Half-Life:
The time required for one half of a radioactive substance to decay into its daughter material.
Halite:
The mineral name for "rock salt". A chemical sedimentary rock that forms from the evaporation of ocean or saline lake waters. It is rarely found at Earth's surface, except in areas of very arid climate. It is often mined for use in the chemical industry or for use as a winter highway treatment. Some halite is processed for use as a seasoning for food. Picture of Halite.
Hanging Valley:
A tributary to a U-shaped glacial valley which, instead of entering the valley at the same level as the main stream, enters at a higher elevation, frequently as a waterfall. These different stream levels are a result of the rapid downcutting of the glacier being much faster than the slower downcutting of the tributary stream.
Hard Water:
Water that has a significant amount of dissolved calcium and magnesium ions. This water performs poorly with most soaps and detergents and leaves a scaly deposit in containers where it is heated or evaporates. It can frequently be improved through the use of home-based water treatment systems.
Headwater(s):
The upper portions of a drainage basin where the tributaries of a stream first begin flow.
Heat Flow:
The movement of heat energy from the core of the Earth towards the surface.
Hematite:
An iron oxide mineral that is commonly used as an ore of iron. Picture of Hematite.
Hogback:
A narrow ridge with steeply inclined sides of nearly equal slopes. Formed by differential erosion of steeply dipping rock units.
Hornfels:
A nonfoliated metamorphic rock that is typically formed by contact metamorphism around igneous intrusions. Picture of Hornfels.
Horst:
An elongated block of high topographic relief that is bounded on two sides by steep normal faults. Produced in an area of crustal extension.
Hot Spot:
A volcanic center located within a lithospheric plate that is thought to be caused by a plume of hot mantle material rising from depth.
Hot Spring:
A natural spring that delivers water to the surface that is of higher temperature than the human body.
Humus:
The dark portion of a soil that consists of organic material that is well enough decayed that the original source material can not be identified.
Hydraulic Conductivity:
The ability of a porous material to transmit a fluid. Permeability.
Hydrocarbon:
Any organic chemical compound (gaseous, liquid or solid) that is composed of carbon and hydrogen. The term is frequently used in reference to fossil fuels, specifically crude oil and natural gas.
Hydroelectric power:
The production of electrical energy through the use of flowing or falling water.
Hydrograph:
A graph that shows the change of a water-related variable over time. Example: A stream discharge hydrograph shows the change in discharge of a stream over time.
Hydrologic Cycle:
The natural cycling of Earth's water between the atmosphere, surface and subsurface through the processes of evaporation, transpiration, percolation, infiltration, runoff and precipitation.
Hydrology:
The science of Earth's water, its movement, abundance, chemistry and distribution on, above and below Earth's surface.
Hydrolysis:
A chemical reaction involving water that results in the breakdown of mineral material.
Hydrothermal:
Pertaining to hot water, the actions of hot water or the products produced by the actions of hot water.
Hydrothermal Deposits:
Mineral deposits that are formed by the actions of hot water or gases associated with a magmatic source.
Hydrothermal Metamorphism:
Alteration of rock by hot waters or gases associated with a magmatic source.
Hydrothermal Vein:
A deposit of minerals precipitated in a fracture by the actions of hot water or gases associated with a magmatic source.
Hypocenter:
A point beneath earth's surface where the vibrations of an earthquake are thought to have originated. Also known as the focus.