P Flashcards
Pacific Ring of Fire
The ring of volcanoes to be found around the Pacific Rim.
Many of the Rim’s coastal areas are subduction zones, hence the pattern of activity.
Pacific Rim
The countries at the margins of the Pacific ocean.
Palaeoclimate
Evidence of past climate that can be seen in the present e.g. glacial landforms in non-glacial areas, oxygen isotopes in ice deposits.
Palaeomagnetism
Evidence of past differences in the alignment of the Earth’s magnetic field.
Provides some of the strongest evidence for sea-floor spreading.
Paleozoic
An era of geologic time lasting from 570m to 245m years ago.
Palustrine
Literally of bogs, marshes or swamps.
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
Literally soil formation.
Pelean eruption
After the 1902 eruption of Mount Pele 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
Literally 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
Literallu 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.
Phreatic divide
An underground watershed.
Marks the outer source of groundwater flow to a particular river.
May be caused by sloped bedding planes for example.
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.