Thursday, November 23rd, 2017

* C horizon-The lowest soil layer composed of partly weathered bedrock grading downward into unweathered parent rock.
* Calcite-A common rock-forming mineral, caco3.
* Caldera-A large circular depression caused by an explosive volcanic eruption.
* Caliche-A hard soil layer formed when calcium carbonate precipitates and cements the soil.
* Calorie- A unit of heat energy. The amount of heat required to raise the temperature of 1 gram (cubic Centimeter) of water 1 degree Celsius.
* Calving-A process in which large chunks of ice break off from tidewater glaciers to form icebergs.
* Cap rock-An impermeable rock, usually shale, that prevents oil or gas from escaping upward from a reservoir.
* Capacity-The maximum quantity of sediment that a stream can carry.
* Capillary action-The action by which water is pulled upward through small pores by electrical attraction to the pore walls.
* Carbonate -A compound containing carbon and oxygen; an example is calcium carbonate (limestone).
* Carbonate platform-An extensive accumulation of limestone such as the Florida Keys and the Bahamas, formed on a continental shelf in warm regions where sediment does not muddy the water and reef-building organisms thrive.
* Carbonate rocks-Rocks such as limestone and dolomite made up primarily of carbonate minerals.
* Catastrophism-The model that Earth change occurs through a series of rare but cataclysmic events.
* Cation-A positively charged ion.
* Cavern-An underground cavity or series of chambers created when groundwater dissolves large amounts of rock, usually limestone. (syn: cave)
* Celestial sphere-An imaginary sphere around the Earth that all the stars and planets are placed on.
* Celestial spheres-A hypothetical series of concentric spheres centered at the center of the Earth. Aristotle postulated that the Sun, Moon, planets, and stars are imbedded in the spheres.
* Cementation-The process by which clastic sediment is lithified by precipitation of a mineral cement among the grains of the sediment.
* Cenozoic era-The latest of the four eras into which geologic time is subdivided; 65 million years ago to the present.
* Cenozoic- the current and most recent era of geologic time, starting 65 million years ago.
* Chalk-A very fine grained, soft, earthy, white to gray bioclastic limestone made of the shells and skeletons of marine microorganisms.
* Chemical bond-The linkage between atoms in molecules and between molecules and ions in crystals.
* Chemical sedimentary rock-Rocks such as rock salt, that form by direct precipitation of minerals from solution.
* Chemical weathering- breakdown or decomposition of a rock that takes place when minerals are changed into different substances.
* Chemical weathering-The chemical decomposition of rocks and minerals by exposure to air, water, and other chemicals in the environment.
* Chert-A hard, dense, sedimentary rock composed of microcrystalline quartz. (syn: flint)
* Chlorofluorocarbons (CFC's)- gases containing chlorine, fluorine and carbon atoms that break down the ozone layer and weaken protection from ultraviolet waves.
* Chromosphere-A turbulent diffuse gaseous layer of the Sun that lies above the photosphere.
* Cinder Cone- A volcanic cone built entirely of loose fragmented material (pyroclastics.)
* Cinder cone-A small volcano, as high as 300 meters, made up of loose pyroclastic fragments blasted out of a central vent.
* Cinders (volcanic)-Glassy pyroclastic volcanic fragments 4 to 32 millimeters in size.
* Cirque- A steep-walled horseshoe-shaped recess high on a mountain that is formed by glacial erosion.
* Cirque-A steep-walled semi-circular depression eroded into a mountain peak by a glacier.
* Cirrus- A principal cloud type present at high altitudes, generally above 7000 meters, and composed of ice crystals. Cirrus comes from the Latin term for "curl or wisp of hair."
* Cirrus cloud-A wispy, high-level cloud.
* Clastic rocks- sedimentary rocks formed from fragments of other rocks.
* Clastic sedimentary rock-Rock composed of lithified clastic sediment.
* Clastic sediment-Sediment composed of fragments of weathered rock that have been transported some distance from their place of origin.
* Clay-Any clastic mineral particle less than 1/256 millimeter in diameter. Also a group of layer silicate minerals.
* Claystone-A fine-grained clastic sedimentary rock composed predominantly of clay minerals and small amounts of quartz and other minerals of clay size.
* Clean Water Act-A federal law mandating the cleaning of the nation's rivers, lakes, and wetlands, and forbidding the discharge of pollutants into waterways.
* Cleavage - The way crystalline minerals split or break along an even plane (planar surfaces).
* Cleavage-The tendency of some minerals to break along certain crystallographic planes.
* Climate- typical weather patterns over a period of years in a given location
* Climate-The composite pattern of long-term weather conditions that can be expected in a given region. Climate refers to yearly cycles of temperature, wind, rainfall, etc., and not to daily variations (see "weather").
* Cloud - A visible collection of minute particle matter, such as water droplets and/or ice crystals, in the free air. A cloud forms in the atmosphere as a result of condensation of water vapor. Condensation nuclei, such as in smoke or dust particles, form a surface upon which water vapor can condense.
* Cloud Base- For a given cloud or cloud layer, it is the level in the atmosphere cloud particles (droplets or ice crystals) become visible.
* Cloud Droplets- Small drops of liquid water, approximately 4 to 100 micrometers in diameter, that remain suspended in the air. They are smaller in size than either drizzle or rain drops. An aggregate of cloud droplets forms a visible cloud.
* Cloud-A collection of minute water droplets or ice crystals in air.
* Coal-A flammable organic sedimentary rock formed from partially decomposed plant material and composed mainly of carbon.
* Coalescence - The merging of two water drops into a single larger drop.
* Cobbles-Rounded rock fragments in the 64 to 256 mm size range, larger than pebbles and smaller than boulders.
* Cold front- the leading edge of an advancing cold air mass that is under running and displacing the warmer air in its path. Generally, with the passage of a cold front, the temperature and humidity decrease, the pressure rises, and the wind shifts (usually from the southwest to the northwest in the Northern Hemisphere). Precipitation is generally at and/or behind the front, and with a fast-moving system, a squall line may develop ahead of the front.
* Cold front-A front that forms when moving cold air collides with stationary or slower moving warm air. The dense, cold air distorts into a blunt wedge and pushes under the warmer air, creating a narrow band of violent weather commonly accompanied by cumulus and cumulonimbus clouds.
* Column-A dripstone or speleothem formed when a stalactite and a stalagmite meet and fuse together.
* Columnar joint-A regularly spaced crack that commonly develops in lava flows forming five or six sided columns.
* Coma -The dust and gas surrounding an active comet's nucleus.
* Coma-The bright outer sheath of a comet.
* Comet- An object which circles the sun in a non-circular orbit. Commonly made up of a large mass of rock debris and ice.
* Comet-An interplanetary body composed of loosely bound rock and ice, that forms a bright head and extended fuzzy tail when it enters the inner potion of the solar system.
* Compaction-Tighter packing of sedimentary grains causing weak lithification and a decrease in porosity, usually resulting from the weight of overlying sediment.
* Competence-A measure of the largest particles that a stream can transport.
* Composite cone-A volcano that consists of alternate layers of unconsolidated pyroclastic material and lava flows. (syn: stratovolcano)
* 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.
* Compound-A pure substance composed of two or more elements whose composition is constant.
* 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. Usage of compression waves.
* Compressive stress-Stress that acts to shorten an object by squeezing it.
* Condensation Level- The altitude at which a rising air parcel reaches saturation, usually the cloud base height.
* Condensation Nuclei- Liquid or solid particles, such as those in smoke or dust, that provide a surface upon which water vapor can condense into cloud droplets or form ice crystals.
* Condensation- The change of state of water from the vapor to the liquid phase. Results in liberation of 80 calories per cubic centimeter.
* Conduction- the movement of heat to an object by its contact with a hotter object.
* Conduction-The transport of heat by atomic or molecular motion.
* Cone of depression-A cone-like depression in the water table formed when water is pumped out of a well more rapidly than it can flow through the aquifer.
* Confining pressure-See "confining stress."
* Confining stress-A form of stress that develops when rock or sediment is buried. Confining stress compresses rocks but does not distort them because the compressive force acts equally in all directions.
* Conformable-The condition in which sedimentary layers were deposited continuously without interruption.
* Conglomerate-A coarse-grained clastic sedimentary rock, composed of rounded fragments larger than 2 mm in diameter cemented in a fine-grained matrix of sand or silt.
* Constellation- a group of stars that appears to form a pattern in the sky.
* Constellation-One of 88 groups of stars that astronomers refer to for convenience in referring to the positions of objects in the night sky.
* Consumption-Any process that uses water, and then returns it to the Earth far from its source.
* Contact metamorphic ore deposit-An ore deposit formed by contact metamorphism.
* Contact metamorphism- the process of rock-forming that results when hot magma forces its way into overlying rock and changes that rock.
* Contact metamorphism-Metamorphism caused by heating of country rock, and/or addition of fluids, from a nearby igneous intrusion.
* Contact-A boundary between two different rock types or between rocks of different ages.
* Continental air mass - An air mass with continental (dry) characteristics. It is a secondary characteristic of an air mass classification, signified by the small "c" before the primary characteristic, which is based on source region. For example, cP is an air mass that is continental polar in nature.
* Continental climate- large yearly temperature ranges
* Continental Crust- Solid, outer layers of the earth, including the rocks of the continents; thick, low density, granitic, and old.
* Continental crust-The predominantly granitic portion of the crust, 20 to 70 kilometers thick, that makes up 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.
* Continental drift-The theory proposed by Alfred Wegener that continents were once joined together and later split and drifted apart. The continental drift theory has been replaced by the more complete plate tectonics theory.
* Continental glacier-A glacier that forms a continuous cover of ice over areas of 50,000 square kilometers or more and spreads outward in all directions under the influence of its own weight. (syn: ice sheet)
* Continental margin-The region between the shoreline of a continent and the deep ocean basins including the continental shelf, continental slope, and continental rise. Also the region where thick, granitic continental crust joins thinner, basaltic oceanic crust.
* Continental rifting-The process by which a continent is pulled apart at a divergent plate boundary.
* Continental rise-An apron of sediment between the continental slope and the deep sea floor.
* Continental shelf- Portions of the continental land masses covered by sea water. Extend varying distances outward from the exposed continental margins. Usually, the continental shelf will be wider along a passive continental margin, and narrower along an active margin.
* Continental shelf-A shallow, nearly level area of continental crust covered by sediment and sedimentary rocks that is submerged below sea level at the edge of a continent between the shoreline and the continental slope.
* Continental slope-The relatively steep (3-6 degree) underwater slope between the continental shelf and the continental rise.
* Contour interval- the difference in elevation between two consecutive contour lines
* Contour line- line on a topographic map that connects points on land that have the same elevation.
* Contrail - Acronym for CONdensation TRAIL. A cloud-like streamer or trail often seen behind aircraft flying in clear, cold, humid air. A vapor trail is created when the water vapor from the engine exhaust gases are added to the atmosphere.
* Control rod-A column of neutron-absorbing alloys that are spaced among fuel rods to fine-tune nuclear fission in a reactor.
* Convection -Fluid (gas or liquid) circulation driven by temperature and density differences; the transfer of heat by this automatic circulation (currents). Hot fluids rise, cold fluids sink.
* Convection-The transport of heat by the movement of currents. In meteorology, horizontal air flow is called advection, whereas convection is reserved for vertical air flow.
* Convective Clouds- Clouds formed atop rising air columns. Cumulus clouds are convective clouds.
* Convective zone-The subsurface zone in a star where energy is transmitted primarily by convection.
* Convergence- The flow of the wind resulting in a horizontal inflow of air into a region. Convergence of winds near the surface are associated with upward motion known in meteorology as convection. The opposite of convergence is divergence.
* Convergent boundary-A boundary where two lithospheric plates collide head-on.
* Converging plate boundaries- a boundary where two lithospheric plates come together.
* Coquina-A bioclastic limestone consisting of coarse shell fragments cemented together.
* Core, inner- spherical center of the Earth, about 1200 km in diameter and made of solid iron and nickel.
* Core, outer- the zone of Earth's interior, extending about 2250 km between the inner core and mantle and made of liquid iron and nickel.
* Core-The innermost region of the Earth probably consisting of iron and nickel.
* Coriolis Effect- the effect of Earth's rotation that causes the deflection of moving objects towards or away from the equator. North of the equator, winds curve to the right. South, to the left.
* Coriolis effect-The deflection of air or water currents caused by the rotation of the Earth.
* Corona- The very hot outermost layer of a star's atmosphere. Our Sun's corona can only be seen during a total solar eclipse.
* Corona-The luminous irregular envelope of highly ionized gas outside the chromosphere of the Sun.
* Correlation- the process of matching rock layers from different locations.
* Correlation-Demonstration of the equivalence of rocks or geologic features age from different locations.
* Cosmic ray -Electromagnetic rays of extremely high frequency and energy; cosmic rays usually interact with the atoms of the atmosphere before reaching the surface of the Earth. Some cosmic rays come from outside the solar system while others are emitted from the Sun and pass through holes in the corona.
* Cost-benefit analysis-A system of analysis that attempts to weigh the cost of an act or policy, such as pollution control, directly against the economic benefits.
* Country rock-The older rock intruded by a younger igneous intrusion or mineral deposit.
* Crater -1) A depression formed by the impact of a meteorite. 2) A depression around the orifice of a volcano.
* Crater-A bowl-like depression at the summit of the volcano.
* Craton-A segment of continental crust, usually in the interior of a continent, that has been tectonically stable for a long time commonly a billion years or longer.
* Cratons -The relatively stable portions of continents composed of shield areas and platform sediments; typically, cratons are bounded by tectonically active regions characterized by uplift, faulting and volcanic activity.
* Creep-The slow movement of unconsolidated material downslope under the influence of gravity.
* Crest (of a wave)-The highest part of a wave.
* Cretaceous period -A geological term denoting the interval of Earth history beginning around 144 million years ago and ending 66 million years ago.
* Cretaceous-Tertiary boundary -A major stratigraphic boundary on Earth marking the end of the Mesozoic Era, best known as the age of the dinosaurs. The boundary is defined by a global extinction event that caused the abrupt demise of the majority of all life on Earth. see Key bed
* Crevasse-A fracture or crack in the upper 40 to 50 meters of a glacier.
* Cross cutting relationships - A fundamental principle of geology, which states that rocks that cut through other rocks are younger than the rocks being cut.
* Cross-bedding-An arrangement of small beds at an angle to the main sedimentary layering.
* Cross-cutting relationship-Any relationship in which younger rocks or geological structures interrupt or cut across older rocks or structures.
* Crust- outer layer of Earth that covers the mantle. The continental crust is thicker, older, less dense, and granitic. The oceanic crust is thinner, younger, more dense, and basaltic.
* Crust-The Earth's outermost layer about 7 to 70 kilometers thick, composed of relatively low-density silicate rocks.
* Crystal face-A planar surface that develops if a crystal grows freely in an uncrowded environment.
* Crystal habit-The shape in which individual crystals grow and the manner in which crystals grow together in aggregates.
* Crystal settling-A process in which the crystals that solidify first from a cooling magma settle to the bottom of a magma chamber because the solid minerals are more dense than liquid magma.
* Crystal- solid substance in which the atoms are arranged in an orderly pattern which repeats over and over again.
* Crystal-A solid element or compound whose atoms are arranged in a regular, orderly, periodically repeated array.
* Crystalline -Rock types made up of crystals or crystal fragments, such as metamorphic rocks that recrystallized in high temperature or pressure environments, or igneous rocks that formed from cooling of a melt.
* Crystalline structure-The orderly, repetitive arrangement of atoms in a crystal.
* Cumulonimbus cloud-A cumulus cloud from which precipitation is falling.
* Cumulus- A principal cloud type of vertical elements having a flat base and dense, bulging upper portion resembling a heap or pile. The base of cumulus clouds is generally found from 500 to 3000 meters Large cumulonimbus clouds may extend to over 18,000 meters and be topped with anvil-shaped ice clouds. Cumulus is derived from the Latin for "heap."
* Cumulus cloud-A column-like cloud with a flat bottom and a billowy top.
* Curie point-The temperature below which rocks can retain magnetism.
* Current - A horizontal movement of water, such as the Gulf Stream off the east coast of North America, or air, such as the jet stream.
* Current-A continuous flow of water in a concerted direction.
* Curtain of Fire- A row of coalescing lava fountains along a fissure; a typical feature of a Hawaiian-type eruption.
* Cyclone-A low pressure region with its accompanying surface wind. Also a synonym for a tropical cyclone, or hurricane.
* Cyclonic- Air flow around the center of a surface Low. In the Northern Hemisphere, this flow is counterclockwise as seen from above. (In the Southern Hemisphere, it is clockwise.) Also, any rotation in the direction of the Earth's rotation.

* Daughter isotope-An isotope formed by radioactive decay of another isotope.
* 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).
* Debris flow-A type of mass wasting in which particles move as a fluid and more than half of the particles are larger than sand.
* Deflation-Erosion by wind.
* Deformation-Folding, faulting and other changes in shape of rocks or minerals in response to mechanical forces, such as those that occur in tectonically active regions.
* Degeneracy pressure-The strength of the atomic particles that holds a white dwarf star from further collapse.
* Delta- A fan-shaped deposit of sediment formed at the mouth of a stream or river.
* Delta-The nearly flat, alluvial, fan-shaped tract of land at the mouth of a stream.
* Density- A ratio between the mass and volume of a substance. A measure of how tightly packed the atoms of a substance are. Measured in grams per cubic centimeter. Varies by the mineral or substance. For example, gold has a high density, while quartz has a low density. The density of water is 1.0, iron is 7.9, and lead is 11.3. D=m/v. Breaking a pure mineral in half does NOT change it's density.
* Deposition-The laying-down of rock-forming materials by any natural agent.
* Depression contour- contour lines (with marks on the inside) indicating a drop in elevation towards the center. Example: crater
* Desert pavement-A continuous cover of stones created as wind erodes fine sediment, leaving larger rocks behind.
* Desert-A region with less than 25 cm of rainfall a year. Also defined as a region that supports only a sparse plant cover.
* Desertification-A process by which semiarid land is converted to desert, often by improper farming or by climate change.
* Devonian- A period of time in the Paleozoic Era that covered the time span between 408 and 360 million years.
* Dew Point or Dew Point Temperature- The temperature to which air must be cooled for saturation to occur.
* Dew point-The temperature at which the relative humidity of air reaches 100 percent, and the air becomes saturated. If saturated air cools below the dew point, some of the water vapor generally condenses into liquid droplets (although sometimes the relative humidity can rise above 100 percent).
* Dew-Moisture condensed onto objects from the atmosphere, usually during the night, when the ground and leaf surfaces become cooler than the surrounding air.
* Differential weathering-The process by which certain rocks weathers more rapidly than adjacent rocks usually resulting in an uneven surface.
* Dike- A sheetlike body of igneous rock that cuts across layering or contacts in the rock into which it intrudes.
* Dike-A sheet-like igneous rock that cuts across the structure of country rock.
* Directed stress-Stress that acts most strongly in one direction.
* Discharge- The volume of water flowing past a given point in a stream in a given amount of time.
* Discharge-The volume of water flowing downstream per unit time. It is measured in units of cubic meters per second (m3/sec).
* Disconformity-A type of unconformity in which the sedimentary layers above and below the unconformity are parallel.
* Discordant-Pertaining to a dike or other feature that cuts across sedimentary layers or other kinds of layering in country rock.
* Disk -The visible surface of the Sun (or any heavenly body) projected against the sky.
* Disseminated ore deposit-A large low-grade ore deposit in which generally fine-grained metal-bearing minerals are widely scattered throughout a rock body in sufficient concentration to make the deposit economical to mine.
* Dissolved load-The portion of a stream's sediment load that is carried in solution.
* Distributary-A channel that flows outward from the main stream channel, such as is commonly found in deltas.
* Divergence- The flow of the wind resulting in a horizontal outflow of air from a region. The opposite of divergence is convergence.
* Divergent boundary-The boundary or zone where lithospheric plates separate from each other. (syn: spreading center)
* Diverging plate boundaries- a boundary where two lithospheric plates move apart. New lithosphere is formed here.
* Diversion-All processes that transfer ground or surface water from its natural place and path in the hydrologic cycle to a new place and path to serve human needs.
* Divide- The higher land separating two adjacent drainage basins.
* Docking-The accretion of island arcs or microcontinents onto a continental margin.
* Doldrums- the rainy equatorial belt of low pressure and slowly rising air.
* Doldrums-A region of the Earth near the Equator in which hot, humid air moves vertically upward, forming a vast low-pressure region. Local squalls and rainstorms are common, and steady winds are rare.
* Dolomite-A common rock-forming mineral, camg(CO3)2.
* Dome-A circular or elliptical anticlinal structure.
* Doppler effect -The apparent change in wavelength of sound or light caused by the motion of the source, observer or both.
* Doppler effect-The observed change in frequency of light or sound that occurs when the source of the wave is moving relative to the observer.
* Doppler Radar- Weather radar that measures direction and speed of a moving object, such as drops of precipitation, by determining whether atmospheric motion is horizontally toward or away from the radar. Using the Doppler effect, it measures the velocity of particles. Named for J. Christian Doppler, an Austrian physicist, who in 1842 explained why the whistle of an approaching train had a higher pitch than the same whistle when the train was going away.
* Dormant volcano- This term is used to describe a volcano which is presently inactive but which may erupt again. The major volcanic cones of the Cascade Mountains (in Washington, Oregon, and California) are believed to be dormant rather than extinct.
* Downbursts- Surface winds in excess of 62 km/hr (39 mph) caused by a small-scale downdraft from the base of a convective cloud. Downbursts occur in regions of a severe thunderstorm where the air is accelerated downward by exceptionally strong evaporative cooling occurs (a dry downburst) or by very heavy rain which drags dry air down with it (a wet downburst). When the rapidly descending air strikes the ground, it spreads outward in all directions in a circle, like a fast-running faucet hitting the sink bottom.
* Downcutting-Downward erosion by a stream.
* Drainage Basin- The area of land drained by a river system.
* Drainage basin-The region that is ultimately drained by a single river.
* Drift (glacial)- General term for material deposited by a glacier.
* Drift (glacial)-Any rock or sediment transported and deposited by a glacier or by glacial meltwater.
* Drought - Abnormal dry weather for a specific area that is sufficiently prolonged for the lack of water to cause serious hydrological imbalance.
* Drumlin- a long, canoe-shaped hill made of till and shaped by an advancing glacier.
* Drumlin-An elongate hill formed when a glacier flows over and reshapes a mound of till or stratified drift.
* Dry adiabatic lapse rate-The rate of cooling that occurs when dry air rises without gain or loss of heat.
* Dry-bulb thermometer - A thermometer used to measure the ambient temperature. The temperature recorded is considered identical to air temperature. One of the two thermometers that make up a psychrometer.
* Dune-A mound or ridge of wind-deposited sand.
* Dust Bowl - The term given to the area of the Great Plains including Texas, Oklahoma, Kansas, Colorado, and New Mexico that was most greatly affected during the Great Drought of the 1930's. Tons of unprotected soil were eroded by winds.