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.)
Sandstone:
A sedimentary rock composed of sand-sized particles (1/16 to 2 millimeters in diameter). Picture of Sandstone.
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. Picture of Schist.
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. Picture of Scoria.
Sea-Floor Spreading:
The process that occurs at mid-ocean ridges in which convection currents below pull the plates apart and create new sea floor.
Seamount:
A mountain on the sea floor that has at least 1000 meters of local relief. Most seamounts are shield volcanoes. (See also Guyot.)
Sediment:
A loose, unconsolidated deposit of weathering debris, chemical precipitates or biological debris that accumulates on Earth's surface.
Sedimentary Rock:
A rock formed from the accumulation and consolidation of sediment, usually in layered deposits.
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.
Seepage:
The slow movement of water through the pore spaces of a solid material. This term is also applied to a loss of water by infiltration through the bottom of a stream, canal, irrigation ditch, reservoir or other body of water.
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.
Seismic Discontinuity:
A surface separating rocks that transmit seismic waves at different velocities.
Seismicity:
The study of the worldwide distribution of earthquakes over time and the probability of an earthquake occurring in a specific location.
Service Well:
A well drilled to support production from other wells. Some reasons for support wells are: gas injection, water injection, steam injection, salt water disposal, water supply, observation, or combustion air injection.
Settling Pond:
An open pond where waste or process water is allowed to stand while suspended materials settle out.
Shale:
a clastic sedimentary rock that is made up of clay-size (less then 1/256 millimeter in diameter) weathering debris. It typically breaks into thin flat pieces. Picture of Shale.
Short Ton:
A unit of weight that equals 2,000 pounds.
Shut In:
A well that is capable of production but which is temporarily closed for repair, cleaning or inaccessibility to a market.
Signing Bonus:
Money paid to a mineral rights owner in exchange for granting a lease. This payment may be in addition to rental or royalty payments.
Siltstone:
A clastic sedimentary rock that forms from silt-size (between 1/256 and 1/16 millimeter diameter) weathering debris. Picture of Siltstone.
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.
Slate:
A foliated metamorphic rock that is formed through the metamorphism of shale. It is a low grade metamorphic rock that splits into thin pieces. Picture of Slate.
Solution:
A chemical weathering process in which a material is dissolved. Also, the transport of dissolved ions by the water of a stream.
Storm Sewer:
A sewer system that collects surface runoff instead of waste water. These two types of water are kept separate because they require different processing before release to the environment.
Storm Surge:
The piling up of water along a shoreline cause by the sustained winds of a strong storm - usually a hurricane..
Strain:
A change in the volume or shape of a rock mass in response to stress.
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.
Stratovolcano:
A volcanic cone made up of alternating layers of lava flows and pyroclastics. Also known as a composite cone.
Streak:
The color of a mineral in powdered form. Streak is normally determined by scraping a specimen across a surface of unglazed porcelain known as a "streak plate".
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.
Stress:
A force acting upon or within a mass or rock, expressed in terms of unit weight per surface area such as tons per square inch.
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:
The geographic direction of a line created by the intersection of a plane and the horizontal. Often used to describe the geographic "trend" of a fold or fault.
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.
Strombolian Eruption:
A type of volcanic eruption characterized by fountains of lava jetting from a lava-filled central crater.
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.
Submarine Canyon:
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.
Subsidence:
A lowering of the land surface in response to subsurface weathering, collapse or slow settlement of underground mines, or the production of subsurface fluids such as ground water or oil.
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.
S-wave:
Secondary seismic waves. A seismic wave with a direction of vibration that is perpendicular to the direction of travel. S-waves are slower than P-waves and travel only through solids.
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.
Syncline:
A trough-shaped fold with youngest strata in the center.
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.