C Index Glossary geology Science
C Index Glossary geology Science
Caldera
A large, bowl-shaped crater associated with a volcanic vent. A caldera can form from a volcanic blast or the collapse of a volcanic cone into an emptied magma chamber.
-A vast depression at the top of a volcanic cone, formed when an eruption substantially empties the reservoir of magma beneath the cone's summit. Eventually the summit collapses inward, creating a caldera. A caldera may be more than 15 kilometers in diameter and more than 1000 meters deep.
caliche
A white soil horizon consisting of calcium carbonate, typical of arid and semi-arid areas. Brief heavy rains dissolve calcium carbonate in the upper layers of soil and transport it downward; the rainwater then evaporates rapidly, leaving the calcium carbonate to form a new, solid layer of soil.
capacity
The ability of a given stream to carry sediment, measured as the maximum quantity it can transport past a given point on the channel bank in a given amount of time. See also competence.
capillary fringe
The lowest part of the zone of aeration, marked by the rising of water from the water table due to the attraction of the water molecules to mineral surfaces and other molecules, and to pressure from the zone of saturation below.
carbon-14 dating
A form of radiometric dating that relies on the 5730-year half-life of radioactive carbon-14, which decays into nitrogen-14, to determine the age of rocks in which carbon-14 is present. Carbon-14 dating is used for rocks from 100 to 100,000 years old.
carbonate
One of several minerals containing one central carbon atom with strong covalent bonds to three oxygen atoms and typically having ionic bonds to one or more positive ions.
catastrophism
The hypothesis that a series of immense, brief, worldwide upheavals changed the Earth's crust greatly and can account for the development of mountains, valleys, and other features of the Earth. See also uniformitarianism.
cave
A naturally formed opening beneath the surface of the Earth, generally formed by dissolution of carbonate bedrock. Caves may also form by erosion of coastal bedrock, partial melting of glaciers, or solidification of lava into hollow tubes.
Cementation
The processes through which chemical precipitates form within the pore spaces of a sediment and help bind it into a sedimentary rock.
-The diagenetic process by which sediment grains are bound together by precipitated minerals originally dissolved during the chemical weathering of preexisting rocks.
Cenozoic Era
The latest era of the Phanerozoic Eon, following the Mesozoic Era and continuing to the present time, and marked by the presence of a wide variety of mammals, including the first hominids.
chemical sediment
Sediment that is composed of previously dissolved minerals that have either precipitated from evaporated water or been extracted from water by living organisms and deposited when the organisms died or discarded their shells
Cinder Cone
A pyroclastic cone composed primarily of cinders. A cone-shaped hill that consists of pyroclastic materials ejected from a volcanic vent.
cinders
Glassy, porous, pyroclastic rock fragments.
cirque glacier
A small alpine glacier that forms inside a cirque, typically near the head of a valley.
clay mineral
One of a group of hydrous silicate minerals, such as kaolinite and smectite, the extremely small particle size of which imparts the ability to adsorb water. Clay minerals are the stable endproducts of the chemical weathering of feldspars.
cleavage
The tendency of certain minerals to break along distinct planes in their crystal structures where the bonds are weakest. Cleavage is tested by striking or hammering a mineral, and is classified by the number of surfaces it produces and the angles between adjacent surfaces.
coast
The area of dry land that borders on a body of water.
cockpit karst
A karst environment marked by numerous closely spaced, irregular depressions and steep, conical hills.
col
A high mountain pass that forms when part of an arete erodes.
competence
The ability of a given stream to carry sediment, measured as the diameter of the largest particle that the stream can transport. See also capacity.
compound
An electrically neutral substance that consists of two or more elements combined in specific, constant proportions. A compound typically has physical characteristics different from those of its constituent elements.
compression
Stress that reduces the volume or length of a rock, as that produced by the convergence of plate margins.
concordant
Of or being a pluton that lies parallel to the surrounding layers of rock. See also discordant.
cone of depression
An area in a water table along which water has descended into a well to replace water drawn out, leaving a gap shaped like an inverted cone.
confining pressure
See lithostatic pressure.
conglomerate
A clastic rock composed of particles more than 2 millimeters in diameter and marked by the roundness of its component grains and rock fragments.
continental collision
The convergence of two continental plates, resulting in the formation of mountain ranges.
plate tectonics
The theory that the Earth's lithosphere consists of large, rigid plates that move horizontally in response to the flow of the asthenosphere beneath them, and that interactions among the plates at their borders cause most major geologic activity, including the creation of oceans, continents, mountains, volcanoes, and earth quakes.
continental drift
The hypothesis, proposed by Alfred Wegener, that today's continents broke off from a single supercontinent and then plowed through the ocean floors into their present positions. This explanation of the shapes and locations of Earth's current continents evolved into the theory of plate tectonics.
continental ice sheet
An unconfined glacier that covers much or all of a continent.
convection cell
The cycle of movement in the asthenosphere that causes the plates of the lithosphere to move. Heated material in the asthenosphere becomes less dense and rises toward the solid lithosphere, through which it cannot rise further and therefore begins to move horizontally, dragging the lithosphere along with it and pushing forward the cooler, denser material in its path. The cooler material eventually sinks down lower into the mantle, becoming heated there and rising up again, continuing the cycle. See also plate tectonics.
convergence
The coming together of two lithospheric plates. Convergence causes subduction when one or both plates is oceanic, and mountain formation when both plates are continental. See also divergence.
core
The innermost layer of the Earth, consisting primarily of pure metals such as iron and nickel. The core is the densest layer of the Earth, and is divided into the outer core, which is believed to be liquid, and the inner core, which is believed to be solid. See also crust and mantle.
correlation
The process of determining that two or more geographically distant rocks or rock strata originated in the same time period.
country rock
1. The preexisting rock into which a magma intrudes. 2. The preexisting rock surrounding a pluton.
covalent bond
The combination of two or more atoms by sharing electrons so as to achieve chemical stability under the octet rule. Atoms that form covalent bonds generally have outer energy levels containing three, four, or five electrons. Covalent bonds are generally stronger than other bonds.
crater
See volcanic crater.
creep
The slowest form of mass movement, measured in millimeters or centimeters per year and occurring on virtually all slopes.
cross bed
A bed made up of particles dropped from a moving cur- rent, as of wind or water, and marked by a downward slope that indicates the direction of the current that deposited them.
crust
The outermost layer of the Earth, consisting of relatively low- density rocks. See also core and mantle.
crystal
A mineral in which the systematic internal arrangement of atoms is outwardly reflected as a latticework of repeated three- dimensional units that form a geometric solid with a surface consisting of symmetrical planes.
crystal structure
1. The geometric pattern created by the systematic internal arrangement of atoms in a mineral. 2. The systematic internal arrangement of atoms in a mineral. See also crystal.
crystalline
Marked by the systematic internal arrangement of atoms.
current
1. A broad flow of ocean water that maintains a stable direction and differs from the surrounding water in such features as temperature and salinity. 2. The water in such a flow.
Caprock
A strata of erosion-resistant sedimentary rock (usually limestone) found in arid areas. Caprock forms the top layer of most mesas and buttes.
Carrying Capacity
The number of people that an area can support given the quality of the natural environment and the level of technology of the population.
cartographer
A person who draws or makes maps or charts.
chondrules
Small nuggets of rocky material that exist in certain meteorites. These droplets of matter are believed to have condensed from our solar system's original nebula about five billion years ago. Their primary element is iron.
continental platform
Continental platforms are the regions adjacent to and surrounding the continental shields. They are typically a relatively thin veneer of sedimentary rock that buries the edges of the shields.
continental shield
Broad areas of exposed ancient crystalline rocks in the cores of the Earth's continents. These rocks are typically the oldest on the continentes, many more than 2.5 billion years old.
craton
The segment of the Earth's continents that have remained tectonically stable and relatively earthquake-free for a vast period of time. The craton is composed of the continental shield and the surrounding continental platform.
CBD
The central business district of an urban area, typically containing an intense concentration of office and retail activities.
Chaparral
A dense, impenetrable thicket of shrubs or dwarf trees.
Chinook
A warm, dry wind experienced along the eastern side of the Rocky Mountains in the
Climax Vegetation
The vegetation that would exist in an area if growth had proceeded undisturbed for an extended period. This would be the "final" collection of plant types that presumably would remain forever, or until the stable conditions were somehow disturbed.
Confluence
The place at which two streams flow together to form one larger stream.
Coniferous
Bearing cones; from the conifer family.
continent
One of the large, continuous areas of the Earth into which the land surface is divided.
Continental Climate
The type of climate found in the interior of the major continents in the middle, or temperate, latitudes. The climate is characterized by a great seasonal variation in temperatures, four distinct seasons, and a relatively small annual precipitation.
Continental Divide
The line of high ground that separates the oceanic drainage basins of a continent; the river systems of a continent on opposite sides of a continental divide flow toward different oceans.
Continentality
The quality or state of being a continent.
Conurbation
An extensive urban area formed when two or more cities, originally separate, coalesce to form a continuous metropolitan region.
Core Area
The portion of a country that contains its economic, political, intellectual, and cultural focus. It is often the center of creativity and change (see Hearth).
Coulee
A dry canyon eroded by Pleistocene floods that cut into the lava beds of the Columbia Plateau in the western
Crop
lien System
- A farm financing scheme whereby money is loaned at the beginning of a growing season to pay for farming operations, with the subsequent harvest used as collateral for the loan.
Culture
The accumulated habits, attitudes, and beliefs of a group of people that define for them their general behavior and way of life; the total set of learned activities of a people.
Culture Hearth
The area from which the culture of a group diffused (see Hearth).
Cut-and-Sew Industry
The manufacture of basic ready-to-wear clothing. Such facilities usually have a small fixed investment in the manufacturing facility.
Carbonate Rock
A rock made up primarily of carbonate minerals (minerals containing the CO3 anionic structure). Limestone (made up primarily of calicite - CaCO3) and dolostone (made up primarily of dolomite - CaMg (CO3)2 are the most common examples.
Carbonic Acid
A weak acid (H2CO3) that forms from the reaction of water and carbon dioxide. Most rain water is a very weak carbonic acid solution formed by the reaction of rain with small amounts of carbon dioxide in the atmosphere.
Cataclastic Rock
A breccia of powdered rock formed by crushing and shearing during tectonic movements.
Cement
A solid precipitate of calcium carbonate, silica, iron oxide, clay minerals or other materials that forms within the pore spaces of a sediment and binds it into a sedimentary rock.
Chemical Sedimentary Rock
A rock that forms from the precipitation of mineral material from solution. Examples are chert and rock salt.
Chemical Weathering
The breaking down of surface rock material by solution or chemical alteration. Common alteration processes are oxidation and hydrolysis.
Chert
A microcrystalline or cryptocrystalline sedimentary rock material composed of SiO2. Occurs as nodules and concretionary masses and less frequently as a layered deposit.
- A member of a group of sedimentary rocks that consist primarily of microscopic silica crystals. Chert may be either organic or inorganic, but the most common forms are inorganic.
C-horizon
The lowest horizon of a soil profile. It is below the B-horizon and is made up of weathered bedrock.
capillary action
the means by which liquid moves through the porous spaces in a solid, such as soil, plant roots, and the capillary blood vessels in our bodies due to the forces of adhesion, cohesion, and surface tension. Capillary action is essential in carrying substances and nutrients from one place to another in plants and animals.
commercial water use
water used for motels, hotels, restaurants, office buildings, other commercial facilities, and institutions. Water for commercial uses comes both from public-supplied sources, such as a county water department, and self-supplied sources, such as local wells.
condensation
the process of water vapor in the air turning into liquid water. Water drops on the outside of a cold glass of water are condensed water. Condensation is the opposite process of evaporation .
Carbonate ion
The anion group CO3 with a charge of minus two.
Carbonate platform
A submarine or intertidal shelf whose elevation is maintained by active shallow water carbonate deposition.
Cation
Any ion with a positive electric charge.
Central vent
The largest vent of a volcano, situated at the center of its cone.
Clastic rock
A sedimentary rock formed from mineral particles (clasts) that were mechanically transported.
consumptive use
that part of water withdrawn that is evaporated, transpired by plants, incorporated into products or crops, consumed by humans or livestock, or otherwise removed from the immediate water environment. Also referred to as water consumed.
conveyance loss
water that is lost in transit from a pipe, canal, or ditch by leakage or evaporation. Generally, the water is not available for further use; however, leakage from an irrigation ditch, for example, may percolate to a ground-water source and be available for further use.
Cirque
A bowl-shaped depression with very steep sides that forms at the head of a mountain glacier. Forms from cold-climate weathering processes including frost wedging and plucking.
Clastic
A sedimentary rock (such as shale, siltstone, sandstone or conglomerate) or sediment (such as mud, silt, sand, or pebbles). An accumulation of transported weathering debris.
Clay
A clastic mineral particle of any composition that has a grain size smaller than 1/256 mm. The term is also used in reference to a broad category of hydrous silicate minerals in which the silica tetrahedrons are arranged into sheets.
Coal
A brown or black sedimentary rock that forms from accumulated plant debris. A combustible rock that contains at least 50% (by weight) carbon compounds.
Coastal Plain
An area of low relief along a continental margin that is underlain by thick, gently dipping sediments.
Compaction
A compression process that reorients and reshapes the grains of a sediment in response to the weight of overlying deposits.
Composite Cone
A cone-shaped volcanic mountain composed of alternating layers of cinders and lava flows. Also known as a stratovolcano.
Contact Metamorphism
Alteration of a rock, mainly by heat, which occurs adjacent to a dike, sill, magma chamber or other magma body.
Contour Line
A line on a map that traces locations where the value of a variable is constant. For example, contour lines of elevation trace points of equal elevation across the map. All points on the "ten foot" contour line are ten feet above sea level.
Contour Map
A map that shows the change in value of a variable over a geographic area through the use of contour lines. For example, a contour map of elevation has lines that trace points of equal elevation across the map. See also contour line and topographic map.
Cubic Feet Per Second
(cfs) A unit of measure frequently used to quantify the rate of flow of a stream. It is equal to a volume of water one foot high and one foot wide moving a linear distance of one foot in one second.
- One "cfs" is equal to 7.48 gallons of water flowing each second. As an example, if your car's gas tank is 2 feet by 1 foot by 1 foot (2 cubic feet), then gas flowing at a rate of 1 cubic foot/second would fill the tank in two seconds.