Glossary

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Habitat - 

Location where a plant or animal lives.

Hadean - 

Geologic eon that occurred from 3800 to 4600 million years ago. The Earth's oldest rocks date to the end of this time period.

Hadley Cell - 

Three-dimensional atmospheric circulation cell located at roughly 0 to 30° North and South of the equator. The Hadley cell consists of rising air (intertropical convergence zone) at the equator and descending air (subtropical highs) at 30° North and South.

Hail - 

Hail is a solid form of precipitation that has a diameter greater than 5 millimeters. Occasionally, hailstones can be the size of golf balls or larger. Hailstones of this size can be quite destructive. The intense updrafts in mature thunderstorm clouds are a necessary requirement for hail formation.

Hair Hygrometer - 

Hygrometer that uses the expansion and contraction of hair to determine atmospheric humidity.

Halite - 

Sedimentary rock created by the chemical precipitation of sodium and chlorine.

Hamada - 

A very flat desert area of exposed bedrock.

Hanging Valley - 

A secondary valley that enters a main valley at an elevation well above the main valley's floor. These features are result of past erosion caused by alpine glaciers. Hanging valleys are often the site of spectacular waterfalls.

Hanging Wall - 

The topmost surface of an inclined fault.

Hardpan - 

Impervious layer found within the soil. It can result from the precipitation of iron, illuviation of clay or the cementing of sand and gravel by calcium carbonate precipitates.

Headlands - 

A strip of land that juts seaward from the coastline. This feature normally bordered by a cliff.

Headwaters - 

Upper portion of stream's drainage system.

Heat - 

Heat is defined as energy in the process of being transferred from one object to another because of the temperature difference between them. In the atmosphere, heat is commonly transferred by conduction, convection, advection, and radiation.

Heat Capacity - 

Is the ratio of the amount of heat energy absorbed by a substance compared to its corresponding temperature rise.

Heat Energy - 

A form of energy created by the combined internal motion of atoms in a substance.

Heat Island - 

The dome of relatively warm air which develops over the center of urbanized areas.

Helical Flow - 

Movement of water within a stream that occurs as spiral flows.

Heterosphere - 

The upper layer in a two part classification of the atmosphere based on the general homogeneity of chemical composition. In this layer, oxygen atoms and nitrogen molecules dominate and remain constant in their relative quantities. The heterosphere extends upward from a height of 80 to 100 kilometers depending on latitude. Below this layer is the homosphere.

High Pressure - 

An area of atmospheric pressure within the Earth's atmosphere that is above average. If this system is on the Earth's surface and contains circular wind flow and enclosed isobars it is called an anticyclone.

HIV - 

Short for human immunodeficiency virus. Any of various strains of a retrovirus of the genus Lentivirus that cause AIDS by infecting the body's immune system.

Holocene Epoch - 

Period of time from about 10,000 years ago to today. During this period glaciers retreated because of a warmer global climate. Time of modern humans.

Homeostasis - 

A constant or non-changing state of equilibrium in a system despite changes in external conditions.

Homeostatic - 

A constant or non-changing state of equilibrium in a system despite changes in external conditions.

Homosphere - 

The lower layer in a two part classification of the atmosphere based on the general homogeneity of chemical composition. In this layer, nitrogen, oxygen, argon, carbon dioxide, and the trace gases dominate and remain constant in their relative proportions. The homosphere extends from the Earth's surface to a height of 80 to 100 kilometers depending on latitude. Above this layer is the heterosphere.

Horizon - 

(1) A surface separating two beds in sedimentary rock.
(2) A layer within a soil showing unique pedogenic characteristics. Four major horizons are normally found in a soil profile: A, B, C, and O.
(3) Point at which the visible edge of the Earth's surface meets the sky.

Horn - 

Pyramidal peak that forms when several cirques erode a mountain from three or more sides.

Horst Fault - 

A fault that is produced when two reverse faults cause a block of rock to be push up.

Host - 

Organism that develops disease from a pathogen or is being feed on by a parasite.

Hot Spot - 

A volcanic area on the surface of the Earth created by a rising plume of magma.

HP - 

An area of atmospheric pressure within the Earth's atmosphere that is above average. If this system is on the Earth's surface and contains circular wind flow and enclosed isobars it is called an anticyclone.

Human Geography - 

Field of knowledge that studies human-made features and phenomena on the Earth from a spatial perspective. Sub-discipline of Geography.

Human-Land Tradition - 

Academic tradition in modern Geography that investigates human interactions with the environment.

Humidity - 

A general term used to describe the amount of water vapor found in the atmosphere.

Humus - 

Dark colored semi-soluble organic substance formed from decomposition of soil organic matter.

Hurricane - 

An intense cyclonic storm consisting of an organized mass of thunderstorms that develops over the warm oceans of the tropics. To be classified as a hurricane, winds speeds in the storm must be greater than 118 kilometers per hour.

Hydration - 

A form of chemical weathering that involves the rigid attachment of H+ and OH- ions to the atoms and molecules of a mineral.

Hydraulic Gradient - 

The slope of the water table or aquifer. The hydraulic gradient influences the direction and rate of groundwater flow.

Hydrograph - 

A graph describing stream discharge over time.

Hydrologic Cycle - 

Model that describes the movement of water between the hydrosphere, lithosphere, atmosphere, and biosphere.

Hydrology - 

Field of physical geography that studies the hydrosphere.

Hydrolysis - 

Chemical weathering process that involves the reaction between mineral ions and the ions of water (OH- and H+), and results in the decomposition of the rock surface by forming new compounds, and by increasing the pH of the solution involve through the release of the hydroxide ions.

Hydrosphere - 

The hydrosphere describes the waters of the Earth. Water exists on the Earth in various stores, including the: atmosphere, oceans, lakes, rivers, glaciers, snowfields and groundwater. Water moves from one store to another by way of: evaporation, condensation, precipitation, deposition, runoff, infiltration, sublimation, transpiration, and groundwater flow.

Hydrostatic Pressure - 

Force caused by water under pressure.

Hygrometer - 

An instrument for measuring atmospheric humidity.

Hygroscopic - 

Substances that have the ability to absorb water and therefore accelerate the condensation process.

Hypothesis - 

A tentative assumption that is made for the purpose of empirical scientific testing. A hypothesis becomes a theory when repeated testing and evidence suggests the hypothesis has a strong chance of being correct.

Hypothesis Testing - 

Process where an alternative and a null hypothesis are statistically tested for the purpose of falsifying a hypothesis.