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616 Cards in this Set

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Adiabatic
A process in which heat does not enter or leave a system. In the atmospheric sciences, adiabatic processes are often used to model internal energy changes in rising and descending parcels of air in the atmosphere. When a parcel of air rises in expands because of a reduction in pressure. If no other non-adiabatic processes occur (like condensation, evaporation and radiation), expansion causes the parcel of air to cool at a set rate of 0.98° Celsius per 100 meters. The opposite occurs when a parcel of air descends in the atmosphere. The air in a descending parcel becomes compressed. Compression causes the temperature within the parcel to increase at a rate of 0.98° Celsius per 100 meters.
Adiabatic Cooling
The cooling of a rising parcel of air due to adiabatic processes.
Advection
Advection involves the transfer of heat energy by means of horizontal mass motions through a medium.
Ablation
Surface removal of ice or snow from a glacier or snowfield by melting, sublimation, and/or calving.
Ablation Zone
Region in a glacier where there is a surface net removal of snow and/or ice by melting, sublimation, and/or calving.
Absolute Humidity
Measurement of atmospheric humidity. Absolute humidity is the mass of water vapor in a given volume of air (this measurement is not influenced by the mass of the air). Normally expressed in grams of water vapor per cubic meter of atmosphere at a specific temperature.
Absorption (Atmospheric)
Atmospheric absorption is defined as a process in which solar radiation is retained by a substance and converted into heat energy. The creation of heat energy also causes the substance to emit its own radiation. In general, the absorption of solar radiation by substances in the Earth's atmosphere results in temperatures that get no higher than 1800° Celsius. According to Wien's Law, bodies with temperatures at this level or lower would emit their radiation in the longwave band.
Abyssal Fan
Fan shaped accumulation of sediment from rivers that is deposited at the base of a submarine canyon within a ocean basin.
Accretion
The growth of the continental masses over geologic time via the addition of marine sediments. These sediments are added on to the edges of the continents through tectonic collision with other oceanic or continental plates.
Accumulation
Surface addition of snow to a glacier or snowfield.
Accumulation Zone
(1) Region in a glacier where there is a surface net addition of snow.
(2) Part of a hillslope that has a net gain of material leading to a progressive raising of the slope's surface.
Active Layer
Upper zone of soil in higher latitude locations that experiences daily and seasonal freeze-thaw cycles.
Actual Evapotranspiration
Is the amount of water that is actually removed from a surface due to the processes of evaporation and transpiration.
Adaptive Radiation
The evolution of a number of new species from one or a few ancestor species over many thousands or millions of years. Normally occurs after a mass extinction creates a number of vacant ecological niches or when a radical change in the environment produces new ecological niches.
Advection Fog
Fog generated when winds flow over a surface with a different temperature. Two types of advection fog exist. When warm air flows over a cold surface it can produce fog through contact cooling. Cold air blowing over a warm moist surface produces a form of advection fog know as evaporation fog.
Aeolian
Geomorphic process involving wind. Alternative spelling eolian.
Aeolian Landform
Is a landform formed from the erosion or deposition of weathered surface materials by wind. This includes landforms with some of the following geomorphic features: sand dunes, deflation hollows, and desert pavement. Alternative spelling eolian landform.
Aftershock
Smaller earth tremors that occur seconds to weeks after a major earthquake event.
Aggradation
Readjustment of the stream profile where the stream channel is raised by the deposition of bed load.
Air Mass
A body of air whose temperature and humidity characteristics remain relatively constant over a horizontal distance of hundreds to thousands of kilometers. Air masses develop their climatic characteristics by remaining stationary over a source region for a number of days. Air masses are classified according to their temperature and humidity characteristics.
Aeolian
Geomorphic process involving wind. Alternative spelling eolian.
Aeolian Landform
Is a landform formed from the erosion or deposition of weathered surface materials by wind. This includes landforms with some of the following geomorphic features: sand dunes, deflation hollows, and desert pavement. Alternative spelling eolian landform.
Aftershock
Smaller earth tremors that occur seconds to weeks after a major earthquake event.
Aggradation
Readjustment of the stream profile where the stream channel is raised by the deposition of bed load.
Air Mass
A body of air whose temperature and humidity characteristics remain relatively constant over a horizontal distance of hundreds to thousands of kilometers. Air masses develop their climatic characteristics by remaining stationary over a source region for a number of days. Air masses are classified according to their temperature and humidity characteristics.
Albedo
Is the reflectivity of a surface.
Aleutian Low
Subpolar low pressure system found near the Aleutian Islands. Most developed during the winter season. This large-scale pressure system spawns mid-latitude cyclones.
Allophane
Hydrated aluminosilicate substance ordinarily found associated with clay minerals.
Alluvial Fan
Large fan shaped terrestrial deposit of alluvial sediment on which a braided stream flows over. Form as stream load is deposited because of a reduction in the velocity of stream flow.
Alluvial Terraces
Flat elevated benches composed of unconsolidated alluvium found either side of a stream channel. Formed when a stream down cuts into its floodplain.
Alluvium
Sediment that originates from a stream.
Alpine Glacier
Small glacier that occupies a U-shaped valley on a mountain. Also called a mountain glacier.
Alpine Permafrost
Form of permafrost that exists at high altitudes in mountainous environments.
Alpine Tundra
High altitude biome dominated by a few species of dwarf shrubs, a few grasses, sedges, lichens, and mosses. Productivity is low in this biome because of the extremes of climate. Quite similar to tundra.
Altitude
Vertical distance above sea-level.
Altocumulus Clouds
Middle altitude cloud that is colored from white to gray. This cloud is composed of a mixture of water droplets and ice crystals. It appears in the atmosphere as layers or patches that are well rounded and commonly wavelike. Found in an altitude range from 2,000 to 8,000 meters.
Altostratus Clouds
Gray-looking middle altitude cloud that is composed of water droplets and ice crystals. Appears in the atmosphere as dense sheet like layer. Can be recognized from stratus clouds by the fact that you can see the Sun through it. Found in an altitude range from 2,000 to 8,000 meters.
Amphibole
A group of double chained inosilicate minerals whose basic chemical unit is the tetrahedron (SiO 4 ). They are common rock forming minerals and are found in most igneous and metamorphic rocks. They form at low temperatures with the presence of water in the crystallization environment. There are about 60 recognized mineral types in this group.
Andesite
An extrusive igneous rock that develops from a magma that is chemically between felsic and mafic and whose mineral crystals are fine.
Andisols
These soils develop from parent materials that are volcanic in origin.
Anemometer
Mechanical instrument used to measure wind speed. These instruments commonly employee three methods to measure this phenomenon: 1) A device with three or four open cups attached to a rotating spinal. The speed of rotation is then converted into a measurement of wind speed; 2) A pressure plate that measures the force exerted by the moving wind at right angles; 3) An instrument consisting of a heated-wire where electrical resistance (temperature of the wire) is adjusted to account for heat lost by air flow. The faster the wind the greater the heat loss and thus the more energy that is required to keep the wire at a constant temperature. As a result, wind speed is measured through the drain of electrical current.
Aneroid Barometer
Barometer that measures atmospheric pressure via the expansion and contraction of a sealed hollow cell which is partially depleted of air.
Angle of Incidence
Angle at which the Sun's rays or insolation strike the Earth's surface. If the Sun is positioned directly over head or 90° from the horizon, the incoming insolation strikes the surface of the Earth at right angles and is most intense.
Angle of Repose
Measurement commonly used in civil engineering. It is the maximum angle at which a material can be inclined without failing. Geomorpologist use this measurement for determining the stability of slope to mass movements.
Antarctic Circle
Latitude of 66.5° South. The northern limit of the area of the Earth that experiences 24 hours of darkness or 24 hours of day at least one day during the year.
Antarctic High
A region of high pressure that occupies central Antarctic throughout the year. This pressure system is responsible for very cold temperatures and extremely low humidity.
Anticline
A fold in rock layers that forms an arch.
Anticyclone
An atmospheric pressure system consisting of an area of high pressure and outward circular surface wind flow. In the Northern Hemisphere winds from an anticyclone blow clockwise, while Southern Hemisphere systems blow counterclockwise.
Aphelion
It is the point in the Earth's orbit when it is farthest from the Sun (152.5 million kilometers). Aphelion occurs on the 3rd or 4th of July.
Aquiclude
Rock formations that are impermeable to groundwater water.
Aquifer
Rock formations that store groundwater water.
Aquifer Recharge Area
Surface area that provides water for an aquifer.
Archean
Geologic eon that occurred from 2500 to 3800 million years ago. During this time period, the first single-celled prokaryote organisms evolved and developed.
Archipelago
A group of islands that have an arc shaped distribution. These islands are usually of volcanic origin and are associated with subduction zones.
Arête
Sharp topographic ridge that separates cirques on a mountain that is or has been glaciated.
Arkose
A type of sedimentary sandstone that contains a large quantity of weathered feldspar grains. This type of sedimentary rock forms in arid conditions.
Artesian Water
Groundwater that is confined by two impermeable layers beneath the Earth's surface.
Artesian Well
A well where the water rises and flows out to the surface because of hydrostatic pressure.
Asthenosphere
Zone in the Earth's mantle that exhibits plastic properties. Located below the lithosphere at between 100 and 200 kilometers.
Atmospheric Pressure
Weight of the atmosphere on a surface.
Atmospheric Stability
Relative stability of parcels of air relative to the atmosphere that surrounds them.
Aurora
Multicolored lights that appear in the upper atmosphere (ionosphere) over the polar regions and visible from locations in the middle and high latitudes. Caused by the interaction of solar wind with oxygen and nitrogen gas in the atmosphere. Aurora in the Northern Hemisphere are called aurora borelis and aurora australis in the Southern Hemisphere.
Autumnal Equinox
One of two days during the year when the declination of the Sun is at the equator. The autumnal equinox denotes the first day of the fall season. For the Northern Hemisphere, the date of autumnal equinox on either September 22 or 23 (changes yearly). March 20 or 21 is the date of the autumnal equinox in the Southern Hemisphere. During the autumnal equinox, all locations on the Earth (except the poles) experience equal (12 hour) day and night.
Available Water
Portion of the capillary water that is available for plant root uptake.
Backshore slope
Sloping bank landward of the shore. This coastal feature is composed of relatively non-mobile sediments.
Backswamp
Marshy low lying area in a stream's floodplain. Commonly found behind levees.
Backwash
The return water flow of swash. This sheet of water flows back to ocean because of gravity.
Badlands
(1) Term used to describe a part of South Dakota.
(2) Term used to describe a semi-arid landscape that has been influenced by heavy fluvial erosion. Characterized by deep ravines and gullies, shape ridges, and a generally barren surface.
Bajada
Consecutive series of alluvial fans forming along the edge of a linear mountain range. Surface of this feature undulates in a rolling fashion as one moves from the center of one alluvial fan to another. Normally occurs in arid climates.
Bank-Caving
Collapse of stream bank material into a stream channel.
Barchan Dune
Crescent shaped sand dune that has its long axis transverse to the wind and its crescent tips pointed downwind.
Barometer
Instrument that measures atmospheric pressure.
Basal Sliding
The sliding of a glacier over the surface it rests on. Caused by the gradient of the slope and the weight of the glacier's mass.
Basalt
A dark colored fine grained igneous rock formed from mafic magma.
Basalt Plateau
Extensive continental deposits of basaltic volcanic rock.
Basaltic Magma
Mafic magma that forms basaltic igneous rocks.
Base Flow
Rate of discharge in a stream where only the throughflow and groundwater flow from subsurface aquifers contribute to the overall flow.
Base Level
The subterranean elevation below which a stream cannot vertically erode sediment. For many streams this hypothetical elevation is sea-level.
Basement Rock
Very old granite and metamorphic rocks found in continental crust. These rocks make up the continental shield.
Basin
A topographic rock structure whose shape is concave downwards.
Batholith
A large mass of subsurface intrusive igneous rock that has its origins from mantle magma.
Bay
A body of sheltered water found in a crescent shaped coastal configuration of land.
Beach
The terrestrial interface area in between land and a water body where there are accumulations of unconsolidated sediments like sand and gravel. These deposits are laid down by the action of breaking waves.
Beaufort Wind Scale
Descriptive system that determines wind speed by noting the effect of the wind on the environment. Originally developed for use at sea by Admiral Beaufort of the British Navy in 1806.
Bed Load
Portion of the stream load that is carried along the stream bed without being permanently suspend in the flowing water.
Bergschrund
A deep crevasse commonly found at the head of an alpine glacier. Forms when the glacial ice pulls away from the mountain side.
Berm
Low hill of sand that forms along coastal beaches.
Bermuda High
High pressure system that develops over the western subtropical North Atlantic. Also called Azores High.
Big Bang
Theory that suggests that about 15 billion years ago all of the matter and energy in the Universe was concentrated into an area smaller than a atom. At this instant, matter, energy, space and time did not exist. Then suddenly, the Universe began to expand at an incredible rate and matter, energy, space and time came into being. As the Universe expanded, matter began to coalesce into gas clouds, and then stars and planets. Some scientists believe that this expansion is finite and will one day cease. After this point in time, the Universe will begin to collapse until a Big Crunch occurs.
Black Body
Is a body that emits electromagnetic radiation, at any temperature, at the maximum possible rate per unit surface area. This body also absorbs all electromagnetic radiation that is intercepted by it.
Blowout Depression
Saucer shaped depressions created by wind erosion. At the leeward end of the feature there usually is a deposit of sand. Blowouts are found in coastal beach areas and in arid and semiarid regions of the world. These features are smaller than a deflation hollow.
Body Wave
Type of seismic wave that travels through the interior of Earth.
Bottomset Bed
Horizontal deltaic deposit of alluvial sediment composed of fine silt and clay.
Bowen Reaction Series
Model that explains the origin of the various types of igneous rocks. It suggests that the presence or absence of particular minerals in igneous rocks depends on the temperature of crystallization and on the magma's original chemical composition.
Braided Stream
Shallow stream channel that is subdivided into a number of continually shifting smaller channels that are separated by bar deposits.
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.
Canadian Shield
Very old igneous and metamorphic shield rock that covers much of northern Canada. Created more than two to three billion years ago.
Canyon
Steep-sided valley where depth is considerably greater than width. These features are the result of stream erosion.
Carbonation
Is a form of chemical weathering where carbonate and bicarbonate ions react with minerals that contain calcium, magnesium, potassium, and sodium.
Catastrophism
General theory that suggests that certain phenomena on the Earth are the result of catastrophic events. For example, the Biblical Flood is responsible for sedimentary rock formations and the extinction of the dinosaurs.
Cave
A natural cavity or recess that is roughly positioned horizontally to the surface of the Earth.
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.
Chalk
Form of limestone. This sedimentary rock is composed of the shells and skeletons of marine microorganisms.
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.
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.
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.
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.
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.
Climate
General pattern of weather conditions for a region over a long period time (at least 30 years).
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 Talik
Is a form of localized unfrozen ground (talik) in an area of permafrost. It is completely enclosed by permafrost in all directions.
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.
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.
Col
Saddle like depression found between two mountain peaks. Formed when two opposing cirque glaciers back erode an arête.
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.
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.
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.
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.
Continental Arctic Air Mass (A)
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 Glacier
Largest type of glacier with a surface coverage in the order of 5 million square kilometers.
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.
Continental Polar Air Mass (cP)
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 Tropical Air Mass (cT)
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.
Contour (Line)
Line on a topographic map that connects all points with the same elevation.
Continuous Permafrost
Form of permafrost that exists across a landscape as an unbroken layer.
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.
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.
Counter-Radiation
Redirection of the Earth's longwave
Creep
Slow mass movement of soil downslope. Occurs where the stresses on the slope material are too small to create a rapid failure.
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.
Crust
Earth's outer most layer of solid rock. Between 7 to 70 kilometers thick.
Cryosol Soil
This soil is common to high latitude tundra environments. The main identifying feature of this soil is a layer of permafrost within one meter of the soil surface.
Cryotic
Something that is frozen.
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.
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.
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.
Debris Flow
A type of mass movement where there is a downslope flow of a saturated mass of soil, sediment, and rock debris.
Deflation
Process where wind erosion creates blowout depressions or deflation hollows by removing and transporting sediment and soil.
Deflation Hollow
A surface depression or hollow commonly found in arid and semiarid regions caused by wind erosion. Also see the related blowout depression.
Degradation
Readjustment of the stream profile where the stream channel is lowered by the erosion of the stream bed. Usually associated with high discharges.
Delta
Large deposit of alluvial sediment located at the mouth of a stream where it enters a body of standing water.
Dendritic
Term used to describe the stream channel pattern that is completely random. Resembles the branching pattern of blood vessels or tree branches.
Deposition
(1) The change in state of matter from gas to solid that occurs with cooling. Usually used in meteorology when discussing the formation of ice from water vapor. This process releases latent heat energy to the environment.
(2) Laying down of sediment transported by wind, water, or ice.
Depositional Landform
Is a landform formed from the deposition of weathered and eroded surface materials. On occasion, these deposits can be compressed, altered by pressure, heat and chemical processes to become sedimentary rocks. This includes landforms with some of the following geomorphic features: beaches, deltas, floodplains, and glacial moraines.
Depression
(1) Concave hollow found on the Earth's surface.
(2) Term used to describe a cyclone or an atmospheric low pressure system.
Deranged Drainage
Drainage pattern that is highly irregular. Areas that have experienced continental glaciation may have this type of drainage pattern.
Desertification
Conversion of marginal rangeland or cropland to a more desert like land type.
Detrital Rock
Sedimentary rock that is composed of particles transported to their place of deposition by erosional processes. Examples of such rock include sandstone and shale.
Devonian
Geologic period that occurred roughly 360 to 408 million years ago. During this period, the first amphibians and trees appear.
Dew Point
Dew point is the temperature at which water vapor saturates from an air mass into liquid or solid usually forming rain, snow, frost or dew. Dew point normally occurs when a mass of air has a relative humidity of 100%.
Diorite
A coarse grained igneous rock of intrusive origin that is darker and chemically more mafic than granite.
Discontinuous Permafrost
Form of permafrost that contains numerous scattered pockets of unfrozen ground.
Dissolved Load
Portion of the stream load that is in solution in the flowing water.
Distributary
A smaller branching stream channel that flows away from a main stream channel. Common on deltas. Opposite of tributary.
Divergence
Horizontal outflow of wind from an area. In a surface divergence, outflow originates from the upper atmosphere.
Divide
The topographic ridge that separates drainage basins.
Doldrums
Area of low atmospheric pressure and calm westerly winds located at the equator. Similar to Intertropical Convergence Zone.
Dune
(1) Stream bed deposit found streams whose channel is composed mainly of sand and silt. Dunes are about 10 or more centimeters in height and are spaced a meter or more apart and are common in streams with high velocities.
(2) Terrestrial deposit of sand that resembles a mound or ridge that was formed from aeolian processes.
Drainage Basin
Land surface region drained by a length of stream channel.
Drainage Divide
Topographic border between adjacent drainage basins or watersheds.
Drainage Pattern
Geometric pattern that a stream's channels take in the landscape. These patterns are controlled by factors such as slope, climate, vegetation, and bedrock resistance to erosion.
Drift
Any material deposited by a glacier.
Drought
Climatic condition where water loss due to evapotranspiration is greater than water inputs through precipitation.
Drumlin
A hill shaped deposit of till. The shape of these features resembles an elongated teaspoon laying bowl down. The tapered end of the drumlin points to the direction of glacier advance. Drumlins come in assorted sizes. Lengths can range from 100 to 5,000 meters and heights can be as great as 200 meters.
Dry Adiabatic Lapse Rate (DALR)
The rate of decline in the temperature of a rising parcel of air before it has reached saturation. This rate of temperature decline is 9.8° Celsius per 1000 meters because of adiabatic cooling.
Dry Line
A boundary the separates dry and moist air in the warm sector of a mid-latitude cyclone wave. Found ahead of the cold front.
Dyke
Thin vertical veins of igneous rock that form when magma enters and cools in fractures found within the crust. Also see intrusive igneous rock.
Earthquake
Is a sudden motion or trembling in the Earth. The motion is caused by the quick release of slowly accumulated energy in the form of seismic waves. Most earthquakes are produced along faults, tectonic plate boundaries, or along the mid-oceanic ridges.
Earthquake Focus
Point of stress release in an earthquake.
Easterly Wave
Atmospheric disturbance in the tropical trade winds. Occasionally these systems intensify into hurricanes.
Effusive Eruption
Volcanic eruption where low-viscosity basaltic magma is released. This type of eruption is not explosive and tends to form shield volcanoes.
Elastic Rebound Theory
Theory that describes how earthquakes arise from the horizontal movement of adjacent tectonic plates along a linear strike-slip fault. This theory suggests that the two plates moving in opposite directions become locked for some period of time because of friction. However, the accumulating stress overcomes the friction and causes the plate to suddenly move over a short time period which generates an earthquake.
El Nino
Name given to the occasional development of warm ocean surface waters along the coast of Ecuador and Peru. When this warming occurs the tropical Pacific trade winds weaken and the usual upwelling of cold, nutrient rich deep ocean water off the coast of Ecuador and Peru is reduced. The El Nino normally occurs around Christmas and lasts usually for a few weeks to a few months. Sometimes an extremely warm event can develop that lasts for much longer time periods.
Endogenic
Refers to a system that is internal to the Earth.
Entrainment
One of three distinct processes involved in erosion. More specifically, it is the process of particle lifting by an agent of erosion.
Environmental Lapse Rate (ELR
The rate of air temperature increase or decrease with altitude. The average ELR in the troposphere is an air temperature decrease of 6.5° Celsius per 1000 meters rise in elevation.
Eon
Longest geologic time unit.
Epicenter
Surface location of an earthquake's focus.
Epoch
Geologic time unit that is shorter than a period.
Equinox
Two days during the year when the declination of the Sun is at the equator. The September equinox occurs on September 22 or 23. The March equinox occurs on March 20 or 21. On these days, all locations on our planet (except the poles) experience equal (12 hour) day and night.
Era
Geologic time unit that is shorter than an eon but longer than a period.
Erosion
The removal of weathered sediment or rocks by the forces of wind, water, and ice.
Erratic
A large rock boulder that has been transported by glaciers away from its origin and deposited in a region of dissimilar rock.
Esker
Long twisting ridges of sand and gravel found on the Earth's surface. Created when the deposits of subsurface glacial streams are placed on the ground after glacial melting.
Estuary
Somewhat enclosed coastal area at the mouth of a river where nutrient rich fresh water meets with salty ocean water.
Eutrophication
Physical, chemical and biological changes in a water body as a result of the input nitrogen and phosphorus.
Eutrophic Lake
Lake that has an excessive supply of nutrients, mostly in the form of nitrates and phosphates.
Evaporation
the process by which liquid water is converted into a gaseous state. Evaporation can only occur when water is available. It also requires that the humidity of the atmosphere be less than the evaporating surface (at 100% relative humidity there is no more evaporation). The evaporation process requires large amounts of energy. For example, the evaporation of one gram of water at a temperature of 100° Celsius requires 540 calories of heat energy (600 calories at 0° Celsius).
Evaporation Fog
A type of fog produced from the advection of cold air over warm water or warm or moist land. This type of fog is sometimes called steam fog or sea smoke.
Evapotranspiration
Combined loss of water to the atmosphere via the processes of evaporation and transpiration.
Exogenic
Refers to a system that is external to the Earth.
Exotic Stream
A stream that has a course that begins in a humid climate and end in an arid climate. Because of reductions in precipitation and and increases in evaporation, the discharge of these streams deceases downslope. Examples of such streams are the Nile and Colorado Rivers.
Explosive Eruption
Volcanic eruption where high-viscosity granite-rich magma causes an explosion of ash and pyroclastic material. This type of eruption is common to composite and caldera volcanoes.
Extrusive Igneous Rock
Igneous rock that forms on the surface of the Earth.
Eye
Area in the center of a hurricane that is devoid of clouds.
Fault
A fracture in rock caused by stress.
Fault Plane
The plane that represents the fracture surface of a fault.
Feldspar
A group of common aluminum silicate minerals that contains potassium, sodium, or calcium.
Felsic Magma
Magma that is relatively rich in silica, sodium, aluminum, and potassium. This type of magma solidifies to form rocks relatively rich in silica, sodium, aluminum, and potassium.
Ferrel Cell
Three-dimensional atmospheric circulation cell located at roughly 30 to 60° North and South of the equator.
Ferricretes
Sedimentary rock created by the chemical precipitation of iron.
Field Capacity
The water remaining in a soil after the complete draining of the soil's gravitational water.
Firn
Névé on a glacier that survives the year's ablation season.
Firn Limit
The lower boundary of the zone of accumulation on a glacier where snow accumulates on an annual basis.
Fissure
Opening or crack in the Earth's crust.
Fjord
A glacial valley or glacial trough found along the coast that is now filled with a mixture of fresh water and seawater.
Flash Flood
A rapid and short-lived increase in the amount of runoff water entering a stream resulting in a flood.
Floodplain
Relatively flat area found alongside the stream channel that is prone to flooding and receives alluvium deposits from these inundation events.
Föhn Wind
European equivalent of chinook wind.
Fog
Fog exists if the atmospheric visibility near the Earth's surface is reduced to 1 kilometer or less. Fog can be composed of water droplets, ice crystals or smoke particles. Fogs composed primarily of water droplets are classified according to the process that causes the air to cool to saturation. Common types of this type of fog include: radiation fog; upslope fog; advection fog; evaporation fog; ice fog; and frontal fog.
Fold
Wavelike layers in rock strata that are the result of compression.
Folding
The deformation of rock layers because of compressive forces to form folds.
Foliation
Process where once randomly distributed platy minerals in a rock become reoriented, because of metamorphism, in a parallel manner.
Foreset Bed
Deltaic deposit of alluvial sediment that is angled 5 to 25° from horizontal. Most of the delta is made up of these deposits.
Foreshock
Small earth tremors that occur seconds to weeks before a significant earthquake event.
Freezing Rain
A type of precipitation. Occurs when liquid rain hits a cold surface and then immediately freezes into ice. For this to occur, a surface temperature inversion is usually required. In such an inversion, the surface must have a temperature below freezing, while the temperature of the atmosphere where the precipitation forms is above freezing.
Fresh Water
Water that is relatively free of salts.
Frictional Force
Force acting on wind near the Earth's surface due to frictional roughness. Causes the deceleration of wind.
Front
Transition zone between air masses with different weather characteristics.
Frontal Fog
Is a type of fog that is associated with weather fronts, particularly warm fronts. This type of fog develops when frontal precipitation falling into the colder air ahead of the warm front causes the air to become saturated through evaporation.
Frontal Lifting
Lifting of a warmer or less dense air mass by a colder or more dense air mass at a frontal transitional zone.
Frost
Deposition of ice at the Earth's surface because of atmospheric cooling.
Frost Point
Is the temperature at which water vapor saturates from an air mass into solid usually forming snow or frost.
Frost Wedging
A process of physical weathering in which water freezes in a crack and exerts force on the rock causing further rupture.
Fujita Tornado Intensity Scale
Tornado classification system developed by T. Theodore Fujita. This system six levels from F0 to F5. These levels are based on the estimated speed of the tornado's winds from proxy information like property damage.
Funnel Cloud
A tornado which is beginning its descent from the base of a cumulonimbus cloud. This severe weather event may or may not reach the ground surface.
Gabbro
An intrusive igneous rock that develops from mafic magma and whose mineral crystals are coarse. Mineralogically this rock is identical to basalt.
Galaxy
An assemblage of millions to hundreds of billions of stars.
Gelifluction
Form of mass movement in periglacial environment where a permafrost layer exists. It is characterized by the movement of soil material over the permafrost layer and the formation of lobe-shaped features. Also see solifluction.
General Circulation Model (GCM)
Computer-based climate model that produces future forecast of weather and climate conditions for regions of the Earth or the complete planet. Uses complex mathematical equations and physical relationships to determine a variety of climate variables in a three-dimensional grid.
Geology
The field of knowledge that studies the origin, structure, chemical composition, and history of the Earth and other planets.
Geomorphic Threshold
The amount of slow accumulated change a landform can take before it suddenly moves into an accelerated rate of change that takes it to a new system state.
Geostrophic Wind
Horizontal wind in the upper atmosphere that moves parallel to isobars. Results from a balance between pressure gradient force and Coriolis force.
Glacial (glaciation)
1) Period of time during an ice age when glaciers advance because of colder temperatures.
(2) Involving glaciers and moving ice. Usually pertaining to processes associated with glaciers.
Glacial Drift
A generic term applied to all glacial and glaciofluvial deposits.
Glacial Ice
A very dense form frozen water that is much harder than snow, névé, or firn.
Glacial Lake
A natural impoundment of meltwater at the front of a glacier.
Glacial Retreat
The backwards movement of the snout of a glacier.
Glacial Polish
The abrasion of bedrock surfaces by materials carried on the bottom of a glacier. This process leaves these surfaces smooth and shiny.
Glacial Surge
A rapid forward movement of the snout of a glacier.
Glacial Trough
A deep U-shaped valley with steep valley walls that was formed from glacial erosion. At the base of many of these valleys are cirques.
Glacial Uplift
Upward movement of the Earth's crust following isostatic depression from the weight of the continental glaciers.
Glacier
A large long lasting accumulation of snow and ice that develops on land. Most glaciers flow along topographic gradients because of their weight and gravity.
Glaciofluvial
Geomorphic feature whose origin is related to the processes associated with glacial meltwater.
Gneiss
A metamorphosed coarse grained igneous rock. In this rock you get the recrystallization of quartz, feldspars, micas and amphiboles into bands.
Graben Fault
This fault is produced when tensional stresses result in the subsidence of a block of rock. On a large scale these features are known as Rift Valleys.
Graded Stream
A stream that has a long profile that is in equilibrium with the general slope of the landscape. A graded profile is concave and smooth. Stream's maintain their grade through a balance between erosion, transportation, and deposition. Erosion removes material from bumps in the profile and deposition fills in dips.
Gradient
The steepness of a slope as measured in degrees, percentage, or as a distance ratio (rise/run).
Gradient Wind
Horizontal wind in the upper atmosphere that moves parallel to curved isobars. Results from a balance between pressure gradient force, Coriolis force, and centripetal force.
Granite
Medium to coarse grained igneous rock that is rich in quartz and potassium feldspar. Derived from felsic magma.
Granitic Magma
Felsic magma that generates mainly granitic rocks.
Graupel
A type of precipitation that consists of a snow crystal and a raindrop frozen together. Also called snow pellets.
Gravel
A term used to describe unconsolidated sediments composed of rock fragments. These rock fragments have a size that is greater than 2 millimeters.
Gravitational Water
Water that moves through soil due to gravitational forces. Soil water in excess of hygroscopic water and capillary water.
Ground Frost
Frost that penetrates the soil surface in response to freezing temperatures.
Ground Ice
General term used to describe all bodies of ice in the ground surface of the permafrost layer.
Ground Moraine
A thick layer of till deposited by a melting glacier.
Groundwater
Water that occupies the pore spaces found in some types of bedrock.
Groundwater Recharge
The replenishment of groundwater with surface water.
Gulf Stream
Warm ocean current that originates in and around the Caribbean and flows across the North Atlantic to northwest Europe.
Gust Front
A boundary found ahead of a thunderstorm that separates cold storm downdrafts from warm humid surface air. Winds in this phenomenon are strong and fast.
Gypsum
Sedimentary rock created by the chemical precipitation of calcium, sulfur, and oxygen.
Hadean
Geologic eon that occurred from 3800 to 4600 million years ago. The Earth's oldest rocks date to the end of this time period.
Hadley Cell
Three-dimensional atmospheric circulation cell located at roughly 0 to 30° North and South of the equator. The Hadley cell consists of rising air (intertropical convergence zone) at the equator and descending air (subtropical highs) at 30° North and South.
Hail
Hail is a solid form of precipitation that has a diameter greater than 5 millimeters. Occasionally, hailstones can be the size of golf balls or larger. Hailstones of this size can be quite destructive. The intense updrafts in mature thunderstorm clouds are a necessary requirement for hail formation.
Halite
Sedimentary rock created by the chemical precipitation of sodium and chlorine.
Hanging Valley
A secondary valley that enters a main valley at an elevation well above the main valley's floor. These features are result of past erosion caused by alpine glaciers. Hanging valleys are often the site of spectacular waterfalls.
Hardpan
Impervious layer found within the soil. It can result from the precipitation of iron, illuviation of clay or the cementing of sand and gravel by calcium carbonate precipitates.
Headwaters
Upper portion of stream's drainage system.
High Pressure
An area of atmospheric pressure within the Earth's atmosphere that is above average. If this system is on the Earth's surface and contains circular wind flow and enclosed isobars it is called an anticyclone.
Holocene Epoch
Period of time from about 10,000 years ago to today. During this period glaciers retreated because of a warmer global climate. Time of modern humans.
Horn
Pyramidal peak that forms when several cirques erode a mountain from three or more sides.
Horst Fault
A fault that is produced when two reverse faults cause a block of rock to be push up.
Hot Spot
A volcanic area on the surface of the Earth created by a rising plume of magma.
Hurricane
An intense cyclonic storm consisting of an organized mass of thunderstorms that develops over the warm oceans of the tropics. To be classified as a hurricane, winds speeds in the storm must be greater than 118 kilometers per hour.
Hydraulic Gradient
The slope of the water table or aquifer. The hydraulic gradient influences the direction and rate of groundwater flow.
Hydrograph
A graph describing stream discharge over time.
Hydrostatic Pressure
Force caused by water under pressure.
Hygrometer
An instrument for measuring atmospheric humidity.
Hygroscopic
Substances that have the ability to absorb water and therefore accelerate the condensation process.
Hygroscopic Water
Water held within 0.0002 millimeters of the surface of a soil particle. This water is essentially non-mobile and can only be removed from the soil through heating.
Ice Age
Period of time when glaciers dominate the landscape of the Earth. The last major Ice Age was during the Pleistocene epoch.
Iceberg
A mass of ice found floating in the ocean or a lake. Often icebergs form when ice calves from land-based glaciers into the water body. Icebergs can be dangerous to shipping in high and mid-latitude regions of the ocean because 90 percent of their mass lies below the ocean surface.
Ice Cap
Large dome-shaped glacier found covering a large expanse of land. Smaller than an ice sheet.
Ice Fall
An area of crevassed ice on a glacier. Caused when the base of the glacier flows over steep topography.
Ice Fall
An area of crevassed ice on a glacier. Caused when the base of the glacier flows over steep topography.
Ice Field
Large level area of glacial ice found covering a large expanse of land. Similar in size to an ice cap but does not have a dome-shape.
Ice Jam
The accumulation of ice at a specific location along a stream channel. Can cause the reduction of stream flow down stream of the obstruction and flooding upstream.
Icelandic Low
Subpolar low pressure system found near Iceland. Most developed during the winter season. This large-scale pressure system spawns mid-latitude cyclones.
Ice Pellets
A type of precipitation. Ice pellets or sleet are transparent or translucent spheres of frozen water that fall from clouds. Ice pellets have a diameter less than 5 millimeters. To form, this type of precipitation requires an environment where raindrops develop in an atmosphere where air temperature is above freezing. These raindrops then fall into a lower layer of air with freezing temperatures. In this lower layer of cold air, the raindrops freeze into small ice pellets. Like freezing rain, an air temperature inversion is required for development of ice pellets.
Ice Sheet
A dome-shaped glacier covering an area greater than 50,000 square kilometers. Greenland and Antarctica are considered ice sheets. During the glacial advances of the Pleistocene ice sheets covered large areas of North America, Europe, and Asia. Larger than an ice cap.
Ice Shelf
Large flat layer of ice that extends from the edge of the Antarctic ice cap into the Antarctic Ocean. Source of icebergs.
Ice Wedge
Wedge-shaped, ice body composed of vertically oriented ground ice that extends into the top of a permafrost layer. These features are approximately 2 to 3 meters wide at their top and extend into the soil about 8 to 10 meters. Form in cracks that develop in the soil during winter because of thermal contraction. In the spring, these cracks fill with liquid water from melting snow which subsequently re-freezes. The freezing process causes the water to expand in volume increasing the size and depth of the crack. The now large crack fills with more liquid water and again it freezes causing the crack to enlarge.This process continues for many cycles until the ice wedge reaches its maximum size.
Igneous Rock
Rocks formed by solidification of molten magma either beneath (intrusive igneous rock) or at (extrusive igneous rocks) the Earth's surface.
Infiltration
The absorption and downward movement of water into the soil layer.
Infiltration Capacity
The ability of a soil to absorb surface water.
Inner Core
Inner region of the Earth's core. It is thought to be solid iron and nickel with a density of about 13 grams per cubic centimeter. It also has a diameter of about 1220 kilometers.
Insolation Weathering
Form of physical weathering. Involves the physical breakdown of minerals and rock due to thermal expansion and contraction.
Instability
Atmospheric condition where a parcel of air is warmer that the surrounding air in the immediate environment. This condition causes the parcel to rise in the atmosphere. Also see unstable atmosphere.
Interception
Is the capture of precipitation by the plant canopy and its subsequent return to the atmosphere through evaporation or sublimation. The amount of precipitation intercepted by plants varies with leaf type, canopy architecture, wind speed, available radiation, temperature, and the humidity of the atmosphere.
Interglacial
Period of time during an ice age when glaciers retreated because of milder temperatures.
Intertropical Convergence Zone (ITCZ)
Zone of low atmospheric pressure and ascending air located at or near the equator. Rising air currents are due to global wind convergence and convection from thermal heating. Location of the thermal equator.
Intrusive Igneous Rock
A mass of igneous rock that forms when magma from the mantle migrates upward and cools and crystallizes near, but not at, the Earth's surface. Also called plutonic igneous rock. Also see dyke, sill, and batholith.
Island Arc
A line of volcanic islands found of the ocean that have been created by the convergence of two tectonic plates and the subsequent subduction of one of the plates beneath the other. Subduction cause magma plumes to rise to the Earth's surface creating the volcanic islands.
Isobar
Lines on a map joining points of equal atmospheric pressure.
Isostacy
The buoyant condition of the Earth's crust floating in the asthenosphere. The greater the weight of the crust the deeper it floats into the asthenosphere. When weight is remove the crust rises higher.
Isostatic Depression
Large scale sinking of the crust into the asthenosphere because of an increase in weight on the crustal surface. Common in areas of continental glaciation where the crust was depressed by the weight of the ice.
Isostatic Rebound
The upward movement of the Earth's crust following isostatic depression.
Isothermal Layer
Vertical layer in the atmosphere where temperature remains unchanged. In the Earth's atmosphere, three isothermal layers are found in the lower regions of the stratosphere, mesosphere, and the thermosphere.
Isotopic Dating
Dating technique used to determine the age of rock and mineral through the decay of radioactive elements.
Jet Stream
Relatively fast uniform winds concentrated within the upper atmosphere in a narrow band. A number of jet streams have been identified in the atmosphere. The polar jet stream exists in the mid-latitudes at an altitude of approximately 10 kilometers. This jet stream flows from west to east at average speeds, depending on the time of year, between 110 to 185 kilometers per hour. Another strong jet stream occurs above the sub-tropical highs at an altitude of 13 kilometers. This jet stream is commonly called the subtropical jet stream. The subtropical jet stream's winds are not as strong as the polar jet stream.
Joint
A fracture in a rock where no movement has taken place or where no movement has taken place perpendicular to the surface of the fracture. Important in rock weathering because it increases the exposed surface area.
Jurassic
Geologic period that occurred roughly 144 to 208 million years ago. During this period, the first birds and mammals appear and large areas of the continents are covered by shallow seas.
Kame
A steep conical hill composed of glaciofluvial sediments. This feature develops when glacial crevasses and depressions in stagnant glacial ice are filled with sand and gravel deposits from sediment loaded meltwater.
Kame Terrace
A long flat ridge composed of glaciofluvial sediment. This feature forms along the margin of a valley glacier where the glacial ice meets the valley's slope. Sediment is deposited by laterally flowing meltwater streams.
Kaolinite
A type of clay that is widespread in tropical and subtropical regions. It is produced from the weathering of granite.
Karst
Landform type with limestone bedrock and dominated by geomorphic features created from solution chemical weathering.
Katabatic Wind
Any wind blowing down the slope of a mountain.
Kettle Hole
Depression found in glacial deposits. Created when a piece of ice from a retreating glacier becomes embedded in soft glacial till or glacial drift deposits. Many are filled with water to form a small lake or pond.
Kettle Moraine
An area of glaciofluvial influenced moraine deposits pitted with kames and kettle holes.
Köppen Climate Classification
System that uses monthly precipitation and temperature data and total annual precipitation data to classify a location's climate into one of five main categories: Tropical Moist Climates; Dry Climates; Moist Mid-latitude Climates with Mild Winters; Moist Mid-Latitude Climates with Cold Winters; and Polar Climates. These categories are further divided into number of subcategories. First developed in 1918 by German biologist W. Köppen, this system has undergone a number of modifications.
Lahar
A very rapid type of downslope mass movement that involving mudflows from volcanic ash.
Landfall
The coastline location where a tropical storm or hurricane moves from ocean onto land.
Landslide
Term used to describe the downslope movement of soil, rock, and other weathered materials because of gravity.
La Nina
Condition opposite of an El Nino. In a La Nina, the tropical Pacific trade winds become very strong and an abnormal accumulation of cold water occurs in the central and eastern Pacific Ocean.
Laminar Flow
Movement of water within a stream that occurs as uninterrupted parallel flows. Laminar flow generally occurs in areas where friction is low.
Latent Heat
Is the energy required to change a substance to a higher state of matter (solid > liquid > gas). This same energy is released from the substance when the change of state is reversed (gas > liquid > solid).
Lateral Moraine
Moraine that is found along the sides of a glacier. Commonly found on glaciers that occupy a valley.
Laurasia
Northern section of Pangaea.
Lava
Molten magma released from a volcanic vent or fissure.
Leaf Drip
The rain water that fall to the ground surface from plant leaves after it has been intercepted by these structures.
Lee
Side of a slope that is opposite to the direction of flow of ice, wind, or water. Opposite of stoss.
Levee
Ridge of coarse deposits found alongside the stream channels and elevated above the floodplain. Forms from the deposition of sediment during floods.
Limestone
Sedimentary rock composed of carbonate minerals, especially calcium carbonate. Limestone can be created by clastic and non-clastic processes. Clastic limestones are formed from the break up and deposition of shells, coral and other marine organisms by wave-action and ocean currents. Non-clastic limestones can be formed either as a precipitate or by the lithification of coral reefs, marine organism shells, or marine organism skeletons.
Liquefaction
Temporary transformation of a soil mass of soil or sediment into a fluid mass. Occurs when the cohesion of particles in the soil or sediment is lost. Often triggered by seismic waves from an earthquake. For this condition to take place the pore spaces between soil particles must be at or near saturation.
Lithification
Process by which sediments are consolidated into sedimentary rock.
Loam
A soil that contains a roughly equal mixture of clay, sand, and silt. Good for growing most crops.
Loess
Deposits of silt laid down by aeolian processes over extensive areas of the mid-latitudes during glacial and postglacial times.
Longshore Transport
The transport of sediment in water parallel to a shoreline.
Long Wave
A large wave in the polar jet stream and the westerlies that extends from the middle to the upper troposphere. Often associated with the formation of a mid-latitude cyclone at the ground surface. Contrasts with short waves. Also called Rossby waves.
Low Pressure
An area of atmospheric pressure within the Earth's atmosphere that is below average. If this system is on the Earth's surface and contains circular wind flow and enclosed isobars it is called a cyclone.
Lower Mantle
Layer of the Earth's interior extending from 670 to 2,900 kilometers below the surface crust. Composed of ultramafic rock. This layer is hot and plastic and part of the mantle layer.
Lysimeter
Meteorological instrument used to measure potential and actual evapotranspiration.
Mafic Magma
Magma that is relative poor in silica but rich in calcium, magnesium, and iron content. This type of magma solidifies to form rocks relatively rich in calcium, magnesium, and iron but poor in silica.
Magma
Molten rock originating from the Earth's interior.
Magma Plume
A rising vertical mass of magma originating from the mantle.
Magnetic Field
The space influence by magnetic force. The Earth's magnetic field is believed to be generated by the planet's core.
Magnetic Reversal
A change in the polarity of the Earth's magnetic field. In the past 4 million years there have been nine reversals.
Magnetosphere
Zone that surrounds the Earth that is influenced by the Earth's magnetic field.
Mantle
Layer of the Earth's interior composed of mostly solid rock that extends from the base of crust to a depth of about 2,900 kilometers.
Marble
Metamorphic rock created by the recrystallization of calcite and/or dolomite.
Maritime Effect
The effect that large ocean bodies have on the climate of locations or regions. This effect results in a lower range in surface air temperature at both daily and annual scales. Also see Continental Effect.
Maritime Polar Air Mass (mP)
Air mass that forms over extensive ocean areas of the middle to high latitudes. Around North America, these air mass system form over the Atlantic and Pacific oceans at the middle latitudes. Maritime Polar air masses are mild and humid in summer and cool and humid in winter. In the Northern Hemisphere, maritime polar air masses are normally unstable during the winter. In the summer, atmospheric stability depends on the position of the air mass relative to a continent. Around North America, Maritime Polar air masses found over the Atlantic are stable in summer, while Pacific systems tend to be unstable.
Maritime Tropical Air Mass (mT)
Air mass that forms over extensive ocean areas of the low latitudes. Around North America, these system form over the Gulf of Mexico and the eastern tropical Pacific. Maritime Tropical air masses are warm and humid in both winter and summer. In the Northern Hemisphere, maritime tropical air masses can normally stable during the whole year if they have form just west of a continent. If they form just east of a continent, these air masses will be unstable in both winter and summer.
Meander
Sinuous shaped stream channel. Usually found in streams flowing over a very shallow elevation grade.
Medial Moraine
Deposit of material found down the center of a glacier. Created when two glacier and their lateral moraines merge.
Meltwater
Water produced from the melting of snow and/or glacial ice.
Mesa
A flat topped hill that rises sharply above the surrounding landscape. The top of this hill is usually capped by a rock formation that is more resistant to weathering and erosion.
Mesocyclone
A cylinder of cyclonically flowing air that form vertically in a severe thunderstorm. They measure about 3 to 10 kilometers across. About 50% of them spawn tornadoes.
Mesosphere
Atmospheric layer found between the stratosphere and the thermosphere. Usually located at an average altitude of 50 to 80 kilometers above the Earth's surface. Air temperature within the mesosphere decreases with increasing altitude.
Mesozoic
Geologic era that occurred from 245 to 65 million years ago.
Metamorphic Rock
A rock that forms from the recrystallization of igneous, sedimentary or other metamorphic rocks through pressure increase, temperature rise, or chemical alteration.
Mid-Latitude Cyclone
Cyclonic storm that forms primarily in the middle latitudes. Its formation is triggered by the development of troughs in the polar jet stream. These storms also contain warm, cold and occluded fronts. Atmospheric pressure in their center can get as low as 970 millibars. Also called wave cyclones or frontal cyclones.
Mid-Oceanic Ridge
Chain of submarine mountains where oceanic crust is created from rising magma plumes and volcanic activity. Also associated with this feature is plate divergence which creates a rift zone.
Milky Way Galaxy
Aggregation of about 400 billion stars in a flattened, disk-shaped structure in space. Our solar system is found in this structure.
Mineral
Component of rocks. A naturally occurring inorganic solid with a crystalline structure and a specific chemical composition.
Mississippian
Geologic period that occurred roughly 320 to 360 million years ago. During this period, insects undergo major speciation and ferns first appear. Trees become a dominant plant form on continents.
Mixing Ratio
The ratio between the weight (mass) of water vapor (or some other gas) held in the atmosphere compared to the weight of the dry air in a given volume of air. Usually measured in grams water vapor (or gas) per kilogram of dry air.
Moho Discontinuity
The lower boundary of the crust. At this boundary seismic wave velocities show an increase in speed as they enter the upper mantle.
Monocline
A fold in layered rock that creates a slight bend.
Monsoon
A regional scale wind system that predictably change direction with the passing of the seasons. Monsoon winds blow from land to sea in the winter, and from sea to land in the summer. Summer monsoons are often accompanied with precipitation.
Moraine
A hill of glacial till deposited directly by a glacier.
Mountain Breeze
Local thermal circulation pattern found in areas of topographic relief. In this circulation system, surface winds blow from areas of higher elevation to valley bottoms during the night.
Mouth
End of a stream. Point at which a stream enters a lake, sea, or ocean.
Mudflow
Form of mass movement where fine textured sediments and soil mix with water to create a liquid flow.
Mudstone
Fine grained sedimentary rock composed of lithified silt and clay particles.
Muskeg
Poorly drained marshes or swamps found overlying permafrost.
Needle Ice
A form of periglacial ground ice that consists of groups ice slivers at or immediately below the ground surface. Needle ice is about a few centimeters long.
Neutral Atmosphere
Condition in the atmosphere where isolated air parcels do not have a tendency to rise or sink. The parcels of air tend to be same temperature as the air that surrounds them.
Névé
Partially melted and compacted snow that has a density of at least 500 kilograms per cubic meter.
Nickpoint
Point on the long profile of a stream where the gradient is broken sudden drop in elevation. Nickpoints are the locations of rapids and waterfalls.
Nimbostratus Clouds
Dark, gray low altitude cloud that produces continuous precipitation in the form of rain or snow. Found in an altitude range from the surface to 3,000 meters.
Nivation
Process where snow patches initiate erosion through physical weathering, meltwater flow, and gelifluction.
Noctilucent Clouds
High altitude clouds composed of ice crystals that appear to glow silver or bright blue shortly after sunset.
Non-Clastic Sedimentary Rock
Sedimentary rocks that are created either from chemical precipitation and crystallization, or by the lithification once living organic matter.
Normal Fault
Vertical fault where one slab of the rock is displaced up and the other slab down. It is created by tensional forces acting in opposite directions.
Normal Lapse Rate
Average rate of air temperature change with altitude in the troposphere. This value is approximately a decrease of 6.5° Celsius per 1000 meters rise in elevation.
Nuee Ardente
A glowing cloud of dense hot volcanic gas and ash that moves downslope at high speeds, incinerating the landscape.
Obsidian
Glassy dark colored volcanic rock. Usually composed of rhyolite.
Occluded Front
A transition zone in the atmosphere where an advancing cold air mass sandwiches a warm air mass between another cold air mass pushing the warm air into the upper atmosphere.
Ocean Current
Large scale horizontal flow of ocean water that is persistent and driven by atmospheric circulation.
Oceanic Crust
Basaltic portion of the Earth's crust that makes up the ocean basins. Approximately 5 to 10 kilometers thick
Oceanic Plate
A rigid, independent segment of the lithosphere composed of mainly basalt that floats on the viscous plastic asthenosphere and moves over the surface of the Earth. The Earth's oceanic plates are an average 75 kilometers thick and were formed less than several hundred million years ago at one of the Earth's mid-oceanic ridges.
Ocean Trench
Deep depression found at the edge of the ocean floor. Represents area of tectonic plate subduction.
Oligotrophic Lake
Lake with a low supply of nutrients in its waters. Also see eutrophic lake and mesotrophic lake.
Olivine
Common silicate mineral found in rocks formed from mafic magma. Its chemical composition varies between Mg2SiO4 and Fe2SiO4.
Open Talik
Is a form of localized unfrozen ground (talik) in an area of permafrost. It is open to the ground surface but enclosed to permafrost below and at its sides.
Orogenesis
The process of mountain building through tectonic forces of compression and volcanism.
Orogenic Belt
A major range of mountains on the continents.
Orographic Uplift
Uplift of an air mass because of a topographic obstruction. Uplift also causes the cooling of the air mass. If enough cooling occurs condensation can occur and form into orographic precipitation.
Orographic Precipitation
Is precipitation that forms when air is forced to rise because of the physical presence of elevated land. As the parcel rises it cools as a result of adiabatic expansion at a rate of approximately 10° Celsius per 1,000 meters until saturation. The large amounts of precipitation along the west coast of Canada are due mainly to this process.
Outer Core
Outer region of the Earth's core. It is believed to be liquid nickel and iron and has a density of about 11 grams per cubic centimeter. It surrounds the inner core and has an average thickness of about 2,250 kilometers.
Outgassing
The release of gas from cooling molten rock or the interior of the Earth. Much of the atmosphere's gaseous constituents, like water vapor, nitrogen, and argon, came from outgassing.
Outwash
Glaciofluvial sediments deposited by meltwater streams at the edge of a glacier.
Outwash Plain
A flat or gentle sloping surface of glaciofluvial sediments deposited by meltwater streams at the edge of a glacier. Usually found in close spatial association with moraines.
Overbank Flow
Movement of flood waters outside a stream channel during period of high discharge.
Overland Flow
The topographic movement of a thin film of water from precipitation to lower elevations. With time, this water will begin to organizing its flow into small channels called rills. The rills converge to form progressively larger channels until stream channels are formed. Occurs when the infiltration capacity of an area's soil has been exceeded. Also called sheet flow or runoff.
Oxbow Lake
Is portion of abandoned stream channel filled with stagnant water and cut off from the rest of the stream. Oxbow lakes are created when meanders are cut off from the rest of the channel because of lateral stream erosion.
Ozone
Tri-atomic oxygen that exists in the Earth's atmosphere as a gas.
Pacific High
High pressure system that develops over the central Pacific Ocean near the Hawaiian Islands. Also called the Hawaiian High.
Paleozoic
Geologic era that occurred from 570 to 245 million years ago.
Pan
(2) Compact soil horizon that has a high clay content.
(3) Large natural basin or depression found in desert climates.
Pangaea
Hypothetical super continent that existed in the geological past. Its break-up created the current configuration of landmasses found on the Earth.
Paternoster Lakes
A linear series of mountain valley lakes that are formed from glacial erosion. They form behind glacial moraines or in glacially carved out rock basins. The name of this feature is related to the series of lakes looking like a string of beads.
Patterned Ground
Term used to describe a number of surface features found in periglacial environments. These features can resemble circles, polygons, nets, steps, and stripes. The development of some of these shapes is thought to be the result of freeze-thaw action.
Peak Annual Flow
The largest discharge produced by a stream during a one year period.
Pediment
A gradually sloping bedrock surface located at the base of fluvial-eroded mountain range. Found in arid locations and normally covered by fluvial deposits.
Pediplain
An arid landscape of little relief that is occasionally interrupted by the presence of scattered inselbergs. Formed by the coalescence of several pediments.
Perched Water Table
Water table that is positioned above the normal water table for an area because of the presence of a impermeable rock layer.
Percolation
Vertical movement or infiltration of water from the Earth's surface to its subsurface. Movement usually stops when the flowing water reaches the water table.
Peridotite
Coarse grained ultramafic igneous rock composed mainly of olivine and pyroxene. The mantle is though to be composed primarily of this rock type.
Periglacial
Landforms created by processes associated with intense freeze-thaw action in an area high latitude areas or near an alpine or continental glacier.
Perihelion
It is the point in the Earth's orbit when it is closest to the Sun (147.5 million km). Perihelion occurs on the 3rd or 4th of January.
Period
Geologic time unit that is shorter than an era but longer than a epoch.
Permafrost
Zone of permanently frozen water found in high latitude soils and sediments.
Permeability
A measure of the ability of soil, sediments, and rock to transport water horizontally and vertically. Permeability is dependent on the porosity of the medium the water is flowing through. Some rocks like granite have very poor permeability, while rocks like shale are actually quite pervious. As for soils, sand is the most pervious, while clay has the lowest permeability
Phanerozoic
Geologic eon that occurs from 2500 million years ago to today. During this time period, life becomes more diversified and complex.
Physical Weathering
Breakdown of rock and minerals into small sized particles through mechanical stress.
Piedmont Glacier
A large glacier formed from the merger of several alpine glaciers.
Pingo
A large conical mound that contains an ice core. This feature can be up to 60 to 70 meters in height. Form in regions of permafrost. Common in the Mackenzie Delta region of Canada. Also see the related palsa.
Pitted Topography
Landscape characterized by numerous kettle holes on a glacial outwash plain.
Plane of the Ecliptic
Hypothetical two-dimensional surface in which the Earth's orbit around the Sun occurs.
Plateau Basalt
An accumulation of horizontal flows of basaltic lava.
Plate Tectonics
Theory suggesting that the Earth's surface is composed of a number of oceanic and continental plates. Driven by convection currents in the mantle, these plates have the ability to slowly move across the Earth's plastic asthenosphere. This theory is very important to geology and geomorphology because it helps to explain the occurrence and formation of mountains, folds, faults, volcanoes, earthquakes, ocean trenches, and the mid-oceanic ridges.
Platform
Horizontal sedimentary deposits found on top of continental shield deposits.
Pleistocene Epoch (Ice Age)
Period of time from about 2 million years ago to 10,000 years ago. During this period areas of land at higher and middle latitudes where covered with glacial ice.
Plucking
Erosive process of particle detachment by moving glacial ice. In this process, basal ice freezes in rock surface cracks. As the main body of the glacial ice moves material around the ice in the cracks is pulled and plucked out. Also called quarrying.
Pluton
Any mass of intrusive igneous rock.
Point Bar
Stream bar deposit that is normally located on the inside of a channel bend.
Polar Cell
Three-dimensional atmospheric circulation cell located at roughly 60 to 90° North and South of the equator. Vertical air flow in the Polar cell consists of rising air at the polar font and descending air at the polar vortex.
Polar Front
Weather front located typically in the mid-latitudes that separates arctic and polar air masses from tropical air masses. Along the polar front we get the development of the mid-latitude cyclone. Above the polar front exists the polar jet stream.
Polar High
Surface area of atmospheric high pressure located at about 90° North and South latitude. These high pressure systems produced by vertically descending air currents from the polar vortex.
Polar Jet Stream
Relatively fast uniform winds concentrated within the upper atmosphere in a narrow band. The polar jet stream exists in the mid-latitudes at an altitude of approximately 10 kilometers. This jet stream flows from west to east at speeds between 110 to 185 kilometers per hour. Also see jet stream and subtropical jet stream.
Polar Stratospheric Clouds
High altitude clouds found in the stratosphere where the temperature is less than -85° Celsius. Commonly found over Antarctica. Have a role in the creation of the ozone hole over Antarctica.
Pore Ice
A form of periglacial ground ice that is found in the spaces that exist between particles of soil.
Porosity
The void spaces found in rock, sediment, or soil. Commonly measured as the percentage of void space in a volume of substance.
Potential Evapotranspiration
Is a measure of the ability of the atmosphere to remove water from the surface through the processes of evaporation and transpiration assuming no limitation on water supply.
Precambrian
Span of geologic time that dates from 4.6 billion to 570 million years ago. Made up of three geologic eras: Hadean, Archean, and Proterozoic.
Precession of the Equinox
Wobble in the Earth's polar axis. This motion influences the timing aphelion and perihelion over a cyclical period of 23,000 years.
Precipitation
(1) Is any aqueous deposit, in liquid or solid form, that develops in a saturated atmosphere (relative humidity equals 100%) and falls to the ground generally from clouds. Most clouds, however, do not produce precipitation. In many clouds, water droplets and ice crystals are too small to overcome natural updrafts found in the atmosphere. As a result, the tiny water droplets and ice crystals remain suspended in the atmosphere as clouds.
(2) The state of being precipitated from a solution.
Pressure Gradient Force
Force due to spatial differences in atmospheric pressure. Usually expressed in millibars or kilopascals per unit distance (meters or kilometers). This force is primarily responsible for the formation of wind.
Pressure Melting Point
Temperature at which minerals deep within the Earth and ice below the surface of a glacier are caused to melt because of the introduction of pressure.
Proterozoic
Geologic eon that occurred from 570 to 2500 million years ago. During this time period, the first single-celled and multi-celled eukaryotic organisms evolved and developed.
Psychrometer
Instrument used to measure atmospheric humidity. It consists of two thermometers (wet-bulb and a dry-bulb) one of which has its bulb covered by a moistened wick. Humidity is determined by the difference in readings between the two thermometers after air has passed over both of them for a specific time period.
P-Wave
A seismic wave that moves material in push-pull fashion in the direction of its travel. This type of seismic wave can travel through solids, liquids, and gases. Also called a primary wave.
Pyroclastic Material
Pieces of volcanic rock thrown out in a volcanic explosion.
Quartz
Mineral with the chemical formula SiO2. Quartz is common in continental crust but rare in oceanic crust.
Quartzite
Metamorphic rock rich in quartz created by the recrystallization of sandstone.
Quaternary
Geologic period that occurred roughly 1.6 million years ago to today. During much of this period continental glaciers in the Northern Hemisphere covered large regions of land surface in the high and mid-latitudes. Homo sapiens appear about 200,000 years BP (before present) and become the first species to alter the Earth's environment on a large-scale.
Radiation Fog
A type of fog that is also called ground fog. Radiation fog is generated by near surface cooling by radiation loss during the evening hours. For the fog to develop, the overnight cooling must cause saturation occur. This type of fog is normally quite shallow.
Rainshadow Effect
Reduction of precipitation commonly found on the leeward side of a mountain. The reduction in precipitation is the result of compression warming of descending air.
Recessional Moraine
Moraine that is created during a pause in the retreat of a glacier. Also called a stadial moraine.
Recharge Area
The area on the Earth's surface that receives water for storage into a particular aquifer.
Recurrence Interval
The average time period that separates natural events of a specific magnitude. For example, floods of a specific stream discharge level.
Reflection (Atmospheric
Process where insolation is redirect by 180° after striking a particle. This redirection causes 100% loss. Most of the reflection in the Earth's atmosphere occurs in clouds because of light's interception with particles of liquid and frozen water. The reflectivity of a cloud can range from 40-90%.
Regolith
Loose layer of rocky material overlying bedrock.
Relative Humidity
The ratio between the actual amount of water vapor held in the atmosphere compared to the amount required for saturation. Relative humidity is influenced by temperature and atmospheric pressure.
Reverse Fault
This vertical fault develops when compressional force causes the displacement of one block of rock over another.
Rhyolite
A fine grained extrusive igneous rock that is rich in quartz and potassium feldspar. Derived from felsic magma.
Ribbon Falls
Spectacular narrow waterfalls that occur at the edge of a hanging valley.
Richter Scale
A logarithmic measurement scale of earthquake magnitude. This scale measures the energy released by the largest seismic wave associated with the earthquake.
Rift
Zone between two diverging tectonic plates. The mid-oceanic ridge is an area where such plate divergence is occurring.
Rill
A very small steep sided channel carrying water. This landscape feature is intermittent and forms for only a short period of time after a rainfall.
Rime
Deposit of ice crystals that occurs when fog or super cooled water droplets comes in contact with an object with a temperature below freezing (0° Celsius). This deposit develops outward on the windward side of the object.
Roche Moutonnee
A feature of glacial erosion that resembles an asymmetrical rock mound. It is smooth and gently sloping on the side of ice advance. The lee-side of this feature is steep and jagged.
Rock Cycle
General model describing the geomorphic and geologic processes involved in the creation, modification and recycling of rocks.
Rockfall
Type of mass movement that involves the detachment and movement of a small block of rock from a cliff face to its base. Normally occurs when the rock has well defined bedding planes that are exaggerated by freeze-thaw action or thermal expansion and contraction.
Rock Slide
Large scale mass movement of rock materials downslope.
Roll Cloud
A dense, cigar shaped cloud found above the gust front of a thunderstorm. Air within the cloud rotates around the long axis.
Runoff
The topographic flow of water from precipitation to stream channels located at lower elevations. Occurs when the infiltration capacity of an area's soil has been exceeded. It also refers to the water leaving an area of drainage. Also called overland flow.
Ultramafic
Rock that is rich in magnesium and iron content.
Unconfined Aquifer
Aquifer that is not restricted by impervious layers of rock.
Unconfined Groundwater
Groundwater that is not restricted by impervious layers of rock.
Undercut Bank
Steep bank found on the inside of stream meanders. Formed by the erosion that occurs when a stream channel moves horizontally.
Uniformitarianism
Is a theory that rejects the idea that catastrophic forces were responsible for the current conditions on the Earth. The theory suggested instead, that continuing uniformity of existing processes were responsible for the present and past conditions of this planet.
Universe
All of the observable phenomena in the celestial cosmos.
Unloading
The releasing of downward pressure on rocks because of removal of overlying material by erosion.
Unstable Atmosphere
Condition in the atmosphere where isolated air parcels have a tendency to rise. The parcels of air tend to be warmer than the air that surrounds them.
Upper Mantle
Layer of the Earth's interior extending from the base of the crust to 670 kilometers below the surface. Part of the Earth's mantle layer. The upper mantle is composed of peridotite, an ultramafic magma primarily made up of the minerals olivine and pyroxene. The top layer of the upper mantle, 100-350 km below surface, is called the asthenosphere.
Upslope Fog
Fog produced by air flowing over topographic barriers. As the air is forced to rise, it is cooled by adiabatic expansion. Upslope fog is most common on the windward slopes of hills or mountains.
Valley
A linear depression in the landscape that slopes down to a stream, lake or the ocean. Formed by water and/or ice erosion.
Vapor Pressure
Pressure exerted by water vapor molecules in a given quantity of atmosphere.
Varve
A thin yearly deposit of sediment found on the bottom of a lake. Within each yearly varve, there are variations in the color and the texture of the material deposited. The thickness of the varve and its associated layers can be used to reconstruct past environmental conditions influencing the lake.
Ventifact
A loose piece of rock that has been polished smooth by wind transported particles. Common in arid environments.
Volcanic Ash
Small sized particles ejected from explosive volcanoes.
Volcanic Pipe
A dyke reaches the surface of the Earth. Also called volcanic neck
Volcanic Vent
An opening on a volcano through which lava is released and rock fragments and ash are ejected.
Volcano
An elevated area of land created from the release of lava and ejection of ash and rock fragments from and volcanic vent.
Warm Front
A transition zone in the atmosphere where an advancing warm air mass displaces a cold air mass.
Wash
(1) Coarse alluvial sediments.
(2) The downslope movement of small particles of soil by overland flow. Also called sheetwash.
(3) A term used in the United States for a shallow intermittent stream channel found in arid and semi-arid regions.
Water Consumption
The complete removal of water from some type of source, like groundwater, for some use by humans. This water is not returned to the source. Compare with water withdrawal.
Waterfall
(1) A location in the long profile of a stream where water flows vertically. A nickpoint.
(2) Verical drop in elevation that causes a stream's dischange to flow vertically.
Watershed
Catchment area of a drainage basin.
Waterspout
A vortex of rapidly moving air over water that is associated with some thunderstorms.
Water Table
Top surface of groundwater.
Weather
The state of the atmosphere at a specific time and place.
Weathering
Physical, chemical or biological breakdown of rocks and minerals into smaller sized particles.
Westerlies
Dominant winds of the mid-latitudes. These winds move from the subtropical highs to the subpolar lows from west to east.
Wet Deposition
The transport of gases and minute liquid and solid particles from the atmosphere to the ground surface with the aid of precipitation or fog.
Wetland
Natural land-use type that is covered by salt water or fresh water for some time period. This land type can be identified by the presence of particular plant species or characteristic conditions.
Wien's Law
This radiation law suggests that the wavelength of maximum emission of any body is inversely proportional to its absolute temperature. The following equation mathematically describes this law:
lmax = C/T
where lmax is the body's maximum emitted wavelength of radiation in micrometers (µm),
C is a constant equal to 0.2897,
and T is the temperature of the body in Kelvins.
Wilting Point
The point at which the rate of water leaving a plant's leaves is greater than the water uptake by the roots. At this point the plant will fail to recover its turgidity.
Wind Ripples
Wind ripples are miniature sand dunes between 5 centimeters and 2 meters in length and 0.1 to 5 centimeters in height. They are created by saltation when the sand grains are of similar size and the wind has a constant speed. Also called sand ripples.
Windward
Upwind side or side directly influenced to the direction that the wind blows from.
Yazoo Tributary
Small tributary channel that is prevented from joining the main stream channel by the presence of levees. Yazoo tributaries tend to flow on the floodplain parallel to the main stream channel
Zonal
Movement of wind or ocean waters in a direction that is roughly parallel to the lines of latitude.
Zone of Accumulation
Area of a glacier where additions of snow exceed losses of ice from melting, evaporation, and sublimation.
Zone of Ablation
Area of a glacier where losses of ice from melting, evaporation, and sublimation exceed additions of snow annually.
Zone of Aeration
Horizontal zone that extends from the top of the water table to the ground surface. Soil and rock pore spaces in this zone may and may not have water.
Zone of Saturation
Groundwater zone within the Earth's bedrock where all available pores spaces are filled by water. Found beneath the water table.
Salinization
Pedogenic process that concentrates salts at or near the soil surface because evapotranspiration greatly exceeds water inputs from precipitation.
Saltation
Transport of sediment initiated by moving air or water where particles move from a resting surface to the transport medium in quick continuous repeated cycles.
Saltwater Intrusion
The invasion of saltwater into freshwater aquifers in coastal and inland areas. This condition can be cause when groundwater, which charges the aquifer, is withdrawn faster than it is recharged by precipitation.
Sand Dune
A hill or ridge of aeolian sand deposits with a minimum height of less than one meter and a maximum height of about 50 meters. Found in hot deserts and along sandy coastlines.
Sandstone
A type of sedimentary rock that contains a large quantity of weathered quartz grains.
Sand Wedge
A form of ice wedge that contains accumulations of wind blown sand in long vertical layers. A form of periglacial ground ice.
Saturated Adiabatic Lapse Rate (SALR)
The rate of decline in the temperature of a rising parcel of air after it has reached saturation. This rate is less than the dry adiabatic lapse rate (9.8° Celsius per 1000 meters) because of the heat energy added to the ascending air parcel from condensation and deposition processes.
Saturation Mixing Ratio
Mass of water vapor that a kilogram of dry air can hold at saturation. Measured in grams.
Schist
A medium to coarse grained metamorphic rock with well developed bedding planes derived from the foliated recrystrallization of platy like minerals like mica.
Scour
(1) Refers to the erosive power of water.
(2) Abrasive effects of rocks and sediments incorporated in the ice base of a glacier.
Sea-Floor Spreading
The process of oceanic crust creation and sea-floor movement that occurs at the mid-oceanic ridge.
Seamount
A volcanic mountain found on an ocean basin that has an origin not related to a mid-oceanic ridge or a tectonic subduction zone.
Sediment
Solid material that has been or is being eroded, transported, and deposited. Transport can be due to fluvial, marine, glacial or aeolian agents.
Sedimentary Rock
Rocks formed by the deposition, alteration and/or compression, and lithification of weathered rock debris, chemical precipitates, or organic sediments. Also see clastic vs non-clastic sedimentary rocks.
Seepage
(1) The gradual movement of water into the soil layer.
(2) Slow movement of sub-surface water to the surface. This flow is not great enough to call it a spring.
Segregated Ice
A form of periglacial ground ice that consists of almost pure ice that often exists as an extensive horizontal layer. The ice layer grows because of the active migration of water from around the feature. These features are found just below the active layer.
Seif
(1) A large sand dune that is elongated in the general direction of the dominant winds.
(2) A sand dune formed by winds from multiple directions.
Seismic
Shaking displacement usually caused by an earthquake.
Shale
Fine grained sedimentary rock composed of lithified clay particles.
Shear Stress
Stress caused by forces operating parallel to each other but in opposite directions.
Shear Wave
A seismic wave that creates wave-like motion perpendicular to the direction of seismic energy propagation. Also called S-wave.
Sheeting
A form of physical weathering of rock where surface sheets of material fracture and exfoliate because of pressure release. Also see exfoliation dome.
Sheetwash
The removal of loose surface materials by overland flow. Process of erosion.
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.
Shield Volcano
Volcano created from alternate layers of lava flows. Shield volcanoes are slightly sloping having a gradient between 6 and 12°. Their height can be as high as 9000 meters. The chemistry of the magma of these volcanoes is basaltic.
Short Wave
A small wave in the polar jet stream and the westerlies that extends from the middle to the upper troposphere. Often associated with the formation of a mid-latitude cyclone at the ground surface. Contrasts with long waves.
Sial Layer
The part of the crust that forms the continents and is composed of relatively light, granitic rocks.
Siberian High
High pressure system that develops in winter over northern central Asia.
Silicate Magma
Magma that is felsic in composition.
Sill
Horizontal planes of igneous rock that run parallel to the grain of the original rock deposits.They form when magma enters and cools in bedding planes found within the crust. Also see intrusive igneous rock.
Siltstone
Fine grained sedimentary rock composed of lithified silt particles.
Sima Layer
The part of the crust that forms the ocean basins and lower layers in the crust and is composed of relatively heavy, basaltic rocks.
Sinkhole
A pit like hole in found in areas of karst. These features are caused by the weathering of limestone or dolomite by subsurface drainage. Also called a sink or doline.
Slate
A fine grained metamorphic rock with well developed bedding planes derived from the slight recrystrallization of shale.
Snout
Front end of a glacier. Also called the terminus.
Snow
A type of solid precipitation that forms in clouds with an air temperature below freezing. Snow forms when water vapor deposits directly as a solid on a deposition nuclei. Snowflakes begin their life as very tiny crystals developing on a six-sided hexagonal deposition nuclei. The developing snowflak, then grows fastest at the six points of the nuclei as these surfaces are more exposed to atmosphere's water vapor. Snowfall is most common with the frontal lifting associated with mid-latitude cyclones during fall, winter, and spring months when air temperatures are below freezing.
Snow Line
Altitudinal or latitudinal limit separating zones where snow does not melt during the summer season from areas in which it does. Similar to the concept of firm limit except that it is not limited to glaciers.
Snowfield
An area of permanent snow accumulation. Usually at high altitudes or latitudes.
Snow Pellets
A form of precipitation also known as graupel. Snow pellets are white, spherical bits of ice with a maximum diameter of 5 millimeters. Snow pellets develop when supercooled droplets freeze on snowflakes. Snow pellets often fall for a brief time period when precipitation transforms from ice pellets to snow. Snow pellets can be easily distinguished from packed snowflakes as they tend to bounce when they strike the ground. Packed snowflakes are not dense enough to cause them to bounce.
Soil
Layer of unconsolidated material found at the Earth's surface that has been influenced by the soil forming factors: climate, relief, parent material, time, and organisms. Soil normally consists of weathered mineral particles, dead and living organic matter, air space, and the soil solution.
Soil Moisture Recharge
The process of water filling the pore space found in a soil (storage).
Solifluction
Form of mass movement in environments that experience freeze-thaw action. It is characterized by the slow movement of soil material downslope and the formation of lobe-shaped features. Also see gelifluction.
Southern Oscillation
Reversal of atmospheric circulation in tropical Pacific Ocean that triggers the development of an El Nino.
Spheroidal Weathering
A type of below ground chemical weathering where the corners of jointed rocks become rounded over time. Rock changes from a rectangular to more round shape.
Sporadic Permafrost
Form of permafrost that exists as small islands of frozen ground in otherwise unfrozen soil and sediments.
Squall Line
A band of thunderstorm development found ahead of a cold front.
Stable Atmosphere
Condition in the atmosphere where isolated air parcels have a tendency to sink. The parcels of air tend to be cooler than the air that surrounds them.
Star
A large and very massive, self-luminous celestial body of gas that illuminates via the radiation derived from its internal source of energy.
Stationary Front
A transition zone in the atmosphere where there is little movement of opposing air masses and winds blow towards the front from opposite directions.
Stephan-Boltzmann Law
This radiation law suggests the amount of radiation given off by a body is proportional to the 4th power of its temperature as measured in Kelvin units. This law can be expressed by the following simple equation:
E* = sT 4
where E* is the amount of radiation emitted by the body in Watts per square meter,
s is a constant equal to 0.0000000567,
and T is the temperature of the body in Kelvins.
Stoma (pl. Stomata)
Small opening on the surface of a plant that is used for gas exchange.
Stoss
Side of a slope that faces the direction of flow of ice, wind, or water. Opposite of lee.
Stratified Drift
A type of glacial drift that has been partially sorted by glaciofluvial meltwater.
Strata
The layers or beds found in sedimentary rock.
Stratocumulus Clouds
Low altitude gray colored cloud composed of water droplets that has a patchy appearance. Each cloud patch consists of a rounded mass. This cloud has a somewhat uniform base and normally covers the entire sky. Between the patches blue sky can be seen. Found in an altitude range from the surface to 3,000 meters.
Stratosphere
Atmospheric layer found at an average altitude of 11 to 50 kilometers above the Earth's surface. Within the stratosphere exists the ozone layer. Ozone's absorption of ultraviolet sunlight causes air temperature within the stratosphere to increase with altitude.
Stratus Clouds
Low altitude gray colored cloud composed of water droplets. This cloud has a uniform base and normally covers the entire sky. It is also quite thick and can obscure the Sun. Light precipitation is often found falling from it. Found in an altitude range from the surface to 3,000 meters.
Stream
A long narrow channel of water that flows as a function of gravity and elevation across the Earth's surface. Many streams empty into lakes, seas or oceans.
Stream Discharge
A river or stream's rate of flow over a particular period of time. Usually measured by a current meter and expressed in cubic meters per second. Stream discharge depends on the volume and velocity of the flow.
Stream Gradient
The change in elevation from a stream's headwaters to its mouth expressed in degrees, percentage, or as a distance ratio (rise/run).
Stream Load
Refers to the material or sediment carried by a stream. In normally consists of three components: bed load (pebbles and sand which move along the stream bed without being permanently suspend in the flowing water), suspended load (silts and clays in suspension) and dissolved load (material in solution).
Striations
Grooves of scratches found in surface rock that are the result of glacial abrasion.
Structural Landform
Is a landform created by massive Earth movements due to plate tectonics. This includes landforms with some of the following geomorphic features: fold mountains, rift valleys, and volcanoes.
Subduction (Tectonic)
Process of plate tectonics where one lithospheric plate is pushed below another into the asthenosphere.
Subduction Zone
Linear area where tectonic subduction takes place.
Sublimation
Process where ice changes into water vapor without first becoming liquid. This process requires approximately 680 calories of heat energy for each gram of water converted.
Subpolar 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. However, melting does occur in the accumulation zone in the summer. One of the three types of glaciers: cold glacier; temperate glacier; and subpolar glacier.
Subtropical High Pressure Zone
Surface zone of atmospheric high pressure located at about 30° North and South latitude. These high pressure systems produced by vertically descending air currents from the Hadley cell.
Subtropical Jet Stream
Relatively fast uniform winds concentrated within the upper atmosphere in a narrow band. The subtropical jet stream exists in the subtropics at an altitude of approximately 13 kilometers. This jet stream flows from west to east and has a speed that is somewhat slower that the polar jet stream. Also see jet stream.
Suspended Load
Portion of the stream load that is carried almost permanently suspended in flowing water.
Syncline
A fold in rock layers that forms a trough-like bend.