- This article is about the landform. Mountain was also the name given to the steam locomotive type classified as 4-8-2 in the Whyte notation. Mountain was also the name of a rock band in the late 1960s and
early 1970s.
A mountain is a landform that extends above the surrounding
terrain in a limited area. A mountain is generally much higher and steeper than a
hill, but there is considerable overlap, and usage often depends on local custom; see also Dune.
A mountain is usually produced by the movement of lithospheric
plates, either orogenic movement or epeirogenic movement. The
compressional forces, isostatic uplift and intrusion of igneous matter
forces surface rock upwards, creating a landform higher than the surrounding features. The height of the feature makes it either
a hill or, if higher and steeper, a mountain. The absolute heights of features termed mountains and hills vary greatly according
to an area's topography. The major mountains tend to occur in long linear arcs,
indicating tectonic plate boundaries and activity. Mountain creation tends to occur in discrete periods, referred to as orogenies
(orogeny). Two types of mountain are formed depending on how the rock reacts to the tectonic forces - block mountains or fold
mountains.
Some isolated mountains were produced by volcanoes, including many apparently
small islands that reach a great height above the ocean floor.
Block mountains are created when large areas are widely broken up by faults creating large vertical displacements. The
uplifted blocks are block mountains or horsts. The intervening dropped blocks
are termed graben, these can be small or form extensive rift valley systems.
This form of landscape can be seen in East Africa, the Vosges, the Basin and Range province of Western
North America and the Rhine
valley.
Where rock does not fault it folds, either symmetrically or asymmetrically. The upfolds are anticlines and the
downfolds are synclines, in asymmetric folding there may also be recumbent and overturned folds. The Jura mountains are
an example of folding. Over time, erosion can bring about an inversion of relief, the soft upthrust rock is worn away so the
anticlines are actually lower than the tougher rock of the synclines.
The height of a mountain is that above mean sea level. Thus a mountain may be
higher than another one even if the top is closer to the center of the earth.
The highest mountain on Earth is Mount Everest, set in the world's most significant mountain range, the Himalayas. Another contender for this title is Mauna Loa, which
stands taller than Mount Everest when measured from its base on the ocean floor but not in terms of summit altitude above sea
level. The summit of Mount Chimborazo in Ecuador is 2,150 m further
away from the Earth's centre than that of Everest, since the Earth bulges at the equator, but at 6,272 m it is not even the tallest peak in the Andes. The
tallest mountain in the solar system is Olympus Mons, located on Mars.
Some mountains are very difficult to climb, and offer spectacular views. Some people therefore enjoy the sport of mountaineering. Mountains are also the site for the sport of downhill skiing.
A popular form of playing at the beach is making
a sand "mountain".
See also
|