Geologic Glossary
This glossary contains simplified definitions for technical terms used within this site.
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Ddata baseA set of words, numbers, locations, or other data put into a computer program. Data bases are set up so that related pieces of information can be easily retrieved and compiled. daughter productAn isotope produced by decay of a radioactive element.
debris flowA type of landslide made up of a mixture of water-saturated rock debris and soil with a consistency similar to wet cement. Debris flows move rapidly downslope under the influence of gravity. Sometimes referred to as earth flows or mud flows. deflationRemoval of loose material by wind. deformationGeneral term for folding, faulting, and other processes resulting from shear, compression, and extension of rocks. deltaA fan-shaped deposit that forms where a stream enters a lake or ocean and drops its load of sediment. densityThe weight per unit volume of a material. desertA region with an average annual rainfall of 10 inches or less. desert varnish A gray or reddish-brown layer on rock
surfaces that darkens and thickens with increasing age. Desert varnish results from microbial
life processes that precipitate thin skins of clays and manganese oxide minerals.
The thicknesses can be used to determine the amount of time the surface of a rock has been
exposed. depositAny accumulation of sediment. desert pavementA closely-packed surface layer of coarse pebbles and gravel. desiccateTo dry out, usually by evaporation of water. diagenesisA group of processes that cause physical and chemical changes in sediment after it has been deposited and buried under another layer of sediment. Diagenesis may culminate in lithification of sediment, turning it into solid rock. diapirForceful, upward intrusion of a rock mass into overlying rock. In the case of an igneous diapir, the intruding rock may be magma or a crystal-rich mush, either of which is less dense than the surrounding rock. dikeA sheet-like or tabular-shaped igneous intrusion that cuts across the sedimentary layering, metamorphic foliation, or other texture of a pre-existing rock.
dioriteIntrusive igneous rock made of plagioclase feldspar and amphibole and/or pyroxene. Similar to gabbro only not as so dark, and containing less iron and magnesium. dipA measure of the angle between the flat horizon and the slope of a sedimentary layer, fault plane, metamorphic foliation, or other geologic structure. disappearing streamIn karst areas, streams often disappear into the ground usually at a sinkhole. dischargeThe amount of water issuing from a spring or in a stream that passes a specific point in a given period of time. dissolutionThe process of chemical weathering of bedrock in which the combination of water and acid slowly removes mineral compounds from solid bedrock and carries them away in liquid solution. Also called chemical solution. divergent plate boundaryA boundary in which two tectonic plates move apart.
drainageAny channel that carries water. drainage basinThe land area drained by a stream. dolineSee sinkhole dolomiteA magnesium-rich carbonate sedimentary rock. Also, a magnesium-rich carbonate mineral (CaMgCO3) duneA usually asymmetrical hill of wind-deposited sand.
durable crustAn outer rind or crust formed on a rock. Durable crusts form when rock chemically reacts with water and possibly atmospheric dust, producing a hard outer surface that resists weathering. |
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