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M - Magma to Mull - Geography Dictionary

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Magma – molten rock below the surface, either held within the crust or in the mantle.

Magma plume – a rising body of magma within the mantle.

Malaria – a fever caused by a single-cell parasite. It is borne by certain species of mosquito and transferred to humans by mosquito bite. In many warm, tropical areas of the world it is endemic. Although its range has diminished, global warming threatens to expand it once again. Once caught, it cannot yet be fully eradicated but can be controlled if treated early. In strong adults it will likely recur throughout the lifetime but it will kill weaker individuals. Hundreds of millions are infected each year and it is responsible for 1 million deaths per year worldwide, 90% in Africa.

Malnutrition -the body response to a lack of food in terms of the calorific energy intake or a lack of the right food in terms of the proportions of energy, minerals, protein, and vitamins. Can expose people to disease by weakening resistance, or kill people through organ failure.

Malthus, Thomas Robert -in geography, renowned for his theory of population as it relates to resources. Based on the principles that food production increases at an arithmetic rate, whereas population increases at an exponential rate, Malthus stated that population had to outstrip resources over time. He suggested that this would trigger both preventative checks, such as postponement of marriage or reduction of family size, and positive checks, such as famine or war, to reduce population. Unforeseen changes in technology and agricultural organization discredited his theory as massive food production increases through the nineteenth and twentieth centuries negated his ideas. However, his theory has found new favour in the late twentieth century as neo-Malthusianism.

Mangrove swamp -a type of wetland forest made up of salt-adapted trees found in the inter-tidal zone of tropical coast areas. Provide a rich habitat for strong biodiversity and help protect coasts from erosion.

Mann, P. -proposed, in 1965, a model of urban land-use which integrated the ideas of Burgess and Hoyt into a single model for British cities. The model was made up of concentric circles divided into wedge-shaped sectors which allowed for the more segmented nature of development and redevelopment in urban environments in the real world.

Manning N -after Robert Manning. A formula of river velocity:

                                    v= R0.67  x  S0.5


where R is hydraulic radius, S is channel slope and n is Manning roughness coefficient.

Manningroughness coefficient -after Robert Manning. A measure of channel resistance which is used as part of a formula to calculate velocity (Manning N). The values vary between 0.02 for smooth channels and 0.10 for very rough channels.

Mantle -the layer of the earth between the crust and the core. The upper part is the lithosphere (which includes the crust above). The majority of the mantle is the asthenosphere which extends to a depth of 2900km. Mostly made of silicates, iron and magnesium.

Manufacturing industry -businesses that convert raw materials into finished products or component products, and those that convert or assemble component products into finished products.

Map projection -the system of representing the three-dimensional surface of the world into the two-dimensional surface of a piece of paper.

Maquis -scrub vegetation made up of plants such as heathers which can grow up to 3 metres in height. It is found on areas of impermeable rock in Mediterranean regions where the original forests have been cleared by humans.

Mariculture -a branch of aquaculture specializing in the cultivation of marine organisms in salt water usually by enclosing a cubic volume of a natural waterway. May be for food e.g.  fish, shellfish & seaweed  or non-food e.g. cosmetics & jewellery.

Marina -a man-made dock or mooring area, protected from the sea, particularly for the mooring of pleasure craft.

Maritime -of the sea.

Maritime climate -the climate of land areas in coastal regions where the characteristics of the climate are clearly affected by the proximity to the water mass. For example, the UK has a very different climate to continental areas at the same latitude.

Market -can be seen in two ways:

  • a place where goods and/or services are offered for sale.

  • the demand for a good or service in an area from local to global scale.

Market economy -one run on laissez-faire principles.

Market gardening -highly intensive (in capital terms) farming of flowers, fruit and very perishable vegetables on a commercial basis. Usually located close to urban areas as an immediate market, but large enterprises may also distribute at national and regional scale.

Market town -a town whose main function is to act as a market place for the surrounding area.

Marram grass -a species of grass that is tolerant of dry, sand dune environments. Important as a stabilizing factor in the development of a psammosere.

Marxism -a political theory and/or practice where the emancipation of the working classes through class struggle is seen both as the driving force of history and the goal of modern society. Developed by Karl Marx and Fredrich Engels, and most famously presented in their Communist Manifesto of 1848. In depth analysis here:

Mass production -the production of finished goods on a very large scale i.e. large numbers of units coming from a single production facility or factory.

Mass movement -the downslope movement en masse of rock, earth or water. For an excellent overview see:

Material index: after Weber,

    MI=   weight of raw materials needed to produce a unit of finished product

                        the weight of a unit of finished product

Mean Annual Flood -over a series of years, the mean average of the maximum flood discharges experienced in a particular river. Recurrence interval should be once every 2.33 years.

Meander -an exaggerated, looping, bend in a river. Once formed, meanders grow in such a way that they will eventually cut themselves off from the river and cease to exist. Flow around the outer bend is faster than on the inner meaning erosion occurs there to undercut the outer bank and material is moved across the meander and deposited on the slower inner bend. The meander can therefore migrate across the land on which it flows -usually a lower course floodplain. Thus, over time, the 'neck' of the loop closes until it joins and the river takes the shortest route, cutting off the meander and forming an ox-bow lake.

Mechanical weathering -see physical weathering.

Mechanisation -the replacement of human and/or animal labour with machines.

Mediterranean climate -climatic characteristics first identified around the Mediterranean region but since discovered to exist in the Cape region of South Africa, central California, central Chile, and the parts of southern Australia having a west facing coastline. Annual temperature range is approximately 15˚C, with summers being very hot and winters mild. Annual precipitation is 400-700mm, most of which falls during winter months. This is the result of the ITCZ coming closer in summer and squeezing the sub-tropical high pressure zone of descending air into these areas. In winter, the movement of the ITCZ away pulls the Ferrel/Polar convergence into these zones bringing westerly winds and weather associated with depressions.

Megalopolis -vast expanse of essentially continuous built-up area created by merging urban centres. Coined particularly in the U.S.A. where urban sprawl has blurred the distinctions between certain cities, e.g. BosWash: the extensive built-up area from Boston, through Massachusetts to Washington D.C.

Meltwater -liquid water that has come from melting snow or ice.

Meridian -a line tracing a circle that passes through both poles.

Mesa -a flat-topped hill standing up from a plain.

Mesosphere -the layer of the atmosphere above the stratosphere. Air temperature once again declines with altitude.

Mesozoic -an era of geologic time lasting from 245m to 65m years ago.

Metamorphic rock -rocks created by the chemical alteration of existing rocks under the influence of temperature, pressure, or both.

Meteorology -the study of the atmosphere.

Methane (CH4) -a naturally occurring gas which is associated with decomposition and with oil deposits. It is a greenhouse gas and burning it, or releasing it to the atmosphere will lead to the creation of carbon dioxide and water vapour, both themselves greenhouse gases. It is therefore of great importance in climate change.

Microclimate -the local climate conditions that show variations to the general climate conditions of the wider environment.

Mid-oceanic ridge -an elongated range of undersea mountains formed by the extrusion of lava, combined with the upward pressure of a convection plume, at a divergent plate margin.

Migration -properly, any movement of a living organism across space, or between locations. In geography, most commonly applied to population movements. It can be used to describe daily and seasonal movements (e.g. commuting and holidaying), but is most usefully applied to movements lasting longer than one year. Generally classified by motivating reason:

  • forced e.g. poverty, war, famine.

  • voluntary e.g. looking for better work, education.

While not definitive, forced migrations are usually made by large numbers of people from the area suffering the motivating factor whereas voluntary migrations are made by individuals, though the motivating factor could effect a collection of individuals from the same source area.

Milankovitch, Milutin -proposed climate variations are due to variations in the amount of insolation caused by variations in the earth orbit and positioning in space.

Mining -extraction of minerals from the crust for industrial use.

Mist -a light fog. Visibility usually remains beyond 1 kilometre.

Mistral -the French term for a katabatic wind.

Mitigation – management strategies which involve a direct attempt to stop or reverse the perceived problem or build work-around solutions.

Mixed economy -the most common form of national economic organization, somewhere between a command economy and a market economy. The degree of government intervention is the basis of most political division in countries using this system.

Moho -see Mohorovicic discontinuity.

Mohorovicic discontinuity (Moho) -after Mohorovicic, the junction between the crust and the mantle.

Monoculture -an agricultural system in which the cultivation of a single crop is the norm.

Monopoly -control of supply of a product or service to a particular market. In its pure form this would mean a single supplier, but his rarely occurs. Highly dominant suppliers can however exert monopolistic controls in certain circumstances.

Monsoon -a seasonal prevailing wind. Two types:

  • summer monsoon: intense heating of a continental mass in summer months due to the arrival of the heat equator causes convectional uplift over the continent and hence low pressure. This draws warm moist air from relatively higher pressure maritime areas bringing high levels of rainfall and humidity.

  • winter monsoon: reverse of the summer system. The heat equator is now over the maritime area and draws cool, dry air from the continental mass which means cool, dry winter months for the monsoon region.

Moor -open, often hilly, expanse of land characterized by wet, spongy, peaty soils and vegetation such as moss, coarse grass and heather.

Mor -a humus layer with high levels of acidity. Dark, even black in colour, not fully decomposed and lacking in nutrients.

Moraine -debris deposited by a glacier. Three main types:

  • terminal moraine -marks the furthest point the glacier reached as it ulldozed' material ahead of the ice mass.

  • lateral moraine -deposits of load carried at the edges of the glacier.

  • medial moraine -deposits of the load carried in the middle of the glacier where two lateral moraines came together from tributary glacier.

Morphology -lit. form, shape or structure. Can be applied in physical geography e.g. the morphology of a hill, or human geography e.g. the morphology of a village.

Mouth -where a river meets a body of water.

Mudflow -a fairly rapid mass movement usually occurring after heavy rainfall.

Mull -a dark, crumbly, nutrient rich humus layer.

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