<b>Amateur<br>Geologist</b> Enter our Shop  
 

Geological Glossary - S

A B C D E F G H I J K L M N O P Q R S T U V W X Y Z
S wave "Secondary wave, a shear or transverse elastic wave, usually the most prominent wave on a seismogram; travels more slowly than P-waves and thus arrives later on seismograms. Shear, secondary, rotational, tangential, equivoluminal, distortional, transverse or shake wave. These waves carry energy through the Earth in very complex patterns of transverse (crosswise) waves. These waves move more slowly than P wave, but in an earthquake they are usually bigger. S wave cannot travel through the outer core because these waves cannot exist in fluids, such as air, water or molten rock."
ScS Seismic phase consisting of a shear wave traveling down through the mantle that is reflected at the core-mantle boundary and returns to the earth's surface as a shear wave. ScSn denotes a multiple ScS wave that is further reflected n-1 times at the earth's free surface.
Silurian A period in the geologic time scale that spans from 438 to 408 million years ago.
Soret effect (thermal diffusivity) Solute flux due to a temperature gradient.
A B C D E F G H I J K L M N O P Q R S T U V W X Y Z
salt water intrusion The invasion of fresh surface or groundwater by salt water.
sand Loose particles of rock or mineral (sediment) that range in size from 0.0625 - 2.0 millimeters in diameter.
sandblasting A physical weathering process in which rock is eroded by the impact of sand grain carried by the wind, frequently leading to ventifact formation of pebble and cobble.
sandstone A detrital sedimentary rock composed of grain from 1/16 to 2 millimeters in diameter, dominated in most sandstone by quartz, feldspar, and rock fragments, bound together by a cement of silica, carbonate, or other mineral or a matrix of clay minerals.
sanidine A type of potassium feldspar that form only at high temperature. Common in potassium-rich volcanic rock.
saprolite Fine-grained weathering zone with microscopic or submicroscopic porosity occurring immediately above parent material bedrock. Saprolite is not contaminated by invasion of detritus from above and may or may not be isovolumetric.
sapropel "Lithified organic-rich marine sediment deposited under anoxic conditions. If the organic content is very high, the sediments lithify to become black shale; if dilution by clay or other materials occurs, the sediments lithify to become marlstone."
scarp A cliff formed by faulting, erosion, or landslide. (=escarpment)
schist Metamorphic rock usually derived from fine-grained sedimentary rock such as shale. Individual mineral in schist have grown during metamorphism so that they are easily visible to the naked eye. Schists are named for their mineral constituents. For example, mica schist is conspicuously rich in mica such as biotite or muscovite.
schistosity The parallel layering of individual platy or prismtic mineral, usually mica or hornblende, that have grown during metamorphism so that they are easily visible to the naked eye.
scoria Very bubbly (vesicular) basalt or andesite. Both scoria and pumice develop their bubbly textures when escaping gas is trapped as lava solidifies. Scoria is more dense and darker than pumice.
sea aerosol Colloidal-size particles of substances derived from the sea surface.
sea stack Sea stacks are blocks of erosion-resistant rock isolated from the land by sea.
sea-floor spreading The mechanism by which new sea floor crust is created at ridges in divergence zones and adjacent plate are moved apart to make room. This process may continue at 0.5 to 10 centimeters/year through many geologic periods.
seamount An elevation of the sea floor, 1000 m or higher, either flat-topped (called a guyot) or peaked (called a seapeak). Seamounts may be either discrete, arranged in a linear or random grouping, or connected at their bases and aligned along a ridge or rise
secondary coast A mature coast that has been carved by wave action over a long period of time.
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.
sediment Rock debris commonly produced by mechanical or chemical weathering processes.
sedimentary Sedimentary rocks are formed from pre-existing rocks or pieces of once-living organisms. They form from deposits that accumulate on the Earth’s surface. Sedimentary rocks often have distinctive layering or bedding.
sedimentary A rock formed by the accumulation and cementation of mineral grain transported by wind, water, or ice to the site of deposition or chemically precipitated at the depositional site.
sedimentary petrology Study of the composition, characteristics and origin of sediment and sedimentary rocks.
sedimentary structure "Any structure of a sedimentary or weakly metamorphosed rock that was formed at the time of deposition; includes bedding, cross-bedding, graded bedding, ripple, scour marks, mud-cracks. "
sedimentation The process of deposition of mineral grain or precipitates in bed or other accumulations. Seif dune
seiche A free or standing wave oscillation of the surface of water in an enclosed basin that is initiated by local atmospheric changes, tidal current or earthquake. Similar to water sloshing in a bathtub.
seif dune A longitudanal dune having one side rounded, the other side being a steep slip face, and a long sharp edge on the top.
seismic Pertaining to earthquake activity.
seismic belt An elongated earthquake zone, for example, circum-Pacific, Mediterranean, Rocky Mountain. About 60% of the world's earthquakes occur in the circum-Pacific seismic belt.
seismic constant In building codes dealing with earthquake hazards, an arbitrarily-set acceleration value (in units of gravity) that a building must withstand.
seismic discontinuity Regionally extensive, thin zones in the crust or mantle where seismic velocities change abruptly. May be the result of changes in composition, mineral phase or structural character.
seismic profile The data collected from a set of seis-toographs arranged in a straight line with an artificial seismic source, especially the times of P-wave arrival.
seismic reflection A mode of seismic prospecting in which the seismic profile is examined for wave that have reflected from near-horizontal strata below the surface.
seismic refraction A mode of seismic prospecting in which the seismic profile is examined for wave that have been refracted upward from seismic discontinuities below the profile. Greater depths may be reached than through seismic reflection.
seismic sea wave A tsunami generated by an undersea earthquake.
seismic surface wave A seismic wave that follows the earth's surface only, with a speed less than that of S-waves. There are Raleigh waves (forward and vertical vibrations) and Love wave (transverse vibrations).
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. "
seismic zone A region in which earthquake are known to occur.
seismicity " The world-wide or local distribution of earthquake in space and time; a general term for the number of earthquakes in a unit of time. "
seismogram A written record of an earthquake recorded by a seismograph.
seismograph "An instrument that records seismic wave; that is vibrations of the earth. Used to record and measure earthquake. "
serpentine "A family of silicate mineral rich in magnesium and water, derived from low-temperature alteration or metamorphism of the minerals in ultramafic rock. Rocks made up of serpentine minerals are called serpentinite. Serpentine minerals are light to dark green, commonly varied in hue, and greasy looking; the mineral feels slippery."
sferics Natural atmospheric fluctuations of the electromagnetic fields, caused mainly by thunderstorm activity in the range of 1-10E5 Hz.
shale Sedimentary rock derived from mud. Commonly finely laminated (bedded). Particles in shale are commonly clay mineral mixed with tiny grain of quartz eroded from pre-existing rocks. Shaley means like a shale or having some shale component, as in shaley sandstone.
shearing The motion of surfaces sliding past one another.
sheetwash Overland flow of water in thin sheets
shield Tectonically stable, low-lying Precambrian nucleus of continent. Commonly contains the metamorphosed roots of ancient orogenic activity.
shield "A large area of exposed basement rocks in a craton, commonly with a very gently convex surface, surrounded by sediment-covered platforms; e.g., Canadian Shield, Baltic Shield. The rocks of virtually all shield areas are Precambrian."
shield volcano A gently sloping volcano in the shape of a flattened dome built almost exclusively of mafic lava flows. The Hawaiian Islands are a good example.
shields An extensive area of a continental plate where the igneous and metamorphic are exposed and have approached equilibrium in respect to erosion and isostasy. The rocks of a shield are usually Precambrian.
shock metamorphism Characteristic changes in rock mineralogy caused by the compression of a passing shock wave.
shock wave Moving wave of strong compression that usually travels faster than sound in the medium.
shrink-swell Refers to the property of many clay to swell when wetted and shrink when dried.
sial "A petrologic name for the upper layer of the Earth's crust, composed of rocks that are rich in silica and alumina; it may be the source of granitic magma. It is characteristic of the upper continental crust. Etymol: an acronym for silica + alumina."
signal-to-noise ratio A quantitative measure of the statistical detectability of a signal, expressed as a ratio of the magnitude of the signal relative to the variability. For first detection of a CO2-induced climate change, the model signal is the mean change or anomaly in some climatic variable, usually surface air temperatures, attributed by a numerical model to increased concentrations of carbon dioxide. Observed noise is the standards deviation or natural variability computed from observations of that variable and agjusted for sample size, autocorrelation and time averaging.
silica Silicon dioxide (SiO2). One of the most common compounds in the Earth’s crust. Common window glass is made of silica. The building block of the mineral quartz and other silicate minerals.
silicate Refers to the chemical unit silicon tetroxide, SiO4, the fundamental building block of silicate mineral. Silicate minerals make up most rocks we see at the Earth’s surface.
siliceous Generally refers to a rock rich in quartz.
sill A sill is a flat, roughly horizontal, igneous intrusion that lies parallel to the enclosing layer of rock.
sillimanite An aluminum-rich silicate found only in metamorphic rocks that form at high temperature and pressure.
silt Loose particles of rock or mineral (sediment) that range in size from 0.002 - 0.0625 millimeters in diameter. Silt is finer than sand, but coarser than clay.
siltstone A sedimentary rock made mostly of silt-sized grain.
sima A term used to describe the more magnesium-rich igneous rocks (basalt, gabbro, and peridotite) of the ocean crust. Sima rocks are denser than the continental (sial) rocks.
sinkhole A depression in the surface commonly found in in karst landscapes. Sinkholes often form where limestone or some other soluble rock is partially dissolved by groundwater, then collapses to form a depression. Sinkholes are often bowl-shaped and can be a few to many hundreds of meters in diameter. Also known as dolines.
skin depth Measure of the effective depth of penetration of electromagnetic fields. It is defined as the depth at which the amplitude of an electromagnetic field drops to 37% of its surface value.
slate A fine grained argillaceous rock that has good cleavage (slatey cleavage) that can be easily split into slabs ana thin plate. Most slate is formed by low grade metamorphism.
slatey cleavage A parallel form of cleavage that is developed in fine grained rocks when they are subjected to low grade metamorphism.
slump A type of landslide in which a mass of rock breaks away along a curved surface and rotates more or less intact downslope. The sliding mass of rock is called a slump block.
slump block See slump
smectite Group of clay, those most susceptible to shrink-swell
snowline The lower limit of any year's permanent snowfall. Separates the Zone of Accumulation from the Zone of Ablation.
soft mode Molecular vibrational mode for which the atomic displacement track the structural changes followed during a displacive phase transition. The frequency of the soft mode goes to zero at the transition temperature or pressure.
soil In a geologic sense of the term, a weathered horizon at the earth's surface. During periods of landscape stability, various physical and chemical processes modify the upper few meters of the surface. Typically, new mineral assemblages such as clay are introduced, as is organic matter, and calcium carbonate if the climate is dry. Once a soil is buried by other sediment, it is then referred to as a paleosol.
soil profile Vertical section of the soil through all of its distinct layer (horizons) produced by the soil-forming process and extending into the parent material.
solid state In metamorphism, indicates the change of mineral identity without melting. All ion migration occurs while the rock (or pre-glacial ice) is still solid.
solifluction The flow of wet material that takes place at the surface when the ground in a permafrost area is patially thawed.
solute Organic or inorganic species that is dissolved in groundwater.
spasmodic tremor "Continuous seismic signal with pulsating high-frequency appearance; can be composed of discrete earthquake occurring closely spaced in time or can be phaseless."
speleology The exploration and study of cave.
speleothem A deposit formed in cave when calcium carbonate (CaCO3) or some other mineral precipitates from drips or thin films of water. Stalactites and stalagmite are common speleothem.
spines Horn-like projections formed upon a lava dome.
spontaneous magnetization Magnetization resulting from cooperative behavior of unpaired spins within a crystal lattice, creating a magnetic moment that is independent of the external field.
spread The layout of seismometer or geophone group from which data from a single shot (the explosive charge) are recorded simultaneously.
spreading axes An imaginary axis through the Earth about which a set of tectonic plate move. The movement of a diverging plate can be decribed as rotation around a spreading axis.
spreading center An elongated region where two plate are being pulled away from each other. New crust is formed as molten rock is forced upward into the gap. Examples of spreading center include the Mid-Atlantic Ridge and the East African Rift.
spring A surface flow of groundwater which occurs any time the water table intersects the surface.
stable platform Large areas of craton that have not been significantly uplifted above or submerged below sea level. Sedimentary rocks are nearly horizontal.
stalactite A mineral deposit (speleothem) which hangs downwards from a roof or wall of a cave. See stalagmite.
stalagmite A mineral deposit (speleothem) which projects upwards from a cave floor. See stalactite.
stitching pluton Plutons of roughly the same age which that intruded several tectonic terrane after the terranes were faulted together. The pluton do not really sew the terranes together, but they help record when terranes were assembled.
stochastic inversion Method for computing Gaussian coefficients (or equivalent parameters) that is based on a priori estimates of parameter and noise covariances.
stock Relatively small globular or columnar-shaped pluton. Like a batholith only smaller.
stope block Stope blocks form when injection of intrusive igneous rock weakens the solid rock surrounding it, causing blocks to loosen and sink into the molten mass.
strain "Change in a volume of a system induced by deformation; it is positive for dilation and negative for contraction and is distinct from regolith or volume reduction, which may be an isovolumetric removal of soluble constituents in solution without deformation."
stratification A structure of sedimentary rocks, which have recognizable parallel bed of considerable lateral extent.
stratigraphic sequence A set of bed deposited that reflects the geologic history of a region.
stratigraphy The science of the description, correlation, and classification of strata in sedimentary rocks, including the interpretation of the depositional environments of those strata.
stratovolcano A volcano composed of both lava flows and pyroclastic material. Also called Composite volcanoes. Common at convergent boundaries. Excellent examples in the U.S. include Mt. St. Helens, Mt. Shasta, and the other peaks of the Cascade Range of California, Oregon and Washington.
streak " The fine deposit of mineral dust left on an abrasive surface when a mineral is scraped across it; especially the characteristic color of the dust. "
streak plate A ceramic abrasive surface for streak tests.
stream capture A process of erosion where one stream erodes headward, diverting some of another stream’s drainage into its own channel. Also called stream piracy.
stream order The hierarchical number of a stream segment in dendritic drainage
stream piracy See stream capture
streaming flow A tranquil flow slower than shooting flow.
stress A quantity describing the forces acting on each part of a body in units of force per unit area. Striation
stress probing Measurement of in situ stresses in a dedicated small-diamter hole drilled ahead of the primary drill bit.
striations (glacial) Grooves eroded into bedrock by rock debris frozen into the base of a glacier.
strike "The angle between true North and the horizontal line contained in any planar feature (inclined bed, dike, fault plane, etc.); also the geographic direction of this horizontal line. "
strike valley A valley eroded parallel to the strike of the underlying strata.
strike-slip fault A fault where the movement occurs parellel to the strike of the fault.
strike-slip fault General term for a vertical fault with horizontal displacement vector producing lateral relative motion of the rock on either side.
stringer A thin, discontinuous mineral vein or rock layer.
stromatolite A fossil form representing the growth habit of an algal mat
structure The shapes and position of rocks and their relationships to each other.
subduction Process of one crustal plate sliding down and below another crustal plate as the two converge. The subduction zone is the area between the two plates, somewhat like a giant reverse fault.
subduction Process of one crustal plate sliding down and below another crustal plate as the two converge. The subduction zone is the area between the two plates, somewhat like a giant reverse fault.
subduction zone An elongated region along which a plate descends relative to another plate, for example, the descent of the Nazca plate beneath the South American plate along the Peru-Chile Trench.
subduction zone An elongated region along which a plate descends relative to another plate, for example, the descent of the Nazca plate beneath the South American plate along the Peru-Chile Trench.
sublimation The direct change from the solid to the vapor phase (without passing through the liquid phase). Commonly occurs in ice and snow fields on sunny days above the snowline.
submarine canyon An elongated, steep-walled cleft running across or partially across the Continental Shelf, the continental borderland and/or slope, the bottom of which grades continually downwards
submarine fan Fan or cone-shaped accumulation of sedimentary debris--sand, gravel, mud--under the ocean along the edge of the land, either a continent or a volcanic arc. Fans may be a few miles to a hundred or so miles across.
submicroscopic Not resolvable in a microscope.
subsidence A gentle epeirogenic movement where a broad area of the crust sinks without appreciable deformation.
subsolidus convection Convection via solid-state deformational processes.
superposed stream A stream that flows through resistant formation because its course was established at a higher level on uniform rocks before down-cutting began.
superposition, Principle of The principle stated by Steno that, except in extremely deformed strata, a bed that overlies another bed is always the younger.
supersaturation The unstable state of a solution that contains more solute than its solubility allows.
surf The breaking or tumbling forward of water wave as they approach the shore.
surf zone An offshore belt along which the wave collapse into breaker as they approach the shore.
surface of the earth The value given is the depth below the surface of the mean spheroid. The mean spheroid is a uniform approximation to the true shape of the Earth. No adjustment is made to the depth due to any differences between the true Earth and the mean spheroid. For example, the minimum depth that will be given is 0 kilometers even though a quake directly under Mount Everest (elevation 8848 meters) could legitimately have a depth of -6 kilometers and still be 2 kilometers underground. On the other hand, a depth of 10 kilometers would actually be more than 1 kilometer above the ocean floor of Challenger Deep (elevation -11,033 meters) in the Marianas Trench of the Pacific Ocean.
surface waves Waves that move over the surface of the Earth. Rayleigh wave and Love wave are surface waves.
surficial deposit Any loose, unconsolidated sedimentary deposit lying on bedrock.
suspended load "Part of the total stream load that is carried in suspension free from contact with the stream bed; it consists mainly of clay, silt, and fine sand."
suspension bed The part of the sediment carried along by the water flowing above the stream bed.
suture zone Lineation in continental lithosphere marking the location of an earlier plate collision that led to the amalgamation of formnerly separate continental masses.
swash The landward rush of water from a breaking wave up the slope of the beach.
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.
symbiosis The interaction of two mutually supporting species who do not compete with or prey upon each other.
syncline " A large fold whose limb are higher than its center; a fold with the youngest strata in the center. "
system (stratigraphy) A stratigraphic unit larger than a series, consisting of all the rocks deposited in one period of an era.
© 2002,2003 Amateur Geologist™, All rights reserved.