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Radiolarian ooze
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A siliceous deep-sea sediment composed largely of the skeletons of radiolaria. Radiolarite
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Rayleigh wave
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A type of surface wave having a retrograde elliptical motion at the Earth's surface similar to the waves caused when a stone is dropped into a pond. These are the slowest but often the largest and most destructive of the wave types caused by an earthquake. They are usually felt as a rolling or rocking motion and in the case of major earthquake can be seen as they approach. Named after Lord Rayleigh, the English physicist who predicted its existence.
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Richter scale
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"The system used to measure the strength of an earthquake. Developed by Charles Richter in 1935 as a means of categorizing local earthquakes. It is a collection of mathematical formulas; it is not a physical device. "
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Roche Mountonnée
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A small symetrical shaped hill formed by glacial erosion. The upper sides are rounded and smoothed whilw the lower sides are rough due to quarrying by the glacier.
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radial drainage
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A system of streams running in a radial pattern away from the center of a circular elevation, such as a volcano or dome.
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radiative transfer
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One mechanism for the movement of heat, in which it takes the form of long-wavelength infrared radiation.
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radiocarbon dating
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"The age of organic material determined by the amounts of carbon isotope 12, 13 and 14. The ratio of 12 to 14 is about the same in all living things but when a plant or animal dies, no more carbon is taken on. Carbon 12 and 13 are stable isotopes and the amounts remain the same even in dead material. Carbon 14 is an radioactive isotope that decays radioactively until none is left; . Thus, the ratio records the time elapsed since death. Since carbon 14 decays relatively rapidly, the method is only reliable for the last 40,000 years. See radiometric age."
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radiolarian
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Radiolarians are microscopic, single-celled animals that have existed in the ocean throughout the Phanerozoic Eon. . Although they are closely-related to the blob-like amoebas you see in high school biology class, radiolarian are exceptionally elegant creatures. Radiolarians have elaborate skeletons made mostly of silica. They extract the silica from the sea water they live in. They catch their food as they float in the ocean currents by sticking long, sticky, finger-like projections called pseudopodia through the many holes in their skeleton.
After they die, their skeletons may sink to the ocean bottom. If a thick enough layer of skeletons accumulates, they may eventually harden to form chert, a very hard, often colorful, rock.
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radiolarian chert
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A rock made up of the spherical siliceous shells of radiolarian which are single-celled planktonic animals (protozoans).
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radiometric age
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The approximate age of a geologic event, feature, fossil, or rock in years. Radiometric ages, sometimes termed 'absolute' ages, are determined by using natural radioactive 'clocks'. See radiocarbon dating.
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radiometric dating
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A dating method that uses measurements of certain radioactive isotope to calculate the age in years (absolute age) of rocks and mineral.
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ray
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A linear landform of the lunar surface emanating from a large crater and extending as much as 100 kilometers outward, probably consisting of fine ejecta thrown out by the impact of a meteorite.
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reaction series
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A series of chemical reactions occurring in a cooling magma by which a mineral formed at high temperature becomes unstable in the melt and reacts to form another mineral (see also Discontinuous reaction series).
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recharge
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The process by which water is added to a reservoir or zone of saturation, often by runoff or percolation from the soil surface.
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recharge area
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Region in which there is a net addition of water to the groundwater system (recharge) as a result of infiltration from surface water bodies or an excess of precipitation over, evapotranspiration and runoff.
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recrystallization
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The growth of new mineral grain in a rock at the expense of old grains, which supply the material.
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rectangular drainage
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A system of streams in which each straight segment of each stream takes one of two characteristic perpendicular directions, with right-angle bends between. The streams are usually following two perpendicular sets of joint.
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recumbent fold
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An overturned fold with both limb nearly horizontal.
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recurrence Interval
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The approximate length of time between earthquake in a specific seismically active area.
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reflectivity
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The ratio of the energy carried by a wave that is reflected from a surface to the energy of a wave incident on the surface.
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refraction (wave)
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The departure of a wave from its original direction of travel at the interface with a material of different index of refraction (light) or seismic wave velocity (see also Seismic refraction).
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regional metamorphism
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Metamorphism occurring over a wide area and caused by deep burial and high internal temperatures of the Earth.
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regolith
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Any solid material lying on top of bedrock. Includes soil, alluvium, and rock fragments weathered from the bedrock.
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regolith reduction
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Diminishment in volume and mass of parent material to a smaller volume and mass of weathered soil residue as mobile constituents are carried away, in solution or by aeolian transport.
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regression
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A drop in sea level that causes an area of the Earth to be uncovered by sea water, ending marine deposition.
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relative dating
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The process of placing rocks and geologic structure in the correct chronological order. This process does not yield age in number of years. See radiometric dating.
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relict
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The structure or mineral of the parent rock that can still be seen in a metamorphic rock.
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relief
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"A term used loosely for the physical shape, configuration, or general unevenness of a part of the Earth's surface, considered with reference to variations of height and slope or to irregularities of the land surface; the elevation or differences in elevation, considered collectively, of a land surface"
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remote sensing
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The study of Earth surface conditions and materials from airplanes and satellites by means of photography, spectroscopy, or radar.
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replacement deposit
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A deposit of ore mineral by hydrothermal solutions that have first dissolved the original mineral to form a small cavity.
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reservoir
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Any natural or artificial holding area used to store, regulate, or control a substance.
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residual enrichment
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Increase in the enrichment factor of a relatively immobile element by virtue of hydrochemical leaching of mobile species.
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respiration
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The chemical reaction by which carbohydrates are oxidized and by which all animals and plants convert their food into energy. Carbon dioxide is released and oxygen used up.
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reverse fault
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General term for a fault dipping between 30ø and vertical, and with the hanging wall moving up with respect to the foot wall.
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reverse weathering
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Collection of processes that lead to return of protons consumed in the process of chemical weathering to earth's surface system.
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reversed polarity
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Geomagnetic polarity that is opposite to the present polarity.
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reversible reaction
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A chemical reaction which can proceed in either direction, depending on the concentration of reacting materials.
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rheidity
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(1) The ability of a substance to yield to viscous flow under large strain. (2) One thousand times the time required for a substance to stop changing shape when stress is no longer applied.
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rheology
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Science of the deformation and flow of matter.
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rhyolite
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A volcanic rock (or lava) chemically equivalent to granite with 69 percent silica or more and is rich in potassium and sodium. Usually light colored, very fine-grained or glassy-looking. May have tiny visible crystal of quartz and/or feldspar dispersed in a glassy white, green, or pink groundmass.
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ribbon chert
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Chert and shale in thin alternating bed. The beds resemble parallel ribbons stretched over an outcrop.
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ridge (mid-ocean)
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A major linear elevated landform of the ocean floor, from 200 to 20,000 kilometers in extent. It is not a single ridge, but resembles a mountain range and may have a central rift valley.
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rift structure
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"A long, narrow structural trough that is bounded by normal fault; a graben of regional extent"
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rift system
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"The oceanic ridge formed where tectonic plate are separating and a new crust is being created; also, their land counterparts, such as the East African Rift. "
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rift valley
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A fault trough formed in a divergence zone or other area of tension.
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rift zone
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A region of Earth’s crust along which divergence is taking place. A linear zone of volcanic activity and faulting usually associated with diverging plate or crustal stretching.
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right-lateral fault
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A strike-slip fault on which the displacement of the far block is to the right when viewed from either side.
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ring current
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Electrical current at about three earth radii from the center of the earth. The current results from charged particles trapped in the geomagnetic field.
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ring dike
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A dike in the form of a segment of a cone or cylinder, having an arcuare outcrop.
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ring of fire
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A zone of volcanoes, earthquake, and mountain-building encircling the Pacific Ocean formed where plate collide.
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rip current
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A current that flows strongly away from the sea shore through gaps in the surf zone at intervals along the shoreline.
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ripple
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A very small dune of sand or silt whose long dimension is formed at right angles to the current.
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rock
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Rocks are made of different kinds of mineral, or broken pieces of crystal, or broken pieces of rocks. Some rocks are made of the shells of once-living animals, or of compressed pieces of plants. Rocks are divided into three basic types, igneous, sedimentary and metamorphic, depending upon how they were formed.
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rock cycle
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"The geologic cycle, with emphasis on the rocks produced; sedimentary rocks are metamor-phosed to metamorphic rocks, or melted to create igneous rocks, and all rocks may be uplifted and eroded to make sediments, which lithify to sedimentary rocks. "
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rock cycle
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The rock cycle refers to the many ways that rocks are generated, deformed, eroded, uplifted, buried, and eventually re-generated as new rocks. The Earth is always changing. Igneous, metamorphic, and sedimentary rocks erode to form sediment. Sediment undergoes burial, lithification, and deformation to form new rock. Sedimentary rock undergoes metamorphism at greater depths or is uplifted and exposed to erosion. Metamorphic rock may become buried to a depth at which melting occurs and the magma generated makes its way to the surface to form new igneous rock and to renew the cycle.
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rock flour
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A glacial sediment of extremely fine (silt-and clay-size) ground rock formed by abrasion of rocks at the base of the glacier.
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rock glacier
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A glacier-like mass of rock fragments or talus with interstitial ice that moves downhill under the force of gravity.
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rockfall
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Falling, bouncing, and rolling of debris down slope.
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rockslide
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A landslide involving mainly large blocks of detached bedrock with little or no soil or sand.
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root of a volcano
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Plutonic igneous rock formed from magma that crystallized beneath the volcano it once fed.
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runoff
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The amount of rain water directly leaving an area in surface drainage, as opposed to the amount that seep out as groundwater.
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rupture strength
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The greatest stress that a material can sustain without fracturing at one atmosphere pressure.
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rupture zone
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The area of the Earth through which faulting occurred during an earthquake. For very small earthquakes, this zone could be the size of a pinhead, but in the case of a great earthquake the rupture zone may extend several hundred kilometers in length and tens of kilometers in width.
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