Glossary - Fundamentals of the Physical Environment - page 898

Microclimate The climate of the land surface, extending no more than a few metres
above ground and strongly influenced by its material, morphological and organic
components.
Mid - ocean ridge A broad, linear ridge emerging from the ocean floor along rising
mantle plumes and the focus of rifting and sea-floor spreading; basalt effusion forms
new oceanic crust at this constructive margin .
Migmatization The mineralogical and structural alteration of rock at extreme ranges of
temperature and pressure, causing significant remelt.
Mineralization The decomposition of organic compounds, which results in the
production of mineral nutrients in ionic form.
Minerogenic sediment Sediment (or soil) derived solely from inorganic, mineral
sources.
Minor nutrient A plant nutrient needed in relatively small amounts (e.g. calcium,
sulphur, magnesium).
Misfit stream A stream which appears to underfit its valley, as indicated by its
diminutive size and meander wavelengths being much shorter than those of the valley
itself; attributed to a climatically related reduction in stream discharge.
Mistral A dry, cold air outflow moving south and channelled along the lower Rhône
valley in France.
Moder Surface organic matter, intermediate in form between mull and mor, and
consisting mostly of partly humified plant remains.
Mohr - Coulomb criteria The failure criteria for Earth materials which defines a state of
limiting equilibrium when the shear stress acting on the material exactly equals the
material's internal shear strength comprising cohesion, internal friction and normal
stress.
Molasse The sedimentary product of syn-tectonic or early post-tectonic erosion of a new
orogen , consisting of coarse clastic , and mostly terrestrial sediments.
Mollisols A soil order (USDA classification) characterized by base-rich soils with a dark,
organic-rich surface horizon.
Monadnock An isolated mountain in a peneplain , representing a residual feature of
extensive denudation.
Monoclimax theory The theory of climax vegetation which emphasizes that only one
type of climax will ultimately develop in a specified climatic region; it will be in
stable equilibrium with climate and soil.
Montane Said of the mountain forest belt or used more generally to denote a
characteristic of mountainous terrain.
Montane forest A cool, mountain forest community.
Montmorillonite An expanding 2:1 type of clay mineral; isomorphous replacement of
aluminium by iron and magnesium is common in the alumina sheet.
Mor An acid organic matter horizon consisting of litter (leaves, twigs, wood) overlying
partly decomposed, fermenting plant remains.
Moraine Ridge-like accumulations of glacier debris, carried as glacier surface medial
and lateral moraines or deposited at the ice margin by a variety of passive release or
active push processes; it is mostly composed of glacial till with admixed glaciofluvial
sediment and is also known as ground moraine when deposited in extensive,
amorphous sheets.