Glossary of Terms: M

Macronutrient

Nutritional element required by an organism in relatively large quantities.

 

Mafic Magma

Magma that is relative poor in silica but rich in calcium, magnesium, and iron content. This type of magma solidifies to form rocks relatively rich in calcium, magnesium, and iron but poor in silica.

 

Magma

Molten rock originating from the Earth's interior.

 

Magma Plume

A rising vertical mass of magma originating from the mantle.

 

Magnetic Declination

The horizontal angle between true north and magnetic north or true south and magnetic south.

 

Magnetic Field

The space influence by magnetic force. The Earth's magnetic field is believed to be generated by the planet's core.

 

Magnetic North

See North Magnetic Pole.

 

Magnetic Reversal

A change in the polarity of the Earth's magnetic field. In the past 4 million years there have been nine reversals.

 

Magnetic South

See South Magnetic Pole.

 

Magnetosphere

Zone that surrounds the Earth that is influenced by the Earth's magnetic field.

 

Magnitude

(1) The quantifiable size of a natural event.

(2) A quantitative measure of the size of an earthquake using the Richter scale.

 

Mammal

Group of warm blooded vertebrate animals. Common characteristics found in these organisms include: hair, milk secretion, diaphragm for respiration, lower jaw composed of a single pair of bones, middle ear containing three bones, and presence of only a left systemic arch.

 

Mangrove

Treed wetlands located on the coastlines in warm tropical climates.

 

Mantle

Layer of the Earth's interior composed of mostly solid rock that extends from the base of crust to a depth of about 2,900 kilometers.

 

Map

An abstraction of the real world that is used to depict, analyze, store, and communicate spatially organized information about physical and cultural phenomena.

 

Map Projection

Cartographic process used to represent the Earth's three-dimensional surface onto a two-dimension map. This process creates some type of distortion artifact on the map.

 

Map Scale

Ratio between the distance between two points found on a map compared to the actual distance between these points in the real world.

 

Marble

Metamorphic rock created by the recrystallization of calcite and/or dolomite.

 

March Equinox

One of two days during a year when the declination of the Sun is at the equator. The March equinox denotes the first day of spring in the Northern Hemisphere. In the Southern Hemisphere, this date marks the first day of fall. During the March equinox, all locations on the Earth (except the poles) experience equal (12 hour) day and night. The March equinox occurs on either March 20 or 21.

 

Marine

With reference to ocean environments and processes.

 

Maritime Effect

The effect that large ocean bodies have on the climate of locations or regions. This effect results in a lower range in surface air temperature at both daily and annual scales. Also see Continental Effect.

 

Maritime Polar Air Mass (mP)

Air mass that forms over extensive ocean areas of the middle to high latitudes. Around North America, these air mass system form over the Atlantic and Pacific oceans at the middle latitudes. Maritime Polar air masses are mild and humid in summer and cool and humid in winter. In the Northern Hemisphere, maritime polar air masses are normally unstable during the winter. In the summer, atmospheric stability depends on the position of the air mass relative to a continent. Around North America, Maritime Polar air masses found over the Atlantic are stable in summer, while Pacific systems tend to be unstable.

 

Maritime Tropical Air Mass (mT)

Air mass that forms over extensive ocean areas of the low latitudes. Around North America, these system form over the Gulf of Mexico and the eastern tropical Pacific. Maritime Tropical air masses are warm and humid in both winter and summer. In the Northern Hemisphere, maritime tropical air masses can normally stable during the whole year if they have form just west of a continent. If they form just east of a continent, these air masses will be unstable in both winter and summer.

 

Mass

Refers to the amount of material found in an object (usually of unit volume).

 

Mass Balance

The relative balance between the input and output of material within a system.

 

Mass Extinction

A catastrophic, widespread perturbation where major groups of species become extinct in a relatively short time compared to normal background extinctions.

 

Mass Movement

General term that describes the downslope movement of sediment, soil, and rock material.

 

Mass Number

Total number of neutrons and protons in the nucleus of an atom. Approximate measure of the mass of an atom. Also see atomic number.

 

Mass Wasting

General term that describes the downslope movement of sediment, soil, and rock material.

 

Matric Force

Force that holds soil water from 0.0002 to 0.06 millimeters from the surface of soil particles. This force is due to two processes: soil particle surface molecular attraction (adhesion and absorption) to water and the cohesion that water molecules have to each other. This force declines in strength with distance from the soil particle. The force becomes nonexistent past 0.06 millimeters.

 

Matter

Is the material (atoms and molecules) that constructs things on the Earth and in the Universe.

 

Maunder Minimum

Period from 1645 to 1715 during which the Sun had very little sunspot activity.

 

MDC

See more developed country.

 

Mean

Statistical measure of central tendency in a set of data. The mean is calculated by adding all of the data values and dividing this quantity by the total number of data values.

 

Mean Sea-Level

The average height of the ocean surface as determined from the mean of all tidal levels recorded at hourly intervals.

 

Mean Solar Day

Time it takes to complete one Earth rotation relative to the position of the Sun (for example, from midnight to midnight). This measurement takes 24 hours and is longer than a sidereal day because it includes the effect of the Earth's movement (Earth revolution) around the Sun.

 

Meander

Sinuous shaped stream channel. Usually found in streams flowing over a very shallow elevation grade.

 

Medial Moraine

Deposit of material found down the center of a glacier. Created when two glacier and their lateral moraines merge.

 

Median

Statistical measure of central tendency in a set of data. The median is the value halfway through a data set where the values have been ordered from lowest to highest. In an even data set, the median is the average of the two halfway values.

 

Mediterranean Scrubland

See chaparral.

 

Melting

The physical process of a solid becoming a liquid. For water, this process requires approximately 80 calories of heat energy for each gram converted.

 

Meltwater

Water produced from the melting of snow and/or glacial ice.

 

Mercalli Scale

A scale for rating the power of an earthquake.

 

Mercator Projection

Map projection system that presents true compass direction. Distortion is manifested in terms of area. Area distortion makes continents in the middle and high latitudes seem larger than they should be. Specifically designed for nautical navigation.

 

Mercury Barometer

Type of barometer that measures changes in atmospheric pressure by the height of a column of mercury in a U-shaped tube which has one end sealed and the other end immersed in an open container of mercury. The force of the pressure exerted by the atmosphere on the mercury in the open container pushes mercury up the other end of the tube. The height of this level is then used as a measure of atmospheric pressure relative to the surface level of the mercury in the container.

 

Meridian

A circular arc that meets at the poles and connects all places of the same longitude.

 

Meridional

Movement of wind or ocean waters in a direction that is roughly perpendicular to the lines of latitude.

 

Meridional Transport

Transport of atmospheric and oceanic energy from the equator to the poles.

 

Mesa

A flat topped hill that rises sharply above the surrounding landscape. The top of this hill is usually capped by a rock formation that is more resistant to weathering and erosion.

 

Mesocyclone

A cylinder of cyclonically flowing air that form vertically in a severe thunderstorm. They measure about 3 to 10 kilometers across. About 50% of them spawn tornadoes.

 

Mesopause

Thin boundary layer found between the mesosphere and the thermosphere. It is usually found at an average altitude of 80 kilometers. Coldest temperatures in the atmosphere are found at the mesopause.

 

Mesophyte

Plants that have moderate water requirements.

 

Mesoscale Convective Complex

A cluster of thunderstorms covering an area of 100,000 kilometers or more. Convective circulation within this system encourages the growth of new thunderstorms for up to 18 hours.

 

Mesosphere

Atmospheric layer found between the stratosphere and the thermosphere. Usually located at an average altitude of 50 to 80 kilometers above the Earth's surface. Air temperature within the mesosphere decreases with increasing altitude.

 

Mesotrophic Lake

Lake with a moderate nutrient supply. Also see eutrophic lake and oligotrophic lake.

 

Mesozoic

Geologic era that occurred from 245 to 65 million years ago.

 

Metabolism

Describes all of the enzymatic reactions performed by the cells of an organism.

 

Metamorphic Rock

A rock that forms from the recrystallization of igneous, sedimentary or other metamorphic rocks through pressure increase, temperature rise, or chemical alteration.

 

Metamorphism

Process that creates metamorphic rocks.

 

Metasomatic Metamorphism

Form of metamorphism that causes the chemical replacement of elements in rock minerals when gases and liquids permeate into bedrock.

 

Meteor

A body of matter that enters the Earth's atmosphere from space. While traveling through the atmosphere, these objects begin to burn because of friction and are sometimes seen as luminous streaks in the sky by ground observers. Many of these objects burn up completely and never reach the Earth's surface.

 

Meteorology

The scientific study of the atmosphere and its associated phenomena.

 

Methane

Methane is very strong greenhouse gas found in the atmosphere. Methane concentrations in the atmosphere have increased by more than 140% since 1750. The primary sources for the additional methane added to the atmosphere (in order of importance) are: rice cultivation, domestic grazing animals, termites, landfills, coal mining, and oil and gas extraction. Chemical formula for methane is CH₄.

 

Mica

Silicate mineral that exhibits a platy crystal structure and perfect cleavage. Common forms of mica are biotite and muscovite.

 

Micronutrient

Nutritional element required by an organism in relatively very small quantities.

 

Microorganism

Extremely small organism that can only be seen using a microscope.

 

Microwave Radiation

Form of electromagnetic radiation with a wavelength between 0.1 to 100 centimeters.

 

Mid-Latitude Cyclone

Cyclonic storm that forms primarily in the middle latitudes. Its formation is triggered by the development of troughs in the polar jet stream. These storms also contain warm, cold and occluded fronts. Atmospheric pressure in their center can get as low as 970 millibars. Also called wave cyclones or frontal cyclones.

 

Mid-Oceanic Ridge

Chain of submarine mountains where oceanic crust is created from rising magma plumes and volcanic activity. Also associated with this feature is plate divergence which creates a rift zone.

 

Migration

Movement of organisms in an intentional way between two points in space. Many migrations are seasonal.

 

Milankovitch Theory

Theory proposed by Milutin Milankovitch that suggests that changes in the Earth's climate are cause by variations in solar radiation received at the Earth's surface. These variations are due to cyclical changes in the geometric relationship between the Earth and the Sun.

 

Milky Way Galaxy

Aggregation of about 400 billion stars in a flattened, disk-shaped structure in space. Our solar system is found in this structure.

 

Military Grid Reference System

A simplified subset of the Universal Transverse Mercator (UTM) Grid System. This rectangular coordinate system used to find location of points on the Earth's surface. Based on the Universal Transverse Mercator projection system.

 

Miller Cylindrical Projection

Map projection that mathematically projects the Earth's surface onto a cylinder that is tangent at the equator. Directions and distances are only true at the equator. Distance, area, and shape distortion increases as one moves towards the poles. Very popular projection used in world maps.

 

Millibar (mb)

A unit measurements for quantifying force. Used to measure atmospheric pressure. Equivalent to 1000 dynes per square centimeter.

 

Mineral

Component of rocks. A naturally occurring inorganic solid with a crystalline structure and a specific chemical composition. Over 2,000 types of minerals have been classified.

 

Mineralization

Decomposition of organic matter into its inorganic elemental components.

 

Mississippian

Geologic period that occurred roughly 320 to 360 million years ago. During this period, insects undergo major speciation and ferns first appear. Trees become a dominant plant form on continents.

 

Mistral

Term used to describe a katabatic wind in southern France.

 

Mitochondria

Organelle in a cell that oxidizes organic (see respiration) energy for use in cellular metabolism.

 

Mixed Tide

Tides that have a higher high water and lower high water as well as higher low water and lower low water per tidal period.

 

Mixing Ratio

The ratio between the weight (mass) of water vapor (or some other gas) held in the atmosphere compared to the weight of the dry air in a given volume of air. Usually measured in grams water vapor (or gas) per kilogram of dry air.

 

Mode

Statistical measure of central tendency in a set of data. The mode is the most frequently occurring value in a data set. Data sets can contain two or more mode values that occur with the same frequency.

 

Model

(1) Generalization of reality.

(2) System describing how a phenomenon functions.

(3) Mathematical representation of a system from which predictions or inferences can be made.

 

Moho Discontinuity

The lower boundary of the crust. At this boundary seismic wave velocities show an increase in speed as they enter the upper mantle.

 

Moist Adiabatic Lapse Rate

See saturated adiabatic lapse rate.

 

Molecule

Minute particle that consists of connected atoms of one or many elements.

 

Mollisols

Soil order (type) of the United States Natural Resources Conservation Service Soil Classification System. A mollisol soil is typically found in semiarid grassland environments. They are rich in organic matter and have an abundance of calcium carbonate nodules within the profile.

 

Mollweide Projection

Map projection system that tries to present more accurate representations of area. Distortion is mainly manifested in terms of map direction and distance.

 

Monera

Group, at the kingdom level, in the classification of life. Unicellular organisms that have a prokaryotic cell type.

 

Monocline

A fold in layered rock that creates a slight bend.

 

Monsoon

A regional scale wind system that predictably change direction with the passing of the seasons. Monsoon winds blow from land to sea in the winter, and from sea to land in the summer. Summer monsoons are often accompanied with precipitation.

 

Montmorillonite

A type of clay that has a large capacity to shrink and expand with wetting and drying.

 

Montreal Protocol

Treaty signed in 1987 by 24 nations to cut the emissions of chlorofluorocarbons (CFCs) into the atmosphere. Since 1987 the treaty has been amended to quicken the reduction in CFC production and use.

 

Moraine

A hill of glacial till deposited directly by a glacier.

 

More Developed Country (MDC)

A highly industrialized country characterized by significant technological development, high per capita income, and low population growth rates. Examples of such countries include the United States, Canada, Japan, and many countries in Europe. Also see less developed country.

 

Morphological System

This is a system where we understand the relationships between elements and their attributes in a vague sense based only on measured features or correlations. In other words, we understand the form or morphology a system has based on the connections between its elements. We do not understand exactly how the processes work to transfer energy and/or matter through the connections between the elements.

 

Morphometry

The measurement of shape. Measurements are then manipulated statistically or mathematically to discover inherent properties.

 

Moss

About 9,500 species of plants that belong to the division bryophyta. These low growing plants are common in moist habitats.

 

Mountain Breeze

Local thermal circulation pattern found in areas of topographic relief. In this circulation system, surface winds blow from areas of higher elevation to valley bottoms during the night.

 

Mouth

End of a stream. Point at which a stream enters a lake, sea, or ocean.

 

Movement

A term used in geography that deals with the migration, transport, communication, and interaction of natural and human-made phenomena across the spatial dimension.

 

Mudflow

Form of mass movement where fine textured sediments and soil mix with water to create a liquid flow.

 

Mudstone

Fine grained sedimentary rock composed of lithified silt and clay particles.

 

Multispectral Scanner (MSS)

Remote sensing device found on Landsat satellites that acquires images in four spectral bands from visible to reflected infrared.

 

Muscovite

Rock forming mineral of the mica group.

 

Muskeg

Poorly drained marshes or swamps found overlying permafrost.

 

Mutation

Change in the structure of a gene or chromosome.

 

Mutualism

Interspecific interaction where both species experience and increase in their fitness after interacting with the other species. Mutualistic interactions between species can be of two types: symbiotic or nonsymbiotic.

 

Mycorrhizae

Mutualistic association of a fungus with the root of higher plant. In this relationship, the fungus helps the plant in extracting certain nutrients from the soil. In exchange, the fungus is provided with a habitat and nutrition in the form of carbohydrates.

 

 

Citation: Pidwirny, M. (2006). "Glossary of Terms: M". Fundamentals of Physical Geography, 2nd Edition. Date Viewed. http://www.physicalgeography.net/physgeoglos/m.html