Glossary Database

Select a Letter to view the associated terms.

 Glossary Term: 


 Dacite  A fined grained extrusive rock equivalent to the intrusive granodiorite.
 dam breaching  To remove all or part of a dam.
 Daughter isotope  Daughter isotopes are produced from the radioactive decay of parent isotopes. They may be at a permanent stable state, or break down even further.
 Debris flow  The rapid downslope movement of debris (rock, soil, and mud).
 Debris slide  The downward movement of predominantly unconsolidated earth and rock debris in which the mass does not show backward rotation but slides or rolls forward, forming an irregular hummocky deposit resembling a moraine.
 Decade  Ten years.
 Decay product  See daughter isotope.
 Deciduous  falling off or being shed during a certain season or at a partial stage of growth such as leaves or antlers (Morris 1992).
 Declination  The horizontal angle in any given location between true north and magnetic north. Can also be called a magnetic variation.
 Deep-focus earthquake  An earthquake that originates at a depth greater than 300 km.
 Deep-marine environment  The sedimentary environment of the abyssal plains.
 Deep-sea fan  A cone-shaped or fan-shaped deposit of land-derived sediment located seaward of large rivers or submarine canyons. Synonymous with abyssal cone, abyssal fan, submarine cone.
 Deep-sea trench  See trench.
 Defecate  to extrude feces from the bowel.
 Deflation  Erosion of loose rock particles by wind.
 Deflation basin  A shallow depression formed by wind erosion where groundwater solution activity has left unconsolidated sediment exposed at the surface.
 Delayed implantation  usually, the fertilized egg implants in the wall of the female's uterus shortly after mating and fertilization. However, in delayed implantation, the fertilized egg does not implant in the female's uterus until much later, thus implantation is delayed. Once implantation occurs the fertilized egg quickly becomes a developing embryo. This process is found in family Mustelidae (weasel family) and family Ursidae (bear family).
 Delta  A body of sediment deposited at the mouth of a river. Many are roughly triangular in shape.
 Dendritic drainage pattern  A branching stream pattern, resembling the branching of certain trees, such as oaks and maples.
 Density  1.) Mass per unit volume, expressed in grams per cubic centimeter (g/cm3). 2.) A term used to describe populations. It refers to the number of animals per unit area, such as the number of mice per acre or hectare.
 Density current  A current that flows as a result of differences in density. In oceans, density currents are produced by differences in temperature, salinity, and turbidity (the concentration of material held in suspension).
 dentary  The largest and most anterior bone of the lower jaw.
 Dentition  1. the kind, number, and arrangement of the teeth of man and animals. 2. the development and cutting or eruption of teeth (Morris 1992).
 Deposition  The settling of materials out of a transporting medium.
 depressed  Flattened from top to bottom.
 Deranged drainage  A distinctively disordered drainage pattern formed in a recently glaciated area. It is characterized by irregular direction of stream flow, few short tributaries, swampy areas, and many lakes.
 Dermal  of or relating to the dermis of the skin (Morris 1992).
 Desert climate  A climate with generally high temperatures, high rates of evaporation, and low precipitation. Most deserts lie at about 30 degrees north or south of the equator.
 Desert pavement  A veneer of pebbles left in place where wind has removed the finer material.
 Desertification  The process of transforming and land into a barren desert. Often induced by human activities or climate change.
 Desiccation  1.) The process of drying out. With reference to sedimentation, the loss of water from pore spaces by evaporation or compaction. 2.)any process of moisture removal (Morris 1992).
 Detrital  1. Pertaining to detritus. 2. A rock formed from detritus.
 Detritus  1.) A general term for loose rock fragments produced by mechanical weathering. Also used in reference to other small particles of inorganic or organic matter. 2) Organic matter produced by the decay or disintegration of a substance or tissue (Morris 1992).
 Dewlap  a fold of skin hanging from the neck of some bovines, reptiles, and birds (Morris 1992).
 Diapause  A state of halted development. Insects typically overwinter in this state, waiting until spring to continue growing and molting or to finish pupating.
 Diatom  1.) A microscopic plant, which secretes a silica-rich shell, which nest inside each other like two petri dishes. 2.)The common name for the Bacillariophyceae, a class of unicellular microscopic algae with a symmetrical siliceous exoskeleton (Morris 1992).
 Dichotomous key  A device for identifying organisms based on the answers to a series of questions, with each question involving alternate choices (Morris 1992).
 Differential erosion  Variation in the rate of erosion on different rock masses. As a result of differential erosion, resistant rocks form steep cliffs, whereas nonresistant rocks form gentle slopes.
 Differentiated planet  A planetary body in which various elements and minerals are separated according to density and concentrated at different levels. Earth, for example, is differentiated, with heavy metals (iron and nickel) concentrated in the core; lighter minerals in the mantle; and still lighter materials in the crust, hydrosphere, and atmosphere.
 Diffraction  The spreading of a wave motion, such as light as it passes an obstacle and expands into the region that is behind the obstacle. differentiation See magmatic differentiation, planetary differentiation, sedimentary differentiation.
 Dike  A tabular intrusive rock that cuts across strata or other structural features of the surrounding rock.
 Dike swarm  A group of associated dikes.
 Dimorphism  the existence of distinct genetically determined forms of the same species, such as distinct male and female forms or distinct young and mature forms (Morris 1992).
 Diorite  A phaneritic intrusive igneous rock consisting mostly of intermediate plagioclase feldspar and pyroxene, with some amphibole and biotite.
 Dip  The angle between the horizontal plane and a structural surface (such as a bedding plane, a joint, a fault, foliation, or other planar features).
 Diptera  the true flies, an order of insects with sucking mouth parts; nearly all posses a hind pair of wings modified to serve as stabilizers during flight (Morris 1992).
 Disappearing stream  A stream that disappears into an underground channel and does not reappear in the same, or even in an adjacent, drainage basin. In karst regions, streams commonly disappear into sinkholes and follow channels through caves.
 Discharge  Rate of flow; the volume of water moving through a given cross section of a stream or aquifer in a given unit of time.
 Disconformity  A nonconformity in which beds above and below are parallel.
 Discontinuity  A sudden or rapid change in physical properties of rocks within the Earth. Discontinuities are recognized by seismic data. See also: Mohorovicic discontinuity.
 Dispersal  (Dispersion) the movement of organisms or their spores or gametes throughout the ecological niche of that particular organism (Morris 1992).
 Dissolution  The process by which materials are dissolved.
 Dissolve  To break up, melt, or to become liquid.
 Dissolved load  The part of a stream's load that is carried in solution.
 Distributary  Any of the numerous stream branches into which a river divides where it reaches its delta.
 Diurnal  Relating to the daytime; occurring during daylight hours (Morris 1992). A mammal that is active mostly during daylight hours is said to be diurnal. Voles tend to be diurnal rather than nocturnal which refers to the night.
 Divergent  To move in different directions. For example, divergent plate margins are lithospheric plates that are moving apart.
 Divergent plate boundary  A plate margin formed where the lithosphere splits into plates that drift apart from one another. Divergent plate boundaries are areas subject to tension, where new crust is generated by igneous activity. See also: oceanic ridge.
 Diversity  an assortment of species and or objects contained within a discussed environment.
 Divide  A ridge separating two adjacent drainage basins.
 Dolomite  1. A mineral composed of CaMg(CO3)2. 2. A sedimentary rock composed primarily of the mineral dolomite.
 Dolostone  A sedimentary rock composed mostly of the mineral dolomite. At times, referred to simply as dolomite.
 Dome  1. structural geology. An uplift that is circular or elliptical in map view, with beds dipping away in all directions from a central area. 2. topography. A general term for any dome-shaped landform.
 Dorsal  1.) Of or lying near the back (Morris 1992). 2.) The back or upper third of the fish; opposite of ventral.
 dorsal fin  Back fin, with rays or spines.
 dorsal lobe  Any lobe on the dorsal or top side.
 Dorsal nectary organ  An organ located on the rear of some caterpillars which emits a sugary solution consumed by ants. The ants feed on the solution and in turn protect the caterpillar from predators. It is also called a honey gland.
 Dorsolateral  Pertaining to the side and the back (Behler 1988).
 Downwarp  A downward bend or subsidence of a part of Earth's crust.
 Drainage   manner by which waters of an area flow off in surface streams.
 Drainage basin  The total area that contributes water to a single drainage system.
 Drainage system  An integrated system of tributaries and a trunk stream, which collect and funnel surface water to the sea, a lake, or some other body of water.
 Drift  A general term for sediment deposited directly on land by glacial ice or deposited in lakes, oceans, or streams as a result of glaciation.
 Drip curtain  A thin sheet of dripstone hanging from the ceiling or wall of a cave.
 Dripstone  A cave deposit formed by precipitation of calcium carbonate from groundwater entering an underground cavern.
 Drought  A period of time when precipitation is well below normal.
 Drumlin  A smooth, glacially streamlined hill that is elongate in the direction of ice movement. Drumlins are generally composed of till.
 DTU (hatchery)  (Daily Temperature Unit) one degree Fahrenheit above freezing (32oF) for a 24 hour period.
 Ductile  Easily bent. Contrast with brittle.
 Duff layer  Organic matter in various stages of decomposition on the floor of the forest (Stein 1966).
 Dune  A low mound of fine-grained material that accumulates as a result of sediment transport in a current system. Dunes have characteristic geometric forms that are maintained as they migrate. Sand dunes are commonly classified according to shape. See also: barchan dune, longitudinal dune, parabolic dune, seif dune, star dune, and transverse dune.