux is the rate of transfer of matter among systems.

Focus The focus is the point underground where rock first ruptures to generate an earthquake.

Foliation A foliation is a two-dimensional sheeted structure in rocks.

Fossil A fossil is the remains or indications of former life, preserved in rocks.

Fossil assemblage A fossil assemblage is a group of fossil species found together in a specific sedimentary layer or sequence. The fossils are commonly inferred to have lived together.

Fossil fuel Fossil fuel is a general term for hydrocarbon deposits (principally oil, natural gas, and coal) ultimately derived from organisms that once lived on land or in the oceans.

Fossil succession Fossil succession refers to the sequence of fossil types in a distinctive order that represents changes in the biosphere through geologic time.

Frequency Frequency is the number of vibrations that a seismic wave completes in a given period of time; it is commonly measured in cycles per second (hertz, Hz).

Friction Friction is resistance to movement along a contact between two bodies such as blocks of rock or sand grains.

Fuel cell A fuel cell is a device that uses a catalyst to combine hydrogen and oxygen, producing an electric current that can power machines.

G

Gabbro Gabbro is the igneous rock that crystallizes from mafic (basaltic) magma in the crust.

Gaining stream A gaining stream is one that receives groundwater discharges because its channel lies below the water table.

Generic soil screening level A generic soil screening level is the concentration of a particular chemical in a soil that signals when further analysis of the risk to people is indicated.

Geologic time scale The geologic time scale is a chronologic arrangement of the periods and events in geologic time.

Geologic time Geologic time refers to periods of time long enough to give us a perspective on and understanding of Earth’s history.

Geo-sequestration Geo-sequestration is the storage of carbon in underground reservoirs.

Geosphere The geosphere is the solid Earth and all its parts, including molten parts within Earth.

Geothermal energy Geothermal energy is heat stored in the Earth’s crust.

Glacial maximum A glacial maximum is a period during which ice sheets reached their maximum extent.

Glacier A glacier is a large mass of ice, formed at least in part on land by the compaction and recrystallization of snow, moving slowly by creep under the influence of gravitational forces, and surviving from year to year.

Global Climate Model (GCM) A global climate model is a quantitative simulation that represents the interactions of the major components of the climate system: solar radiation, atmosphere, oceans, land, and ice.

Gondwanaland Gondwanaland is the name of a supercontinent that included the southern continents of South America, Africa, Antarctica and Australia, along with India. It is thought to have formed from the splitting apart of Pangaea about 200 million years ago.

Grade Grade is the concentration of a valuable mineral or element in a mineral deposit.

Gradient Gradient is the “slope” of a stream—the angle between the water surface or the channel floor and the horizontal, measured in the direction of flow.

Granite Granite is a type of rock, typical of continental crust, containing less-dense elements including calcium, sodium, potassium, aluminum, silicon, and oxygen.

Greenhouse gas A greenhouse gas is a minor constituent of Earth’s atmosphere, such as carbon dioxide, that can absorb and reradiate energy, causing the atmosphere’s temperature to rise.

Groin A groin is a low, narrow barrier built perpendicular to the shore to capture sand from the longshore drift, thwart beach erosion, or rebuild a beach that has eroded away.

Groundwater Groundwater is water that infiltrates the ground and completely fills all open spaces: voids as big as caverns, fractures in rocks, even tiny cavities between mineral grains. It is the part of the subsurface water that is in the saturated zone.

Groundwater mining Goundwater mining is the pumping out of groundwater faster than it can be replenished.

H

Half-life The half-life of a radioactive isotope is the time it takes for half of the atoms in a sample to decay.

Heat pump A heat pump is a device that circulates a fluid to warm or cool a building by transferring heat from a relatively low-temperature reservoir to one at a higher temperature.

High-Level radioactive Waste (HLW) High-level radioactive waste is waste from nuclear reactors including used (spent) fuel and material left over from reprocessing spent fuel.

Horizon A horizon is a stratified layer within a soil approximately parallel to the land surface and differing from adjacent layers in physical, chemical, and biological properties.

Hot spot Hot spots are places where voluminous mantle material rises and melts to form mafic magma.

Humus Humus is a general term for the organic matter that imparts a dark color to upper levels of soil.

Hurricane A hurricane is a tropical cyclone, especially in the North Atlantic and eastern North Pacific basins, with sustained near-surface wind speed of at least 64 knots (73 mph).

Hydrocarbon A hydrocarbon is any organic compound consisting solely of carbon and hydrogen.

Hydrograph A hydrograph is a plot of a river’s discharge (or height in some cases) over time.

Hydropower Hydropower is power, mostly in the form of electricity, derived from water flowing under the influence of gravity.

Hydrosphere The hydrosphere is all the water in the oceans, lakes, rivers, underground, and in the permanent ice accumulations.

Hypothesis A hypothesis is a tentative explanation that is consistent with all we know about a situation or problem.

I

Ice sheet An ice sheet is an area where glaciers coalesce and cover more than 50,000 km² (31,000 mi²).

Igneous rock An igneous rock is a rock formed from molten material (magma in the crust and lava on Earth’s surface).

Intensity Intensity is a measure of the amount of shaking and other effects by an earthquake at a particular location. It is measured in terms of its effect on people and structures.

Interglacial period An interglacial period is the time interval between two successive glacial maximums.

Intraplate earthquake An intraplate earthquake is one that occurs within a tectonic plate rather than at a plate boundary.

Intraplate volcano An intraplate volcano is one that is far from any plate boundary and therefore considered unrelated to subduction or seafloor spreading processes.

Ion An ion is an atom or molecule that has an electric charge, either as a result of chemical reactions or from interactions with radiation.

Ionosphere The ionosphere is the upper part of the atmosphere, coinciding with the thermosphere, where solar radiation ionizes some of the constituent gas molecules.

Island arc An island arc is a chain of volcanoes in an ocean that forms above a subduction zone.

Isotope Isotopes are forms of an element with different atomic masses. All atoms of an element have the same number of protons in their nucleus, but the atoms of different isotopes differ from one another in having different numbers of neutrons.

J

Jetty A jetty is an engineering structure extending more or less perpendicularly from the shore into a body of water, designed to direct and confine the current or tide, to protect a harbor, or to prevent shoaling of a navigable inlet. Generally larger than groins, they are often built in pairs on either side of a harbor entrance, inlet, or the mouth of a river.

K

Karst terrain Karst terrain is a type of topography that is formed on limestone, gypsum, and other soluble rocks, where bedrock dissolution has created underground openings such as caves.

L

Lahar A lahar is a wet debris flow originating on the flanks of a volcano. Lahars are a slurry of ash, lava debris, and water, as well as any other material such as soil, rocks, and trees that the flow picks up on the way down the slope.

Landslide Landslide is a general term for mass movements that involve relatively coherent blocks of soil and rock material.

Laterite A laterite is an oxisol rich in oxides of iron, aluminum, or both that develops in a tropical or forested warm to temperate climate as a residual product of weathering.

Lava Lava is molten rock erupted onto Earth’s surface.

Lava tube A lava tube is a roofed conduit that lava flows through from an eruptive vent to a depositional site.

Leachate Leachate is liquid formed by leaching, such as a solution containing contaminants picked up through the leaching of waste in a landfill.

Leaching Leaching is a mineral processing technique that removes metals from an ore by dissolving them in a percolating solution.

Levee A levee is an artificial bank constructed along a stream to increase its channel area and enable more discharge if needed.

Limestone Limestone is a sedimentary rock consisting chiefly of calcium carbonate, primarily in the form of the mineral calcite.

Liquefaction Liquefaction is the change of a water-saturated and unconsolidated surface material, such as soil, from a solid to a liquid state when internal strength is lost—typically caused by earthquake shaking.

Lithified Sediment is lithified when it changes into solid rock, commonly through processes related to compaction.

Lithosphere The lithosphere is the shallowest physical layer in the geosphere, made up of strong, rigid rocks that can break when they move. It includes rocks of the oceanic crust, the continental crust, and the top portion of the underlying upper mantle.

Load Load is the material that is moved or carried by a stream, including bed load, suspended load, and dissolved load.

Longitudinal profile A longitudinal profile shows the elevation of a stream channel along its length, from the source to the mouth.

Longshore current A longshore current is a current that flows along a shore as a result of waves approaching the coast at an angle. They are generally confined to the surf zone.

Longshore drift Longshore drift is sediment that is moved along a shore by longshore currents.

Losing stream A losing stream is one that loses water into the ground because its channel lies above the water table. It serves as a recharge point for the local groundwater system.

M

Mafic Mafic is a compositional name for igneous rocks with abundant ferromagnesium minerals. Mafic rocks are rich in iron, magnesium, and calcium, and are most characteristic of oceanic crust.

Magma Magma is molten rock within the geosphere.

Magma chamber A magma chamber is a reservoir of magma in the shallow part of the lithosphere from which volcanic materials are derived.

Magnetic reversal A magnetic reversal is a 180-degree shift in the orientation of Earth’s magnetic field—the north magnetic pole becomes the south magnetic pole and vice versa when a magnetic reversal occurs.

Magnetic stripes Magnetic stripes are alternating regions of strong and weak magnetic strength that occur in oceanic crust parallel to spreading centers at mid-ocean ridges.

Magnitude Magnitude is a measure of the strength of an earthquake as determined by seismograph observations.

Mantle The mantle, the largest part of the geosphere, is the part of Earth’s internal structure between the crust and the core. The mantle has parts that are dynamic and changing (asthenosphere) as well as an upper part, adjacent to the crust, that is rigid and part of the lithosphere.

Mass extinction A mass extinction is a relatively short period in geological time during which a significant percentage of Earth’s species become extinct.

Mass movement A mass movement is an individual episode of mass wasting.

Mass wasting Mass wasting is a general term for the downslope movement of earth materials under the influence of gravity.

Maximum Contaminant Level (MCL) A MCL is the highest level of a contaminant that is allowed in drinking water.

Meander Meanders are sinuous curves, bends, loops, or turns in the course of a stream, formed as the stream shifts its course laterally as it flows across its floodplain.

Meltdown A meltdown is a severe overheating of a nuclear reactor core, resulting in melting of the core and escape of radiation.

Mesosphere The mesosphere is the part of the Earth’s atmosphere above the stratosphere where temperatures decrease upward.

Metallurgy Metallurgy is a set of processes that separate metals from their host minerals.

Metamorphic rock A metamorphic rock is a rock that has changed in response to temperature and pressure.

Milling Milling breaks ore into individual mineral grains, tiny particles the consistency of silt, sand, and clay.

Mineral A mineral is a naturally occurring inorganic solid made up of an element or a combination of elements (a compound) that has an ordered arrangement of atoms and a characteristic chemical composition.

Mineral deposit A mineral deposit is a concentration of useful minerals in Earth’s crust.

Modified Mercalli Scale The Modified Mercalli Scale ranks earthquake intensities on a 12-point scale, expressed as Roman numerals from I (not felt by people) to XII (damage nearly total).

Mohorovicic´ discontinuity (Moho) The Mohorovicic´ discontinuity is the place within the geosphere where seismic waves passing downward abruptly accelerate at the base of the crust. It marks the boundary between the crust and upper mantle.

Mollisol Mollisol is a soil order characteristic of grasslands (prairies); in these soils the A horizon is thick and dark-colored from the accumulation of organic material from plant roots.

Moment magnitude Moment magnitude (M_w) is a numerical scale of the amount of energy released by an earthquake. It is calculated from the total area of the fault that ruptures, how far the rocks move along the fault during the earthquake, and the strength of the rock that ruptures.

Moraine A moraine is a body of rock debris carried and moved by glaciers.

Mouth The mouth is the place where a stream discharges into a larger stream, a lake, or the ocean.

N

National Environmental Policy Act (NEPA) NEPA is a federal statute that requires all federal agencies to further a national policy “to promote efforts which will prevent or eliminate damage to the environment and biosphere” and “enrich the understanding of the ecological systems and natural resources important to the Nation.” It also established a Council on Environmental Quality. The act can be applied to any project, federal, state or local, that involves federal funding or work performed by the federal government, and requires EISs for such projects.

National Pollutant Discharge Elimination System (NPDES) NPDES is a permit program, established by the CWA, that controls water pollution by regulating point sources that discharge pollutants into waters of the United States.

National Priority List (NPL) The NPL is the list of hazardous waste sites recognized as a priority for continued study and potential cleanup under CERCLA.

Natural selection Natural selection is the process in nature by which organisms better adapted to their environment tend to survive, out-reproduce less well-adapted members of their population, and transmit their genetic characteristics in increasing numbers to succeeding generations.

Nonconsumptive use A nonconsumptive use of water is one that allows it to be used subsequently for other purposes or discharged back to its source.

Nonpoint sources (of pollution) Nonpoint sources are those that release pollutants to the environment over a large area.

Nonrenewable resource A nonrenewable resource is one that is not replenished as fast as it is being used.

Normal fault A normal fault is an inclined break in the lithosphere where the upper block of rock has moved down relative to the lower block.

Nuclear fission Nuclear fission is the splitting of unstable atomic nuclei, accompanied by release of energy in the form of radiation and heat.

Nuclear fusion Nuclear fusion is the process of combining atomic nuclei of lighter elements to form heavier elements, accompanied by release of tremendous amounts of energy.

O

Oceanic crust Oceanic crust is the crust under the oceans. It is thin and consists mostly of the volcanic rock basalt.

Oil sand (tar sand) Oil sand is a sandstone impregnated with bitumen, a thick tar-like substance that must be heated or mixed with less viscous hydrocarbons before it will flow.

Oil shale Oil shale is an organic-rich sedimentary rock that is capable of generating oil but that hasn’t experienced the temperatures and pressures needed to convert the organic material (kerogen) to oil.

Open pit An open pit is a surface excavation to extract useful rocks or minerals.

Ore Ore is the part of a mineral deposit that can be profitably mined and recovered at current and projected commodity prices.

Outcrop An outcrop is a surface exposure of the solid geosphere.

Oxbow lake An oxbow lake is a crescent-shaped body of standing water in an abandoned channel of a meandering stream.

Oxidation Oxidation is the chemical reaction that combines oxygen with other elements. It is especially common where the atmosphere, hydrosphere, and geosphere interact.

Oxisol Oxisol is a soil order characteristic of warm, wet tropical forests; these are deeply weathered soils that have been leached of much of their original mineral content.

Ozone Ozone (O₃) is a molecule consisting of three oxygen atoms.

Ozone layer The ozone layer is a part of the atmosphere that overlaps the boundary between the troposphere and stratosphere where natural ozone (O₃) is concentrated.

P

P (primary) waves P waves are seismic body waves that alternatively push and pull (that is, compress and expand) rocks along their direction of travel. They are the fastest of the seismic waves.

Pahoehoe Pahoehoe is a Hawaiian term for a type of basaltic lava flow typified by a smooth, billowy, or ropy surface.

Paleomagnetism Paleomagnetism is the magnetism preserved in magnetic minerals at the time they formed.

Pangaea Pangaea is the name of the supercontinent that formed about 250 million years ago. All of Earth’s continents were amalgamated in Pangaea.

Parts per million (ppm) Parts per million is a measure of concentration, equivalent to about one drop in 50 L (13 gal) of water.

Peak oil production Peak oil production refers to the time when nothing more can be done to increase production and the amount of oil produced will begin to decline.

Period The period of a seismic wave is the interval of time required for one complete peak to peak vibration to pass by a seismometer.

Permeability Permeability is the property or capacity of a porous rock, sediment, or soil to let a fluid such as water pass through.

pH pH is the measure of a soil’s acidity; a pH less than 7 is acidic, a pH of 7 is neutral, and a pH greater than 7 is alkaline.

Photosynthesis Photosynthesis is the process by which certain organisms, especially plants, use energy from sunlight to convert carbon dioxide and water into simple sugars that can be used for food. Oxygen is released by most photosynthetic reactions.

Photovoltaic cell A photovoltaic cell is a semiconductor device that converts the energy of sunlight into electric energy.

Phytoremediation Phytoremediation is the use of plants to remove contaminants from soil.

Plate (lithospheric plate, tectonic plate) A plate is a discrete piece of lithosphere that moves relative to other pieces.

Plate tectonics Plate tectonics is the unifying theory that explains the dynamic nature of the geosphere and its relation to the interaction of tectonic plates.

Plutonic igneous rock A plutonic igneous rock is a rock that crystallizes from magma within the crust.

Point sources (of pollution) Point sources are those that release pollutants from a specific site such as a pipe, ditch, tunnel, well, container, concentrated animal-feeding operation, or floating craft.

Policy Policy is a term that encompasses both specific plans of action and principles that guide future decisions.

Pollutant A pollutant is any substance that makes air unsafe or dirty.

Pore pressure Pore pressure is the pressure transmitted by the fluid that fills the voids between particles of a soil or rock mass.

Porosity Porosity is the percentage of an Earth material consisting of void spaces—small openings (pores) between particles of sand, silt, clay, or gravel, or fractures and hollows within a body of solid rock.

Potentially Responsible Party (PRP) A PRP is any individual, company, or other party potentially liable for payment of CERCLA cleanup costs, including companies that generate hazardous substances disposed of at a CERCLA site, current and former owners and operators of the site, and transporters who selected the site for disposal of hazardous substances.

Precession Precession is the change in direction of Earth’s axis over long periods of time.

Precursor A precursor is a physical or seismic phenomena that may indicate a pending earthquake.

Prospect A prospect is an area that is a potential site of mineral deposits, based on geologic, geochemical, or geophysical indications.

Pumice Pumice is cavity-rich, glassy, volcanic rock that formed from magma containing abundant gas bubbles.

Pyroclastic flow A pyroclastic flow is a current of pyroclastic material, usually very hot and composed of a mixture of gases and particles of rock and lava, that flows along the ground surface.

Pyroclastics Pyroclastics are volcanic materials erupted into the atmosphere.

Q

Quartz Quartz is the mineral that contains the two most abundant elements in the crust, silicon and oxygen; it contains one atom of silicon for every two atoms of oxygen.

Quick clay Quick clay is composed of silt grains surrounded by a jumble of thin, platy clay minerals, forming a chaotic “house of cards” structure filled with water. Quick clay can lose all or nearly all internal strength upon being disturbed.

R

Radiometric dating Radiometric dating is the determination of a natural material’s age by measuring the concentrations of radioactive elements and their decay products included within the material. Radiometric dating determines the absolute or numerical age of geologic materials in years before the present.

Reclamation Reclamation is the conversion of disturbed land to land suitable for habitat or other uses. It commonly involves reshaping of the land surface to resist erosion, covering it with soil, and planting new vegetation to help stabilize the land surface.

Recurrence interval A flood recurrence interval is the average time between past flood events of a similar size.

Refining Refining is the processing of petroleum to produce marketable products such as gasoline or diesel fuel.

Regional subsidence Regional subsidence is gradual lowering of the land surface over a large area.

Relative age A relative age identifies whether one material or event is older or younger than another.

Renewable resource A renewable resource is one that will continue to be available because it is naturally replenished as fast as, or faster than, it is being consumed.

Reservoir A reservoir is a place where specified matter or energy is stored in a system.

Residence time Residence time is the average amount of time that specified matter spends in a defined system reservoir.

Resisting force Resisting force is a general term for the forces that oppose gravity in surface materials.

Resource Conservation and Recovery Act (RCRA) RCRA is a federal statute that establishes policies that cover the generation, storage, transport, and disposal of solid and hazardous waste.

Reverse fault A reverse fault is an inclined break in the lithosphere where the upper block of rock has moved up relative to the lower block.

Reverse osmosis Reverse osmosis is a process for separating dissolved constituents from water by pumping it through special filters whose tiny openings allow water molecules to pass, but not salt and other minerals.

Revetment A revetment is generally a lighter-duty structure than a seawall or bulkhead, used to protect embankments or beaches from erosion by near-shore currents or light wave activity.

Richter magnitude scale The Richter magnitude scale represents the size of an earthquake based on the strongest seismic wave amplitude recorded at a standard distance of 100 kilometers (62 mi) from the epicenter with a standard torsion seismograph.

Ridge (oceanic ridge, mid-ocean ridge) An oceanic ridge is an underwater mountain range that formed at a spreading center along a divergent plate boundary.

Rift A rift is a place where crust is extending and breaking apart. Along a rift, hot material in the mantle rises and the overlying crust thins and weakens as it is warmed and stretched.

Rip current A rip current is a plume-shaped current that conveys the water from breaking waves back through the surf zone.

Rock A rock is a solid part of the geosphere that is most commonly an aggregate of one or more minerals.

Rock cycle The rock cycle is a sequence of changes in rocks of the crust, produced by weathering, erosion, sedimentation, lithification, metamorphism, and igneous processes.

Rotational slide In a rotational slide, the unstable material slides downward and outward along a concave surface (like the bowl of a spoon) rather than a planar surface.

Runoff Runoff is a general term for surface water that flows overland to and within streams; it is the part of precipitation that accumulates in surface streams.

S

S (secondary or shear) waves S waves are seismic body waves that vibrate rock perpendicular to the direction of wave movement—that is, up and down or side to side, as in waves on a shaken rope. Typically about half as fast as P waves, they do not travel through liquids or through the outer core of the Earth.

Salination Salination is the contamination of soil by salt.

Salinity Salinity is a measure of water’s concentration of dissolved salt.

Saltwater intrusion Saltwater intrusion is the movement of saltwater into a freshwater aquifer, commonly because of the withdrawal of groundwater in coastal areas and estuaries.

Scarp A scarp is a steep slope or bank on Earth’s surface created by movement on a fault.

Scientific method The scientific method is a systematic approach to exploring and explaining how the natural world operates. It is an iterative process of inquiry that involves acquiring data, formulating questions, devising hypotheses, making predictions from hypotheses, and carrying out observations to support or refute hypotheses.

Seafloor spreading Seafloor spreading is the movement of newly formed oceanic crust away from mid-ocean ridges.

Seawall A seawall is a massive structure, built onshore, designed to withstand the full force of storm waves.

Sedimentary basin A sedimentary basin is a large area where sediment accumulates.

Sedimentary rock A sedimentary rock is a rock that formed from either clastic or chemical sediments.

Sedimentation Sedimentation is the process of depositing sediments.

Seismic gap A seismic gap is a segment of a fault that has not ruptured recently relative to neighboring segments.

Seismic survey A seismic survey uses seismic waves to image the subsurface character and geometry of rocks.

Seismic waves Seismic waves is a general term for elastic waves (vibrations) in Earth, typically produced by earthquakes (although they can also be generated artificially).

Seismogram A seismogram is a record of ground motion measured by a seismometer.

Seismology Seismology is the study of earthquakes, and of the structure of the Earth, by means of both natural and artificially generated seismic waves.

Seismometer A seismometer is an instrument that measures ground motions caused by passing seismic waves.

Shear strength Shear strength is a measure of how well the soil resists forces before fracturing internally.

Sheet flow Sheet flow is thin nonchannelized overland flow of water taking the form of a thin, continuous film and not concentrated into channels larger than rills.

Shield volcano A shield volcano is a volcano in the shape of a broad, low dome built by successive flows of fluid basaltic lava.

Silica Silica is the general term for the chemical compound that contains one atom of silicon for every two atoms of oxygen (SiO₂).

Silicate mineral A silicate mineral is one that includes silicon and oxygen tetrahedra in its internal structure.

Sink A sink is a system reservoir where matter has a very long residence time. Sinks isolate matter from system interactions.

Sinkhole A sinkhole is a circular depression in karst terrain.

Slag Slag is the glassy waste material left over from smelting.

Slide Slide is a general term for a mass movement that moves down-slope along a sloping surface, as opposed to free falling, tumbling, or bouncing.

Slope failure Slope failure occurs when the driving force is greater than the resisting forces, resulting in the gradual or rapid downslope movement of surface material or rock.

Slump Slump is an alternative term for a rotational slide.

Smelting Smelting is a metallurgical technique that separates metal from minerals by heating them to their melting point.

Smog Smog is a dense, hazy air pollution that obscures visibility, produced by the photochemical reaction of sunlight with hydrocarbons and nitrogen oxides released into the atmosphere, especially by automotive emissions.

Soil orders Soil orders are categories of soil variations within a systematic classification scheme used to describe and compare them, based on the presence or absence of diagnostic horizons or other special properties.

Soil profile A soil profile is a vertical section of a soil through all its stratified horizons.

Spodosol Spodosol is a soil order characteristic of cool, moist coniferous forest regions; these soils are acidic and typically have a subsurface accumulation of humus that is combined with aluminum and iron oxides or hydroxides.

Stage Stage is the height of a water surface above an arbitrarily established plane, commonly the bed level of a stream.

Stakeholder A stakeholder is anyone interested in or affected by an action.

State Environmental Policy Act (SEPA) SEPA is a state statute modeled after NEPA that requires state and local agencies to consider the likely environmental consequences of a proposed action before approving or denying it.

Steady state A steady-state system is one in which the transfers of matter or energy in and out are approximately equal. As a result, the system appears not to change.

Storm surge A storm surge is a high mass of water piled up against the coast, caused primarily by strong winds offshore; it is most severe during high tide.

Stratosphere The stratosphere is the part of the atmosphere between the troposphere and mesosphere where temperatures increase upward.

Stratovolcano A stratovolcano is a volcano constructed of alternating layers of lava and pyroclastic deposits, along with abundant igneous intrusions. Also called a composite volcano.

Strike-slip fault A strike-slip fault is a surface between two blocks of rock along which one block slides horizontally past the other.

Subduction Subduction is the sinking of a lithospheric plate into the mantle along a convergent plate boundary.

Subduction zone A subduction zone is the inclined part of a convergent plate boundary where oceanic lithosphere is sinking into the mantle.

Subsidence Subsidence is the sudden sinking or gradual downward settling of Earth’s surface with little or no horizontal motion.

Superfund Superfund is another term for CERCLA.

Surf zone The surf zone is the turbulent area along a shore created by breaking waves.

Surface waves Surface waves are seismic waves that travel along Earth’s outer edges rather than through its interior.

Sustainable Sustainable means that something is capable of being continued with minimal long-term effect on the environment. In a human context, it means that the needs of the present generation are met without compromising the ability of future generations to meet their needs.

System A system is a group of interacting, interrelated, or interdependent parts that together form a whole.

T

Tailings Tailings are leftover material from mineral processing, especially the milling and flotation of sulfide minerals, that is discarded.

Talus Talus is a pile of angular rock fragments that have fallen from a cliff or steep rocky slope above.

Tephra Tephra is collective term used for all pyroclastic material, regardless of size, shape, or origin, that is ejected during an explosive volcanic eruption.

Theory In science, a theory integrates a number of extensively tested hypotheses into a well-accepted unifying framework. A theory explains a large set of observations and relationships and has been verified independently by many researchers.

Thermosphere The thermosphere is the outer atmospheric layer above the mesosphere. Temperatures decrease upward through the thermosphere and the concentrations of gases gradually decrease as the thermosphere merges with empty space.

Thrust fault A thrust fault is a low-angle reverse fault; the surface along which blocks of rock move has a low inclination.

Tide The tide is the daily rise and fall of sea level that results from the gravitational attraction of the Sun and Moon.

Topsoil Topsoil is a general term for the upper layer of a soil that typically contains high levels of organic material and the root systems of surface vegetation.

Total Maximum Daily Load (TMDL) TMDL is the amount of pollutant that a water body can receive without exceeding its water quality standard.

Transform fault A transform fault is a type of strike-slip fault that converts movements at divergent or convergent plate boundaries into lateral sliding.

Transform plate boundary A transform plate boundary is the boundary along which two tectonic plates move laterally past each other.

Translational slide A translational slide is the movement of a largely intact mass, sliding as a single coherent block or a group of blocks on a surface that is roughly parallel to the general ground surface.

Trap A trap is a place in the geosphere where impermeable barriers prevent the further movement of oil or gas, allowing them to accumulate; it consists of a reservoir rock that contains the oil or gas and an impermeable roof rock.

Trench (oceanic trench) A trench is a long, narrow depression in the seafloor. Trenches are the deepest parts of the oceans, formed where a tectonic plate sinks into the mantle along a convergent plate boundary.

Tributary A tributary is a stream feeding, joining, or flowing into a larger stream.

Troposphere The troposphere is the lowest part of the atmosphere, where most of the atmosphere’s matter is concentrated and most of what people call weather occurs.

Trunk river The trunk or main river is the principal, largest, or dominating river of any given area or drainage system.

Tsunami A tsunami is a large ocean wave commonly generated by movement of the seafloor during a subduction-zone earthquake.

Tuff Tuff is lithified volcanic ash.

U

Unconfined aquifer An unconfined aquifer is an aquifer that is overlain by permeable Earth material.

Unconsolidated material Unconsolidated material is loose, nonaggregated Earth material such as soil, sand, and broken rock debris.

V

Vein A vein is a long, narrow, sheet-like concentration of minerals, commonly localized along a fault or other fracture.

Viscosity Viscosity is a substance’s resistance to flow.

Volatile Organic Compound (VOC) A volatile organic compound is an easily vaporized compound of carbon and hydrogen, such as gasoline or solvents like toluene, xylene, and tetrachloroethylene.

Volcanic arc A volcanic arc is a chain of volcanoes on land that forms above a subduction zone.

Volcanic Explosivity Index (VEI) The volcanic explosivity index is a scale of numbers from 0 to 8, used to compare volcanic eruptions on the basis of the volume of material ejected by past eruptions, the height of the eruption column, the style of the eruption (lava flows versus explosive eruptions, for example), and how long the eruption lasted.

Volcanic igneous rock Volcanic igneous rocks form from lava and other material erupted at a volcano.

Volcano A volcano is a place where molten rock, or magma, rises from great depths to the uppermost levels of the crust and onto the surface.

W

Waste rock Waste rock is the rock that must be broken and disposed of in order to gain access to and excavate ore; it is valueless rock that must be removed or set aside in mining.

Watershed A watershed is the region drained by, or contributing water to, a stream, lake, or other body of water.

Water table The water table is the top of the saturated zone. From the water table to the surface, the open spaces in the ground are only partly filled with water.

Weathering Weathering is a set of physical and chemical processes that change rocks at Earth’s surface.

Wetland A wetland is an area that is regularly wet or flooded and has a water table that stands at or above the land surface for at least part of the year.