Glossary of Terms: R

Radarsat

Satellite program established by the Canadian Space Agency for the purpose of remotely sensing the Earth's resources. Radarsat uses an active sensing system that transmits microwaves. See the following website for more information - Radarsat.

 

Radiant Energy

Energy in the form of electromagnetic waves and photons. In some cases it refers to the radiation emitted from the Sun.

 

Radiation

The emission of energy from an object in the form of electromagnetic waves and photons.

 

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.

 

Radioactive Decay

Natural decay of the nucleus of an atom where alpha or beta particle and/or gamma rays are released at a fixed rate.

 

Radioisotope or Radioactive Isotope

A unstable isotope of an element. This material decays spontaneously and releases subatomic particles and electromagnetic energy.

 

Radiometer

General name for an instrument used to measure radiation over a specific wavelength range.

 

Rain

A form of precipitation. It is any liquid deposit that falls from clouds in the atmosphere to the ground surface. Rain normally has a diameter between than 0.5 and 5.0 millimeters.

 

Raindrop Impact

Force exerted by a falling raindrop on a rock, sediment, or soil surface.

 

Rain Gauge

Instrument that measures the rain that falls at a location over a period of time.

 

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.

 

Rainsplash

Soil erosion caused from the impact of raindrops.

 

Rainwash

The erosion of soil by overland flow. Normally occurs in concert with rainsplash.

 

Random

Process or event that occurs by chance.

 

Range

A statistical measure of the dispersion of observation values in a data set. Determined by taking the difference between the largest and the smallest observed value.

 

Rangeland

Land-use type that supplies vegetation for consumption by grazing and browsing animals. This land-use type is normally not intensively managed.

 

Reach

An expanse of a stream channel.

 

Realized Niche

Describes the part of the fundamental niche that a species actually occupies.

 

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.

 

Rectangular Coordinate System

System that measures the location of points on the Earth on a two-dimensional coordinate plane. See the Universal Transverse Mercator (UTM) Grid System.

 

Recumbent Fold

A fold in which the axial plane is almost horizontal.

 

Recurrence Interval

The average time period that separates natural events of a specific magnitude. For example, floods of a specific stream discharge level.

 

Reduction

(1) Chemical process that involves the removal of oxygen from a compound.

(2) A form of chemical weathering.

 

Reef

A ridge of rocks found in the tidal zone along a coastline. One common type of reef is the coral reef.

 

Re-Entrants

A prominent indentation in an escarpment, ridge or shoreline.

 

Reference Map

Map that shows natural and human-made objects from the geographical environment with an emphasis on location. Compare with thematic map.

 

Reflected Infrared Radiation

Form of electromagnetic radiation with a wavelength between 0.7 to 3.0 micrometers (µm).

 

Reflected Wave

A water wave that reflects off the shore or another obstacle and is redirected towards the sea or lake.

 

Reflection

Process of returning sound or light waves back to their source.

 

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%.

 

Refraction

Process where insolation is redirect to a new direction of travel after entering another medium.

 

Reg

A rocky desert landscape. See desert pavement.

 

Region

A term used in geography that describes an area of the Earth where some natural or human-made phenomena display similar traits.

 

Regional Metamorphism

Large scale metamorphic modification of existing rock through the heat and pressure of plutons created at tectonic zones of subduction.

 

Regolith

Loose layer of rocky material overlying bedrock.

 

Regosol Soil

Soil order (type) of the Canadian System of Soil Classification. This type is any young underdeveloped soil that lacks identifying soil horizons.

 

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.

 

Relief

The range of topographic elevation within a specific area.

 

Remote Sensing

The gathering of information from an object or surface without direct contact.

 

Remote Sensor

Mechanical devices used to remotely sense an object or phenomenon.

 

Representative Fraction

The expression of map scale as a mathematical ratio.

 

Reptile

Group of terrestrial vertebrate animals that includes turtles, tortoises, snakes, lizards, crocodiles, and alligators.

 

Resource

Anything obtained from the environment to meet the needs of a species.

 

Resource Partitioning

The evolutionary process of species living in the same ecosystem dividing up resources so that each species develops dissimilar resource requirements to avoid competition. Also see ecological niche, fundamental niche, and realized niche.

 

Respiration

Is the typical process where mitochondria of cells of organisms release chemical energy from sugar and other organic molecules through chemical oxidation. This process occurs in both plants and animals. In most organisms, respiration releases the energy required for all metabolic processes. This chemical reaction can be described by the following simple equation:

C ₆ H ₁₂ O ₆ + 6O ₂ >>> 6CO ₂ + 6H ₂ O + released energy

 

Retrogressive Succession

Succession where the plant community becomes simplistic and contains fewer species and less biomass over time.

 

Reverse Fault

This vertical fault develops when compressional force causes the displacement of one block of rock over another.

 

Revolution

See Earth revolution.

 

R Horizon

Soil horizon found beneath the C horizon. Consists of consolidated rock showing little sign of weathering or pedogenesis.

 

Rhumb Line

A line of constant compass direction or bearing which crosses the meridians at the same angle. A part of a great circle.

 

Rhyolite

A fine grained extrusive igneous rock that is rich in quartz and potassium feldspar. Derived from felsic magma.

 

Ria Coast

An extensively carved out coast with conspicuous headlands and deep re-entrants.

 

Ribbon Falls

Spectacular narrow waterfalls that occur at the edge of a hanging valley.

 

Ribonucleic Acid (RNA)

Form of nucleic acid. Ribonucleic acid is used by most organisms to read the genetic information found in DNA and to produce specific organic molecules used in the development and functioning of cells.

 

Richter Scale

A logarithmic measurement scale of earthquake magnitude. This scale measures the energy released by the largest seismic wave associated with the earthquake.

 

Riffle

Bar deposit found on the bed of streams. Associated with these deposits are pools.

 

Rift

Zone between two diverging tectonic plates. The mid-oceanic ridge is an area where such plate divergence is occurring.

 

Rift Valley

Steep sided valley found on the Earth's surface created by tectonic rifting.

 

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.

 

Ring of Fire

See Circum-Pacific Belt.

 

Rip Current

A strong relatively narrow current of water that flows seaward against breaking waves.

 

Ripple

Stream bed deposit found streams. Ripples are only a few centimeters in height and spacing and are found in slow moving streams with fine textured beds.

 

River

A long narrow channel of water that flows as a function of gravity and elevation across the Earth's surface. Many rivers empty into lakes, seas, or oceans.

 

Robinson Projection

Map projection system that tries to present more accurate representations of area. Distortion is mainly manifested in terms of map direction and distance.

 

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

A compact and consolidated mass of mineral matter. Three types of rock are recognized: igneous, sedimentary, and metamorphic.

 

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 Flour

Very finely ground rock fragments that form between the base of a glacier and the underlying bedrock surface.

 

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.

 

Rossby Wave

See long wave.

 

Rotation

See Earth rotation.

 

Rotational Slip

Form of mass movement where material moves suddenly along a curvilinear plane. Also called a slump.

 

r-Selected Species (Malthusian Strategy)

A species that shows the following characteristics: short life span; early reproduction; low biomass; and the potential to produce large numbers of usually small offspring in a short period of time. Also see K-selected species.

 

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.

 

 

Citation: Pidwirny, M. (2006). "Glossary of Terms: R". Fundamentals of Physical Geography, 2nd Edition. Date Viewed. http://www.physicalgeography.net/physgeoglos/r.html