Geological Glossary - H

A B C D E F G H I J K L M N O P Q R S T U V W X Y Z
Holocene	The most recent epoch of the Quaternary period covering approximately the last 10,000 years.
Hooke's Law	The principle that the stress within a solid is proportional to the strain. It holds only for strains of a few percent or less.
A B C D E F G H I J K L M N O P Q R S T U V W X Y Z
half-life	The time required for half of a homogeneous sample of radioactive material to decay.
halite	Halite (NaCl) is a mineral and is known commonly as salt - the same salt that we sprinkle on our food. Like gypsum, it is an evaporite mineral that form from seawater
hanging valley	A former glacial tributary valley that enters a larger glacial valley above its base, high up on the valley wall.
hard water	Water that contains suficient dissolved calcium and magnesium to cause a carbonate scale to form when the water is boiled or to prevent the sudsing of soap.
hardness	A measure of a mineral's resistance to scratching. The hardness of a mineral is measured by scratching it against another substance of known hardness.
harmonic tremor	A continuous release of seismic energy typically associated with the underground movement of magma. It contrasts distinctly with the sudden release and rapid decrease of seismic energy associated with the more common type of earthquake caused by slippage along a fault. The seismic signal is characterized by a nearly monotonic sinusoidal appearance and low frequency (0.5-5 Hz).
headland	Headlands are projections of land that stick out into a sea or lake.
heat conduction	The transfer of the rapid vibrational energy of atom and molecules, which constitutes heat energy, through the mechanism of atomic or molecular impact.
heat engine	A device that transfers heat from a place of high temperature to a place of lower temperature and does mechanical work in the process.
heat sink	That portion of a thermodynamic system that absorbs unused heat.
hertz	The unit of frequency equal to one cycle per second.
hill	A natural land elevation, usually less than 1000 feet above its surroundings, with a rounded outline. The distinction between hill and mountain depends on the locality.
hinge	The part of a fold that is the most sharply curved.
historical biogeography	"Discipline that deals with the ever-changing distribution of organisms, marine and non-marine, over the earth's surface through geologic time; i.e., the historical counterpart of present-day biogeography, which discusses the modern distribution of all living organism."
hogback	A formation similar to a Cuesta in that it is a ridge formed by slower erosion of hard strata, but having two steep, equally inclined slope.
homopycnal	Describes water entering a lake that has the same density as the lake water.
hoodoo	A column or pillar of rock of varying hardness. Its unique shape is the result of differential erosion.
hornblende	See amphibole.
hornblende schist	A schist rich in hornblende. Generally with abundant plagioclase feldspar as well. Grades into amphibolite.
hornfels	Usually formed by contact metamorphism. A dark, very fine-grained metamorphic rock of uniform grain size showing no foliation. It is produced by the recrystallization, at high-temperature and low-pressure, by heat from a nearby igneous intrusion. From the German, meaning horn rock.
horst	An elongate block of rock uplifted along roughly parallel fault.
hot spring	A spring whose waters are above both human body and soil temperature as a result ofpluto-nism at depth.
hotspot	An area of concentrated heat in the mantle that produces magma that rises to the Earth’s surface to form volcanic island. The volcanic activity of the Hawaiian Islands is one example. Hot spots generally persist for millions of years.
humic acids	Suite of organic acids (RCOOH) of indefinite composition and molecular structure produced by decomposition and condensation reactions. Operationally defined as being solubilized from peat, humus, soil, sediment or other material by dilute-alkali extraction.
humus	The decayed part of the organic matter in a soil.
hydration	A chemical reaction, usually in weathering, which adds water or OH to a mineral structure.
hydraulic conductivity	A measure of the permeability of a rock or soil
hydrocarbon	An organic chemical compound made up of carbon and hydrogen atom arranged in chains or rings.
hydrologic cycle	The constant circulation of water from the sea, through the atmosphere, to the land, and its eventual return to the atmosphere by way of transpiration and evaporation from the sea and the land surfaces
hydrologic cycle	The cyclical movement of water from the ocean to the atmosphere, through rain to the surface, through runoff and groundwater to streams, and back to the sea.
hydrologic system	The cycle occuring between rain and return to the sea,
hydrology	The science that deals with water on and beneath the Earth surface.
hydrolysis	A chemical reaction between water and another chemical compound such as a mineral. For example, water reacts with orthoclase to form the clay mineral kaolinite.
hydrosphere	The aqueous envelope of the Earth, including the oceans, freshwater lakes, rivers, saline lakes and inland seas, soil moisture and vadose water, groundwater and atmospheric vapor.
hydrosphere	"The waters of the Earth, as distinguished from the rocks (lithosphere), living things (biosphere), and the air (atmosphere). Includes the waters of the ocean; rivers, lakes, and other bodies of surface water in liquid form on the continent; snow, ice, and glacier; and liquid water, ice, and water vapor in both the unsaturated and saturated zones below the land surface. Included by some, but excluded by others, is water in the atmosphere, which includes water vapor, clouds, and all forms of precipitation while still in the atmosphere."
hydrostatic pressure	The pressure at a point in a body of liquid that is due to the weight of liquid above it.
hydrothermal activity	Interaction of an aqueous solution with rock at high temperature and pressure, leading to alteration of the rock and dissolution of some of the rock mineral and formation of others.
hydrothermal activity	Any process involving high-temperature groundwater, especially the alteration and emplacement of mineral and the formation of hot spring and geyser.
hydrothermal vein	A cluster of mineral precipitated by hydrothermal activity in a rock cavity.
hydrous	Literally, with water. Refers to mineral or other materials which have water as a primary constituent.
hyperpycnal	Describes water that is denser than the water in the lake it enters.
hypocenter	"The calculated point below the epicenter at which an earthquake actually begins; the focus. "
hypsometric diagram	A graph that shows in any way the relative amounts of the Earth's surface at different elevation with regard to sea level.