Glossary - Sociology (A-Z)

Absolute poverty- a deprivation of resources that is life threatening

Civil religion- a quasi-religious loyalty binding individuals in a basically secular society

Class system- a system of social stratification based on individual achievement

Colonialism- the process by which some nations enrich themselves through political and economic control of other countries

Cultural lag- the fact that cultural elements change at different rates, which may disrupt a cultural system

Cultural relativism- the practice of judging a culture by its own standards

Culture- the beliefs, values, behavior, and material objects that define a people’s way of life

Culture shock- persona disorientation that accompanies exposure to an unfamiliar way of life

Davis-Moore thesis- the assertion that social stratification is a universal pattern because it has beneficial consequences for the operation of a society

Dramaturgical analysis- Erving Goffman’s term for the investigation of social interaction in terms of theatrical performance

Endogamy- marriage between people of the same social category

Ethnicity- a shared cultural heritage

Ethnocentrism- the practice of judging another culture by the standards of one’s own culture

Exogamy- marriage between people of different social categories

Gender- the significance a society attaches to biological categories of female and male

Generalized other- George Herbert Mead’s term for widespread cultural norms and values we use as references in evaluating ourselves

Global perspective- the study of the larger world and our society’s place in it

Groupthink- the tendency of group members to conform by adopting a narrow view of some issue

Homogamy- marriage between people with the same social characteristics

Humanizing bureaucracy- fostering an organizational atmosphere that recognized and encourages the contributions of everyone

Ingroup- a social group commanding a member’s esteem and loyalty whose identity is in part based on an “outgroup”, or opposition group

Liberation theology- a fusion of Christian principles with political activism, often Marxist in character

Looking-glass-self- Cooley’s assertion that the self is based on how others respond to us; seeing ourselves through the eyes of others and their reactions and feedback they give us about ourselves

Multiculturalism- an educational program recognizing past and present cultural diversity in U.S. society and promoting the equality of all cultural traditions

Multinational corporation- a large corporation that operates in many different countries

Neocolonialism-a new form of global power relationships that involves not direct political control but, rather through economic exploitation and political manipulation by multinational corporations often support by their governments

Nonverbal communication- communication using body movements, gestures, and facial expressions rather that speech

Norms- rules, guidelines and expectations by which a society guides the behavior of its members

Nuclear family- (conjugal family) a family unit composed of one or more parents and their children

Outgroup- a social group toward which one feels competition or opposition

Pluralism- a state in which racial and ethnic minorities are distinct but have social parity (equality)

Prejudice- an attitude involving a rigid and irrational generalization about an entire category of people, usually remarking on their inferiority

Race- a category composed of humans who share certain biologically transmitted traits that members of a society deem socially significant; in reality biology doesn’t recognize “races” because the differences genetically are too small and insignificant

Rationalization of society- Max Weber’s term for the historical change from tradition to more scientifically based rationality as the dominant mode of human thought

Rational-legal authority- (also bureaucratic authority) power legitimized by legally enacted rules and regulations

Religion- a social institution involving beliefs and practices based upon a conception of the sacred

Role- behavior expected of someone who holds a particular status

Role set- a number of roles attached to a single person

Sapir-Whorf hypothesis- a hypothesis stating that people perceive the world through the cultural lens of their unique language

Scapegoat- a person or category of people, typically with little power, whom people unfairly blame for their own troubles

Secularization- the historical decline in the importance of the supernatural and the sacred; a declining influence of religion in everyday life

Sexual harassment- comments, gesture, or physical contact of a sexual nature that is deliberate, repeated and unwelcome

Social-conflict paradigm- a framework for building theory based on the assumption that society is characterized by inequality and conflict that generate change

Socialization- the lifelong social experience by which individuals develop human potential and learn patters of their culture

Social stratification- a system by which society ranks categories of people in a hierarchy

Society- people who interact in a defined territory and share culture

Sociocultural evolution- the Lenskis’ term for the process of change that results from a society’s gaining new cultural information, particularly technology

State capitalism- an economic and political system in which companies are privately owned although they cooperate closely with the government

Status- a recognized social position and identity that an individual occupies

Stereotype- a set of overgeneralizations concerning some category of people, some positive stereotypes exists, but most are negative

Stigma- a powerfully negative social label that radically changes a person’s self-concept and social identity

Structural-functional paradigm- a framework for building theory based on the assumption that society is a complex system whose parts work together to promote stability

Subculture- cultural patterns that distinguish some segment of a society’s population; variations within a society regarding some aspects of religion, or language, or traditions/customs, or outward symbols/appearance that sets them apart from the mainstream or dominant culture

Sustainable ecosystem- the human use of the natural environment to meet the needs of the present generation without threatening the prospects of future generations

Symbolic-interaction paradigm-a theoretical framework based on the assumption that society is the product of the everyday interactions of individuals

Thomas theorem-W.I. Thomas’s assertion that situations we define as real become real in their consequences ("America is behind the spread of secularism, modernization and capitalism, so we must attack them with terrorism"; "Iraq has weapons of mass destruction and will use them against us, so we must attack them")

Urban renewal- government programs intended to revitalize cities

Values-culturally defined standards by which people judge desirability, goodness, and beauty, and which serve as broad guidelines for social living as well as public policies

Glossary - English Grammar (A-Z)

A

Adjectival

Functioning as an adjective. Phrases and clauses that modify nouns are adjectival.

Adjective

A word that modifies the meaning of a noun.

The little girl climbed quickly up the very tall tree.

Adjectives are capable of comparison:

positive: small, beautiful

comparative: smaller, more beautiful

superlative: smallest, most beautiful.

Adverb

A word that modifies the meaning of a verb, an adjective, or another adverb. They answer the questions "how?" "when?" "where?" etc.

The little girl climbed quickly up the very tall tree.

Adverbs are capable of comparison:

positive fast, quickly

comparative faster, more quickly

superlative fastest, most quickly.

Adverbial

Functioning as an adverb. Phrases and clauses that modify verbs, adjectives, and other adverbs are adverbial.

Article

One of a set of three words: the, the definite article; aand an, the two forms of the indefinite article.

Auxiliary

A "helping verb" like "have" or "should" or "was."

I should have been trying to please them, but I forgot.

C

Case

The use of word form to indicate grammatical function. The form "I" identifies the pronoun as either a subject or a subject completion, "my" or "mine" indicates possession, while "me" is the equivalent object form. Noun endings only indicate whether or not the noun is a possessive: Lara, Lara's.

Clause

A group of words containing a complete predication. Clauses belong to two types: (1) subordinate, relative, or dependent clauses (italicised below) function only when conjoined to (2) a main, coordinate, or independent clause, which can--contrariwise--stand by itself.

Before Tanya or I arrived, it had become late and cold, so we left.

Completion

A word or group of words that combine with a verb to complete the meaning of a predicate. Different verbs take different kinds of completions: objects, indirect objects, subject completions.

Complex sentence

A sentence made up of a main clause together with one or more subordinate or relative clauses.

Barb ran down the street for help while Liz called the police.

Compound Sentence

A sentence made up of two or more independent or main clauses.

Liz ran down the street for help and Barb called the police.

Conjunction

One of a small number of relational (function) words that join words or groups of words together. Conjunctions are of two kinds: some like "and," "or," "for," join words or phrases of equivalent grammatical weight.

Before Tanya or I arrived, it had become late and was turning cold, so we left.

Others, like "since," "when," and sometimes "for," connect subordinate clauses to the rest of the sentence.

Before Tanya or I arrived, it had become late and cold, so we left.

Conjunctive Adverb

An adverb expressing a relationship between main clauses, which can be joined by a semi-colon. Unlike a conjunction, a conjunctive adverb need not come between the main clauses:

I worked hard; nevertheless I did no better than before.

I worked hard; I nevertheless did no better than before.

There are entries for these letters:

G

Gender Specificity

The restriction of noun or pronoun reference to male or female persons or animals. "He" and "chairman" exhibit gender specificity: the former is a very odd pronoun to use for a woman; the latter an incongruous noun when used for the same purpose.

Gerund

A verbal that functions as a noun (as distinct from a participle that functions as an adjective). In the following examples, "Running" is a gerund in the first, and a modifying participle in the second.

Running in every race was Amanda's goal.

Running in every race, Amanda was known to everyone.

Grammar

1. The rules by which native speakers generate acceptable sentences in a language. 2. the study or codification of such rules.

H

Hyper-correct

Too correct; so correct as to be wrong.

That's between Jay and I.

I

Infinitive

The non-finite form of a verb, that is, the form of the verb which is not limited to time, place, or agent. A verbal capable of functioning as a noun, or a modifier, or combined with an auxiliary verb to construct a synthetic verb form. Infinitives can have subjects and completions.

To offer help is better than to refuse it.

Friends and neighbours stopped by to offer help after the fire.

I was able to offer help because I was at hand.

Inflectional System

The pattern of endings indicating different cases or numbers in nouns and pronouns, as well as different tenses in verbs:

Subject: he they who it Mary

Possessive: his their(s) whose its Mary's
Object: him them whom it Mary
Tenses:
give, gave, given
tide, rode, ridden
go, went, gone
sit, sat, sat

Interjection

An exclamatory word intended to express strong feelings.

Interrogation

questioning

M

Modifier

A word or group of words that adds to or refines the meaning of another word. Modifiers are either adjectives or adverbs.

Mood

the form of the verb by which it denotes a state (indicative), a command (imperative), a question (interrogative), or a hypothetical condition (subjunctive).

There are entries for these letters:

N

Negation

A denial; the opposite of affirmation

Mark did not sell his store.

Non-restrictive clause

A clause that adds to our knowledge of whatever it is it modifies but without being crucial to its identification; the opposite of restrictive clause.

The children, who loved ice cream, ran to the Dairy Queen.

Noun

The name of a person, place, or thing. A proper belongs to a particular individual; a common noun identifies a member of a group.

Mark sold his store.

O

Object (direct)

The person or thing affected by the action of the verb; a verb completion

Noel hit the ball; it hit me.

Noel hit me the ball.

Object (indirect)

The person or thing indirectly affected by the action of the verb; a verb completion.

Noel hit me the ball.

Object case

The form that certain pronouns take when they are the object in a sentence. (The object case combines the Old English accusative and dative cases, corresponding roughly to the direct and indirect objects noted above.)

P

Participle

One of two different kinds of verb-derived words which can function as nouns, modifiers, or parts of synthetic verbs. Present participles end with "-ing." Past participles of most verbs end with "-ed" or "-en."

I hate running when I feel tired.

He was running scared.

Parts of Speech

The classes of words from which sentences are constructed: nouns, pronouns, adjectives, verbs, adverbs, prepositions, conjunctions, and interjections etc.

Phrase

A unified group of words which does not include both parts of the actor-act combination that produces predication. The term is a general one, but includes the prepositional phrase as one of its most important classes.

In the box which sat on the porch behind the house was an egg.

Plural

more than one; the opposite of singular.

Possessive Case (traditionally called the genetive case)

The form indicating "possession"; it includes but is not restricted to ownership.

Predicate

what is said about the subject. It comprises a verb, which may stand alone, or the entire verb phrase including complements.

Children read.

Friends and neighbours stopped by to offer help after the event.

Grass is green.

Predication

The act of saying something about a subject.

Preposition

One of a small number of relational (function) words like "in," "on," "behind," etc. which are known as prepositions because they are "pre-posed" or "placed before" the phrases they introduce.

In the box which sat on the porch behind the house was an egg.

Pronoun

A word standing for a noun. There are many different kinds of pronouns, including the following: indefinite pronouns ("some," "any"), demonstrative pronouns ("this," "those"), interrogative pronouns ("who," "which"), personal pronouns ("I," "you," "she"),

There are entries for these letters:

R

Relative pronouns

Which, that, whom> and so on.

Restrictive clause

A clause crucial to the identification of whatever it modifies; the opposite of a non-restrictive clause. The restrictive clause is not set off from the rest of the sentence by commas.

Children who are allergic to milk should avoid ice cream.

S

Singular

One; the opposite of plural.

Subject

The word or words in a sentence about which something is said.

Children read.

Friends and neighbours stopped by to offer help after the event.

Subject Case

Traditionally called nominative case) the form that certain pronouns take when they are the subject or subject completion of a sentence.

Iam here.

This is she.

Subject Completion (also called a subjective completion)

Either a noun or an adjective (a predicate nominative or a predicate adjective) that completes a copulative or linking verb by defining or describing its subject.

The ball appeared round.

Ms. Carswell is a lawyer.

Synthetic verb form

A multi-part verb form expressing one of a variety of possible degrees of pastness, futurity, completeness, habitualness, determination, uncertainty or the like.

I should have been trying to please them, but I forgot.

V

Verb

A word which specifies the action or condition in which the subject of a sentence participates. Predicates comprise a verb with whatever modifiers or complements accompany it.

Friends and neighbours stopped by to offer help after the event.

You seem unhappy.

Verbs are capable of being inflected for tense (and number):

stop (stops) stopped stopped

bite (bites) bit bitten

Verb Phrase

The combination of a verb and an adverb whose combined meaning cannot be deduced from their individual meanings.

Friends and neighbours stopped by to offer help after the event.

Compare:

He stopped by the side of the road.

Verbal

A form of a verb which either (1) does not function as a verb but as a noun or adjective or (2) combines with another verb to form a predicate. Infinitives and participles are verbals.

Glossary - Volcanic (A-Z)

'A'a: Hawaiian word used to describe a lava flow whose surface is broken into rough angular fragments.

Accessory: A mineral whose presence in a rock is not essential to the proper classification of the rock.

Accidental: Pyroclastic rocks that are formed from fragments of non-volcanic rocks or from volcanic rocks not related to the erupting volcano.

Accretionary Lava Ball: A rounded mass, ranging in diameter from a few centimeters to several meters, [carried] on the surface of a lava flow (e.g., 'a'a) or on cinder-cone slopes [and formed] by the molding of viscous lava around a core of already solidified lava.

Acid: A descriptive term applied to igneous rocks with more than 60% silica (SiO2).

Active Volcano: A volcano that is erupting. Also, a volcano that is not presently erupting, but that has erupted within historical time and is considered likely to do so in the future.

Agglutinate: A pyroclastic deposit consisting of an accumulation of originally plastic ejecta and formed by the coherence of the fragments upon solidification.

Alkalic: Rocks which contain above average amounts of sodium and/or potassium for the group of rocks for which it belongs. For example, the basalts of the capping stage of Hawaiian volcanoes are alkalic. They contain more sodium and/or potassium than the shield-building basalts that make the bulk of the volcano.

Andesite: Volcanic rock (or lava) characteristically medium dark in color and containing 54 to 62 percent silica and moderate amounts of iron and magnesium.

Ash: Fine particles of pulverized rock blown from an explosion vent. Measuring less than 1/10 inch in diameter, ash may be either solid or molten when first erupted. By far the most common variety is vitric ash (glassy particles formed by gas bubbles bursting through liquid magma).

Ashfall (Airfall): Volcanic ash that has fallen through the air from an eruption cloud. A deposit so formed is usually well sorted and layered.

Ash Flow: A turbulent mixture of gas and rock fragments, most of which are ash-sized particles, ejected violently from a crater or fissure. The mass of pyroclastics is normally of very high temperature and moves rapidly down the slopes or even along a level surface.

Asthenosphere: The shell within the earth, some tens of kilometers below the surface and of undefined thickness, which is a shell of weakness where plastic movements take place to permit pressure adjustments.

Aquifer: A body of rock that contains significant quantities of water that can be tapped by wells or springs.

Avalanche: A large mass of material or mixtures of material falling or sliding rapidly under the force of gravity. Avalanches often are classified by their content, such as snow, ice, soil, or rock avalanches. A mixture of these materials is a debris avalanche.

Basalt: Volcanic rock (or lava) that characteristically is dark in color, contains 45% to 54% silica, and generally is rich in iron and magnesium.

Basement: The undifferentiated rocks that underlie the rocks of interest in an area.

Basic: A descriptive term applied to igneous rocks (basalt and gabbro) with silica (SiO2) between 44% and 52%.

Bench: The unstable, newly-formed front of a lava delta.

Blister: A swelling of the crust of a lava flow formed by the puffing-up of gas or vapor beneath the flow. Blisters are about 1 meter in diameter and hollow.

Block: Angular chunk of solid rock ejected during an eruption.

Bomb: Fragment of molten or semi-molten rock, 2 1/2 inches to many feet in diameter, which is blown out during an eruption. Because of their plastic condition, bombs are often modified in shape during their flight or upon impact.

Caldera: The Spanish word for cauldron, a basin-shaped volcanic depression; by definition, at least a mile in diameter. Such large depressions are typically formed by the subsidence of volcanoes. Crater Lake occupies the best-known caldera in the Cascades.

Capping Stage: Refers to a stage in the evolution of a typical Hawaiian volcano during which alkalic, basalt, and related rocks build a steeply, sloping cap on the main shield of the volcano. Eruptions are less frequent, but more explosive. The summit caldera may be buried.

Central Vent: A central vent is an opening at the Earth's surface of a volcanic conduit of cylindrical or pipe-like form.

Central Volcano: A volcano constructed by the ejection of debris and lava flows from a central point, forming a more or less symmetrical volcano.

Cinder Cone: A volcanic cone built entirely of loose fragmented material (pyroclastics.)

Cirque: A steep-walled horseshoe-shaped recess high on a mountain that is formed by glacial erosion.

Cleavage: The breaking of a mineral along crystallographic planes, that reflects a crystal structure.

Composite Volcano: A steep volcanic cone built by both lava flows and pyroclastic eruptions.

Compound Volcano: A volcano that consists of a complex of two or more vents, or a volcano that has an associated volcanic dome, either in its crater or on its flanks. Examples are Vesuvius and Mont Pelee.

Compression Waves: Earthquake waves that move like a slinky. As the wave moves to the left, for example, it expands and compresses in the same direction as it moves.

Conduit: A passage followed by magma in a volcano.

Continental Crust: Solid, outer layers of the earth, including the rocks of the continents.

Continental Drift: The theory that horizontal movement of the earth's surface causes slow, relative movements of the continents toward or away from one another.

Country Rocks: The rock intruded by and surrounding an igneous intrusion.

Crater: A steep-sided, usually circular depression formed by either explosion or collapse at a volcanic vent.

Craton: A part of the earth's crust that has attained stability and has been little deformed for a prolonged period.

Curtain of Fire: A row of coalescing lava fountains along a fissure; a typical feature of a Hawaiian-type eruption.

Dacite: Volcanic rock (or lava) that characteristically is light in color and contains 62% to 69% silica and moderate a mounts of sodium and potassium.

Debris Avalanche: A rapid and unusually sudden sliding or flowage of unsorted masses of rock and other material. As applied to the major avalanche involved in the eruption of Mount St. Helens, a rapid mass movement that included fragmented cold and hot volcanic rock, water, snow, glacier ice, trees, and some hot pyroclastic material. Most of the May 18, 1980 deposits in the upper valley of the North Fork Toutle River and in the vicinity of Spirit Lake are from the debris avalanche.

Debris Flow: A mixture of water-saturated rock debris that flows downslope under the force of gravity (also called lahar or mudflow).

Detachment Plane: The surface along which a landslide disconnects from its original position.

Devonian: A period of time in the Paleozoic Era that covered the time span between 400 and 345 million years.

Diatreme: A breccia filled volcanic pipe that was formed by a gaseous explosion.

Dike: A sheetlike body of igneous rock that cuts across layering or contacts in the rock into which it intrudes.

Dome: A steep-sided mass of viscous (doughy) lava extruded from a volcanic vent (often circular in plane view) and spiny, rounded, or flat on top. Its surface is often rough and blocky as a result of fragmentation of the cooler, outer crust during growth of the dome.

Dormant Volcano: Literally, "sleeping." The term is used to describe a volcano which is presently inactive but which may erupt again. Most of the major Cascade volcanoes are believed to be dormant rather than extinct.

Drainage Basin: The area of land drained by a river system.

Echelon: Set of geologic features that are in an overlapping or a staggered arrangement (e.g., faults). Each is relatively short, but collectively they form a linear zone in which the strike of the individual features is oblique to that of the zone as a whole.

Ejecta: Material that is thrown out by a volcano, including pyroclastic material (tephra) and lava bombs.

Episode: An episode is a volcanic event that is distinguished by its duration or style.

Eruption: The process by which solid, liquid, and gaseous materials are ejected into the earth's atmosphere and onto the earth's surface by volcanic activity. Eruptions range from the quiet overflow of liquid rock to the tremendously violent expulsion of pyroclastics.

Eruption Cloud: The column of gases, ash, and larger rock fragments rising from a crater or other vent. If it is of sufficient volume and velocity, this gaseous column may reach many miles into the stratosphere, where high winds will carry it long distances.

Eruptive Vent: The opening through which volcanic material is emitted.

Evacuate: Temporarily move people away from possible danger.

Extinct Volcano: A volcano that is not presently erupting and is not likely to do so for a very long time in the future. Usage of extinct.

Extrusion: The emission of magmatic material at the earth's surface. Also, the structure or form produced by the process (e.g., a lava flow, volcanic dome, or certain pyroclastic rocks).

Fault: A crack or fracture in the earth's surface. Movement along the fault can cause earthquakes or--in the process of mountain-building--can release underlying magma and permit it to rise to the surface.

Fault Scarp A steep slope or cliff formed directly by movement along a fault and representing the exposed surface of the fault before modification by erosion and weathering.

Felsic: An igneous rock having abundant light-colored minerals.

Fire fountain: See also: lava fountain

Fissures: Elongated fractures or cracks on the slopes of a volcano. Fissure eruptions typically produce liquid flows, but pyroclastics may also be ejected.

Flank Eruption: An eruption from the side of a volcano (in contrast to a summit eruption.)

Fluvial: Produced by the action of of flowing water.

Formation: A body of rock identified by lithic characteristics and stratigraphic position and is mappable at the earth's surface or traceable in the subsurface.

Fracture: The manner of breaking due to intense folding or faulting.

Fumarole: A vent or opening through which issue steam, hydrogen sulfide, or other gases. The craters of many dormant volcanoes contain active fumaroles.

Geothermal Energy: Energy derived from the internal heat of the earth.

Geothermal Power: Power generated by using the heat energy of the earth.

Graben: An elongate crustal block that is relatively depressed (downdropped) between two fault systems.

Guyot: A type of seamount that has a platform top. Named for a nineteenth-century Swiss-American geologist.

Hardness: The resistance of a mineral to scratching.

Harmonic Tremor: A continuous release of seismic energy typically associated with the underground movement of magma. It contrasts distinctly with the sudden release and rapid decrease of seismic energy associated with the more common type of earthquake caused by slippage along a fault.

Heat transfer: Movement of heat from one place to another.

Heterolithologic: Material is made up of a heterogeneous mix of different rock types. Instead of being composed on one rock type, it is composed of fragments of many different rocks.

Holocene: The time period from 10,000 years ago to the present. Also, the rocks and deposits of that age.

Horizontal Blast: An explosive eruption in which the resultant cloud of hot ash and other material moves laterally rather than upward.

Horst: A block of the earth's crust, generally long compared to its width, that has been uplifted along faults relative to the rocks on either side.

Hot Spot: A volcanic center, 60 to 120 miles (100 to 200 km) across and persistent for at least a few tens of million of years, that is thought to be the surface expression of a persistent rising plume of hot mantle material. Hot spots are not linked to arcs and may not be associated with ocean ridges.

Hot-spot Volcanoes: Volcanoes related to a persistent heat source in the mantle.

Hyaloclastite: A deposit formed by the flowing or intrusion of lava or magma into water, ice, or water-saturated sediment and its consequent granulation or shattering into small angular fragments.

Hydrothermal Reservoir: An underground zone of porous rock containing hot water.

Hypabyssal: A shallow intrusion of magma or the resulting solidified rock.

Hypocenter: The place on a buried fault where an earthquake occurs.

Ignimbrite: The rock formed by the widespread deposition and consolidation of ash flows and Nuees Ardentes. The term was originally applied only to densely welded deposits but now includes non-welded deposits.

Intensity: A measure of the effects of an earthquake at a particular place. Intensity depends not only on the magnitude of the earthquake, but also on the distance from the epicenter and the local geology.

Intermediate: A descriptive term applied to igneous rocks that are transitional between basic and acidic with silica (SiO2) between 54% and 65%.

Intrusion: The process of emplacement of magma in pre-existing rock. Also, the term refers to igneous rock mass so formed within the surrounding rock.

Joint: A surface of fracture in a rock.

Juvenile: Pyroclastic material derived directly from magma reaching the surface.

Kipuka: An area surrounded by a lava flow.

Laccolith: A body of igneous rocks with a flat bottom and domed top. It is parallel to the layers above and below it.

Lahar: A torrential flow of water-saturated volcanic debris down the slope of a volcano in response to gravity. A type of mudflow.

Landsat: A series of unmanned satellites orbiting at about 706 km (438 miles) above the surface of the earth. The satellites carry cameras similar to video cameras and take images or pictures showing features as small as 30 m or 80 m wide, depending on which camera is used.

Lapilli: Literally, "little stones." Round to angular rock fragments, measuring 1/10 inch to 2 1/2 inches in diameter, which may be ejected in either a solid or molten state.

Lava: Magma which has reached the surface through a volcanic eruption. The term is most commonly applied to streams of liquid rock that flow from a crater or fissure. It also refers to cooled and solidified rock.

Lava Dome: Mass of lava, created by many individual flows, that has built a dome-shaped pile of lava.

Lava Flow: An outpouring of lava onto the land surface from a vent or fissure. Also, a solidified tongue like or sheet-like body formed by outpouring lava.

Lava Fountain: A rhythmic vertical fountainlike eruption of lava.

Lava Lake (Pond): A lake of molten lava, usually basaltic, contained in a vent, crater, or broad depression of a shield volcano.

Lava Shields: A shield volcano made of basaltic lava.

Lava Tube: A tunnel formed when the surface of a lava flow cools and solidifies while the still-molten interior flows through and drains away.

Limu O Pele (Pele Seaweed): Delicate, translucent sheets of spatter filled with tiny glass bubbles.

Lithic: Of or pertaining to stone.

Lithosphere: The rigid crust and uppermost mantle of the earth. Thickness is on the order of 60 miles (100 km). Stronger than the underlying asthenosphere.

Luster: The reflection of light from the surface of a mineral.

Maar: A volcanic crater that is produced by an explosion in an area of low relief, is generally more or less circular, and often contains a lake, pond, or marsh.

Mafic: An igneous composed chiefly of one or more dark-colored minerals.

Magma: Molten rock beneath the surface of the earth.

Magma Chamber: The subterranean cavity containing the gas-rich liquid magma which feeds a volcano.

Magmatic: Pertaining to magma.

Magnitude: A numerical expression of the amount of energy released by an earthquake, determined by measuring earthquake waves on standardized recording instruments (seismographs.) The number scale for magnitudes is logarithmic rather than arithmetic. Therefore, deflections on a seismograph for a magnitude 5 earthquake, for example, are 10 times greater than those for a magnitude 4 earthquake, 100 times greater than for a magnitude 3 earthquake, and so on.

Mantle: The zone of the earth below the crust and above the core.

Matrix: The solid matter in which a fossil or crystal is embedded. Also, a binding substance (e.g., cement in concrete).

Miocene: An epoch in Earth's history from about 24 to 5 million years ago. Also refers to the rocks that formed in that epoch.

Moho: Also called the Mohorovicic discontinuity. The surface or discontinuity that separates the crust from the mantle. The Moho is at a depth of 5-10 km beneath the ocean floor and about 35 km below the continents (but down to 60 km below mountains). Named for Andrija Mohorovicic, a Croatian seismologist.

Monogenetic: A volcano built by a single eruption.

Mudflow: A flowage of water-saturated earth material possessing a high degree of fluidity during movement. A less-saturated flowing mass is often called a debris flow. A mudflow originating on the flank of a volcano is properly called a lahar.

Myth: A fictional story to explain the origin of some person, place, or thing.

Nuees Ardentes: A French term applied to a highly heated mass of gas-charged ash which is expelled with explosive force and moves hurricane speed down the mountainside.

Obsidian: A black or dark-colored volcanic glass, usually composed of rhyolite.

Oceanic Crust: The earth's crust where it underlies oceans.

Pahoehoe: A Hawaiian term for lava with a smooth, billowy, or ropy surface.

Pali: Hawaiian word for steep hills or cliffs.

Pele Hair: A natural spun glass formed by blowing-out during quiet fountaining of fluid lava, cascading lava falls, or turbulent flows, sometimes in association with pele tears. A single strand, with a diameter of less than half a millimeter, may be as long as two meters.

Pele Tears: Small, solidified drops of volcanic glass behind which trail pendants of Pele hair. They may be tear-shaped, spherical, or nearly cylindrical.

Peralkaline: Igneous rocks in which the molecular proportion of aluminum oxide is less than that of sodium and potassium oxides combined.

Phenocryst: A conspicuous, usually large, crystal embedded in porphyritic igneous rock.

Phreatic Eruption (Explosion): An explosive volcanic eruption caused when water and heated volcanic rocks interact to produce a violent expulsion of steam and pulverized rocks. Magma is not involved.

Phreatomagmatic: An explosive volcanic eruption that results from the interaction of surface or subsurface water and magma.

Pillow lava: Interconnected, sack-like bodies of lava formed underwater.

Pipe: A vertical conduit through the Earth's crust below a volcano, through which magmatic materials have passed. Commonly filled with volcanic breccia and fragments of older rock.

Pit Crater: A crater formed by sinking in of the surface, not primarily a vent for lava.

Plastic: Capable of being molded into any form, which is retained.

Plate Tectonics: The theory that the earth's crust is broken into about 10 fragments (plates,) which move in relation to one another, shifting continents, forming new ocean crust, and stimulating volcanic eruptions.

Pleistocene: A epoch in Earth history from about 2-5 million years to 10,000 years ago. Also refers to the rocks and sediment deposited in that epoch.

Plinian Eruption: An explosive eruption in which a steady, turbulent stream of fragmented magma and magmatic gases is released at a high velocity from a vent. Large volumes of tephra and tall eruption columns are characteristic.

Plug: Solidified lava that fills the conduit of a volcano. It is usually more resistant to erosion than the material making up the surrounding cone, and may remain standing as a solitary pinnacle when the rest of the original structure has eroded away.

Plug Dome: The steep-sided, rounded mound formed when viscous lava wells up into a crater and is too stiff to flow away. It piles up as a dome-shaped mass, often completely filling the vent from which it emerged.

Pluton: A large igneous intrusion formed at great depth in the crust.

Polygenetic: Originating in various ways or from various sources.

Precambrian:All geologic time from the beginning of Earth history to 570 million years ago. Also refers to the rocks that formed in that epoch.

Pumice: Light-colored, frothy volcanic rock, usually of dacite or rhyolite composition, formed by the expansion of gas in erupting lava. Commonly seen as lumps or fragments of pea-size and larger, but can also occur abundantly as ash-sized particles.

Pyroclastic: Pertaining to fragmented (clastic) rock material formed by a volcanic explosion or ejection from a volcanic vent.

Pyroclastic Flow: Lateral flowage of a turbulent mixture of hot gases and unsorted pyroclastic material (volcanic fragments, crystals, ash, pumice, and glass shards) that can move at high speed (50 to 100 miles an hour.) The term also can refer to the deposit so formed.

Quaternary: The period of Earth's history from about 2 million years ago to the present; also, the rocks and deposits of that age.

Relief: The vertical difference between the summit of a mountain and the adjacent valley or plain.

Renewed Volcanism State: Refers to a state in the evolution of a typical Hawaiian volcano during which --after a long period of quiescence--lava and tephra erupt intermittently. Erosion and reef building continue.

Repose: The interval of time between volcanic eruptions.

Rhyodacite: An extrusive rock intermediate in composition between dacite and rhyolite.

Rhyolite: Volcanic rock (or lava) that characteristically is light in color, contains 69% silica or more, and is rich in potassium and sodium.

Ridge, Oceanic: A major submarine mountain range.

Rift System: The oceanic ridges formed where tectonic plates are separating and a new crust is being created; also, their on-land counterparts such as the East African Rift.

Rift Zone: A zone of volcanic features associated with underlying dikes. The location of the rift is marked by cracks, faults, and vents.

Ring of Fire: The regions of mountain-building earthquakes and volcanoes which surround the Pacific Ocean.

Scoria: A bomb-size (> 64 mm) pyroclast that is irregular in form and generally very vesicular. It is usually heavier, darker, and more crystalline than pumice.

Seafloor Spreading: The mechanism by which new seafloor crust is created at oceanic ridges and slowly spreads away as plates are separating.

Seamount: A submarine volcano.

Seismograph: An instrument that records seismic waves; that is, vibrations of the earth.

Seismologist: Scientists who study earthquake waves and what they tell us about the inside of the Earth.

Seismometer: An instrument that measures motion of the ground caused by earthquake waves.

Shearing: The motion of surfaces sliding past one another.

Shear Waves: Earthquake waves that move up and down as the wave itself moves. For example, to the left.

Shield Volcano: A gently sloping volcano in the shape of a flattened dome and built almost exclusively of lava flows.

Shoshonite: A trachyandesite composed of olivine and augite phenocrysts in a groundmass of labradorite with alkali feldspar rims, olivine, augite, a small amount of leucite, and some dark-colored glass. Its name is derived from the Shoshone River, Wyoming and given by Iddings in 1895.

Silica: A chemical combination of silicon and oxygen.

Sill: A tabular body of intrusive igneous rock, parallel to the layering of the rocks into which it intrudes.

Skylight: An opening formed by a collapse in the roof of a lava tube.

Solfatara: A type of fumarole, the gases of which are characteristically sulfurous.

Spatter Cone: A low, steep-sided cone of spatter built up on a fissure or vent. It is usually of basaltic material.

Spatter Rampart: A ridge of congealed pyroclastic material (usually basaltic) built up on a fissure or vent.

Specific Gravity: The density of a mineral divided by the density of water.

Spines: Horn-like projections formed upon a lava dome.

Stalactite: A cone shaped deposit of minerals hanging from the roof of a cavern.

Stratigraphic: The study of rock strata, especially of their distribution, deposition, and age.

Stratovolcano:A volcano composed of both lava flows and pyroclastic material.

Streak: The color of a mineral in the powdered form.

Strike-Slip Fault: A nearly vertical fault with side-slipping displacement.

Strombolian Eruption: A type of volcanic eruption characterized by jetting of clots or fountains of fluid basaltic lava from a central crater.

Subduction Zone: The zone of convergence of two tectonic plates, one of which usually overrides the other.

Surge: A ring-shaped cloud of gas and suspended solid debris that moves radially outward at high velocity as a density flow from the base of a vertical eruption column accompanying a volcanic eruption or crater formation.

Talus: A slope formed a the base of a steeper slope, made of fallen and disintegrated materials.

Tephra: Materials of all types and sizes that are erupted from a crater or volcanic vent and deposited from the air.

Tephrochronology: The collection, preparation, petrographic description, and approximate dating of tephra.

Tilt: The angle between the slope of a part of a volcano and some reference. The reference may be the slope of the volcano at some previous time.

Trachyandesite: An extrusive rock intermediate in composition between trachyte and andesite.

Trachybasalt: An extrusive rock intermediate in composition between trachyte and basalt.

Trachyte: A group of fine-grained, generally porphyritic, extrusive igneous rocks having alkali feldspar and minor mafic minerals as the main components, and possibly a small amount of sodic plagioclase.

Tremor: Low amplitude, continuous earthquake activity often associated with magma movement.

Tsunami: A great sea wave produced by a submarine earthquake, volcanic eruption, or large landslide.

Tuff: Rock formed of pyroclastic material.

Tuff Cone: A type of volcanic cone formed by the interaction of basaltic magma and water. Smaller and steeper than a tuff ring.

Tuff Ring: A wide, low-rimmed, well-bedded accumulation of hyalo-clastic debris built around a volcanic vent located in a lake, coastal zone, marsh, or area of abundant ground water.

Tumulus: A doming or small mound on the crest of a lava flow caused by pressure due to the difference in the rate of flow between the cooler crust and the more fluid lava below.

Ultramafic: Igneous rocks made mostly of the mafic minerals hypersthene, augite, and/or olivine.

Unconformity: A substantial break or gap in the geologic record where a rock unit is overlain by another that is not next in stratigraphic sucession, such as an interruption in continuity of a depositional sequence of sedimentary rocks or a break between eroded igneous rocks and younger sedimentary strata. It results from a change that caused deposition to cease for a considerable time, and it normally implies uplift and erosion with loss of the previous formed record.

Vent: The opening at the earth's surface through which volcanic materials issue forth.

Vesicle: A small air pocket or cavity formed in volcanic rock during solidification.

Viscosity: A measure of resistance to flow in a liquid (water has low viscosity while honey has a higher viscosity.)

Volcano: A vent in the surface of the Earth through which magma and associated gases and ash erupt; also, the form or structure (usually conical) that is produced by the ejected material.

Volcanic Arc: A generally curved linear belt of volcanoes above a subduction zone, and the volcanic and plutonic rocks formed there.

Volcanic Complex: A persistent volcanic vent area that has built a complex combination of volcanic landforms.

Volcanic Cone: A mound of loose material that was ejected ballistically.

Volcanic Neck: A massive pillar of rock more resistant to erosion than the lavas and pyroclastic rocks of a volcanic cone.

Vulcan: Roman god of fire and the forge after whom volcanoes are named.

Vulcanian: A type of eruption consisting of the explosive ejection of incandescent fragments of new viscous lava, usually on the form of blocks.

Water Table: The surface between where the pore space in rock is filled with water and where the the pore space in rock is filled with air.

Xenocrysts: A crystal that resembles a phenocryst in igneous rock, but is a foreign to the body of rock in which it occurs.

Xenoliths: A foreign inclusion in an igneous rock.

Glossary - Geology (W-Z)

watershed

See drainage basin.

water table

The surface that lies between the zone of aeration and the underlying zone of saturation.

wave-cut bench

A relatively level surface formed when waves erode the base of a cliff, causing the overlying rock to fall into the surf. A wave-cut bench stands above the water and extends seaward from what remains of the cliff.

wave refraction

The process by which a wave approaching the shore changes direction due to slowing of those parts of the wave that enter shallow water first, causing a sharp decrease in the angle at which the wave approaches until the wave is almost parallel to the coast.

weathering

The process by which exposure to atmospheric agents, such as air or moisture, causes rocks and minerals to break down. This process takes place at or near the Earth's surface. Weathering entails little or no movement of the material that it loosens from the rocks and minerals. See also erosion.

welded tuff

A volcanic igneous rock that forms when still-warm tephra accumulates at the Earth's surface. Because the particles are still warm and soft, they can weld together under the weight of overlying deposits, forming a hard rock.

wetland

A lake, marsh, or swamp that supports wildlife and replenishes the groundwater system.

wind abrasion

The process by which wind erodes bedrock through contact between the bedrock and rock particles carried by the wind.

xenolith

A preexisting rock embedded in a newer igneous rock. Xenoliths are formed when a rising magma incorporates the preexisting rock. If the preexisting rock does not melt, it will not be assimilated into the magma and will therefore remain distinct from the new igneous rock that surrounds it.

X-ray diffraction

The scattering of X rays passed through a mineral sample so as to form a pattern peculiar to the given mineral.

yield point

The maximum stress that a given rock can withstand without becoming permanently deformed

zone of ablation

The part of a glacier in which there is greater overall loss than gain in volume. A zone of ablation can be identified in the summer by an expanse of bare ice. See also zone of accumulation.

zone of accumulation

The part of a glacier in which there is greater overall gain than loss in volume. A zone of accumulation can be identified by a blanket of snow that survives summer melting. See also zone of ablation.

zone of aeration

A region below the Earth's surface that is marked by the presence of both water and air in the pores of rocks and soil. Also called aeration zone.

zone of saturation

A region that lies below the zone of aeration and is marked by the presence of water and the absence of air in the pores of rocks and soil.

Glossary - Geology (U-V)

unconformity

A boundary separating two or more rocks of markedly different ages, marking a gap in the geologic record.

uniformitarianism

The hypothesis that current geologic processes, such as the slow erosion of a coast under the impact of waves, have been occurring in a similar manner throughout the Earth's history and that these processes can account for past geologic events. See also catastrophism.

upwarped mountain

A mountain consisting of a broad area of the Earth's crust that has moved gently upward without much apparent deformation, and usually containing sedimentary, igneous, and metamorphic rocks.

uranium-thorium-lead dating

A form of isotope dating that relies on the extremely long half-life of radioactive isotopes of uranium, which decay into isotopes of lead, to determine the age of rocks in which uranium and lead are present.

valley glacier

An alpine glacier that flows through a preexisting stream valley.

van der Waals bond

A relatively weak kind of intermolecular bond that forms when one side of a molecule develops a slight negative charge because a number of electrons have temporarily moved to that side of the molecule. This negative charge attracts the nuclei of the atoms of a neighboring molecule. The side of the molecule with fewer electrons develops a slight positive charge that attracts the electrons of the atoms of neighboring molecules.

varve

A pair of sediment beds deposited by a lake on its floor, typically consisting of a thick, coarse, light-colored bed deposited in the summer and a thin, fine-grained, dark-colored bed deposited in the winter. Varves are most often found in lakes that freeze in the winter. The number and nature of varves on the bottom of a lake provide information about the lake's age and geologic events that affected the lake's development.

vent

An opening in the Earth's surface through which lava, gases, and hot particles are expelled. Also called volcanic vent and volcano.

ventifact

A stone that has been flattened and sharpened by wind abrasion. Ventifacts are commonly found strewn across a desert floor.

viscosity

A fluid's resistance to flow. Viscosity increases as temperatures decrease.

volcanic arc

A chain of volcanoes fueled by magma that rises from an underlying subducting plate.

volcanic cone

A cone-shaped mountain that forms around a vent from the debris of pyroclastics and lava ejected by numerous eruptions over time.

volcanic crater

A steep, bowl-shaped depression surrounding a vent. A volcanic crater forms when the walls of a vent collapse inward following an eruption.

volcanic dome

A bulb-shaped solid that forms over a vent when lava so viscous that it cannot flow out of the volcanic crater cools and hardens. When a volcanic dome forms, it traps the volcano's gases beneath it. They either escape along a side vent of the volcano or build pressure that causes another eruption and shatters the volcanic dome.

volcanic rock

See extrusive rock.

volcanism

The set of geological processes that result in the expulsion of lava, pyroclastics, and gases at the Earth's surface.

volcano

The solid structure created when lava, gases, and hot particles escape to the Earth's surface through vents. Volcanoes are usually conical. A volcano is "active" when it is erupting or has erupted recently. Volcanoes that have not erupted recently but are considered likely to erupt in the future are said to be "dormant." A volcano that has not erupted for a long time and is not expected to erupt in the future is "extinct."

Glossary - Geology (T)

talus

A pile of rock fragments lying at the bottom of the cliff or steep slope from which they have broken off.

talus slope

The large pile of rocky boulders that accumulates at the foot of a cliff, typically by the mechanical-weathering process of frost-wedging.

tarn

A deep, typically circular lake that forms when a cirque glacier melts.

tectonic creep

The almost constant movement of certain fault blocks that allows strain energy to be released without major earthquakes.

tension

Stress that stretches or extends rocks, so that they become thinner vertically and longer laterally. Tension may be caused by divergence or rifting.

tephra (plural noun)

Pyroclastic materials that fly from an erupting volcano through the air before cooling, and range in size from fine dust to massive blocks.

terminus

The outer margin of a glacier.

theory

A comprehensive explanation of a given set of data that has been repeatedly confirmed by observation and experimentation and has gained general acceptance within the scientific community but has not yet been decisively proven. See also hypothesis and scientific law.

thermal contraction

A form of mechanical weathering in which cold causes a mineral's crystal structure to contract.

thermal expansion

A form of mechanical weathering in which heat causes a mineral's crystal structure to enlarge.

thermal plume

A vertical column of upwelling mantle material, 100 to 250 kilometers in diameter, that rises from beneath a continent or ocean and can be perceived at the Earth's surface as a hot spot. Thermal plumes carry enough energy to move a plate, and they may be found both at plate boundaries and plate interiors.

thrust fault

A reverse fault marked by a dip of 45º or less.

tidal bore

A turbulent, abrupt, wall-like wave that is caused by a flood tide.

tide

1. The cycle of alternate rising and falling of the surface of an ocean or large lake, caused by the gravitational pull of the Sun and especially Moon in interaction with the Earth's rotation. Tides occur on a regular basis, twice every day on most of the Earth. 2. A single rise or fall within this cycle.

topography

The set of physical features, such as mountains, valleys, and the shapes of landforms, that characterizes a given landscape.

transform motion

The movement of two adjacent lithospheric plates in opposite directions along a parallel line at their common edge. Transform motion often causes earthquakes.

transition zone

The seismic discontinuity located in the upper mantle just beneath the asthenosphere and characterized by a marked increase in the velocity of seismic waves.

translatory motion

the movement of water over a significant distance in the direction of a wave.

transverse dune

One of a series of dunes having an especially steep slip face and a gentle windward slope and standing perpendicular to the prevailing wind direction and parallel to each other. Transverse dunes typically form in arid and semi-arid regions with plentiful sand, stable wind direction, and scarce vegetation. A transverse dune may be as much as 100 kilometers long, 200 meters high, and 3 kilometers wide.

tributary

A stream that supplies water to a larger stream.

trunk stream

A large stream into which tributaries carry water and sediment.

tsunami(plural tsunami)

A vast sea wave caused by the sudden dropping or rising of a section of the sea floor following an earthquake. Tsunami may be as much as 30 meters high and 200 kilometers long, may move as fast as 250 kilometers per hour, and may continue to occur for as long as a few days.

Glossary - Geology (S)

sandstone

A clastic rock composed of particles that range in diameter from 1/16 millimeter to 2 millimeters in diameter. Sandstones make up about 25% of all sedimentary rocks.

scarp

The steep cliff face that is formed by a slump.

schist

A coarse-grained, strongly foliated metamorphic rock that develops from phyllite and splits easily into flat, parallel slabs.

scientific law

1. A natural phenomenon that has been proven to occur invariably whenever certain conditions are met. 2. A formal statement describing such a phenomenon and the conditions under which it occurs. Also called law.

scientific methods

Techniques that involve gathering all available data on a subject, forming a hypothesis to explain the data, conducting experiments to test the hypothesis, and modifying or confirming the hypothesis as necessary to account for the experimental results.

sea arch

A landform produced by coastal erosion of a prominent headland. Sea arches form when sea caves are excavated so deeply by crashing waves that two caves eroding on opposite sides of the headland become joined. The overlying rocky roof is left as an arch.

sea cave

The notches in the sides of a prominent coastal rocky headland eroded by crahing waves.

sea-floor spreading

The formation and growth of oceans that occurs following rifting and is characterized by eruptions along mid-ocean ridges, forming new oceanic lithosphere, and expanding ocean basins. See also divergence.

seamount

A conical underwater mountain formed by a volcano and rising 1000 meters or more from the sea floor.

sea stack

A steep, isolated island of rock, separated from a headland by the action of waves, as when the overhanging section of a sea arch is eroded.

seawall

A wall of stone, concrete, or other sturdy material, built along the shoreline to prevent erosion even by the strongest and highest of waves. See also riprap.

secondary coast

A coast shaped primarily by erosion or deposition by sea currents and waves.

secondary enrichment

The process by which a metal deposit becomes concentrated when other minerals are eliminated from the deposit, as through dissolution, precipitation, or weathering.

sediment

A collection of transported fragments or precipitated materials that accumulate, typically in loose layers, as of sand or mud.

sedimentary environment

The continental, oceanic, or coastal surroundings in which sediment accumulates.

sedimentary facies

1. A set of characteristics that distinguish a given section of sedimentary rock from nearby sections. Such characteristics include mineral content, grain size, shape, and density. 2. A section of sedimentary rock so characterized.

sedimentary rock

A rock made from the consolidation of solid fragments, as of other rocks or organic remains, or by precipitation of minerals from solution.

sedimentary structure

A physical characteristic of a detrital sediment that reflects the conditions under which the sediment was deposited.

seismic gap

A locked fault segment that has not experienced seismic activity for a long time. Because stress tends to accumulate in seismic gaps, they often become the sites of major earthquakes.

seismic moment

A numerical means of measuring an earthquake's total energy release. It is calculated by measuring the total length of fault rupture and then factoring in the depth of rupture, total slip along the rupture, and the strength of the faulted rocks.

seismic profiling

The mapping of rocks lying along and beneath the ocean floor by recording the reflections and refractions of seismic waves.

seismic tomography

The process whereby a computer first synthesizes data on the velocities of seismic waves from thousands of recent earthquakes to make a series of images depicting successive planes within the Earth, and then uses these images to construct a three-dimensional representation of the Earth's interior.

seismic wave

One of a series of progressive disturbances that reverberate through the Earth to transmit the energy released from an earthquake.

seismogram

A visual record produced by a seismograph and showing the arrival times and magnitudes of various seismic waves.

seismograph

A machine for measuring the intensity of earthquakes by recording the seismic waves that they generate.

seismology

The study of earthquakes and the structure of the Earth, based on data from seismic waves.

shale

A sedimentary rock composed of detrital sediment particles less than 0.004 millimeter in diameter. Shales tend to be red, brown, black, or gray, and usually originate in relatively still waters.

shearing stress

Stress that slices rocks into parallel blocks that slide in opposite directions along their adjacent sides. Shearing stress may be caused by transform motion.

shield volcano

A low, broad, gently sloping, dome-shaped structure that forms over time as repeated eruptions eject basaltic lava through one or more vents and the lava solidifies in approximately the same volume all around.

shock metamorphism

The metamorphism that results when a meteorite strikes rocks at the Earth's surface. The meteoric impact generates tremendous pressure and extremely high temperatures that cause minerals to shatter and recrystallize, producing new minerals that cannot arise under any other circumstances.

shoreline

The boundary between a body of water and dry land.

silicate

One of several rock-forming minerals that contain silicon, oxygen, and usually one or more other common elements.

silicon oxygen tetrahedron

A four-sided geometric form created by the tight bonding of four oxygen atoms to each other, and also to a single silicon atom that lies in the middle of the form.

sill

A concordant pluton that is substantially wider than it is thick. Sills form within a few kilometers of the Earth's surface. See also dike.

sinkhole

A circular, often funnel-shaped depression in the ground that forms when soluble rocks dissolve.

slate

A fine-grained, foliated metamorphic rock that develops from shale and tends to break into thin, flat sheets.

slide

The mass movement of a single, intact mass of rock, soil, or unconsolidated material along a weak plane, such as a fault, fracture, or bedding plane. A slide may involve as little as a minor displacement of soil or as much as the displacement of an entire mountainside.

slip face

The steep leeward slope of a dune.

slip plane

A weak plane in a rock mass from which material is likely to break off in a slide.

slump

1. A downward and outward slide occurring along a concave slip plane. 2. The material that breaks off in such a slide.

snowline

The lowest point at which snow remains year-round.

soil

The top few meters of regolith, generally including some organic matter derived from plants.

soil horizon

A layer of soil that can be distinguished from the surrounding soil by such features as chemical composition, color, and texture.

soil profile

A vertical strip of soil stretching from the surface down to the bedrock and including all of the successive soil horizons.

solifluction

A form of creep in which soil flows downslope at a rate of 0.5 to 15 centimeters per year. Solifluction occurs in relatively cold regions when the brief warmth of summer thaws only the upper meter or two of regolith, which becomes waterlogged because the underlying ground remains frozen and therefore the water cannot drain down into it.

sorting

The process by which a given transport medium separates out certain particles, as on the basis of size, shape, or density.

source rock

A rock in which hydrocarbons originate.

specific gravity

The ratio of the weight of a particular volume of a given substance to the weight of an equal volume of pure water.

speleothem

A mineral deposit of calcium carbonate that precipitates from solution in a cave.

spheroidal weathering

The process by which chemical weathering, especially by water, decomposes the angles and edges of a rock or boulder, leaving a rounded form from which concentric layers are then stripped away as the weathering continues.

spit

A narrow, fingerlike ridge of sand that extends from land into open water.

stalactite

An icicle-like mineral formation that hangs from the ceiling of a cave and is usually made up of travertine, which precipitates as water rich in dissolved limestone drips down from the cave's ceiling. See also stalagmite.

stalagmite

A cone-shaped mineral deposit that forms on the floor of a cave and is usually made up of travertine, which precipitates as water rich in dissolved limestone drips down from the cave's ceiling. See also stalactite.

star dune

A dune with three or four arms radiating from its usually higher center so that it resembles a star in shape. Star dunes form when winds blow from three or four directions, or when the wind direction shifts frequently.

strain

The change in the shape or volume of a rock that results from stress.

stratovolcano

A cone-shaped volcano built from alternating layers of pyroclastics and viscous andesitic lava. Stratovolcanos tend to be very large and steep.

streak

The color of a mineral in its powdered form. This color is usually determined by rubbing the mineral against an unglazed porcelain slab and observing the mark made by it on the slab.

stream

A body of water found on the Earth's surface and confined to a narrow topographic depression, down which it flows and transports rock particles, sediment, and dissolved particles. Rivers, creeks, brooks, and runs are all streams.

stream discharge

The volume of water to pass a given point on a stream bank per unit of time, usually expressed in cubic meters of water per second.

stream terrace

A level plain lying above and running parallel to a stream bed. A stream terrace is formed when a stream's bed erodes to a substantially lower level, leaving its floodplain high above it.

stress

The force acting on a rock or another solid to deform it, measured in kilograms per square centimeter or pounds per square inch.

striation

One of a group of usually parallel scratches engraved in bedrock by a glacier or other geological agent.

strike 1.

The horizontal line marking the intersection between the inclined plane of a solid geological structure and the Earth's surface. 2. The compass direction of this line, measured in degrees from true north.

strike-slip fault

A fault in which two sections of rock have moved horizontally in opposite directions, parallel to the line of the fracture that divided them. Strike-slip faults are caused by shearing stress.

structural geology

The scientific study of the geological processes that deform the Earth's crust and create mountains.

subduction

The sinking of an oceanic plate edge as a result of convergence with a plate of lesser density. Subduction often causes earthquakes and creates volcano chains.

subsidence

The lowering of the Earth's surface, caused by such factors as compaction, a decrease in groundwater, or the pumping of oil.

sulfate

One of several minerals containing positive sulfur ions bonded to negative oxygen ions.

sulfide

One of several minerals containing negative sulfur ions bonded to one or more positive metallic ions.

surface wave

One of a series of seismic waves that transmits energy from an earthquake's epicenter along the Earth's surface. See also body wave.

surge

To flow more rapidly than usually. Said of a glacier.

suspended load

A body of fine, solid particles, typically of sand, clay, and silt, that travels with stream water without coming in contact with the stream bed.

suture zone

The area where two continental plates have joined together through continental collision. Suture zones are marked by extremely high mountain ranges, such as the Himalayas and the Alps.

S wave (abbreviation for secondary wave)

A body wave that causes the rocks along which it passes to move up and down perpendicular to the direction of its own movement. See also P wave.

S-wave shadow zone

The region within an arc of 154° directly opposite an earthquake's epicenter that is marked by the absence of S waves. The S-wave shadow zone is due to the fact that S waves cannot penetrate the liquid outer core. See also P-wave shadow zone.

syncline

A concave fold, the central part of which contains the youngest section of rock. See also anticline.