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Halophyte a plant that is able to tolerate
environments with a high level of salt. Found usually in
coastal areas or arid areas where
potential
evapotranspiration exceeds
precipitation for large parts of the year.
Halosere
plant succession in a saline environment e.g.
estuary, salt marsh.
Hamada
flat, exposed
bedrock
in an
arid
area.
Hamlet
a small settlement with a purely
residential function. Usually fewer than 100
inhabitants and no services except perhaps a post box.
Harris-Ullman
model of urban land-use based on multiple nuclei i.e. more
than one centre. Used to explain land-use in larger urban
areas such as
conurbations where there are many locales exhibiting
features of
CBDs
as smaller settlements have been enveloped by the growth of
the main city or have coalesced into it with their own
growth.
Hanging
valley a small
glacial
valley entering a larger one someway up the side of
the latter. Created by the differential in
erosion
between the different sized
glaciers
that formed the respective valleys.
Hardpan
a thin crust of material within a soil as a result of the
illuviation of iron and/or aluminium from layers
above or the precipitation of calcium carbonates which
cement sands together.
Hazard
an event or condition which threatens people and property.
May be natural e.g.
earthquake,
blizzard, or
human e.g. industrial waste,
HIV, or a combination
e.g.
drought,
famine.
HDI see
human development index.
Headland
at the coast, land jutting out further into the sea and
separating bays. see also
discordant coast.
Headward erosion -
the lengthening of a
young valley or gully by water erosion at the head of its
valley.
Headwaters
the uppermost portion of a river course close to the
source.
Heat budget
see
energy budget.
Heat
equator the tilt of the earth means that during an orbit
cycle the line of
latitude receiving the most
concentrated
insolation migrates between the
tropics. On 21st June, the sun is most directly
above the Tropic of Cancer and, on 22nd
December, most directly above the Tropic of Capricorn.
Heat island
the warm air found around and above an urban area,
distinct from the air temperature above the surrounding
rural land.
Heathland
an environment of grass and shrubs which develops in
nutrient deficient parts of
temperate areas. In
Europe, they are often the result of forest clearances but
are now deliberately maintained for rough grazing and
shooting estates.
Heavy
industry those secondary industries using bulk raw
materials for both energy (e.g. coal) and production (e.g.
ores). They often manufacture products for other secondary
industries.
Helical (or
helicoidal) flow the spiraling flow of water in meandering
channels caused by the deflection of flow as water hits the
bending banks.
Hemisphere
lit. half a sphere. In geography, the division of the
earth either into north and south by the
equator, or
into east and west by any one line of
longitude.
HEP see
hydro-electric power.
Herbicide
a chemical used to control/prevent weed growth in
arable
farming.
Herbivore
any organism which feeds exclusively on plants (producers).
Heritage
lit. anything that is passed one from one generation to the
next. Commonly applied to the buildings and rural landscape
of a nation and especially in relation to those that are
considered worth keeping for the future.
Hierarchy
organisation by class of importance, status or authority.
Usually a negative correlation between class and number of
members i.e. the higher the class the lower the number of
members of that class.
High-order
good/service one which is high in value and long-lasting
and therefore generally bought infrequently e.g. car,
accountant.
High tide
the highest point to which the sea rises against the land in
its daily vertical movement.
High-yield
variety grain crop which has been selectively bred to
produce seeds which produce far more than otherwise.
Hinterland
(also periphery) the area surrounding a core settlement
from which the settlement gains resources.
Histogram
a bar chart where the vertical (y) axis is frequency and the
horizontal (x) axis is the classes/values of data that have
been measured for frequency.
HIV see
human immunodeficiency virus.
Hi-tech
industry those industries that have developed since the
late 20th century in areas such as electronics,
IT, pharmaceuticals etc. They have a high component of
research and development and are at the forefront of
technological innovation.
Hjulstrψm
curve a graph showing critical stream velocities for the
erosion,
transport and
deposition of
different sizes of
load.
Holocene
the current
geological period, currently about 10,000
years long.
Honeypot
a place special interest, especially with reference to
tourist visitors. Honeypots may be developed deliberately as
a way to concentrate tourists into manageable areas and
reduce pressures on surrounding fragile environments.
Horizon
two uses:
-
the line
where the visible surface appears to meet the sky.
-
in a
soil, a distinct layer having unique characteristics.
Horizontal
integration the merging of firms at the same stage of
production.
Horizontal
transfer - transfer or transmission of energy from lower
latitudes to higher latitudes. Two kinds:
·
in the air
by the movement of air (wind). Highly complex and not fully
understood. Transfers take place between the cells of
general circulation (see
tricellular model) but the
exact mechanisms are not clear.
·
in the
ocean by the existence of warm and cold currents. Warm
currents move energy in surface waters from low to high
latitudes, returning as cold currents at depth.
Horst a raised block of land bordered by fault lines.
Horticulture see
market gardening.
Hot spots a localized area of extreme heat. On earth, they
refer to places where an upward plume of magma comes close
to the surface in a
shield area such as in Hawaii.
The term may also be used to refer to areas of the surface
of the sun giving off unusually large amounts of energy.
Housing association in the UK, non-profit organizations
offering a third way outside of the traditional housing
provision of the private sector and local government.
Originally set up to provide rental accommodation they now
also offer a way for people to become owners. They still
focus on helping lower income groups find appropriate
accommodation.
Hoyt, Homer architect of the
sector model of urban
land-use.
Human Development Index an attempt to make fairer but
still statistical measurements of
development that
became popular at the
UN in the 1990s. Assigned value
between 0 and 1 according to ranking position for each of
the factors of purchasing power of income, literacy rate and
longevity. Theoretical maximum of 3 was index 1. Criticized
for measuring ranking rather than absolute idea of
development, plus probably too biased in favour of
wealth-dependent factors.
Human immunodeficiency virus a virus which forms DNA while
replicating its RNA leading to the development of
Aids.
Humidity the water vapour content of the
atmosphere.
Two main measures are
absolute humidity and
relative humidity. Humidity is controlled by air
temperature (the higher the temperature the more water
vapour can be held) and water availability for
evapotranspiration.
Humus the decomposed organic element of the soil. Is
identified both as an independent
horizon in some
soils, or in the
clay-humus complex. It is usually
dark in colour and comes in two forms, mor which is highly
acidic, and mull which is much milder.
Hurricane term for a
tropical cyclone forming in the
Atlantic or Caribbean. They usually pose a hazard to the
Caribbean islands and south-eastern USA.
Hybrid a plant with certain characteristics achieved by
cross building different plants for their particular
qualities.
Hydration a process of
chemical weathering. Some
minerals take up water and form weaker compounds e.g.
anhydrite + water = gypsum which more readily dissolves. The
expansion can also put physical stress on the rock.
Hydraulic action lit. due to the action of water. In
geography, a process of
erosion whereby flowing water
moves unconsolidated material due to forces of drag.
Hydraulic radius stream efficiency measured by dividing
cross-sectional area of a stream by the
wetted perimeter.
A higher ratio indicates greater efficiency as area will be
greater compared to wetted perimeter and it is the latter
which reduces efficiency through friction.
Hydro-electric power (HEP) electricity produced through the
use of moving water to turn turbines and drive generators.
On a small scale HEP stations can be placed to take
advantage of natural situations such as waterfalls, but
usually they are built on a large scale by damming suitable
valleys to create a reservoir. The water in the reservoir
thus gains potential gravitational energy. When allowed to
fall through the dam to the turbines this energy is
converted to kinetic energy which drives the turbines.
Require huge initial capital outlay but then produce highly
efficient and cheap electricity. Also criticized for
flooding farming land and villages thus displacing people
and changing the environment and the river regime downstream
of the dam. Nevertheless, a non-polluting and renewable form
of energy. Provides a small percentage of world energy but
highly important in some countries having ideal geological,
meteorological and political conditions e.g. Norway and
Sweden.
Hydrograph a graph which combines a bar chart of
precipitation
in a particular event with a line graph of
discharge for a particular river channel in the
catchment area of that event and thus the reaction of
the channel to the precipitation.
Hydrological cycle the circulation of water around the
world between stores by various transfers. At a simple
level: water
evaporates from the ocean, moves with
the
wind,
condenses into
clouds, precipitates and returns to the ocean via a
river.
Hydrolysis process of chemical weathering whereby a
chemical reaction takes place between ions in a mineral and
either the H+ or OH- ions in the
water.
Hydrosere a freshwater environment in which primary plant
succession takes place.
Hygroscopic a substance that attracts water.
Hygroscopic water that water in the soil which exists as a
microscopic level as a layer around particle of clay. It is
held by electrical attraction and is unable to leave the
soil.
Hypothesis the proposition of a relationship between
variables which can then be tested and either rejected or
accepted.
HYV see high yielding variety.
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