Thursday, November 23rd, 2017
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* S wave-A seismic wave consisting of a shearing motion in which the oscillation is perpendicular to the direction of wave travel. S waves travel slower than P waves. (syn: secondary wave)
* S waves - secondary, or shear, earthquake waves, which can travel through solids, but not liquids or gases.
* Salinity-The saltiness of sea water.
* Salinization-A process whereby salts accumulate in soil that is irrigated heavily.
* Salt cracking-A weathering process in which salts that are dissolved in water found in the pores of rock crystallize. This process widens cracks and pushes grains apart.
* Saltation-Sediment transport in which particles bounce and hop along the surface.
* Salt-water intrusion-A condition in coastal regions in which excessive pumping of fresh ground water causes salty ground water to invade an aquifer.
* Sand-Sedimentary grains that range from 1/16 and 2 millimeters in diameter.
* Sandstone-Clastic sedimentary rock comprised primarily of lithified sand.
* Satellite -A body that revolves around a larger body.
* Saturated zone-The region below the water table where all the pores in rock or regolith are filled with water.
* Saturation- the air is completely full of water vapor. Relative humidity is 100%. Air is at the dew point. No more evaporation can occur.
* Saturation-The maximum amount of water vapor that air can hold; the maximum amount of a substance that can dissolve in another substance.
* Schist-A strongly foliated metamorphic rock, that has a well developed parallelism of minerals such as micas.
* Scoria- A very vesicular, extrusive igneous rock. It is usually heavier, darker, and more crystalline than pumice.
* Sea arch-An opening created when a cave is eroded all the way through a narrow headland.
* Sea breeze - a local wind carrying cool ocean air inland, occurs when the pressure over the land decreases due to its rapid heating.
* Sea level- The top of the ocean, where the water meets the atmosphere.
* Sea stack-A pillar of rock left when a sea arch collapses or when the inshore portion of a headland erodes faster than the tip.
* Sea-floor drilling-A process in which drill rigs mounted on offshore platforms or on research vessels cut cylindrical cores from both sediment and rock of the sea floor, which are then brought to the surface for study.
* Seafloor Spreading- The mechanism by which new seafloor crust is created at oceanic ridges and slowly spreads away as plates are separating.
* Sea-floor spreading-The hypothesis that segments of oceanic crust are separating at the mid-oceanic ridge.
* Seamount- A submarine volcano.
* Seamount-A submarine mountain, usually of volcanic origin, that rises 1 kilometer or more above the surrounding sea floor.
* Season- A division of the year according to some regularly recurring event or phenomena, usually astronomical or climatological. The four astronomical seasons- Spring, Summer, Autumn or Fall, and Winter are generally defined by the position of the sun with respect to the Earth's equatorial plane. The four climatological seasons known to most are tied to the astronomical seasons. However, in areas where climate changes little through the year, such as the tropics, there may be only two seasons- the wet and the dry. Seasons may also be defined by other criteria such as- the persistence of prevailing wind directions (the monsoons); biological processes such as growing or dormant; human energy requirements. There may be any number of seasons per year depending on the phenomena used to define them.
* Secondary air pollutant-A pollutant generated by chemical reactions within the atmosphere.
* Secondary and tertiary recovery-Production of oil or gas by artificially augmenting the reservoir energy, as by injection of water, detergent, or other fluid.
* Secondary wave-A seismic wave consisting of a shearing motion in which the oscillation is perpendicular to the direction of wave travel. S waves travel slower than P waves. (syn: S wave)
* Sediment- Rock debris commonly produced by mechanical or chemical weathering processes.
* Sedimentary rock- rocks formed from sediments bound together in some way.
* Sedimentary rock-A rock formed when sediment is lithified.
* Sedimentary structure-Any structure formed in sedimentary rock during deposition or by later sedimentary processes; for example, bedding.
* Sediment-Solid rock or mineral fragments transported and deposited by wind, water, gravity, or ice, precipitated by chemical reactions, or secreted by organisms, and that accumulates as layers in loose, unconsolidated form.
* Seismic profiler-A device used to construct a topographic profile of the ocean floor and to reveal layering in sediment and rock beneath the sea floor.
* Seismic tomography-A technique whereby seismic data from many earthquakes and recording stations are analyzed to provide a three dimensional view of the interior of the Earth.
* Seismic wave-All elastic waves that travel through rock, produced by an earthquake or explosion.
* Seismogram- the recording of an earthquake made by a seismograph.
* Seismogram-The record made by a seismograph.
* Seismograph- An instrument that records seismic waves; that is, vibrations of the earth. Used to record and measure earthquakes
* Seismograph-An instrument that records seismic waves.
* Seismologist- Scientists who study earthquake waves and what they tell us about the inside of the Earth.
* Seismology-The study of earthquake waves and the interpretation of this data to elucidate the structure of the interior of the Earth.
* Shadow zone- a wide area around the Earth on the side opposite the focus of an earthquake where neither P nor S waves are received. The P waves are refracted (bent) away from this zone. The S waves can't travel through the liquid outer core.
* Shale-A fine-grained clastic sedimentary rock with finely layered structure composed predominantly of clay minerals.
* Shear strength-The resistance of materials to being pulled apart along their cross section.
* Shear stress-Stress that acts in parallel but opposite directions.
* Shear Waves- Earthquake waves that move up and down as the wave itself moves. For example, to the left.
* Shearing- The motion of surfaces sliding past one another.
* Sheet flood-A broad, thin sheet of flowing water that is not concentrated into channels, typically in arid regions.
* Shield Volcano- A gently sloping volcano in the shape of a flattened dome and built almost exclusively of lava flows.
* Shield volcano-A large, gently sloping volcanic mountain formed by successive flows of basaltic magma.
* Short-Wave Radiation or Solar Radiation- That portion of the electromagnetic spectrum less than 4,000 nanometers which is received from the sun.
* Shower- Precipitation falling from a convective cloud, characterized by the suddenness with which it starts and stops, by rapid changes of intensity and usually rapid changes in the appearance of the sky.
* Sialic rock-A rock such as granite and rhyolite that contains large proportions of silicon and aluminum.
* Sidereal -Of, relating to, or expressed in relation to stars or constellations.
* Sidereal rotation -Rotation time measured with respect to the fixed stars rather than the Sun or body orbited.
* Silica- A chemical combination of silicon and oxygen.
* Silica tetrahedron- a grouping of one silicon atom and four oxygen atoms in a pyramid shape; the building blocks of silicate minerals
* Silica-Silicon dioxide, sio2. Includes quartz, opal, chert, and many other varieties.
* Silicate -A rock or mineral whose structure is dominated by bonds of silicon and oxygen atoms (ie. Olivine).
* Silicate tetrahedron-A pyramid-shaped structure of a silicon ion bonded to four oxygen ions, (sio4)4-.
* Silicate-All minerals whose crystal structures contain silica tetrahedra. All rocks composed principally of silicate minerals.
* Sill- A sheet of intrusive igneous rock, parallel to the layering of the rocks into which it intrudes. Example- Palisades Sill
* Sill-A tabular or sheetlike igneous intrusion parallel to the grain or layering of country rock.
* Silt-All sedimentary particles from 1/256 to 1/16 millimeter in size.
* Siltstone-Lithified silt.
* Sinkhole-A circular depression in karst topography caused by the collapse of a cavern roof or by dissolution of surface rocks.
* Slate-A compact, fine-grained, low-grade metamorphic rock with slaty cleavage that can be split into slabs and thin plates. Intermediate in grade between shale and phyllite.
* Slaty cleavage-A parallel metamorphic foliation in a plane perpendicular to the direction of tectonic compression.
* Sleet- Frozen rain. Precipitation composed of already frozen droplets - ice pellets - that bounce on impact. Outside the United States, sleet also refers to precipitation with a mixture of rain and snow or rain and ice pellets or quickly melting snow.
* Sleet-Small spheres of ice that develop when raindrops form in a warm cloud and freeze as they fall through a layer of cold air at lower elevation.
* Slide-All types of mass wasting in which the rock or regolith initially moves as a consolidated unit over a fracture surface.
* Slip face-The steep lee side of a dune that is at the angel of repose for loose sand so that the sand slides or slips.
* Slip-The distance that rocks on opposite sides of a fault have moved.
* Slope- (see Gradient)
* Slump-A type of mass wasting in which the rock and regolith move as a consolidated unit with a backward rotation along a concave fracture.
* Smog-Smoky fog. The word is used loosely to define visible air pollution.
* Snow- A type of frozen precipitation composed white translucent ice crystals in a variety of complex hexagonal forms.
* Snow Crystal- One of several types of ice crystal found in snow. A snow crystal is an individual ice crystal whereas a snowflake is usually an aggregate of many single crystals. See Ice Crystals
* Snow Squall- Short, intense snow showers accompanied by strong, gusty winds. Short- term snow accumulations may be significant and visibility greatly reduced. Snow squalls are common along the shores of the Great Lakes and other large lakes. See also, lake-effect snowfall.
* Snowbelt- In general, any area where topographical influences favor increased accumulation of snow over the surrounding region. Usually refers to the areas around large lakes such as the Great Lakes where lake-effect snows produce significantly enhanced winter accumulations.
* Snowflake- A single ice crystal or an aggregate of ice crystals falling from a cloud.
* Snowline- The lower limit of any year's permanent snowfall. Separates the Zone of Accumulation from the Zone of Ablation.
* Snowline-The altitude above which there is permanent snow.
* Soil depletion- a condition in which soil no longer can grow usable crops, brought on by the removal of nutrients during harvesting.
* Soil erosion- removal of valuable topsoil by wind or moving water.
* Soil horizon-A layer of soil that is distinguishable from other horizons because of differences in appearance and in physical and chemical properties.
* Soil- loose, weathered rock and organic material in which plants with roots can grow.
* Soil profile- cross section of soil layers above the bedrock, usually consisting of A-, B-, and C-horizons.
* Soil-moisture belt-The relatively thin, moist surface layer of soil above the unsaturated zone beneath it.
* Soil-Soil scientists define soil as the upper layers of regolith that support plant growth. Engineers define soil synonymous with regolith.
* Solar cell-A device that produces electricity directly from sunlight.
* Solar cycle -The approximately 11-year, quasi-periodic variation in the frequency or number of solar active events.
* Solar eclipse- an eclipse that occurs when the new moon's total shadow, or umbra, falls on Earth.
* Solar eclipse-See "eclipse."
* Solar flares- A magnetic storm on the Sun's surface which shows up as a sudden increase in brightness.
* Solar mass-The mass of our Sun.
* Solar nebula -The large cloud of gas and dust from which the Sun and planets condensed 4.6 billion years ago.
* Solar prominences- Gases trapped at the edge of the Sun which appear to shoot outward from the Sun's surface.
* Solar system- The Sun and all of the planets, comets, etc. Which revolve around it
* Solar wind- A continuous stream of charged particles which are released from the Sun and hurled outward into space at speeds up to 800 kilometers per second. Solar winds are very prominent after solar flare activity.
* Solar wind-A stream of atomic particles shot into space by violent storms occurring in the outer regions of the Sun's atmosphere.
* Solifluction-A type of mass wasting that occurs when water-saturated soil moves slowly over permafrost.
* Solstice- Either of two days when the sun's position overhead at noon is farthest north or south of the equator. These dates are June 21 for the Northern Hemisphere summer solstice, and about December 22 for the Northern Hemisphere winter solstice. The solstices are reversed for the Southern Hemisphere, with the winter solstice on June 21. On June 21, the sun is directly overhead at the Tropic of Cancer (23.5 degrees North Latitude). On December 22, the sun is directly overhead at the Tropic of Capricorn (23.5 degrees South Latitude).
* Solstice-Either of two times per year when the Sun shines directly overhead furthest from the Equator. The solstices mark the beginnings of summer and winter. One solstice occurs on or about June 21 and marks the longest day of the year in the Northern Hemisphere and the shortest day in the Southern Hemisphere. The other solstice occurs on or about December 22, marking the longest day in the Southern Hemisphere and the shortest day in the Northern Hemisphere.
* Source rock-The geologic formation in which oil or gas originates.
* Specific Gravity- The density of a mineral divided by the density of water.
* Specific gravity-The weight of a substance relative to the weight of an equal volume of water.
* Specific Heat- the number of calories (amount of heat) it takes to raise the temperature of one gram of a substance by one degree Celsius. Since water has a higher specific heat than land, bodies of water heat up and cool down more slowly than land.
* Specific heat-The heat required to raise the temperature of one gram of a substance 1 degree Celsius.
* Specific Humidity- The ratio of the mass of water vapor to the total mass of air in a given volume.
* Spectroscope- an instrument that can disperse a beam of light into a spectrum of its component wavelengths.
* Spectrum (electromagnetic)-A pattern of wavelengths into which a beam of light or other electromagnetic radiation is separated. The spectrum is seen as colors, or is photographed, or is detected by an electronic device. An emission spectrum is obtained from radiation emitted from a source. An absorption spectrum is obtained after radiation from a source has passed through a substance that absorbs some of the wavelengths.
* Spectrum -The range of wavelengths and frequencies of electromagnetic energy.
* Speed of light -Light speed equals 299,792,458 meters/second (186,000 miles/second). Einstein's Theory of Relativity implies that nothing can go faster than the speed of light.
* Speed of Sound- The speed that a sound wave travels through a given medium. The speed of sound depends on several properties of the medium, most importantly its density. In the atmosphere, the speed changes with air temperature and pressure. At standard sea-level pressure (101.3 kpa), the speed of sound is 340 meters per second (760 mph).
* Speleothems-Any mineral deposit formed in caves by the action of water.
* Spheroidal weathering-Weathering in which the edges and corners of a rock weather more rapidly than the flat faces, giving rise to a rounded shape.
* Spicule-A small jet of gas at the edge of the Sun. An average spicule is about 700 kilometers across and 7000 kilometers high, and lasts about 5 to 15 minutes.
* Spiral galaxy-A type of galaxy characterized by arms that radiate out from the center like a pinwheel.
* Spit-A small point of sand or gravel extending from shore into a body of water.
* Spreading center-The boundary or zone where lithospheric plates rift or separate from each other. (syn: divergent plate boundary)
* Spring- A surface flow of groundwater which occurs any time the water table intersects the surface.
* Spring- The time between winter and summer. See Equinox.
* Spring tide- a tide of large range occurring at new-moon and full-moon phases. High tides are highest. Low tides are lowest. The gravity of the sun and moon work together. see Neap tide
* Spring tide-A relatively large tide that forms when the Sun, Moon, and earth are aligned.
* Spring-A place where groundwater flows out of the Earth to form a small stream or pool.
* Squalls- 1) A strong wind which arrives suddenly, lasts minutes and ends with a sudden decrease in speed. 2) A severe local storm with strong. Gusty winds and usually precipitation, may be accompanied by thunder and lightning.
* Stalactite-An icicle-like dripstone, deposited from drops of water, that hang from the ceiling of a cavern.
* Stalagmite-A deposit of mineral matter that forms on the floor of a cavern by the action of dripping water.
* State (phase)- The form of a substance- solid, liquid, or gas/vapor.
* Station model- the listing of about 20 different weather observations around the location of a National Weather Service station on a weather map.
* Stationary front-A boundary between two stationary air masses of different temperatures.
* Stationary front-the boundary between two air masses that are not moving.
* Stock-An igneous intrusion with an exposed surface area of less than 100 square kilometers.
* Storm Surge- An abnormal rise local rise in sea level accompanying an intense storm system, either tropical or extratropical caused by the storm pushing a wall of water ahead of it. Storm surge is often the most damaging and deadly part of a tropical hurricane or cyclone, particularly if it arrives at high tide.
* Storm surge-An abnormally high coastal water level created by a combination of strong onshore winds and the low atmospheric pressure of a storm.
* Storm Track- The path followed by the center of a low pressure system or cyclone over a given period of time, usually its lifetime.
* Storm track-A path repeatedly followed by storms.
* Strain-The deformation, (change in size or shape), that results from stress.
* Stratified drift-Sediment that was transported by a glacier and then sorted, deposited, and layered by glacial meltwater.
* Stratigraphic- The study of rock strata, especially of their distribution, deposition, and age.
* Stratocumulus-Low sheet-like clouds with some vertical structure.
* Stratopause-The boundary between the stratosphere and the mesosphere.
* Stratosphere- The region of the atmosphere extending from the tropopause (8 to 15 km altitude) to about 50 km. The temperature of the stratosphere is warmer than the upper troposphere thus making it a region of high stability and low humidity.
* Stratosphere-The layer of air extending from the tropopause to about 55 kilometers. Temperature remains constant and then increases with elevation in the stratosphere.
* Stratovolcano-A steep-sided volcano formed by an alternating series of lava flows and pyroclastic eruptions. (syn; composite volcano)
* Stratus cloud-A horizontally layered, sheet-like cloud.
* Stratus- The lowest clouds, generally found below 3000 meters altitude and often appearing as an overcast deck. Can also be found as scattered patches. Individual cloud elements have very ill-defined edges. Stratus is comes from the Latin word for "layer."
* Streak- The color of a mineral in the powdered form.
* Streak-The color of a fine powder of a mineral usually obtained by rubbing the mineral on an unglazed porcelain streak plate.
* Stream-A moving body of water, confined in a channel, and flowing downslope.
* Stress-The force per unit area exerted against an object.
* Striations (glacial)- Grooves eroded into bedrock by rock debris frozen into the base of a glacier.
* Striations-Parallel scratches in bedrock caused by rocks embedded in the base of a flowing glacier.
* Strike-Slip Fault- A nearly vertical fault with side-slipping horizontal displacement.
* Strike-slip fault-A fault on which the motion is parallel with its strike and is primarily horizontal.
* Subduction -The process of one lithospheric plate descending beneath another.
* Subduction zone (or subduction boundary)-The region or boundary where a lithospheric plate descends into the asthenosphere.
* Subduction zone- The zone of convergence of two tectonic plates, one of which usually overrides the other.
* Subduction-The process in which a lithospheric plate descends beneath another plate and dives into the asthenosphere.
* 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. The opposite of sublimation is deposition.
* Sublimation-The process by which a solid transforms directly to a vapor or a vapor transforms directly to a solid without passing through the liquid phase.
* Submarine canyon-A deep, V-shaped, steep-walled trough eroded into a continental shelf and slope.
* Submarine fan-A large, fan-shaped accumulation of sediment deposited at the bases of many submarine canyons adjacent to the deep-sea floor. (syn: abyssal fan)
* Submergent coastline-A coastline that was recently above sea level but has been drowned either because the land has sunk or sea level has risen.
* Subsidence-Settling of the Earth's surface which can either occur as petroleum or groundwater is removed by natural processes.
* Subsoil - The B-horizon of soil that contains clay and iron oxides washed from the topsoil.
* Succession - A fundamental principle of geology, which states that unless disturbed, the oldest fossils in a rock bed should be at the bottom.
* Summer- 1) The warmest season of the year (except in some tropical regions) and the high sun season. 2) The period between the Summer Solstice and the Autumnal Equinox (June, July and August in the Northern Hemisphere; December, January, February in the Southern Hemisphere).
* Summer Solstice- The date on which the sun reaches the greatest distance north (in the Northern Hemisphere) or south (in the Southern Hemisphere) of the celestial equator. In the Northern Hemisphere, the summer solstice occurs when the sun in overhead at the Tropic of Cancer (latitude 23° 27' N) about June 21. In the Southern Hemisphere, the summer solstice occurs when the sun in overhead at the Tropic of Capricorn (latitude 23° 27' S) about December 22.
* Sun Dog- A popular term used to describe the parhelion, a bright portion of a solar halo which forms on points 22° either side of the sun and at the same elevation. Sun dogs are colored, luminous spots caused by the refraction of light by ice crystals. The term mock sun is also used to describe this optical phenomenon.
* Sunspot- A magnetic storm on the Sun's surface which appears as a dark area. A sunspot is approximately 1500 degrees Celsius cooler than it's surrounding material. The number of sunspots we see on the Sun at any given time appears to cycle every 11 years.
* Sunspot-A cool dark region on the Sun's surface formed by an intense magnetic disturbance.
* Supercontinent-A continent, such as Alfred Wegener's Pangaea, consisting of all or most of the Earth's continental crust joined together to form a single large landmass. At least three supercontinents are thought to have existed during the past 2 billion years, and each broke apart after a few hundred million years.
* Supercooled- A state when the temperature of liquid water falls below 0oC (32oF) without freezing. Although we commonly speak of 0oC as the freezing point of water, water, especially in the droplet form, rarely freezes at this temperature. (Pure ice, on the other hand, melts at 0oC, thus, this temperature should be more correctly called the melting point of ice.) The temperature of freezing varies with the size of the droplet and the concentration of any impurities in the water. Very small droplets of pure water may not freeze spontaneously until the temperature has fallen to -40oC (-40oF).)
* Supercooling-A condition in which water droplets in air do not freeze even when the air cools below the freezing point.
* Superfund-The Comprehensive Environmental Response, Compensation, and Liability Act (CERCLA). An act that provides an emergency fund to clean up chemical hazards and imposes fines for polluting the environment.
* Superior planets -The planets Mars, Jupiter, Saturn, Uranus, Neptune and Pluto are superior planets because their orbits are farther from the Sun than Earth's orbit.
* Supernova-A exploding star that is releasing massive amounts of energy.
* Superposition - A fundamental principle of geology, which states that if a rock bed hasn't been disturbed since it was formed, it is younger than the layer of rock below it.
* Superposition (principle of)-See "principle of superposition."
* Supersaturation-A condition in which the concentration of a solution exceeds the saturation point; a condition in which the relative humidity of air exceeds 100 percent.
* Surface mine-A hole excavated into the Earth's surface for the purpose of recovering mineral or fuel resources.
* Surface processes-All processes that sculpt the Earth's surface, such as erosion, transport, and deposition.
* Surface wave-An earthquake wave that travels along the surface of the Earth, or along a boundary between layers within the Earth. (syn: L wave)
* Surf-The chaotic, turbulence created when a wave breaks near the beach.
* Suspended load-That portion of a stream's load that is carried for a considerable time in suspension, free from contact with the streambed.
* Suspension- the state in which rock materials carried by a river are stirred up and kept from sinking by the turbulence of stream flow.
* Suture-The junction created when two continents or other masses of crust collide and weld into a single mass of continental crust.
* Synchronous rotation -A satellite's rotational period is equal to its orbital period; this causes the same side of a satellite to always face the planet. Synchronous rotation occurs when a planet's gravity produces a tidal bulge in its satellite. The gravitational attraction and bulge acts like a torque, which slows down the satellite until it reaches a synchronous rotation. Example- The same side of the Moon always faces the Earth.
* Syncline-A fold that arches downward and whose center contains the youngest rocks.
* System-Any combination of interrelated, interacting components.
* Syzygy- The alignment of three celestial objects within a solar system (or within any other system of objects in orbit about a star). Syzygy is most often used to refer to the alignment of the Sun, Earth, and Moon at the time of new or full moon. Alignments need not be perfect in order for syzygy to occur: because the orbital planes for any three bodies in the solar system rarely coincide, the geometric centers of three objects that are in syzygy almost never lie along the same line. In general, syzygy occurs whenever an observer on one of the three objects would see the other two objects either in opposition or in conjunction. Opposition occurs when two objects appear 180° apart in the sky as viewed from a third object. Conjunction occurs when two objects appear near one another in the sky as seen from a third object. Solar and lunar eclipses are dramatic results of syzygy. During a solar eclipse, when the Moon is in its new phase, the alignment of the Sun, Earth, and Moon is so nearly perfect that the Moon's shadow falls on the Earth. During a lunar eclipse, which occurs at the time of the full moon, the Moon passes through the Earth's shadow. An occultation is another type of eclipse that can occur during syzygy. For an Earth-based observer, an occultation occurs when the Moon is seen to pass in front of a planet or other member of the solar system. The occultation of a star by the Moon does not qualify as syzygy, since the star is far beyond the limits of the solar system.