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Paleozoic an era of
geologic time lasting from 570m
to 245m years ago.
Pan
see
hardpan.
Pandemic
disease spread over a wide geographical area.
Pangaea
the name that Wegener gave to his proposed single supercontinent in his theory of
continental drift.
Parent-material rock or
regolith from which the
inorganic, mineral component of a soil is derived.
Pastoral
farming the rearing of animals for meat, milk, wool, skins
etc.
Patterned ground in
periglacial areas, the
appearance of lines and polygonal layouts of stones on the
surface produced by the sorting of different sizes of
material during the expansion and contraction of the soil
with
diurnal temperature variation.
Peak
flow the highest
discharge found in a river channel
in response to a particular rainfall or snowmelt event.
Peak
land value point the location of the highest land value in
an urban area.
Peat a
type of soil formed in cold wet conditions which inhibit
full and proper
decomposition of the
litter layer.
Semi decomposed leaves and other litter material remain
recognizable within the soil which can be cut, dried and
burned as fuel in marginal areas where other more efficient
fuels may not be readily available.
Pebble
a smooth, rounded fragment of rock that is larger than
gravel but smaller than a boulder, in the range of 10-100mm
in diameter.
Ped a
structured unit of soil created when particles become
grouped and bound together. Different shapes of unit occur
under different conditions: crumb, block, plate, column and
prism.
Pedestrianisation the temporary or permanent blocking of
streets to vehicular traffic.
Pediment
concave, rock-cut, slope found between a cliff face and a
valley floor in arid and semi-arid areas.
Pedogenesis lit. soil formation.
Pelean
eruption after the 1902 eruption of Mount Pelιe
in Martinique, an extremely violent eruption that begins
with an explosive
pyroclastic cloud.
Pennsylvanian a period of geologic time lasing from 320m
to 286m years ago.
Percolation downward movement of water through soil and
bedrock.
Perennial lit. lasting all year or for several years.
Periglacial the area at the edge of a
glacier or
ice sheet which is not covered by ice but experiences
very cold conditions. May also be used to refer to high
altitude environments or cold high latitudes as well.
Periphery lit. the edge or margins. In human geography,
those areas which have a poor economic status and thus
suffer from the associated social conditions. Unemployment
and crime are high, incomes and general living standards are
low. The area may be geographically marginal to a core
region at a number of scales.
Permafrost frozen ground. Varies widely in scope and depth
and in the period of the year for which it exists. A common
feature of
periglacial environments. See
continuous
permafrost,
discontinuous permafrost and
sporadic permafrost.
Permeable a rock which can absorb water (porous) or
allow water to pass through cracks and joints (pervious).
Permian
a period of
geologic time lasting from 286m to 245m
years ago.
Pervious
allowing water to flow along cracks or joints.
Pesticide any chemical sprayed on crops to prevent disease
or to kill pests which attack the plants. In modern times,
concerns have been raised as to their safety as studies have
not had enough time to see the full long-term effects of
consuming foods treated this way.
Phanerozoic the current eon of geologic time that began
2500m years ago.
Phosphates phosphorous-based fertilizers. Traditional
societies dumped unwanted or unusable fish catches on top of
the soil. In modern times, more phosphates have been derived
from rocks which are quarried or mined.
Photochemical smog a heavy, brown coloured, air pollution
formed by the reaction of vehicle and factory emissions with
sunlight to produce ozone which is harmful to humans,
animals and plants.
Photovoltaic cells a unit, usually of silicon, which is
able to collect and store, temporarily, energy from the sun
to produce electricity.
Physical
weathering (also mechanical weathering) a process of
weathering which results in smaller pieces of the same rock
material being produced.
Phytoplankton a miniscule plant which grows and lives in
the upper layers of the ocean and which forms the basis of
the marine food chain or web.
Piedmont
where a mountain range abruptly falls into a lowland area.
Piedmont
glacier a glacier formed when a valley glacier spills from
an alpine range onto a lowland plain.
Pingo -
a dome-shaped hill in a flat
tundra plain, often
having a depression in the summit. Closed system pingos
occur in areas of continuous permafrost where unfrozen water
beneath lakes becomes overly saturated and then expands as
the permafrost advances. Open system pingos occur when water
within sediments rises towards the surface and then freezes
pushing those sediments upwards.
Pioneer
used to define a species or community of plant(s) that is
first to colonise a previously barren area.
Plagioclimax the combination of plant species in an area
brought about by human interference. Much of the European
landscape is plagioclimax.
Plantation a large-scale form of agriculture in which a
tree or bush species is planted from which a fruit, leaf or
sap is harvested. Crucially the plants are not cut and
replanted each year but remain in situ for a long period of
time while having the relevant part harvested from them.
Planned
economy see
command economy.
Plant
succession the sequence of plant species that inhabit an
area from the
pioneers that first arrive, through to
the
climax community.
Plate
tectonics the theory concerning the structure of the earth
and the processes occurring which explain the configuration
of the continents and the location of earthquakes and
volcanic activity.
There are three types of plate margins, or boundaries
between plates, depending on the two types of crusts that
are interacting: oceanic with oceanic, continental with
continental, or continental with oceanic. The rift
valleys of the Atlantic are an example of an oceanic margin
where divergence has occurred, while oceanic convergence is
illustrated by a striking example in the Pacific. There,
subduction of the Philippine Plate by the Pacific Plate has
created the Mariana Trench, which at 36,198 ft. (10,911 m)
is the deepest depression on Earth.
Playa
a temporary shallow lake with extremely high salinity. Forms
in arid and semi-arid areas and usually evaporates away
relatively quickly leaving behind a flat deposit of salts,
clays and silts.
Pleistocene first
epoch of the
Quaternary, 2
m. years BP to 10,000 BP. Characterised by
glacials
and inter-glacials.
Plucking
a form of
glacial
erosion in which ice
freezes on to rock and pulls it away when the glacier moves
on.
Pluton
intrusive
igneous rock of any mass.
Pluvial
wet period during the
Pleistocene evidenced by
fluvial features
In currently arid areas.
PLVI
see
peak land value intersection.
Podsol
soil type found in cold, wet climatic areas in high
latitudes. As
precipitation exceeds
evapotranspiration the soil becomes waterlogged and
minerals are
leached from the upper layers into the
lower layers. Low organism presence means minimal mixing and
therefore highly defined
horizons.
Point-bar gently sloping inner bank of a meander. The
shorter distance around the inside of the bend requires a
lower velocity and therefore
deposition. Leads to the
encroachment of the inner bend across the channel.
Polar
cell one of the cells of atmospheric circulation in the
tri-cellular model.
Polarization the disparate development of wealth around a
core leaving a much poorer
peripheral area.
Pollen
analysis the study of preserved pollen particles used to
reconstruct past climatic conditions based on the types of
plants prevalent at the time.
Population density number of people per unit area, usually
people per square kilometre.
Population distribution the variation in
population
densities over wide areas.
Population policy government interventions to try and
control high population growth, stimulate low population
growth or control the distribution of people within a
country.
Population structure the ratio of age groups, by sex,
within a population.
Pore
spaces the space between particles in a rock or soil,
usually filled with air or water.
Porosity
the degree to which a rock or soil is
porous.
Porous
the ability to allow water to occupy
pore spaces.
Positive feedback in a
system, those changes which serve to increase the effect.
Potential evapotranspiration theoretical amount of
moisture that could be lost from the surface to the
atmosphere if it were available.
Pothole
two types:
-
bowl-shaped holes found in river beds formed by abrasion
by load caught in eddies.
-
tunnels in limestone areas.
Precambrian a span of geologic time lasting from 4600m to
570m years ago.
Precipitate a solid that has formed out of dissolved
state.
Precipitation two types:
-
movement of water from the atmosphere to the earths
surface.
-
solidification of a substance from a liquid where it has
been held in
solution.
Pressure
gradient in the atmosphere, the rate at which pressure
changes across space. Higher rates of change will create
faster winds.
Pressure
melting point under a glacier, the pressure brought to
bear by the mass of ice above can lower the freezing/meting
point of water.
Pressure
release the removal of overlying rock which releases
pressure on underlying
strata causing them to expand
and crack.
Prevailing wind the direction from which wind most
frequently blows in a particular place.
Primacy
when the primate city is overly large compared to the size
expected according to the
rank-size rule.
Primary
consumers the
herbivores which feed on plants and
are available as food to
carnivores.
Primary
sector in industry, those activities concerned with
extraction and or exploitation of
raw materials.
Primary
succession the colonization of a previously barren area by
a plant community and its development to a
climax
community.
Prime
meridian - 0˚
of
longitude. The line joins the north and south
poles and passes through the Royal Observatory at Greenwich
in east London, England.
Primogeniture inheritance of an estate to the eldest son,
or eldest child, only.
Prisere
the stages that make up a primary succession.
Private
sector the firms in an economy owned by shareholders or
individuals.
Privatization the change of ownership of a firm or
industry sector from government to private hands.
Producer
two types:
·
in human
geography, a company making physical goods from raw
materials.
·
In
physical geography, see
autotroph.
Production the conversion of raw materials into usable
products.
Production-line the organization of a factory so that each
stage of the manufacture is physically next to the one
before and a good moves along the line being added to as it
goes until it is complete.
Productivity the efficiency with which a company turns
inputs into
outputs.
Proportional symbols data presentation where the size of a
symbol, or the divisions of a symbol, are proportional to
the size of the data being represented.
Protectionism the placing of barriers to trade used by a
government to try and promote domestic products over
imports.
Proterozoic an eon of
geologic time lasting from
2500m to 570m years ago.
Psammosere
succession of plants in a sandy
environment such as coastal dunes.
Public
corporation an economic enterprise that has been
nationalized.
Public
sector all enterprises and activities owned and funded by
the government.
Pull
factor an attractive quality of a place which pulls
migrants to it.
Push
factor a negative quality of a place which pushes people
to migrate away from it.
P-wave
a seismic wave released during an earthquake which travels
in a collision fashion and can thus travel through gases,
liquids and solids.
Pyramidal peak the classic, pyramid-shape of a
mountain-top formed when three or four
corries form
on different sides of the mountain and erode backwards
towards each other.
Pyroclastic cloud the cloud of gas, ash, dust, stones and
rocks emitted during a highly explosive
volcanic eruption.
Pyrophytes plants adapted to withstand fire, and to
require fire for regeneration.
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