Glossary Database

Select a Letter to view the associated terms.

 Glossary Term: 


 Ice age  A synonym used for glacial epoch or a time of extensive glacial activity.
 Ice plucking  Usually just called plucking or quarrying. It results when glacial ice freezes in the cracks and crevices of a bedrock projection and eventually pulls it loose.
 Ice sheet  A thick, extensive body of glacial ice that is not confined to valleys. Localized ice sheets are sometimes called ice caps.
 Ice wedging  A type of mechanical weathering in which rocks are broken by the expansion of water as it freezes in joints, pores, or bedding planes. Synonymous with frost wedging.
 Iceberg  A large piece of floating ice that has broken off of a glacier. The greater part of its mass is below sea level.
 IDWR coverage  Area of interest to the Idaho Department of Water Resources.
 Igneous  1. From a magma; said of a rock or mineral that solidified from molten or partly molten material. 2. A rock or mineral that solidified from molten or partly molten material.
 Igneous rock  Rock formed by cooling and solidification of molten silicate minerals (magma). Igneous rocks include volcanic and plutonic rocks.
 Ignimbrite  The rock formed by the widespread deposition and consolidation of ash flows.
 Imbrian Period  The period of lunar history during which the large multi-ring basins, such as Mare Imbrium, were formed and the mare basalts extruded (from 3.9 billion to 3.1 billion years ago).
 Impermeable  Said of a rock, sediment, or soil that is incapable of transmitting fluids under pressure.
 Implantation  the embedding of a fertilized ovum (blastocyst) into the endometrium (Morris 1992).
 Inclination  1. A deviation from the vertical or horizontal. Also the angle of a slope or a dip. 2. magnetic: The angle between the horizontal plane and a magnetic line of force.
 Inclusion  A rock fragment incorporated into a younger igneous rock.
 Incubate  Of a hen, to sit on and hatch eggs (Morris 1992).
 Infiltration  Movement of water through vadose zone into saturated zone.
 Infrared radiation  Electromagnetic energy in the wavelength range of 0.7 to 200 mm. They are invisible rays just beyond the red of the visible light spectrum. Infrared wavelength is longer than visible light but shorter than radio waves.
 Inguinal amplexus  Sexual embrace of anurans; the grasping of the female's body by the male's forelimbs from a dorsal position just above the hind legs. The grip is usually quite strong, and is not released until oviposition is completed (Peters 1964).
 Inorganic  Not organic. Matter that is not of animal or vegetable origin.
 Insectivorous  refers to an animal that feeds primarily on insects, such as bats.
 Instar  Individual growth stage of a caterpillar. Instars are separated by molts.
 Intercalary cartilage  A phalanx-like cartilaginous element inserted between the ultimate and penultimate phalanges in the digits of the frog families (Peters 1964).
 Intermediate-focus earthquake  An earthquake with a focus located at a depth between 70 and 300 km.
 Intermittent stream  A stream through which water flows only part of the time.
 Internal drainage  A drainage system that does not extend to the ocean.
 Internal fertilization  1. broadly, the reproductive condition in animals, such as birds and mammals, when the egg is fertilized within the female's body. 2. specifically, the union of the nuclei of the egg cell and the sperm cell, resulting in the disappearance of their nuclear membranes and the combination of their chromosomes (Morris 1992).
 Interspecific competition  One species subtly depresses another species' survival or breeding success through reduction of critical resources (Gill 1995)
 Interstitial  Pertaining to material in the pore spaces of a rock. Petroleum and groundwater are interstitial fluids. Minerals deposited by groundwater in a sandstone are interstitial minerals.
 Intrasexual competition  competition between the sexes
 Intraspecific nest parasitism  The addition of eggs to another female's nest (Gill 1995)
 Introduce  To bring a species, either inadvertantly or intentionally, from another area into a new area where it has not existed previously. Introduced species are the opposite of native species.
 intromittent  Refers to a modified fin of the male which is used to introduce sperm into the female.
 Intrusion  1. Injection of a magma into a pre-existing rock. 2. A body of rock resulting from the process of intrusion.
 Intrusive   magma that has penetrated into pre-existing rock and solidified
 Intrusive rock  Igneous rock that, while it was fluid, penetrated into or between other rocks and solidified. It can later be exposed at Earth's surface after erosion of the overlying rock.
 Invertebrate  An animal without a backbone such as mollusks or arthropods.
 Inverted valley  A valley that has been filled with lava or other resistant material and has subsequently been eroded into an elongate ridge.
 Ion  An atom or combination of atoms that has gained or lost one or more electrons and thus has a net electrical charge.
 Ionic bond  A chemical bond formed by electrostatic attraction between oppositely charged ions.
 Ionic substitution  The replacement of one kind of ion in a crystal lattice by another kind that is of similar size and electrical charge.
 Iridescent  displaying a shining, rainbowlike range of colors (Morris 1992).
 Iron oxide  A compound consisting of iron (Fe) combined with oxygen (O). It is the rust you see on iron or steel left exposed to oxygen in the air. Hematite (Fe2O3) and Magnetite (Fe3O4) are minerals of iron oxide.
 Irrigation  A method of watering land (usually from a distant source) by directing it through systems of canals, ditches and pipes.
 Island  A landform smaller than a continent and completely surrounded by water.
 Island arc  A chain of volcanic islands. Island arcs are generally convex toward the open ocean. Example: the Aleutian Islands.
 Isostasy  A state of equilibrium, resembling flotation, in which segments of Earth's crust float (on liquid mantle material) at levels determined by their thickness and density. Isostatic equilibrium is attained by flow of material in the mantle.
 Isotope  One of the several forms of a chemical element that have the same number of protons in the nucleus but differ in the number of neutrons and thus differ in atomic weight.
 isthmus  Narrow part of the breast of a fish that projects forward between the gill chambers.