Glossary of Terms: I

Ice

Frozen form of the water molecule. Ice has a specific gravity (0.9166) which is slightly less than water. This difference in specific gravity causes ice to float on water.

 

Ice Age

Period of time when glaciers dominate the landscape of the Earth. The last major Ice Age was during the Pleistocene epoch.

 

Iceberg

A mass of ice found floating in the ocean or a lake. Often icebergs form when ice calves from land-based glaciers into the water body. Icebergs can be dangerous to shipping in high and mid-latitude regions of the ocean because 90 percent of their mass lies below the ocean surface.

 

Ice Cap

Large dome-shaped glacier found covering a large expanse of land. Smaller than an ice sheet.

 

Ice Fall

An area of crevassed ice on a glacier. Caused when the base of the glacier flows over steep topography.

 

Ice Field

Large level area of glacial ice found covering a large expanse of land. Similar in size to an ice cap but does not have a dome-shape.

 

Ice Fog

A fog that is composed of small suspended ice crystals. Common in Arctic locations when temperatures are below -30° Celsius and a abundant supply of water vapor exists.

 

Ice Jam

The accumulation of ice at a specific location along a stream channel. Can cause the reduction of stream flow down stream of the obstruction and flooding upstream.

 

Icelandic Low

Subpolar low pressure system found near Iceland. Most developed during the winter season. This large-scale pressure system spawns mid-latitude cyclones.

 

Ice Lense

Horizontal accumulation of permanently frozen ground ice.

 

Ice Pellets

A type of precipitation. Ice pellets or sleet are transparent or translucent spheres of frozen water that fall from clouds. Ice pellets have a diameter less than 5 millimeters. To form, this type of precipitation requires an environment where raindrops develop in an atmosphere where air temperature is above freezing. These raindrops then fall into a lower layer of air with freezing temperatures. In this lower layer of cold air, the raindrops freeze into small ice pellets. Like freezing rain, an air temperature inversion is required for development of ice pellets.

 

Ice Sheet

A dome-shaped glacier covering an area greater than 50,000 square kilometers. Greenland and Antarctica are considered ice sheets. During the glacial advances of the Pleistocene ice sheets covered large areas of North America, Europe, and Asia. Larger than an ice cap.

 

Ice Shelf

Large flat layer of ice that extends from the edge of the Antarctic ice cap into the Antarctic Ocean. Source of icebergs.

 

Ice Wedge

Wedge-shaped, ice body composed of vertically oriented ground ice that extends into the top of a permafrost layer. These features are approximately 2 to 3 meters wide at their top and extend into the soil about 8 to 10 meters. Form in cracks that develop in the soil during winter because of thermal contraction. In the spring, these cracks fill with liquid water from melting snow which subsequently re-freezes. The freezing process causes the water to expand in volume increasing the size and depth of the crack. The now large crack fills with more liquid water and again it freezes causing the crack to enlarge.This process continues for many cycles until the ice wedge reaches its maximum size.

 

Ideal Gas Law

This law describes the physical relationships that exist between pressure, temperature, volume, and density for gases. Two mathematical equations are commonly used to describe this law:

Pressure x Volume = Constant x Temperature

and

Pressure = Density x Constant x Temperature

 

Igneous Rock

Rocks formed by solidification of molten magma either beneath (intrusive igneous rock) or at (extrusive igneous rocks) the Earth's surface.

 

Illuviation

Deposition of humus, chemical substances, and fine mineral particles in the lower layers of a soil from upper layers because of the downward movement of water through the soil profile. Compare with eluviation.

 

Immigrant Species

Species that migrate into an ecosystem or that are deliberately or accidentally introduced into an ecosystem by humans. Some of these species are beneficial, whereas others can take over and eliminate many native species. Compare with indicator species, keystone species, and native species.

 

Immigration

Migration of an organism into an area for the purpose of changing its residence permanently. Compare with emigration.

 

Inceptisols

Soil order (type) of the United States Natural Resources Conservation Service Soil Classification System. These soils have horizons in the early stages of pedogenesis. Many of these soils are found on glacial drift deposits.

 

Independent Variable

Variable in a statistical test that is thought to be controlling through cause and effect the value of observations in another dependent variable modeled in the test.

 

Index Contour

Contour line that is accentuated in thickness and is often labeled with the appropriate measure of elevation. Index contours occur every four or fifth contour interval and help the map user read elevations on a map.

 

Indicator Species

Species that can be used as a early indicator of environmental degradation to a community or an ecosystem. Compare with immigrant species, keystone species, and native species.

 

Induction

Inference of a generalized conclusion from particular instances. In a science like Physical Geography, inductive reasoning would involve the development of a theory to explain previously collected facts or observed phenomenon.

 

Industrial Revolution

Major change in the economy and society of humans brought on by the use of machines and the efficient production of goods. This period in human history began in England in the late 18th century.

 

Industrial Smog

Form of air pollution that develops in urban areas. This type of air pollution consists of a combination of sulfur dioxide, suspended droplets of sulfuric acid, and a variety of suspended solid particles. Also see photochemical smog.

 

Inferential Statistics

Statistical test that makes generalizations about a population based of the numeric information obtained from a sample based on the laws of probability.

 

Infrared Radiation

Form of electromagnetic radiation with a wavelength between 0.7 and 100 micrometers (µm). Also called longwave radiation.

 

Infiltration

The absorption and downward movement of water into the soil layer.

 

Infiltration Capacity

The ability of a soil to absorb surface water.

 

Infiltration Rate

Rate of absorption and downward movement of water into the soil layer.

 

Inhibition Model of Succession

This model of succession suggests that the change in plant species dominance over time is caused by death and small scale disturbances and variations is plant species longevity and ability to disperse. Over time species turnover favors plant species with longer life spans.

 

Inner Core

Inner region of the Earth's core. It is thought to be solid iron and nickel with a density of about 13 grams per cubic centimeter. It also has a diameter of about 1220 kilometers.

 

Inorganic

Non-living thing. Usually refers to the physical and chemical components of an organism's environment. Some times called abiotic.

 

Inosilicate

Subclass of the silicate class of minerals. Inosilicates have two distinct forms: single and double chain silicates.

 

Input

Addition of matter, energy, or information to a system. Also see output.

 

Insect

Relatively small and simple animals that have a rigid external skeleton, three body sections, three pairs of legs, and antennae. These organisms are the most abundant group of eukaryotes on the Earth.

 

Inselberg

A German term used to describe a steep-sided hill composed of rock that rises from a pediplain.

 

Insolation

Direct or diffused shortwave solar radiation that is received in the Earth's atmosphere or at its surface.

 

Insolation Weathering

Form of physical weathering. Involves the physical breakdown of minerals and rock due to thermal expansion and contraction.

 

Instability

Atmospheric condition where a parcel of air is warmer that the surrounding air in the immediate environment. This condition causes the parcel to rise in the atmosphere. Also see unstable atmosphere.

 

Interaction (biological)

Mutual or reciprocal influence between two or more similar organisms or individuals of different species. Major biotic interactions are: competition, mutualism, predation, parasitism, amensalism, and commensialism.

 

Interception

Is the capture of precipitation by the plant canopy and its subsequent return to the atmosphere through evaporation or sublimation. The amount of precipitation intercepted by plants varies with leaf type, canopy architecture, wind speed, available radiation, temperature, and the humidity of the atmosphere.

 

Interference

Form of competition where an individual directly prevents the physical establishment of another individual in a portion of a habitat.

 

Interglacial

Period of time during an ice age when glaciers retreated because of milder temperatures.

 

Intermittent Stream

A stream that flows only for short periods over a year. Flow events are usually initiated by rainfall.

 

International Date Line

A line drawn almost parallel to the 180 degree longitude meridian that marks the location where each day officially begins. The location of the International Date Line was decided upon by international agreement.

 

Interspecific Interaction

An interaction between different species.

 

Intertropical Convergence Zone (ITCZ)

Zone of low atmospheric pressure and ascending air located at or near the equator. Rising air currents are due to global wind convergence and convection from thermal heating. Location of the thermal equator.

 

Intraspecific Interaction

An interaction occurring between the individuals that make up a single species.

 

Intrusive Igneous Rock

A mass of igneous rock that forms when magma from the mantle migrates upward and cools and crystallizes near, but not at, the Earth's surface. Also called plutonic igneous rock. Also see dyke, sill, and batholith.

 

Inverse Square Law

This law suggests that the amount of radiation passing through a specific area is inversely proportional to the square of the distance of that area from the energy source. Mathematically, the Inverse Square Law is described by the equation:

Intensity = I/d ²

where I is the intensity of the radiation at 1 unit distance and d is the distance traveled in those units.

 

Inversely Proportional

Cause and effect relationship between two variables where a positive or negative change in the quantity of one causes a predictable opposite change in quantity in the other.

 

Invertebrate

Animal that does not have a backbone. Also see vertebrate.

 

Inversion

See temperature inversion.

 

Ion

An atom, molecule or compound that carries either a positive (cation) or negative (anion) electrical charge.

 

Ionizing Radiation

The emission of alpha or beta particles or gamma rays from radioisotopes. These emitted particles can dislodge one or more electrons from atoms they strike. The free electrons can form charged ions in living tissue that can react with and damage cells.

 

Ionosphere

A region in the atmosphere above 50 kilometers from the surface where relatively large concentrations of ions and free electrons exist. The ionosphere is important for human communications because it re-directs AM radio transmissions. This process extends the distance that radio transmissions can travel.

 

Island Arc

A line of volcanic islands found of the ocean that have been created by the convergence of two tectonic plates and the subsequent subduction of one of the plates beneath the other. Subduction cause magma plumes to rise to the Earth's surface creating the volcanic islands.

 

Isobar

Lines on a map joining points of equal atmospheric pressure.

 

Isolated System

A system that has no interactions beyond its boundary layer. Many controlled laboratory experiments are this type of system.

 

Isoline

Lines on a map joining points of equal value.

 

Isostacy

The buoyant condition of the Earth's crust floating in the asthenosphere. The greater the weight of the crust the deeper it floats into the asthenosphere. When weight is removed the crust rises higher.

 

Isostatic Depression

Large scale sinking of the crust into the asthenosphere because of an increase in weight on the crustal surface. Common in areas of continental glaciation where the crust was depressed by the weight of the ice.

 

Isostatic Rebound

The upward movement of the Earth's crust following isostatic depression.

 

Isotherm

Lines on a map joining points of equal temperature.

 

Isothermal Layer

Vertical layer in the atmosphere where temperature remains unchanged. In the Earth's atmosphere, three isothermal layers are found in the lower regions of the stratosphere, mesosphere, and the thermosphere.

Isotope

Form of an element where the number of neutrons in its atomic nucleus is different than the number of protons.

 

Isotopic Dating

Dating technique used to determine the age of rock and mineral through the decay of radioactive elements.

 

 

Citation: Pidwirny, M. (2006). "Glossary of Terms: I". Fundamentals of Physical Geography, 2nd Edition. Date Viewed. http://www.physicalgeography.net/physgeoglos/i.html