Glossary Database

Select a Letter to view the associated terms.

 Glossary Term: 


 Rabies  an acute, usually fatal disease, a form of viral encephalitis, that is transmitted through the saliva of an infected animal (usually a dog, cat, skunk, or raccoon) (Morris 1992).
 Radiation  The emission of fast atomic particles or rays by the nucleus of an atom. The three major types of radiation are alpha, beta, and gamma.
 Radioactive decay  The spontaneous disintegration of the atoms of certain isotopes into new isotopes, which may or may not be stable.
 Radioactivity  The spontaneous disintegration of an atomic nucleus with the emission of energy.
 Radiocarbon  A radioactive isotope of carbon, 14C, which is formed in the atmosphere and is absorbed by living organisms.
 Radiogenic heat  Heat generated by radioactivity.
 Radiolarian  Any actinopod animal belonging to the subclass radiolaria, characterized by a silica skeleton and dwelling in a marine pelagic environment.
 Radiometric dating  Determination of the age in years of a rock or mineral by measuring the proportions of an original radioactive material and its decay product.
 Radiotelemetry  a method of tracking the movements of a specific species.
 Rain shadow desert  A desert found on the leeward side of a mountain range. It forms because moist marine air moving inland produces precipitation on the windward side of the mountain range so that air descending on the leeward side is much warmer and drier.
 Ratio  A fixed relation in degree, number, etc. between two similar things.
 Ravine  A long, deep hollow in the earth eroded by a stream.
 ray  The supporting structure in the fins which is striated and often branched.
 Rayed crater  A meteorite crater that has a system of rays extending like splash marks from the crater rim.
 Rayleigh wave (R-wave)  A type of surface wave in which the individual particles of material move in an elliptic path within a vertical plane in the direction of wave movement.
 Recessional moraine  A ridge of till deposited at the margin of a glacier during a period of temporary stability in its general recession.
 Recharge  Replenishment of a groundwater reservoir (aquifer) by the addition of water.
 Recrystallization  Reorganization of elements of the original minerals in a rock resulting from changes in temperature and pressure and from the activity of pore fluids.
 redd  A nest prepared by a female fish in the stream bed gravel, stones or sand, where she deposits her eggs. Typical for most trout and salmon.
 Reef  A solid structure built of shells and other secretions of marine organisms, particularly coral.
 Reflection  Outward scattering of radiation toward space by the atmosphere or earth's surface.
 Refraction  The deflection of a ray of light or of an energy wave (such as a seismic wave) due to its passage from one medium to another of differing density, (like a wave passing from air to water).
 Regional metamorphism  Metamorphism of large areas of crust, usually during mountain building at convergent plate margins. Contrast with contact metamorphism.
 Regolith  The blanket of soil and loose rock fragments overlying the bedrock.
 Rejuvenated stream  A stream that has had its erosive power renewed by uplift or lowering of the base level or by climatic changes.
 Relative age  The age of a rock or an event as compared with some other rock or event.
 Relative dating  Determination of the chronological order of a sequence of events in relation to one another without reference to their ages measured in years. Relative geologic dating is based primarily on superposition, faunal succession, and crosscutting relations.
 Relative time  Geologic time as determined by relative dating, that is, by placing events in chronological order without reference to their ages measured in years.
 Relief  The difference in elevation between the high and the low parts of an area.
 Reproductive Potential  the number of offspring a female of a given age can be expected to produce (Morris 1992).
 Reservation  Public land set aside in trust for the use of Native Americans.
 Reservoir  A place where water is stored for later use.
 Residence time  The length of time a water molecule remains in a given hydrologic compartment.
 Reticulate  Usually used in herpetology with reference to a color pattern, which has linear markings resembling the meshes of a net (Peters 1964).
 Reverse fault  A fault in which the hanging wall has moved upward in relation to the footwall; a high-angle thrust fault.
 Rhyolite  A fine-grained volcanic rock composed of quartz, K-feldspar, and plagioclase. It is the extrusive equivalent of a granite.
 Rhyolitic lava flow  See rhyolite.
 Richter scale  A logarithmic scale for expressing the magnitude of an earthquake in terms of the energy dissipated in it. A modified version of this scale is commonly used.
 Rift system  A system of faults resulting from extension.
 Rift valley  1. A valley of regional extent formed by block faulting in which tensional stresses tend to pull the crust apart. Synonymous with graben. 2. The down-dropped block along divergent plate margins.
 Right angle  An angle measuring 90 degrees. Two line segments that meet at right angles are said to be perpendicular.
 Rill  A very small stream.
 Rille  Elongate valleys on the Moon's surface, with steep walls and flat bottoms. Rilles can be sinuous lava channels or relatively linear fault-bounded depressions.
 Rim deposit  The material thrown out of a crater accumulates around the rim of the crater as an ejecta blanket.
 Rimrock  1. a ledge of cliff overlooking lower ground and formed by the outcropping of a horizontal layer of resistant rock on an elevated area. 2. a cliff or vertical face of an outcrop or rock in the canyon wall (Morris 1992).
 Rip current  A current formed on the surface of a body of water by the convergence of currents flowing in opposite directions. Rip currents are common along coasts where longshore currents move in opposite directions.
 Riparian  1.) Alongside a stream, river, or other body of water. 2.)a general classification of habitat along streams, ponds and lakes or any water courses.
 Ripple marks  Small waves produced on a surface of sand or mud by the drag of wind or water moving over it.
 River system  A river with all of its tributaries.
 Roche moutonnee  An abraded knob of bedrock formed by an overriding glacier. It typically is striated and has a gentle slope facing the upstream direction of ice movement.
 Rock  Aggregate of minerals that forms an appreciable part of the lithosphere.
 Rock flour  Fine-grained rock particles pulverized by glacial erosion.
 Rock glacier  A mass of poorly sorted, angular boulders cemented with interstitial ice. It moves slowly by the action of gravity.
 Rockfall  The most rapid type of mass movement, in which rocks ranging from large masses to small fragments are loosened from the face of a cliff.
 Rockslide  A landslide in which a newly detached segment of bedrock suddenly slides over an inclined surface of weakness (such as a joint or bedding plane).
 Rocky Mountain Spotted Fever  an acute, infectious, and sometimes fatal tick-borne disease caused by Rickettsia rickettsii; characterized by fever, bone and muscle pain, headache, and rash. The disease occurs only in North and South America(Morris 1992).
 Rod  a rod-shaped cell in the retina that is sensitive to dim light (Morris 1992).
 Roost  1. a perch upon which birds or fowls rest at night. 2. a large cage, house, or place for fowls or birds to roost in (Stein 1966).
 Rufous  Reddish-brown (Morris 1992)
 Ruminant  mammals that have 4 stomachs and chew their cud are ruminants. They are herbivores and the plant material they eat is difficult to digest. In ruminants the 4 digestive chambers accommodate a large number of bacteria which help digest the plant material. Members of the deer family and mountain sheep and goats are all ruminants.
 Rumination  the process of digestion of ruminants, whereby the animal swallows food quickly, and then regurgitates and chews it more thoroughly at a later time until digestion is completed (Morris 1992).
 Runoff  Water flowing over land.
 Rut  is a general term that refers to the breeding period of mammals, especially the deer, elk and moose. During the rut, males exhibit specific behaviors to establish harems or to attract females to mate with.