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Iowa State University - Geology terms Category: Education > University Date & country: 18/11/2013, USA Words: 782

seismograph
An instrument that detects, magnifies, and records vibrations of the Earth, especially earthquakes.

seismology
The study of earthquakes, and of the structure of the Earth by both natural and artificially generated seismic waves.

seismoscop
e An instrument that merely indicates the occurrence of an earthquake.

self-exciting dynamo
In reference to the Earth, the suggestion that movements in the fluid core may help initiate the Earth

shadow zone
A region 100

shale
A mudstone that splits or fractures readily.

shatter cone
A distinctively striated conical structure in rock, ranging from a few centimeters to a few meters in length, believed to have been formed by the passage of a shock wave following meteorite impact.

shear
Rock deformation involving movement past each other of adjacent parts of the rock and parallel to the plane separating them.

shear strength
The resistance of a body to shear stress.

shear stress
The stress on an object operating parallel to the slope on which it lies.

sheeting
A type of jointing produced by pressure release (unloading) or exfoliation .

shield volcano
A volcano in the shape of a flattened cone, broad and low, built by very fluid flows of basaltic lava.

shock lamellae
Closely spaced microscopic planes, distinct from cleavage planes, that occur in shock-metamorphosed minerals and are regarded as important indicators of shock metamorphism.

shock metamorphism
Metamorphism induced in rock by the passage of a high-pressure shock wave acting over a period of time from a few microseconds to a fraction of a minute. The only known natural cause of shock metamorphism is the hypervelocity impact of a meteorite.

shore
Seaward edge of coast between low tide and effective wave action.

shore face
The concave section of the beach from high tide mark down to the ramp between 5 and 20 m off shore.

shore platform
A surface of erosion that slopes gently seaward from a cliff base to the low tide mark.

shoreline
The line separating land and water. Fluctuates as water rises and falls.

sial
The upper layer of the continental crust, so called because it is rich in silica and aluminum oxide. compare sima.

sialic
Enriched in sial.

silica
Silicon dioxide (SiO2) as a pure crystalline substance makes up quartz and related forms such as flint and chalcedony. More generally, silica is the basic chemical constituent common to all silicate minerals and magmas.

silica tetrahedron
The basic structural unit of which all silicates are composed, consisting of a silicon atom surrounded symmetrically by four oxygen atoms. The structure, therefore, has the form of a tetrahedron with an oxygen atom at each corner.

sill
A tabular igneous intrusion that parallels the planar structure of the surrounding rock.

sima
The oceanic crust, also the lower layer of the continental crust, so called because it is enriched in silica and magnesium oxide. compare sial.

sinkhole
Depression in ground surface caused by collapse into a cave below.

sinking stream
A stream that empties into the underground into a cave, usually through a sinkhole.

slate
A compact, fine-grained metamorphic rock that has slaty cleavage.

slaty cleavage
A style of foliation common in metamorphosed mudstones, characterized by nearly flat, sheet-like planes of breakage, similar in appearance to a deck of playing cards. compare cleavage

slickenside
A polished and smoothly striated surface that results from friction along a fault plane.

slide
A mass movement in which material maintains continuous contact with the surface on which it moves.

slip face
Steep face on lee side of sand dune.

slump
Downward and outward rotational movement of Earth materials traveling as a unit or series of units.

smelting
The process of removing metal from ore.

snow line
The elevation at which snow persists throughout the year.

snowfields
Expanses of snow that lie above the snow line.

soil
All unconsolidated materials above bedrock. Natural earthy materials on the Earth

soil horizon
A layer of soil that is distinguishable from adjacent layers by characteristic physical properties such as texture, structure, or color, or by chemical composition.

soil moisture
Ground water in the zone of aeration

soil structure
The combination of soil particles into aggregates or clusters which are separated from adjacent aggregates by surfaces of weakness.

soil texture
The physical nature of the soil, according to its relative proportions of sand, clay, and silt.

sole mark
Develops as an irregularity on the bottom of a stratum. It is a cast of a depression on the top surface of the immediately underlying bed.

solifluction
Turbulent movement of saturated soil or surficial debris.

south magnetic pole
The point on the Earth where a north seeking magnetic needle free to swing in space points directly up.

specific gravity
The ratio of the density of a material to the density of water.

specific retention
(field capacity) The amount of capillary water retained in a soil after the drainage of gravitational moisture.

sphericity
A descriptive term to describe how close a particle

spit
A sandy bar built out from the land into a body of water.

spreading axis
(spreading center) A region of divergence on the Earth

spreading pole
A rotational pole around which a plate appears to rotate on the Earth

spring
Occurs at the intersection of the water table with the ground surface.

stack
An isolated, steep-sided, rocky mass or island just offshore from a rocky headland, usually on a shore platform.

stalactite
An icicle-shaped accumulation of dripstone hanging from cave roof.

stalagmite
A post of dripstone growing up from a cave floor.

star dune
A sand dune built by winds alternating through several directions. Builds vertically rather than migrating and growing laterally.

stick-slip
A jerky, sliding motion associated with fault movement.

stock
A small batholith.

stoping
A process of magmatic intrusion that involves detaching and engulfing pieces of the surrounding rock, so that the magma moves slowly upward.

storm surge
A ridge of high water associated with a hurricane and which floods over the shore .

strain
Change in the shape or volume of a body as a result of stress.

strain rate
The rate at which a body changes shape or volume as a result of stress.

strain seismograph
A seismograph that is designed to detect deformation of the ground by measuring relative displacement of two points.

stratification
The accumulation of material in layers or beds.

stratified drift
Debris washed from a glacier and laid down in well-defined layers.

stratigraphy
The succession and age relation of layered rocks.

stratovolcano
(composite volcano) A volcano that is composed of alternating layers of lava and pyroclastic material, along with abundant dikes and sills. Viscous, intermediate lava may flow from a central vent. Example: Mt. Fuji in Japan.

streak
The color of a mineral in its powdered form, usually obtained by rubbing the mineral against an unglazed porcelain tile to see the mark it makes. A mineral harder than the tile must be pulverized by crushing.

stream capture
see stream piracy.

stream piracy
(stream capture) The natural diversion of the headwaters of one stream into the channel of another stream that has greater erosional activity and flows at a lower level.

stream terrace
A relatively flat surface along a valley, with a steep bank separating it either from the floodplain, or from a lower terrace.

strength
The ability to withstand a stress without permanent deformation.

stress
The force per unit area acting on any surface within a solid; also, by extension, the external pressure which generates the internal force.

striations
Scratches, or small channels, gouged by glacier action. Occur on boulders, pebbles, and bedrock. Striations along bedrock indicate direction of ice movement.

strike
The compass direction of the intersection between a structural surface (e.g., a bedding plane or a fault surface) and the horizontal.

strike-slip fault
(transcurrent fault) A fault on which the movement is parallel to the fault

strip mining
Open pit mining, typically for coal.

subduction zone
A narrow, elongate region in which one lithospheric plate descends relative to another.

sublimation
The process by which matter in the solid state passes directly to the gaseous state without first becoming liquid.

subtropical deserts
Deserts in zones of descending air between 25 degrees and 30 degrees north and south latitude.

superposition
A statement of relative age in layered rocks: In a series of sedimentary rocks that has not been overturned, the topmost layer is always the youngest and the bottommost layer is always the oldest.

surface of discontinuity
In sand dune formation the surface between quiet air of the wind shadow and the rapidly moving air above.

surface wave
compare body wave

surging glacier
A glacier that moves rapidly (tens of meters per day) as it breaks away from the ground surface on which it rests.

suspended load
The amount of material a stream carries in suspension.

suspension
A method of sediment transport in which the turbulence of a fluid is able to keep particles supported in the fluid.

suture
The line of juncture where continental rocks on two converging plates meet. Example: The region in the Himalayas where the Eurasian and Indian-Australian plates meet.

swash and back wash
Uprush of a wave onto the beach followed by the return flow of the water down the beach slope in the intervals between waves.

swells
Persistence of wind-formed waves after wind ceases.

syncline
A fold that is convex downward, or that had such an attitude at some stage in its development. compare anticline.

taconite
A bedded ferruginous chert containing at least 25% iron. A potential iron ore.

tailings
Washed or milled ore that is too poor to be further treated.

talus
A slope built up by the accumulation of rock waste at the foot of a cliff or ridge.

tar
A thick brown to black viscous organic liquid, too thick to migrate easily through most porous sediment.

tar sand
A sand containing tar or asphalt, from which the hydrocarbons may potentially be extracted by distillation.

tarn
A lake in the bedrock basin of a cirque.

tell
An artificial hill formed by the debris of successive human settlements.

temperate glacier
A glacier whose temperature throughout is at, or close to, the pressure point of ice, except in winter when it is frozen for a few meters below the surface.

tensile fracture
A fracture caused by tensional stress in a rock.

tension
A stress that tends to pull a body apart.

tephra
A general term for all pyroclastic material.

terminal moraine
(end moraine) Ridge of till marking farthest extent of glacier.