Glossary Database

Select a Letter to view the associated terms.

 Glossary Term: 


 S wave  1. A seismic body wave in which particles vibrate at right angles to the direction in which the wave travels. Contrast with P wave. 2. Seismic wave that propagates by a shearing motion perpendicular to p-wave; the s stands for secondary because it arrives after the p-wave
 Sag pond  A small lake that forms in a depression, or sag, where active or recent movement along a fault has impounded a stream.
 Sagebrush steppe  A type of dry habitat characterized by sagebrush and other shrubs and short grasses.
 Salinity  The total quantity of dissolved salts in seawater, measured by weight in parts per thousand.
 Salt dome  A dome produced in sedimentary rock by the upward movement of a body of salt.
 Saltation  The transportation of particles in a current of wind or water by a series of bouncing movements.
 Saltatorial  refers to a form of locomotion in which the animal hops as it moves along. This is found in jackrabbits, the western jumping mouse, and even mule deer appear to utilize a form of saltatorial locomotion where all four feet are off the ground at the same time and they run in a springy fashion.
 Saltwater encroachment  Displacement of fresh groundwater by saltwater in coastal areas, due to the greater density of saltwater which typically moves into an aquifer that is being overpumped.
 Sand  Sedimentary material composed of fragments ranging in diameter from 0.0625 to 2 mm. Sand particles are larger than silt particles but smaller than pebbles. Much sand is composed of quartz grains, because quartz is abundant and resists chemical and mechanical disintegration, but other materials, such as shell fragments and rock fragments, can also form sand.
 Sand wave  A wave produced on a surface of sand by the drag of air or water moving over it.
 Sand waves  Include dunes and ripple marks.
 Sandstone  A sedimentary rock composed mostly of sand-size particles, usually cemented by calcite, silica, or iron oxide.
 Saturated zone  The zone in the subsurface in which all pore spaces are filled with water. Contrast with the overlying unsaturated zone. See also: vadose zone; aquifer.
 Scabland  A term usually used to describe surface areas that have been stripped of their soil exposing bare rock; large areas where catastrophic floods have scoured the rocks clean of any loose debris and soil.
 Scale  cartography The ratio between a linear distance on a map and the surface being mapped.
 Scarp  A cliff produced by faulting or erosion.
 Scent scales  Specialized scales on the wings of some butterflies, typically males, which produce pheromones. Also called androconia.
 Schist  A medium-grained or coarse-grained metamorphic rock with strong foliation (schistosity) resulting from parallel orientation of platy minerals, such as mica, chlorite, and talc.
 Schistosity  The type of foliation that characterizes schist, resulting from the parallel arrangement of coarse-grained platy minerals, such as mica, chlorite, and talc.
 Scoria  An igneous rock containing abundant vesicles.
 Scutes  Large scales. Usually means much the same as plate, lamina, shield (Peters 1964).
 Sea arch  An arch cut by wave erosion through a headland.
 Sea cave  A cave formed by wave erosion.
 Sea cliff  A cliff produced by wave erosion.
 Sea floor spreading  The theory that the sea floor spreads laterally away from the oceanic ridge as new lithosphere is created along the crest of the ridge by igneous activity.
 Sea mount  An isolated conical mound rising more than 1000 m above the ocean floor.
 Sea stack  A small, pillar-shaped, rocky island formed by wave erosion through a headland near a sea cliff.
 Secondary coast  A coast formed by marine processes or the growth of marine organisms.
 Secondary wave  See S wave.
 Sedentary  relating to or characterized by a sitting posture (Morris 1992).
 Sediment  Material (such as gravel, sand, mud, and lime) that is transported and deposited by wind, water, ice, or gravity; material that is precipitated from solution; deposits of organic origin (such as coal and coral reefs).
 Sedimentary basin  A low area in the earth's crust, of tectonic origin, in which sediments have accumulated. Such features were drainage basins at the time of sedimentation but are not necessarily so today.
 Sedimentary differentiation  The process in which distinctive sedimentary products (such as sand, shale, and lime) are generated and progressively separated from a rock mass by means of weathering, erosion, transportation, and deposition.
 Sedimentary environment  A place where sediment is deposited and the physical, chemical, and biological conditions that exist there. Examples: rivers, deltas, lakes, shallow-marine shelves.
 Sedimentary rock  Rock formed by the accumulation and consolidation of sediment.
 Sedimentary structure  A feature in a sedimentary rock, formed either contemporaneously with deposition or by sedimentary processes subsequent to deposition.
 Sedimentation  Deposition of sediment by mechanical means from a state of suspension from air or water. The process of forming sediment in layers.
 Seep  A spot where groundwater or other liquids (such as oil) are discharged at Earth's surface.
 Segment  A distinct body region. Caterpillars and the abdomens of butterflies are both comprised of many segments.
 Seif dune  A longitudinal dune of great height and length.
 Seismic  Pertaining to earthquakes or to waves produced by natural or artificial earthquakes.
 Seismic discontinuity  A surface within Earth at which seismic waves velocities abruptly change.
 Seismic ray  The path along which a seismic waves travels. Seismic rays are perpendicular to the wave crest.
 Seismic reflection profile  A profile of the configuration of the ocean floor and shallow sediments on the floor obtained by reflection of artificially produced seismic waves.
 Seismic velocity  The speed with which seismic waves travel through the earth.
 Seismic wave  A wave or vibration produced within Earth by an earthquake or artificial explosion.
 Seismogram  The record made by a seismograph.
 Seismograph  An instrument that detects, records, and measures the various waves produced by an earthquake. Also called seismometer, seismic detector, geophone.
 Seismologist  A person who has specialized in the study of earthquakes and the structure of the earth using seismic exploration.
 Semi-arid climate  Dry climates exhibiting a short wet season supporting the growth of grasses and annual plants.
 Sepal  A structure on the outermost part of a flower, appearing like a small leaf or a petal. A group of sepals enclose the developing flower bud and later open when the flower is mature.
 Septum  A partition or wall (Peters 1964).
 serrate  Saw-like.
 Seta (pl. Setae)  The hairlike structure commonly found on caterpillars and other insects.
 Settling velocity  The rate at which a particle falls through water or air. See also: velocity.
 Sexual dimorphism  is found in mammals when the male and female have distinct differences such as size or other characteristics that make them appear different.
 Shadow zone (seismology)  An area where there is very little or no direct reception of seismic waves from a given earthquake because of refraction of the waves in Earth's core. The shadow zone for P waves is between about 105 and 142 degrees from the epicenter.
 Shale  A fine-grained clastic sedimentary rock formed by consolidation of clay and mud.
 Shallow-focus earthquake  An earthquake with a focus less than 70 km below Earth's surface.
 Shallow-marine environment  The sedimentary environment of the continental shelves, where the water is usually less than 200 m deep.
 Shear  It is the mode of failure in which a portion of a mass of rock on one side of a plane slides past the portion on the opposite side of that plane. Similar to a deck of cards sheared out.
 Sheeting  A set of joints formed essentially parallel to the surface. It allows layers of rock to fall off as the weight of overlying rock is removed by erosion. It is especially well developed in granitic rock.
 Shield  An extensive area of a continent where igneous and metamorphic rocks are exposed and have approached equilibrium with respect to erosion and isostasy. Rocks of the shield are usually very old (that is, more than 600 million years old).
 Shield volcano  A large volcano shaped like a flattened dome and built up almost entirely of numerous flows of fluid basaltic lava. The slopes of shield volcanoes seldom exceed 10 degrees, so that in profile they resemble a shield or broad dome.
 Shore  The zone between the water-line at high tide and the waterline at low tide. A narrow strip of land immediately bordering a body of water, especially a lake or an ocean.
 Silica  Silicon dioxide (SiO2) in any of several mineral forms one of which is quartz.
 Silicate  A mineral containing silicon-oxygen tetrahedra, in which four oxygen atoms surround each silicon atom.
 Silicic  Said of a silica-rich igneous rock or magma. Usually at least 65% or 2/3rds of the rock is composed of silica.
 Silicon-oxygen tetrahedron  The structure of the ion SiO42- in which four oxygen atoms surround a silicon atom to form a four-sided pyramid, or tetrahedron.
 Silk  The threads produced by the specialized salivary glands of a caterpillar.
 Silk girdle  A silken support stucture made by some caterpillars when preparing to pupate. The silk girdle will hold the pupa in an upright position attached to a twig, stem, etc.
 Sill  A tabular body of intrusive rock injected between layers of the enclosing rock.
 Silt  Sedimentary material composed of fragments ranging in diameter from 1/265 to 1/16 mm. Silt particles are larger than clay particles but smaller than sand particles.
 Siltation  deposition of earthy matter, fine sand, or the like by moving or running water (Stein 1966).
 Siltstone  A fine-grained clastic sedimentary rock composed mostly of silt-size particles.
 Sinkhole  A depression formed by the collapse of a cavern roof.
 Slate  A fine-grained metamorphic rock with a characteristic type of foliation (slaty cleavage), resulting from the parallel arrangement of microscopic platy minerals, such as mica and chlorite.
 Slaty cleavage  The type of foliation that characterizes slate, resulting from the parallel arrangement of microscopic platy minerals, such as mica and chlorite. Slaty cleavage forms distinct zones of weakness within a rock, along which it splits into slabs.
 Slip face  See lee slope.
 Slope retreat  Progressive recession of a scarp or the side of a hill or mountain by mass movement and stream erosion.
 Slump  A type of mass movement in which material moves along a curved surface of rupture.
 smolt  A young hatchling, about 3-5 inches in length, that is ready to travel away from its hatching area.
 smolting  Physiological and behavioral changes that prepare fish for the change from fresh to salt water.
 snout  The part of the head in front of the eye.
 Snowline  The line on a glacier separating the area where snow remains from year to year from the area where snow from the previous season melts.
 Sockeye  Oncorhynchus nerka Sockeye is a corruption of 'suk-kegh', a coastal Indian name for the medium-sized salmon. Other regional names include Red Salmon, Blueback Salmon and Big Redfish (redfish because of their brilliant spawning colors). Sockeye have a similar life cycle to that of the Chinook except sockeye will spend only about half as much time in the ocean and, while most other species of Pacific salmon in rivers and streams, sockeye enter only spawn in lakes.
 soft fin rays  The paired, articulated, commonly forked fin rays.
 Soil  The surface material of the continents, produced by disintegration of rock. Regolith that has undergone chemical weathering in place.
 Soil profile  A vertical section of soil showing the soil horizons and parent material.
 Soil water  Water contained in soil pores.
 Solar  Produced by or having to do with the sun. Coming from the sun.
 Solid  The state of matter in which a substance has a definite shape and volume and some fundamental strength.
 Solifluction  A type of mass movement in which material moves slowly downslope in areas where the soil is saturated with water. It commonly occurs in permafrost areas.
 Soluble  Describes a solute that dissolves easily in a solvent.
 Solute  The substance which dissolves in a solvent to form a solution.
 Solution  A liquid that contains a solid (or gaseous) substance completely dissolved in it.
 Solution valley  A valley produced by solution activity, either by dissolution of surface materials or by removal of subsurface materials such as limestone, gypsum, or salt.
 Solvent  The substance in which the solute dissolves. The liquid. Water is so effective at dissolving so many substances, that it is known as 'the universal solvent'.
 Sorting  The separation of particles according to size, shape, or weight. It occurs during transportation by running water or wind.
 Sound wave  A form of energy that creates a wave that can be detected by our ears.
 South pole  Point at which the southern end of the earth's axis of rotation intersects the earth's surface.
 South Pole (magnetic)  One of two ends of a magnet.
 Spatter cone  A low steep-sided volcanic cone built by accumulation of splashes and spatters of lava (usually basaltic) around a fissure or vent.
 spawn  Laying and fertilizing of salmon eggs with milt (sperm).
 Species  A group of individuals biologically capable of interbreeding and which have a common ancestor.
 Speculum  An iridescent patch of color on the wings of certain ducks and other birds (Morris 1992
 Sphere  Any round body having the surface equally distant from the center at all points; globe; ball.
 Spheroidal weathering  The process by which corners and edges of a rock body become rounded as a result of exposure to weathering on all sides, so that the rock acquires a spheroidal or ellipsoidal shape.
 Sphragis  A waxy secretion produced during mating by male Parnassian butterflies. It contains sperm and important nutrients, and is placed at the tip of his mate's abdomen. It remains in place after mating, and prevents the female from mating again. It can sometimes be seen still in place on collected female specimens. In the picture, the sphragis is the heart-shaped attachment at the tip of the abdomen.
 Spine  A thin, rigid, specialized structure on some caterpillars which provides some degree of protection.
 Spiracle  1.) The small opening to the outside from the gill chamber in anuran tadpoles (Peters 1964). 2.) An opening on the back part of the head (above and behind the eye).
 Spit  A sandy bar projecting from the mainland into open water. Spits are formed by deposition of sediment moved by longshore drift.
 Splay  A small deltaic deposit formed on a floodplain where water and sediment are diverted from the main stream through a crevasse in a levee.
 Spreading center (tectonics)  Lithospheric plate boundary along which two plates of oceanic lithosphere are undergoing separation.
 Spring  A place where groundwater flows or seeps naturally to the surface.
 Stable platform  The part of a continent that is covered with flat or gently-tilted sedimentary strata and underlain by a basement complex of igneous and metamorphic rocks. The stable platform has not been extensively affected by crustal deformation.
 Stalactite  An icicle-shaped deposit of dripstone hanging from the roof of a cave.
 Stalagmite  A conical deposit of dripstone built up from a cave floor.
 standard length  The measured straight line distance from the tip of the snout to the base of the caudal fin.
 Star dune  A mound of sand with a high central point and arms radiating in various directions.
 Steelhead (Rainbow) Trout  Oncorhynchus mykiss These fish are ocean-going rainbow trout. They are generally one year old when they begin their journey to the ocean. Steelhead spend one to two years in the ocean prior to returning to their natal streams to spawn.They face identical hazards as salmon on their migrations, and their numbers have also declined. Unlike salmon however, steelhead do not automatically die after they spawn.
 Steppe  refers to arid lands having vegetation that is adapted to dry conditions, and having extreme temperature variations between the hot of the summer season and the cold of the winter season. In Idaho it often has considerable sagebrush.
 Stigma  A section of scent scales located on the forewing of a male butterfly (specifically Hairstreaks and Skippers) that produces pheromones, useful in attracting females. The black streak on each forewing of this skipper is a stigma.
 Stock  A small, roughly circular intrusive body, usually less than 100 km in surface exposure.
 Strata  Layers of rock, usually sedimentary. Plural of stratum.
 Stratification  The layered structure of sedimentary rock.
 Stratosphere  Layer of atmosphere directly above the troposphere lying between 6 and 30 miles (10 and 50km) above the earth. Air too dry to form clouds.
 Stratovolcano  A steep-sided volcano built up of ash, lava flows, and shallow intrusions. Synonymous with composite volcano.
 Streak  The color of a powdered mineral.
 Stream load  The total amount of sediment carried by a stream at a given time.
 Stream order  The hierarchical number of a stream segment. The smallest tributary has the order number of 1, and successively larger tributaries have progressively higher numbers.
 Stream piracy  Diversion of the headwaters of one stream into another stream. The process occurs by headward erosion of a stream having greater erosive power than the stream it captures. Synonomous with stream capture.
 Stream terrace  One of a series of level surfaces in a stream valley representing the dissected remnants of an abandoned floodplain, stream bed, or valley floor produced in a previous stage of erosion or deposition.
 Stress  Force applied to a material that tends to change its dimensions or volume; force per unit area.
 striated  Marked by narrow lines, grooves, etc., which usually lie parallel.
 Striations  Parallel scratches in bedrock caused by rocks embedded in the base of a flowing glacier.
 Strike  The bearing (compass direction) of a horizontal line on a bedding plane, a fault plane, or some other planar structural feature.
 Strike valley  A valley that is eroded parallel to the strike of the underlying nonresistant strata.
 Strike-slip fault  A fault in which movement has occurred parallel to the strike of the fault.
 Strip mining  A method of mining in which soil and rock cover are removed to obtain the sought-after material.
 Subaerial  Occurring beneath the atmosphere or in the open air, with reference to conditions or processes (such as erosion) that occur on the land.
 Subaqueous  Occurring beneath water, with reference to conditions or processes that occur on the floors of rivers, lakes, and oceans.
 Subduction  Subsidence of the leading edge of a lithospheric plate into the mantle.
 Subduction zone  An elongate zone in which one lithospheric plate descends beneath another. A subduction zone is typically marked by an oceanic trench, lines of volcanoes, and crustal deformation associated with mountain building. See also: convergent plate boundary.
 Subglacial  Beneath a glacier.
 Sublimation  The conversion of a solid to a gas without melting. Example: frozen carbon dioxide passes directly from solid to a vapor that is heavier than air, and is known as dry ice.
 Submarine canyon  A V-shaped trench or valley with steep sides cut into a continental shelf or continental slope.
 Subnivean  below the snow.
 Subsidence  A sinking or settling of a part of Earth's crust with respect to the surrounding parts.
 subterminal mouth  A mouth which opens ventrally rather than straight forward from the head. The lower jaw closes within the upper jaw.
 Subterranean  Formed or occurring beneath the earth's surface, or situated within the earth.
 Subtropical climate  Warm to hot, dry summers and mild, rainy winters, which occur on the west side of continents roughly between 30 degrees and 45 degrees latitude. Sometimes called Mediterranean climates.
 Superposition, principle of  The principle that, in a series of sedimentary strata that has not been overturned, the oldest rocks are at the base and the youngest are at the top.
 Surface wave (seismology)  A seismic wave that travels along Earth's surface. Contrast with P waves and S waves, which travel through Earth and at higher velocities.
 Suspended load  The part of a stream's load that is carried in suspension for a considerable period of time without contact with the stream bed. It consists mainly of mud, silt, and sand. Contrast with bed load and dissolved load.
 Suture  A belt of intensely deformed rocks that marks the site of continental collision.
 Swash  The rush of water up onto a beach after a wave breaks.
 swim-up  Developmental stage when newly hatched fry become photopositive, rise to the surface, and begin to feed.
 Symmetric  Both sides of an object are the same (as opposed to asymmetric where both sides of an object are not the same) in size, shape or position.
 symmetrical  Each side being alike in form, size and arrangement of parts.
 Symmetrical fold  A fold in which the two limbs are essentially mirror images of each other.
 Sympatric  describing different species or populations that live in the same geographical area (Morris 1992).
 Syncline  1. A fold in which the limbs dip toward the axis. After erosion, the youngest beds are exposed in the central core of the fold. 2. A fold, generally concave upward, whose core contains stratigraphically younger rocks.