G8 – see Group of Eight.

Gabbro – an intrusive basalt.

Gamma index – a measure of connectivity in a network which compares actual number of edges (e) with maximum possible number of edges for the vertices (v) in that network.

                        γ or e(max) =        e            x 100

                                                3(v-2)

Garden city -in the UK, a planned settlement with low housing density. The brainchild of Ebenezer Howard as a result of social concern for poor urban and rural living conditions for working people. The first was begun in 1903 at Letchworth in Hertfordshire and a full history of the movement can be found at: www.letchworthgardencity.net

Garden festival -in the UK, a large scale renovation of derelict inner-city land by designating it for the planting of specially designed gardens. The improved image of the area would then assist the development of economic and residential projects in the area.

Garrigue -the shrub vegetation of the Mediterranean region where soils are thin and dry and have been converted to growth of herb plants e.g. thyme and rosemary.

GATT -see General Agreement on Tariffs and Trade.

Gavelkind -see fragmentation.

GDP -see gross domestic product.

Gelifluction -a form of mass movement in which thawed upper soil layers move over permafrost.

General Agreement on Tariffs and Trade -precursor to the World Trade Organisation.

General circulation -in the atmosphere, the general pattern of wind and pressure at a global scale. See tricellular model.

Genetically modified crop -the placing of a gene from one organism into another so that the latter can take on a quality of the former that it doesn otherwise have. Thus organisms can be modified to grow larger, faster etc. or to be made immune to certain diseases. Currently highly controversial. Proponents see a wealth of agricultural, nutritional and medicinal problems solved this way. Those against warn of the unknown side effects for the environment and our bodies.

Gentrification -the renovation of the housing fabric in an old, usually inner-city area, when more affluent groups displace lower income groups en masse over a relatively short period of time. May be triggered by a clear event such as the improvement or provision of a better transport link, or by something less tangible such as a fashion trend taking off in the housing market.

Geodesy -the science of measuring the surface of the earth.

Geographic Information System -the creation of a database of geographic information from a variety of sources which allow the cross-referencing and compilation of different data sets so that relationships may be observed or postulated.

Geologic time - The total time involved since formation of the earth to the present time.

Geologic time scale -see http://www.geosociety.org/science/timescale/timescl.htm

Geomorphology -the science of understanding landform formation.

Geostationary orbit -an orbit path that keeps a satellite over the exact same point on the earth surface at all times.

Geostrophic wind -wind blowing parallel to isobars because of deflection of the pressure-gradient force by the Coriolis Force.

Geothermal -heat from within the earth. By pumping water down to hot rock layers where magma is close to the surface, we can use the resultant steam to drive turbines and produce electricity. On a smaller scale the water can be used directly to heat swimming pools and spas and the like.

Ghetto -an area, usually in slum condition, where an ethnic group is dominant.

Gini coefficient -G= ½ Σ(X_i -Y_i)     X_i and Y_i are two sets of data expressed as a percentage. The coefficient shows how alike they are from identical (0) to as unidentical as they could be (100).

GIS -see Geographical Information System.

Glacial -of or pertaining to: or         a cooler period of climate during which glaciers advance (ice age)

Glacial budget -the net result of accumulation and ablation.

Glacial diversion -see diffluence.

Glacial landform -a landform produced by glacial erosion or deposition.

Glacial movement-two types:

• basal slipping -pressure between the ice and the surface creates friction and heat which slightly melts ice in contact. This lubricates the underside of the glacier allowing it to flow.

• internal distortion -gravitational forces can cause some parts of the glacier to move more quickly then others which can eventually lead to cracks appearing in the ice.

Glacial retreat -when ablation exceeds accumulation causing a net loss of ice from the glacier. This usually involves the snout being found at a point in the valley short of the farthest it ever reached. Note that ice still moves downslope but that the zone of ablation now extends further up the valley.

Glacial trough -see glacial valley.

Glacial uplift -the isostatic recovery of land after ice has been removed.

Glacial valley -(also glacial trough) a broad, flat bottomed (U-shaped) valley created by glacial erosion and deposition. The erosion widened, deepened and straightened the original river valley. The deposition created the flat bottom.

Glacier -a mass of ice formed through the accumulation of multiple years of snow input causing compaction and thus the expulsion of air from within the mass.

Gleying - in soils that are waterlogged, reduction of ferric iron to ferrous iron takes place changing the colour of the soil from reddish brown to blue-grey.

Global brand -technically any brand that has been marketed extensively around the world to a wide variety (economically, socially and politically) of countries. More usually applied to those that enjoy the very highest level of recognition.

Global cooling -the cooling of the atmosphere, or more properly the decrease over time in average annual global temperature. Reasons probably include a combination of reduced greenhouse gas content, orbit fluctuations reducing insolation and global dimming.

Global dimming -the term to describe the blocking and/or scattering of insolation by particulate matter in the atmosphere, both natural (e.g. volcanic ash) and due to human activity (e.g. burning coal).

Global village -the idea that the world is 'shrinking' as technology allows faster and cheaper communication at the global scale. Only partly true as access to the enhanced technology is severely limited. Most of the world population remains excluded.

Global warming -the warming of the atmosphere, or more properly the increase over time in average annual global temperature. Reasons probably include increased greenhouse gas content, orbit fluctuations increasing insolation and a decrease in global dimming. The term is now most commonly used to refer to that portion of the warming due to an increased greenhouse gas content caused by human activity.

GNP -see gross national product.

Gondwanaland -a supercontinent proposed by Alfred Wegener after the breakup of Pangaea (the single continent) into two. Gondwanaland was the southerly of these two.

Gorge - deep, narrow, steep (often vertical) -sided valley which usually has a river occupying its entire floor.

GPP -see gross primary productivity. 

Graben - the block of crust at the base of a rift valley which has slipped downwards due to the divergence of the crust on either side.

Graded profile -the long-section or profile of a river from source to mouth. In an ideal form there is a smooth decrease in gradient downstream, inputs equal outputs and energy equals work done. Of course this does not exist in the real world, but the profile exists as a basis for explaining changes in river characteristics downstream.

Gradient - the steepness of a slope.

Granite -a massive, intrusive rock. Detailed description here: http://www.graniteland.com/infos/home/granite

Gravel- A loose mixture of pebbles and rock fragments that are coarser than sand.

Gravitational water -the water in the soil that is unavailable to plants and which flows out of the soil as throughflow to the river channel or percolates into the rock below.

Gravity model -a formula to calculate the likely interaction between two places given their distance apart, size and barriers (or lack of connectivity) between them.

 

                                    I_ij = P_i x P_j

                                           (d_ij)^k

where I is the interaction, P is population, d is distance and k is the resistance to movement. i and j are the two places. Distance could be substituted by time or cost where appropriate.

Green belt -in the UK, an area of land surrounding an urban area in which planning restrictions severely curb new housing, commercial  and industrial developments. Designed to stop urban sprawl. As they generally remain as they were when designated, and as building developments have occurred either in settlements beyond them or taken place as redevelopment of derelict land in the urban area, they can be said to have been a success. Pressure continues to build however, and it remains to be seen whether they will survive.

Greenfield site -one on which no building has taken place.

Greenhouse effect -the class="d-title" name for the system by which the earth retains some insolation. One of the fundamental preconditions for the development of life. Without it temperatures would be too low for water to be anything other than ice, and organisms could not function. Insolation arrives at the atmosphere. A portion of it is reflected back to space or absorbed by water and solids in the atmosphere. About half reaches the surface and again a portion is simply reflected back to space. The rest is absorbed by vegetation or the surface. The energy that is absorbed by the surface is then radiated to the air and is held by the greenhouse gases - carbon dioxide, methane, di-nitrogen oxide, CFCs and water vapour.

http://www.ucar.edu/learn/1_3_1.htm

Greenhouse gas - A gas, such as water vapour, carbon dioxide, methane, chlorofluorocarbons (CFCs) and hydrochlorofluorocarbons (HCFCs), that absorbs and re-emits infrared radiation, warming the earth's surface and contributing to climate change (UNEP, 1998).

Green movement -non-governmental organizations, political parties and, increasingly, public opinion which propose that care for the environment should inform and mould our behaviour much more than it has historically.

Green revolution -most properly refers to the development of higher yield varieties of maize (Mexico) and rice (India) in the 1960s. Now used more widely to refer to the application of these crops along with modern farming techniques across the ELDW. While yields have increased and farmers-livelihoods have been improved, there has also been environmental damage and a widening income gap between richer and poorer farmers, so there is debate over whether these changes have been of net benefit or detriment.

Grike -the crack in a limestone pavement.

Gross domestic product -the total summed value of the output in a country for a year. Usually calculated by measuring expenditure in consumption, investment, government and net exports (exports minus imports). Needs to be adjusted for inflation or the relative purchasing power of money so that countries can be compared. Also often expressed as a per capita figure to take population sizes into account for certain comparisons.

Gross national product -Gross domestic product plus net income from abroad. Net income from abroad is income earned from overseas investment minus the value of income earned by overseas investors in the domestic economy. Needs to be adjusted for inflation or the relative purchasing power of money so that countries can be compared. Also often expressed as a per capita figure to take population sizes into account for certain comparisons.

Gross primary productivity -the addition, through photosynthesis, of organic matter in plants measured in dry grammes per square metre per year.

Ground frost - frost within the upper layers of the soil.

Groundwater -the store of water that has moved by percolation into the lower layers of the soil or the bedrock.

Groundwater flow -the flow of water through the groundwater store.

Groundwater discharge -the reemergence of groundwater to the surface at springs or resurgences, or by seepage.

Groundwater recharge -the addition of water to the groundwater store.

Group of eight -Canada, France, Germany, Italy, Japan, Russia, UK and USA. The world richest countries whose representatives regularly meet at all levels to determine economic, social and political policy which can reverberate around the world due to the collective power of these nations. Formerly the G7, Russia joined in 1998. Keep an eye on when China might come to the table and create the G9.

Growth pole -a particular site, or small area, where economic development is focused setting off wider growth through cumulative causation. While they may have been recognized as occurring naturally in human economic spheres, in modern times governments especially have tried to create them as a tool of economic development at the regional scale.

Growing season -the length of time in the year available for crop growth. Can be defined by gap between last damaging frost of one winter and first damaging frost of the next. Alternatively, the number of consecutive days with temperature above 6蚓.

Groyne -a wooden wall built across a beach from land to sea. Designed in the 19^th century to stop the removal of sand from beaches becoming popular with new tourists, they became important parts of many coastal protection schemes. Discredited in modern times as having too big an impact on other parts of the coast through interrupting the natural process of longshore drift by denying natural beach material to 'downdrift' sections of coast.

Guelta - pools found in overly-deepened portions of river beds in mountainous areas of North Africa. These may be previous plunge pools or any place where higher rates of removal lowered a portion of the bed. Water content need not be permanent.

Guest worker -English translation of a German term for economic migrants, mostly from Turkey. They were labelled so as they came to do low skilled, low paid jobs and it was thought that their stay in Germany would be short. In fact many have become permanent migrants and have been joined by their families.

Gulf Stream -a warm ocean current that originates in the Caribbean and flows north-east across the Atlantic where it becomes the North Atlantic Drift and is responsible for the mildness of the climate in the UK and Ireland.

Gully - channel formed on a poorly vegetated hillside by soil erosion. Only contain water during rainstorm events.

Guyot -an undersea mountain which is characterized by a flattened summit.