S Index Glossary geology Science
S Index Glossary geology Science
Saltation
The transport of sediment in short jumps and bounces above the stream bed or ground by a current that is not strong enough to hold the sediment in continuous suspension. (See suspension and traction for comparison).
Schist
A metamorphic rock containing abundant particles of mica, characterized by strong foliation, and originating from a metamorphism in which directed pressure plays a significant role.
Schistosity
The parallel arrangement of platy or prismatic minerals in a rock that is caused by metamorphism in which directed pressure plays a significant role.
Scoria
An igneous rock of basaltic composition and containing numerous vesicles caused by trapped gases.
Seamount
A mountain on the sea floor that has at least 1000 meters of local relief. Most seamounts are shield volcanoes. (See also Guyot.)
Sedimentary Structure
A structure in a sedimentary rock that forms at or near the time of deposition and reveals information about the depositional environment. Examples include ripple marks, cross-bedding, mud cracks, and graded bedding.
Sedimentation
The process of sediment deposition from out of a suspension or solution.
Seif Dune
A large sand dune that forms parallel to the direction of a strong wind that blows in a consistent direction throughout the year. Also called a longitudinal dune.
Seismicity
The study of the worldwide distribution of earthquakes over time and the probability of an earthquake occurring in a specific location.
Settling Pond
An open pond where waste or process water is allowed to stand while suspended materials settle out.
Sinkhole
A depression in the land surface that results from the collapse or slow settlement of underground voids produced by solution weathering. The rock being dissolved is normally limestone but can also be salt, gypsum or dolostone.
- A circular, often funnel-shaped depression in the ground that forms when soluble rocks dissolve.
Storm Surge
The piling up of water along a shoreline cause by the sustained winds of a strong storm - usually a hurricane..
Sandblasting
A physical weathering process in which rock is eroded by the impact of sand grains carried by the wind, frequently leading to ventifact formation of pebbles and cobbles.
Secular variation
Slow changes in the orientation of the Earth's magnetic field that appear to be long lasting and internal in origin as opposed to rapid fluctuations, which are external in origin.
Seismic profile
The data collected from a set of seismographs arranged in a straight line with an artificial seismic source, especially the times of P-wave arrivals.
Seismic refraction
A mode of seismic prospecting in which the seismic profile is examined for waves that have been refracted upward from seismic discontinuities below the profile. Greater depths may be reached than through seismic reflection.
Seismic surface wave
A seismic wave that follows the earth's surface only, with a speed less than that of S-waves. There are
Seismic transition zone
A seismic discontinuity, found in all parts of the Earth, at which the velocity increases rapidly with depth; especially the one at 300 to 600 kilometers.
Streaming flow
A tranquil flow slower than shooting flow.
Streamline
A curved line representing the successive positions of a particle in a flow as time passes.
Supersaturation
The unstable state of a solution that contains more solute than its solubility allows.
Swell
An oceanic water wave with a wavelength on the order of 30 meters or more and a height of perhaps 2 meters or less that may travel great distances from its source.
scale
The proportional relationship between a linear measurement on a map and the distance it represents on the Earth's surface.
S wave
abbreviation for secondary wave-A body wave that causes the rocks along which it passes to move up and down perpendicular to the direction of its own movement. See also P wave.
S-wave shadow zone
The region within an arc of 1540 directly opposite an earthquake's epicenter that is marked by the absence of S waves. The S-wave shadow zone is due to the fact that S waves can not penetrate the liquid outer core. See also P-wave shadow zone.
sand
1. A particle of rock or mineral material, coarser than silt, that has been transported from its place of origin, as by water or wind. A particle of sand is usually between 1/16 and two millimeters in diameter. Sands are frequently composed of quartz. 2. A loosely connected body of such particles.
sandstone
A clastic rock composed of particles that range in diameter from 1/16 millimeter to 2 millimeters in diameter. Sandstones make up about 25% of all sedimentary rocks.
sea arch
A landform produced by coastal erosion of a prominent headland. Sea arches form when sea caves are excavated so deeply by crashing waves that two caves eroding on opposite sides of the headland become joined. The overlying rocky roof is left as an arch.
sea cave
The notches in the sides of a prominent coastal rocky headland eroded by crahing waves.
seismic moment
A numerical means of measuring an earthquake's total energy release. It is calculated by measuring the total length of fault rupture and then factoring in the depth of rupture, total slip along the rupture, and the strength of the faulted rocks.
solifluction
A form of creep in which soil flows downslope at a rate of 0.5 to 15 centimeters per year. Solifluction occurs in relatively cold regions when the brief warmth of summer thaws only the upper meter or two of regolith, which becomes waterlogged because the underlying ground remains frozen and therefore the water cannot drain down into it.
saturation zone
See zone of saturation.
scarp
The steep cliff face that is formed by a slump.
- Also "escarpment." A steep cliff or steep slope, formed either as a result of faulting or by the erosion of inclined rock strata.
scientific law
1. A natural phenomenon that has been proven to occur invariably whenever certain conditions are met. 2. A formal statement describing such a phenomenon and the conditions under which it occurs. Also called law.
scientific methods
Techniques that involve gathering all available data on a subject, forming an hypothesis to explain the data, con ducting experiments to test the hypothesis, and modifying or con firming the hypothesis as necessary to account for the experimental results.
sea-floor spreading
The formation and growth of oceans that occurs following rifting and is characterized by eruptions along mid-ocean ridges, forming new oceanic lithosphere, and expanding ocean basins. See also divergence.
sea stack
A steep, isolated island of rock, separated from a head land by the action of waves, as when the overhanging section of a sea arch is eroded.
seawall
A wall of stone, concrete, or other sturdy material, built along the shoreline to prevent erosion even by the strongest and highest of waves. See also riprap.
secondary coast
A coast shaped primarily by erosion or deposition by sea currents and waves.
secondary enrichment
The process by which a metal deposit becomes concentrated when other minerals are eliminated from the deposit, as through dissolution, precipitation or weathering.
sedimentary environment
The continental, oceanic, or coastal surroundings in which sediment accumulates.
sedimentary facies
1. A set of characteristics that distinguish a given section of sedimentary rock from nearby sections. Such characteristics include mineral content, grain size, shape, and density. 2. A section of sedimentary rock so characterized.
seismic
Of, concerning, subject to, or produced by an earthquake.
seismic discontinuity
A surface marking the boundary between two layers of the Earth differing in composition. Seismic waves passing through a seismic discontinuity undergo an abrupt change in velocity.
seismic gap
A locked fault segment that has not experienced seismic activity for a long time. Because stress tends to accumulate in seismic gaps, they often become the sites of major earthquakes.
seismic profiling
The mapping of rocks lying along and beneath the ocean floor by recording the reflections and refractions of seismic waves.
seismic tomography
The process whereby a computer first synthesizes data on the velocities of seismic waves from thousands of recent earthquakes in order to make a series of images depicting successive planes within the Earth, and then uses these images to construct a three-dimensional representation of the Earth's interior.
seismic wave
One of a series of progressive disturbances that reverberate through the Earth to transmit the energy released from an earthquake.
seismogram
A visual record produced by a seismograph and showing the arrival times and magnitudes of various seismic waves.
seismograph
A machine for measuring the intensity of earthquakes by recording the seismic waves that they generate.
seismology
The study of earthquakes and the structure of the Earth, based on data from seismic waves.
shale
A sedimentary rock composed of detrital sediment particles less than 0.004 millimeters in diameter. Shales tend to be red, brown, black, or gray, and usually originate in relatively still waters.
shearing stress
Stress that slices rocks into parallel blocks that slide in opposite directions along their adjacent sides. Shearing stress may be caused by transform motion.
shield volcano
A low, broad, gently sloping, dome-shaped structure that forms over time as repeated eruptions eject basaltic lava through one or more vents and the lava solidifies in approximately the same volume all around.
shock metamorphism
The metamorphism that results when a meteorite strikes rocks at the Earth's surface. The meteoric impact generates tremendous pressure and extremely high temperatures that cause minerals to shatter and recrystallize, producing new minerals which cannot arise under any other circumstances.
shoreline
The boundary between a body of water and dry land. silica A compound consisting of silicon and oxygen.
silicate
One of several rock-forming minerals that contain silicon, oxygen, and usually one or more other common elements.
silicon-oxygen tetrahedron
A four-sided geometric form created by the tight bonding of four oxygen atoms to each other, and also to a single silicon atom that lies in the middle of the form.
sill
A concordant pluton that is substantially wider than it is thick. Sills form within a few kilometers of the Earth's surface. See also dike.
silt
1. A particle of rock or mineral material, finer than sand but coarser than clay, that has been transported from its place of origin, typically by wind or water. A particle of silt is usually between 1/16 and 1/256 of a millimeter in diameter. 2. A loosely connected body of such particles.
skarn
A coarse-grained, nonfoliated metamorphic rock containing silicates that are rich in calcium.
slate
A fine-grained, foliated metamorphic rock that develops from shale and tends to break into thin, flat sheets.
slide
The mass movement of a single, intact mass of rock, soil, or unconsolidated material along a weak plane, such as a fault, fracture, or bedding plane. A slide may involve as little as a minor displacement of soil or as much as the displacement of an entire mountainside.
slip face
The steep leeward slope of a dune.
slip plane
A weak plane in a rock mass from which material is likely to break off in a slide.
slump
1. A downward and outward slide occurring along a concave slip plane. 2. The material that breaks off in such a slide.
snowline
The lowest point at which snow remains year-round.
soil
The top few meters of regolith, generally including some organic matter derived from plants.
soil horizon
A layer of soil that can be distinguished from the surrounding soil by such features as chemical composition, color, and texture.
soil profile
A vertical strip of soil stretching from the surface down to the bedrock and including all of the successive soil horizons.
solifiuction
A form of creep in which soil flows downslope at 0.5 to 15 centimeters per year. Solifluction occurs in relatively cold regions when the brief warmth of summer thaws only the upper meter or two of regolith, which becomes waterlogged because the underlying ground remains frozen and therefore the water cannot drain down into it.
sorting
The process by which a given transport medium separates out certain particles, as on the basis of size, shape, or density.
source rock
A rock in which hydrocarbons originate.
specific gravity
The ratio of the weight of a particular volume of a given substance to the weight of an equal volume of pure water.
speleothem
A mineral deposit of calcium carbonate that precipitates from solution in a cave.
spheroidal weathering
The process by which chemical weathering, especially by water, decomposes the angles and edges of a rock or boulder, leaving a rounded form from which concentric layers are then stripped away as the weathering continues
spit
A narrow, fingerlike ridge of sand that extends from land into open water.
stalactite
An icicle-like mineral formation that hangs from the ceiling of a cave and is usually made up of travertine, which precipitates as water rich in dissolved limestone drips down from the cave's ceiling. See also stalagmite.
stalagmite
A cone-shaped mineral deposit that forms on the floor of a cave and is usually made up of travertine, which precipitates as water rich in dissolved limestone drips down from the cave's ceiling. See also stalactite.
star dune
A dune with three or four arms radiating from its usually higher center so that it resembles a star in shape. Star dunes form when winds blow from three or four directions, or when the wind direction shifts frequently.
strain
The change in the shape or volume of a rock that results from stress.
stratovolcano
A cone-shaped volcano built from alternating layers of pyroclastics and viscous andesitic lava. Stratovolcanos tend to be very large and steep.
stratum
plural strata-A layer of sedimentary rock that is visibly distinct from the surrounding layers.
streak
The color of a mineral in its powdered form. This color is usually determined by rubbing the mineral against an unglazed porcelain slab and observing the mark made by it on the slab.
stream discharge
The volume of water to pass a given point on a stream bank per unit of time, usually expressed in cubic meters of water per second.
stream terrace
A level plain lying above and running parallel to a stream bed. A stream terrace is formed when a stream's bed erodes to a substantially lower level, leaving its flood plain high above it.
stress
The force acting on a rock or another solid to deform it, measured in kilograms per square centimeter or pounds per square inch.
striation
One of a group of usually parallel scratches engraved in bedrock by a glacier or other geological agent.
strike
1. The horizontal line marking the intersection between the inclined plane of a solid geological structure and the Earth's surface. 2. The compass direction of this line, measured in degrees from true north.
structural geology
The scientific study of the geological processes that deform the Earth's crust and create mountains.
subduction
The sinking of an oceanic plate edge as a result of convergence with a plate of lesser density. Subduction often causes earthquakes and creates volcano chains.
sulfate
One of several minerals containing positive sulfur ions bonded to negative oxygen ions.
sulfide
One of several minerals containing negative sulfur ions bonded to one or more positive metallic ions.
surge
To flow more rapidly than usually. Said of a glacier.
syncline
A concave fold, the central part of which contains the youngest section of rock. See also anticline.
Scots-Irish
The North American descendants of Protestants from
sea level
The ocean surface.
Second Home
A seasonally occupied dwelling that is not the primary residence of the owner. Such residences are usually found in areas with substantial opportunities for recreation or tourist activity.
Secondary Sector
That portion of a region's economy devoted to the processing of basic materials extracted by the primary sector.
Sharecropping
A form of agricultural tenancy in which the tenant pays for use of the land with a predetermined share of his crop rather than with a cash rent.
Shield
A broad area of very old rocks above sea level. Usually characterized by thin, poor soils and low population densities.
Silage
Fodder (livestock feed) prepared by storing and fermenting green forage plants in a silo.
Silo
Usually a tall, cylindrical structure in which fodder (animal feed) is stored; may be a pit dug for the same purpose.
Site
Features of a place related to the immediate environment on which the place is located (e.g., terrain, soil, subsurface, geology, ground water).
Situation
Features of a place related to its location relative to other places (e.g., accessibility, hinterland quality).
Smog
Mixture of particulate matter and chemical pollutants in the lower atmosphere, usually over urban areas.
SMSA
Standard Metropolitan Statistical Area-A statistical unit of one or more counties that focus on one or more central cities larger than a specified size, or with a total population larger than a specified size. A reflection of urbanization.
Soluble
Capable of being dissolved; in this case, the characteristic of soil minerals that leads them to be carried away in solution by water (see Leaching).
Space Economy
The locational pattern of economic activities and their interconnecting linkages.
Spatial Complementarity
The occurrence of location pairing such that items demanded by one place can be supplied by another.
Spatial Interaction
Movement between locationally separate places.
Staple Product
A product that becomes a major component in trade because it is in steady demand; thus, a product that is basic to the economies of one or more major consuming populations (see Primary Product).
Stratification
A layered structure of sedimentary rocks in which the individual layers can be traced a considerable distance. The layers can be caused by many differences which include materials of different composition, color, grain size or orientation.
Stratigraphic Sequence
The sequence of sedimentary rock layers found in a specific geographic area, arranged in the order of their deposition.
Stratigraphy
The study of sedimentary rock units, including their geographic extent, age, classification, characteristics and formation.
Streak Plate
A piece of unglazed porcelain that is used for determining the streak of a mineral specimen.
Stream Order
A classification system that represents the relative position of streams in a drainage basin. The highest tributaries in the basin are first order streams. These converge to form second order streams, which have only first order streams as their tributaries. Third order streams form by the confluence of two second order streams. The numbering system continues downstream resulting in higher stream orders.
Striations
Scratches or grooves on a rock or sediment surface caused by abrasive action of objects being transported above it by ice, water or wind.
Strike-Slip Fault
A fault with horizontal displacement, typically caused by shear stress.
Stromatolite
A mound-shaped fossil that forms from the repetitious layering of algal mat covered by trapped sediment particles.
Subduction Zone
An area at a convergent plate boundary where an oceanic plate is being forced down into the mantle beneath another plate. These can be identified by a zone of progressively deeper earthquakes.
Sublimation
The process through which ice goes directly into a vapor without passing through the liquid state.
An underwater canyon, carved into the continental shelf. These can be carved by turbidity currents or carved subaerially during a time when sea level was lower.
saline water
water that contains significant amounts of dissolved solids.
secondary wastewater treatment
treatment (following primary wastewater treatment) involving the biological process of reducing suspended, colloidal, and dissolved organic matter in effluent from primary treatment systems and which generally removes 80 to 95 percent of the Biochemical Oxygen Demand (BOD) and suspended matter. Secondary wastewater treatment may be accomplished by biological or chemical-physical methods. Activated sludge and trickling filters are two of the most common means of secondary treatment. It is accomplished by bringing together waste, bacteria, and oxygen in trickling filters or in the activated sludge process. This treatment removes floating and settleable solids and about 90 percent of the oxygen-demanding substances and suspended solids. Disinfection is the final stage of secondary treatment.
sediment
A collection of transported fragments or precipitated materials that accumulate, typically in loose layers, as of sand or mud.
- usually applied to material in suspension in water or recently deposited from suspension. In the plural the word is applied to all kinds of deposits from the waters of streams, lakes, or seas.
sedimentary rock
A rock made from the consolidation of solid fragments, as of other rocks or organic remains, or by precipitation of minerals from solution.
- rock formed of sediment, and specifically:
-(1) sandstone and shale, formed of fragments of other rock transported from their sources and deposited in water; and
-(2) rocks formed by or from secretions of organisms, such as most limestone. Many sedimentary rocks show distinct layering, which is the result of different types of sediment being deposited in succession.
sedimentation tanks
wastewater tanks in which floating wastes are skimmed off and settled solids are removed for disposal.
seepage
-(1) The slow movement of water through small cracks, pores, Interstices, etc., of a material into or out of a body of surface or subsurface water.
-(2) The loss of water by infiltration into the soil from a canal, ditches, laterals, watercourse, reservoir, storage facilities, or other body of water, or from a field.
self-supplied water
water withdrawn from a surface- or ground-water source by a user rather than being obtained from a public supply. An example would be homeowners getting their water from their own well.
sewage treatment plant
a facility designed to receive the wastewater from domestic sources and to remove materials that damage water quality and threaten public health and safety when discharged into receiving streams or bodies of water. The substances removed are classified into four basic areas:
-[1] greases and fats;
-[2] solids from human waste and other sources;
-[3] dissolved pollutants from human waste and decomposition products; and
-[4] dangerous microorganisms.
-Most facilities employ a combination of mechanical removal steps and bacterial decomposition to achieve the desired results. Chlorine is often added to discharges from the plants to reduce the danger of spreading disease by the release of pathogenic bacteria.
sewer
a system of underground pipes that collect and deliver wastewater to treatment facilities or streams.
solute
a substance that is dissolved in another substance, thus forming a solution.
solution
a mixture of a solvent and a solute. In some solutions, such as sugar water, the substances mix so thoroughly that the solute cannot be seen. But in other solutions, such as water mixed with dye, the solution is visibly changed.
solvent
a substance that dissolves other substances, thus forming a solution. Water dissolves more substances than any other, and is known as the "universal solvent".
specific conductance
a measure of the ability of water to conduct an electrical current as measured using a 1-cm cell and expressed in units of electrical conductance, i.e., Siemens per centimeter at 25 degrees Celsius. Specific conductance can be used for approximating the total dissolved solids content of water by testing its capacity to carry an electrical current. In water quality, specific conductance is used in ground water monitoring as an indication of the presence of ions of chemical substances that may have been released by a leaking landfill or other waste storage or disposal facility. A higher specific conductance in water drawn from downgradient wells when compared to upgradient wells indicates possible contamination from the facility.
spray irrigation
an common irrigation method where water is shot from high-pressure sprayers onto crops. Because water is shot high into the air onto crops, some water is lost to evaporation.
storm sewer
a sewer that carries only surface runoff, street wash, and snow melt from the land. In a separate sewer system, storm sewers are completely separate from those that carry domestic and commercial wastewater (sanitary sewers).
stream
A body of water found on the Earth's surface and confined to a narrow topographic depression, down which it flows and transports rock particles, sediment, and dissolved particles. Rivers, creeks, brooks, and runs are all streams.
- a general term for a body of flowing water; natural water course containing water at least part of the year. In hydrology, it is generally applied to the water flowing in a natural channel as distinct from a canal.
streamflow
the water discharge that occurs in a natural channel. A more general term than runoff, streamflow may be applied to discharge whether or not it is affected by diversion or regulation.
subsidence
The lowering of the Earth's surface, caused by such factors as compaction, a decrease in groundwater, or the pumping of oil.
- a dropping of the land surface as a result of ground water being pumped. Cracks and fissures can appear in the land. Subsidence is virtually an irreversible process.
surface tension
the attraction of molecules to each other on a liquid's surface. Thus, a barrier is created between the air and the liquid.
surface water
water that is on the Earth's surface, such as in a stream, river, lake, or reservoir.
suspended sediment
very fine soil particles that remain in suspension in water for a considerable period of time without contact with the bottom. Such material remains in suspension due to the upward components of turbulence and currents and/or by suspension.
suspended-sediment concentration
the ratio of the mass of dry sediment in a water-sediment mixture to the mass of the water-sediment mixture. Typically expressed in milligrams of dry sediment per liter of water-sediment mixture.
suspended solids
solids that are not in true solution and that can be removed by filtration. Such suspended solids usually contribute directly to turbidity. Defined in waste management, these are small particles of solid pollutants that resist separation by conventional methods.
Supercontinent
A large landmass that forms from the convergence of multiple continents.
Superposed Stream
A stream that cuts across resistant bedrock units. This can occur when the stream's course was determined at a previous time and on a previous landscape.
Superposition
The concept that the oldest rock layers are at the bottom of a sequence with younger rock layers deposited on top of them. This can be considered a rule that applies in all situations, except where the rocks are extremely deformed.
Supersaturated Solution
A solution that contains more solute than its solubility allows. Such a solution is unstable and precipitation can be triggered by a variety of events.
Surf
The breaking of waves as they enter shallow water.
Surf Zone
An area of breaking waves bounded by the point of first breakers, then landward to the maximum uprush of waves on the beach.
Surface Wave
A type of seismic wave that travels along Earth's surface.
Suspended Load
Small particles being carried by a stream and held in suspension by the movement of the water. (Also see load, dissolved load, bed load.)
Suspension
Transport of sediment by wind or water currents that are strong enough to keep the sediment particles continuously above the stream bottom or ground. (See traction and saltation for comparison.)
Swash
The rush of a breaking wave up the slope of a beach.
Symbiosis
A relationship between two species who live in close association but do not compete with each other or prey on one another. At least one of the species derives benefit from this association.
System
A stratigraphic unit of major significance which was deposited during a specific time period, and which can be correlated worldwide on the basis of its fossil content.