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C Horizon - 

Soil horizon normally found below the B horizon and above the R horizon. This layer is composed of weathered bedrock that has not been yet significantly affected by the pedogenic processes.

Calcification - 

A dry environment soil-forming process that results in the accumulation of calcium carbonate in surface soil layers.

Calcite - 

Mineral formed from calcium carbonate. Common mineral found in limestone.

Caldera - 

A large circular depression in a volcano.

Caldera Volcano - 

Explosive type of volcano that leaves a large circular depression. Some of these depressions can be as large as 40 kilometers in diameter. These volcanoes form when wet granitic magma quickly rises to the surface of the Earth.

Calving - 

The loss of glacier mass when ice breaks off into a large water body like an ocean or a lake.

Cambrian - 

Geologic period that occurred from 570 to 505 million years ago. During this period, invertebrates become common in the oceans and the Burgess Shale was formed.

Canopy Drip - 

Redirection of a proportion of the rain or snow falling on a plant to the edge of its canopy.

Canyon - 

Steep-sided valley where depth is considerably greater than width. These features are the result of stream erosion.

Capillary Action - 

Movement of water along microscopic channels. This movement is the result of two forces: the adhesion and absorption of water to the walls of the channels; and cohesion of water molecules to each other.

Capillary Water - 

Water that moves horizontally and vertically in soils by the process of capillary action. This water is available for plant use.

Carbon Cycle - 

Storage and cyclic movement of organic and inorganic forms of carbon between the biosphere, lithosphere, hydrosphere, and atmosphere.

Carbon Dioxide - 

Common gas found in the atmosphere. Has the ability to selectively absorb radiation in the longwave band. This absorption causes the greenhouse effect. The concentration of this gas has been steadily increasing in the atmosphere over the last three centuries due to the burning of fossil fuels, deforestation, and land-use change. Some scientists believe higher concentrations of carbon dioxide and other greenhouse gases will result in an enhancement of the greenhouse effect and global warming. The chemical formula for carbon dioxide is CO2.

Carbon Monoxide - 

A colorless, odorless, and tasteless gas that is produced by the incomplete burning of fossil fuels. The chemical formula for carbon monoxide is CO.

Carbonate - 

Compound consisting of a single atom of carbon and three atoms of oxygen. Carbonate has the following chemical structure CO3.

Carbonation - 

Is a form of chemical weathering where carbonate and bicarbonate ions react with minerals that contain calcium, magnesium, potassium, and sodium.

Cardinal Points - 

The four main navigational directions (North, East, South, and West) found on a compass or a map.

Carnivore - 

Heterotrophic organism that consumes living animals or the parts of living animals for food. Examples of carnivores include lions, cheetahs, leopards, frogs, snakes, hawks, and spiders. A carinore can also be called a secondary consumer or tertiary consumer. Also see herbivore, detritivore, scavenger, and omnivore.

Carrying Capacity (K) - 

The maximum size of population of a single species that a certain habitat can support.

Cartography - 

Field of knowledge that studies map construction. The act of creating a map.

Cascading System - 

This is a system where we are primarily interested in the flow of energy and/or matter from one element to another and understand the processes that cause this movement. In a cascading system, we do not fully understand quantitative relationships that exist between elements related to the transfer of energy and/or matter.

Cave - 

A natural cavity or recess that is roughly positioned horizontally to the surface of the Earth.

Cavitation - 

Process of intense erosion due to the surface collapse of air bubbles found in constricted rapid flows of water. Causes the detachment of material from a surface.

Celsius - 

Scale for measuring temperature. In this scale, water boils at 100° and freezes at 0°.

Cenozoic - 

Geologic era that occurred from 65 million years ago to today.

Central Vent - 

The main passage way by which volcanic magma travels to the Earth's surface.

Centripetal Force - 

Force required to keep an object moving in a circular pattern around a center of rotation. This force is directed towards the center of rotation. Common in meteorological phenomena like tornadoes and hurricanes.

CFCs - 

Is an artificially created gas that has become concentrated in the Earth's atmosphere. This very strong greenhouse gas is released from aerosol sprays, refrigerants, and the production of foams. The basic chemical formula for chlorofluorocarbons is CFx Clx .

Chalk - 

Form of limestone. This sedimentary rock is composed of the shells and skeletons of marine microorganisms.

Chemical - 

One of the millions of different elements and compounds found naturally and synthesized by humans.

Chemical Energy - 

Energy consumed or produced in chemical reactions.

Chemical Reaction - 

Reaction between chemicals where there is a change in the chemical composition of the elements or compounds concerned.

Chemical Weathering - 

Breakdown of rock and minerals into small sized particles through chemical decomposition.

Chinook Wind - 

The name of a North American wind that occurs on the leeward side of mountains. This wind is warm and has a low humidity.

Chlorofluorocarbons - 

Is an artificially created gas that has become concentrated in the Earth's atmosphere. This very strong greenhouse gas is released from aerosol sprays, refrigerants, and the production of foams. The basic chemical formula for chlorofluorocarbons is CFx Clx .

Chlorofluorocarbons (CFCs) - 

Is an artificially created gas that has become concentrated in the Earth's atmosphere. This very strong greenhouse gas is released from aerosol sprays, refrigerants, and the production of foams. The basic chemical formula for chlorofluorocarbons is CFx Clx .

Chlorophyll - 

Green pigment found in plants and some bacteria used to capture the energy in light through photosynthesis.

Chloroplast - 

Organelle in a cell that contains chlorophyll and produces organic energy through photosynthesis.

Cinder Cone Volcano - 

A small volcano, between 100 and 400 meters tall, made up of exploded rock blasted out of a central vent at a high velocity. These volcanoes develop from magma of basaltic to intermediate composition.

Circle of Illumination - 

A line that bisects areas on the Earth receiving sunlight and those areas in darkness. Cuts the spherical Earth into lighted and dark halves.

Circum-Pacific Belt - 

A zone circling the edge of the Pacific Ocean basin where tectonic subduction causes the formation of volcanoes and trenches. Also called the ring of fire.

Cirque - 

Glacially eroded rock basin found on mountains. Most alpine glaciers originate from a cirque.

Cirque Glacier - 

Small glacier that just occupies a cirque.

Cirrocumulus Clouds - 

Patchy white high altitude cloud composed of ice crystals. Found in an altitude range from 5,000 to 18,000 meters.

Cirrostratus Clouds - 

High altitude sheet like clouds composed of ice crystals. These thin clouds often cover the entire sky. Found in an altitude range from 5,000 to 18,000 meters.

Cirrus Clouds - 

High altitude cloud composed of ice crystals. The appearance of these clouds is white feather like patches, filaments or thin bands. Found in an altitude range from 5,000 to 18,000 meters.

Classification - 

Process of grouping things into categories.

Clastic Sedimentary Rock - 

Sedimentary rocks that are formed by the lithification of weathered rock debris that has been physically transported and deposited.

Clay - 

Mineral particle with a size less than 0.004 millimeters in diameter. Also see silt and sand.

Cleavage - 

The tendency of some minerals or rocks to break along planes of weakness. This weakness occurs because of the nature of the bonds between mineral grains.

Cliff - 

A tall steep rock face.

Climate - 

General pattern of weather conditions for a region over a long period time (at least 30 years).

Climatology - 

Scientific study of the Earth's climate over long time spans (greater than several days). May also involve the investigation of climate's influence on the biotic and the abiotic environment.

Climograph - 

Two dimensional graph that plots a location's air temperature and precipitation on times scales that range from a 24 hour period to a year.

Closed System - 

Is is a system that transfers energy, but not matter, across its boundary to the surrounding environment. Our planet is often viewed as a closed system.

Closed Talik - 

Is a form of localized unfrozen ground (talik) in an area of permafrost. It is completely enclosed by permafrost in all directions.

Cloud - 

A collection of tiny particles of liquid or solid water occurring above the Earth's surface. Clouds are classified accord to their height of occurrence and shape. The major types of clouds include: Cirrus, Cirrocumulus, Cirrostratus, Altocumulus, Altostratus, Nimbostratus, Stratocumulus, Stratus, Cumulus, and Cumulonimbus.

Coal - 

Sedimentary rock composed of the compacted, lithified and altered remains of plants. Coal is a solid, combustible mixture of organic compounds, hydrocarbons, with 30% to 98% carbon by weight, mixed with various amounts of water and small amounts of sulfur and nitrogen compounds. It is formed in several stages as the remains of plants are subjected to heat and pressure over millions of years.

Coalescence - 

Process where two or more falling raindrops join together into a single larger drop because of a midair collision.

Coastal Dune - 

Sand dune that forms in coastal areas. The sand for its formation is supplied from a beach.

Coastal Wetland - 

Wetland habitat found along a coastline and is covered with ocean salt water for all or part of the year. Examples of this type of habitat include tidal marshes, bays, lagoons, tidal flats, and mangrove swamps.

Coastal Zone - 

Relatively nutrient-rich, shallow part of the ocean that extends from the high-tide mark on land to the edge of the continental shelf.

Coastline - 

The line that separates a land surface from an ocean or sea.

Col - 

Saddle like depression found between two mountain peaks. Formed when two opposing cirque glaciers back erode an arête.

Cold Desert - 

Desert found in the high latitudes and at high altitudes where precipitation is low. Surface air temperatures are generally cold in these dry environments.

Cold Front - 

A transition zone in the atmosphere where an advancing cold air mass displaces a warm air mass.

Cold Glacier - 

Glacier in which the ice found from the its surface to base has a temperature as cold as -30° Celsius throughout the year. This is well below the pressure melting point. Pressure melting can cause the melting of ice at the base of these glaciers. One of the three types of glaciers: cold glacier; temperate glacier; and subpolar glacier.

Colonization - 

Movement of individuals or propagules of a species to a new territory.

Comet - 

A large mass of ice and dust that has an orbit around a star.

Community - 

Refers to all the populations of interacting species found in a specific area or region at a certain time.

Compass - 

Navigation instrument that uses the Earth's magnetic field to determine direction.

Competition - 

Interaction where two or more organisms in the same space require the same resource (e.g., food, water, nesting space, and ground space) which is in limiting supply to the individuals seeking it. Competition can occur at the interspecific or intraspecific biotic levels. Competition may also be the result of two different processes: exploitation or interference.

Competitive Exclusion - 

Situation where no two competitively interacting species can occupy exactly the same fundamental niche indefinitely because of resource limitations. The outcome of this process is the local extinction the species that is a poorer competitor.

Composite Volcano - 

Volcano created from alternate layers of flows and exploded rock. Their height ranges from 100 to 3,500 meters tall. The chemistry of the magma of these volcanoes is quite variable ranging from basalt to granite.

Concrete Space - 

Actual geographic space in the real world. Geographers approximate this space when they try to represent it in a model or map. This approximation is referred to as abstract space.

Condensation - 

The change in state of matter from vapor to liquid that occurs with cooling. Usually used in meteorology when discussing the formation of liquid water from vapor. This process releases latent heat energy to the environment.

Condensation Nuclei - 

Microscopic particle of dust, smoke or salt that allows for condensation of water vapor to water droplets in the atmosphere. Nucleus for the formation of a rain drop. Condensation normally occurs on these particles when relative humidity becomes 100%. Some condensation nuclei, like salt, are hygroscopic and water can condense on them at relative humidities lower than 100%.

Conduction - 

Conduction consists of energy transfer directly from atom to atom and represents the flow of energy along a temperature gradient.

Cone of Depression - 

Cone shaped depression occurring horizontally across a water table. Causes by excessive removal of groundwater by a surface well.

Confined Aquifer - 

Aquifer between two layers of relatively impermeable earth materials, such as clay or shale.

Confined Groundwater - 

Groundwater trapped between two impervious layers of rock.

Conglomerate - 

Coarse grained sedimentary rock composed of rounded rock fragments cemented in a mixture of clay and silt.

Coniferous Vegetation - 

Cone-bearing vegetation of middle and high latitudes that are mostly evergreen and that have needle-shaped or scale like leaves. Compare with deciduous vegetation.

Conservation Biology - 

Multidisciplinary science that deals with the conservation of genes, species, communities, and ecosystems that make up Earth's biodiversity. It generally investigates human effects on biodiversity and tries to develop practical approaches to preserving biodiversity and ecological integrity.

Consumer - 

An organism that receives the nutrients (food) required for maintenance, growth, and reproduction from the consumption of tissues of producers and/or other consumers. Also called a heterotroph. Several different kinds of consumers have been recognized including: carnivores, omnivores, scavengers, herbivores, detritivores, secondary consumers, and tertiary consumers.

Contact Metamorphism - 

Is the small scale metamorphic alteration of rock due to localized heating. It is usually cause by an igneous intrusion like a sill or a dyke.

Continental Arctic Air Mass - 

Air mass that forms over extensive landmass areas of the high latitudes. In the Northern Hemisphere, these system form only in winter over Greenland, northern Canada, northern Siberia, and the Arctic Basin. Continental Arctic air masses are very cold and extremely dry. These air masses are also very stable.

Continental Crust - 

Granitic portion of the Earth's crust that makes up the continents. Thickness of the continental crust varies between 20 to 75 kilometers. See sial layer.

Continental Divide - 

The elevated area that occurs on a continent that divides continental scale drainage basins.

Continental Drift - 

Theory that suggests that the Earth's crust is composed of several continental plates that have the ability to move. First proposed by A. Snider in 1858 and developed by F.B. Taylor (1908) and Alfred Wegener (1915).

Continental Effect - 

The effect that continental surfaces have on the climate of locations or regions. This effect results in a greater range in surface air temperature at both daily and annual scales. Also see maritime effect.

Continental Glacier - 

Largest type of glacier with a surface coverage in the order of 5 million square kilometres.

Continental Ice Sheet - 

Largest type of glacier with a surface coverage in the order of 5 million square kilometres.

Continental Margin - 

The area between a continent's shoreline and the beginning of the ocean floor. It includes the continental shelf, continental rise, and continental slope.

Continental Plate - 

A rigid, independent segment of the lithosphere composed of mainly granite that floats on the viscous plastic asthenosphere and moves over the surface of the Earth. The Earth's continental plates are an average 125 kilometers thick and were formed more than 3 billion years ago. Also see oceanic plate.

Continental Polar Air Mass - 

Air mass that forms over extensive landmass areas of middle to high latitudes. In North America, these system form over northern Canada. Continental Polar air masses are cold and very dry in the winter and cool and dry in the summer. These air masses are also atmospherically stable in both seasons.

Continental Rise - 

Thick layers of sediment found between the continental slope the ocean floor.

Continental Shelf - 

Shallow submerged margin of the continents that lies between the edge of the shoreline and the continental slope. This nearly level area of the continental crust has surface layers composed of sediment or sedimentary rock.

Continental Shelf Break - 

Boundary zone between the continental shelf and slope.

Continental Shield - 

A large stable area of exposed very old (more than 600 million years) igneous and metamorphic rock found on continents. This rock forms the nucleus of the continents.

Continental Slope - 

Steeply sloping portion of continental crust found between the continental shelf and continental rise.

Continental Tropical Air Mass - 

Air mass that forms over extensive landmasses areas of the low latitudes. In North America, these system form over southwestern United States and northern Mexico. Continental Tropical air masses are warm and dry in the winter and hot and dry in the summer. These air masses are also generally unstable in the winter and stable in the summer.

Continuous Permafrost - 

Form of permafrost that exists across a landscape as an unbroken layer.

Contour Interval - 

Difference in elevation between two successive contour lines. The interval at which contours are drawn on a map depends on the amount of the relief depicted and the scale of the map.

Contour Line - 

Line on a topographic map that connects all points with the same elevation.

Convection - 

Convection involves the transfer of heat energy by means of vertical mass motions through a medium.

Convection Current - 

The movement of a gas or a fluid in chaotic vertical mass motions because of heating.

Convectional Lifting - 

The vertical lifting of parcels of air through convective heating of the atmosphere. This process can initiate adiabatic processes inside the air parcel.

Convectional Precipitation - 

Is the formation of precipitation due to surface heating of the air at the ground surface. If enough heating occurs, the mass of air becomes warmer and lighter than the air in the surrounding environment, and just like a hot air balloon it begins to rise, expand and cool. When sufficient cooling has taken place saturation occurs forming precipitation. This process is active in the interior of continents and near the equator forming cumulus clouds and possible later thunderstorms. Rain is usually the precipitation type that is formed, and in most cases this moisture is delivered in large amounts over short periods of time in extremely localized areas.

Convergence - 

Horizontal inflow of wind into an area. Once at the area, the wind then travels vertically.

Convergence Precipitation - 

The formation of precipitation due to the convergence of two air masses. In most cases, the two air masses have different climatological characteristics. One is usually warm and moist, while the other is cold and dry. The leading edge of the latter air mass acts as an inclined wall or front causing the moist warm air to be lifted. Of course the lifting causes the warm moist air mass to cool due to expansion resulting in saturation. This precipitation type is common at the mid-latitudes where cyclones form along the polar front. Also called frontal precipitation.

Convergent Lifting - 

The vertical lifting of parcels of air through the convergence of opposing air masses in the atmosphere. This process can initiate adiabatic processes inside the air parcel.

Coordinated Universal Time - 

Current official world time reference for civil and scientific purposes. Coordinated Universal Time is measured from six standard atomic clocks at the International Bureau of Weights and Measures (BIPM) in Paris, France. Implemented in 1964.

Coral - 

Simple marine animals that live symbiotically with algae. In the symbiotic relationship, the algae provides the coral with nutrients, while the coral provide the algae with a structure to live in. Coral animals secrete calcium carbonate to produce a hard external skeleton.

Coral Bleaching - 

Situation where coral lose their colorful symbiotic algae. Thought to be caused by unusually warm water, changes in salinity of ocean seawater, or excessive exposure to ultraviolet radiation.

Coral Reef - 

Ridge of limestone found generally below the ocean surface. This marine feature is produced by numerous colonies of tiny coral animals, called polyps, that create calcium carbonate structures around themselves for protection. When the corals die, their vacant exterior skeletons form layers that cause the reef to grow. Coral reefs are found in the coastal zones of warm tropical and subtropical oceans.

Core - 

The core is a layer rich in iron and nickel found in the interior of the Earth. It is composed of two sub-layers: the inner core and outer core. The core is about 7,000 kilometers in diameter.

Coriolis Force - 

An apparent force due to the Earth's rotation. Causes moving objects to be deflected to the right in the Northern Hemisphere and to the left in the Southern hemisphere. Coriolis force does not exist on the equator. This force is responsible for the direction of flow in meteorological phenomena like mid-latitude cyclones, hurricanes, and anticyclones.

Correlation Coefficient - 

Statistic that measures the degree of linear association between two variables. Its values vary from between -1 and 1. Perfect positive (the dependent variable increases with an increase in the independent variable) linear association has a correlation coefficient of 1. Perfect negative (the dependent variable decreases with an increase in the independent variable) linear association has a correlation coefficient of -1. Absolutely no association between variables has a value of zero.

Coulee - 

(1) Steep-sided flow of volcanic lava that has solidified.
(2) Abandoned glacial meltwater channel.
(3) Term used in the United States to describe a steep-sided stream valley.

Counter-Radiation - 

Redirection of the Earth's longwave radiation back to the surface because of the greenhouse effect.

Crater - 

Circular depression in the ground surface created by volcanic activity or asteroid impact.

Craton - 

Stable foundation core of the Earth's various plates of continental crust. Composed of the shield and platform.

Creep - 

(1) Slow mass movement of soil downslope. Occurs where the stresses on the slope material are too small to create a rapid failure. See soil creep.
(2) Another term used to describe traction.

Cretaceous - 

Geologic period that occurred roughly 65 to 144 million years ago. During this period, the first flowering plant species appear and dinosaurs are at their greatest diversity. Dinosaurs die out at the end of this period.

Crevasse - 

(1) Opening on a levee that allows for the drainage of water from the floodplain to the stream channel.
(2) Fracture on the brittle surface of a glacier.

Critical Entrainment Velocity - 

Velocity required to entrain a particular sized particle into the moving medium of air or water.

Crust - 

Earth's outer most layer of solid rock. Between 7 to 70 kilometers thick. Two types of crust exist: oceanic crust and continental crust.

Cryostatic Pressure - 

Pressure exerted on a substance by ice at rest.

Cryotic - 

Something that is frozen.

Cumulonimbus Cloud - 

A well developed vertical cloud that often has top shaped like an anvil. These clouds are very dense with condensed and deposited water. Weather associated with this cloud includes: strong winds; hail; lightning; tornadoes; thunder; and heavy rain. When this weather occurs these clouds are then thunderstorms. Can extend in altitude from a few hundred meters above the surface to more than 12,000 meters.

Cumulus Cloud - 

Puffy clouds with relatively flat bases. Cumulus clouds form when moist warm air bubbles vertically escape from the Earth's surface. Found in an altitude range from 300 to 2,000 meters.

Cuspate Foreland - 

Is a triangular accumulation of sand and/or gravel located along the coastline. This feature is formed by the joining of two spits.

Cyclogenesis - 

Process of cyclone formation, maturation, and death.

Cyclone - 

Area of low pressure in the atmosphere that displays circular inward movement of air. In the Northern Hemisphere circulation is counterclockwise, while Southern Hemisphere cyclones have clockwise wind patterns.