Everything about Mountains totally explained
A
mountain is a
landform that extends above the surrounding
terrain in a limited area, with a peak. A mountain is generally steeper than a
hill, but there's no universally accepted standard definition for the height of a mountain or a hill although a mountain usually has an identifiable summit. Mountains cover 64% of
Asia, 36% of
North America, 25% of
Europe, 22% of
South America, 17% of
Australia, and 3% of
Africa. As a whole, 24% of the Earth's land mass is mountainous. 10% of people live in mountainous regions. Most of the world's rivers are fed from mountain sources, and more than half of humanity depends on mountains for water.
The adjective
montane is used to describe mountainous areas and things associated with them.
Definitions
Some authorities define a mountain as a peak with a
topographic prominence over a defined value: for example, according to the
Britannica Student Encyclopedia, the term "generally refers to rises over 2,000
feet (610 m)". The
Encyclopædia Britannica, on the other hand, doesn't prescribe any height, merely stating that "the term has no standardized geological meaning".
In the United Kingdom
In
England and Wales the
Department for Environment, Food and Rural Affairs has defined "mountain" (as a
mass noun) as all land over 600 metres for the purposes of
right to roam legislation. This is a close metric equivalent of 2,000 feet (610 m). The
Land Reform (Scotland) Act 2003 doesn't appear to draw this distinction, and in
Scotland the term "mountain" is more subjective, often being used for hills exceeding 3,000 feet (914.4 m) listed as
Munros. In the United Kingdom the term "hill" is commonly used for all hills and mountains, regardless of height.
In the United States
In the United States, the
U.S. Board on Geographic Names lists hundreds of landscape features under (some as low as 100 feet) named as "mountains." This is true for all parts of the United States, including the west coast where such lofty ranges as the
Cascade Mountains dominate. And yet the Board doesn't attempt to distinguish between such features as mountains, hills, or other prominences, and simply categorizes all of them as
summit, regardless of what they're called or how high they are. However, the Board
does list
and categorize such low mountain ranges as the
Mount Tom Range (with a high point of 1,200 feet; 366 m) as
range.(External Link
)
Height
The height of a mountain is measured as the
elevation of its
summit above mean
sea level. The
Himalayas average 5
km above sea level, while the
Andes average 4 km. The highest mountain on land is
Everest, in the
Himalayas.
Other definitions of height are possible. The peak that's farthest from the center of the
Earth is
Chimborazo in
Ecuador. At above sea level it isn't even the tallest peak in the
Andes, but because Chimborazo is very close to the
equator and the Earth s at the equator, it's further away from the Earth's center than Everest. The peak that rises farthest from its base is
Mauna Kea on
Hawaii, whose peak is above its base on the floor of the
Pacific Ocean.
Even though Everest is the highest mountain on Earth today, there have been much taller mountains in the past. During the
Precambrian era, the
Canadian Shield once had mountains in height that are now eroded down into rolling hills. These formed by the collision of
tectonic plates much like the Himalaya and the
Rocky Mountains.
At (Fraknoi et al., 2004), the tallest known mountain in the
solar system is
Olympus Mons, located on
Mars and is an ancient volcano.
Volcanoes have been known to erupt on other planets and moons in our solar system in our life-times (volcanoes on Venus for example, constantly erupt) and some of them erupt ice instead of lava.
Several years ago, the Hale telescope recorded the first known live images of a volcano erupting on a moon in our solar system.
Characteristics
High mountains, and mountains located closer to the Earth's poles, have elevations that exist in colder layers of the atmosphere. They are consequently often subject to
glaciation and
erosion through frost action. Such processes produce the popularly recognizable mountain
peak shape. Some of these mountains have
glacial lakes, created by melting glaciers; for example, there are an estimated 3,000 glacial lakes in
Bhutan.
Sufficiently tall mountains have very different climatic conditions at the top than at the base, and will thus have different
life zones at different altitudes. The flora and fauna found in these zones tend to become isolated since the conditions above and below a particular zone will be inhospitable to those organisms. These isolated ecological systems are known as
sky islands and/or
microclimates.
Tree forests are forests on mountain sides which attract moisture from the trees, creating a unique
ecosystem. Very tall mountains may be covered in ice or snow.
Mountains are colder than lower ground, because the Sun heats Earth from the ground up. The Sun's radiation travels through the atmosphere to the ground, where Earth absorbs the heat. Air closest to the Earth's surface is, in general, warmest (see
lapse rate for details). Air as high as a mountain is poorly warmed and, therefore, cold. Air temperature normally drops 1 to 2 degrees Celsius (1.8 to 3.6 degrees Fahrenheit) for each 300 meters (1000 feet) of altitude.
Mountains are generally less preferable for
human habitation than lowlands; the weather is often harsher, and there's little level ground suitable for
agriculture. At very high altitudes, there's less
oxygen in the air and less protection against solar radiation (
UV).
Acute mountain sickness (caused by
hypoxia - a lack of oxygen in the blood) affects over half of lowlanders who spend more than a few hours above 3,500 meters (11,483 feet).
A number of mountains and mountain ranges of the world have been left in their natural state, and are today primarily used for
recreation, while others are used for
logging,
mining,
grazing, or see little use of any sort at all. Some mountains offer spectacular views from their summits, while others are densely wooded. Summit accessibility ranges from mountain to mountain; height, steepness, latitude, terrain, weather, and the presence or lack thereof of
roads,
lifts, or
tramways are all factors that affect accessibility.
Hiking,
backpacking,
mountaineering,
rock climbing,
ice climbing,
downhill skiing, and
snowboarding are recreational activities typically enjoyed on mountains. Mountains that support heavy recreational use (especially downhill skiing) are often the locations of
mountain resorts.
Types of mountains
Mountains can be characterized in several ways. Some mountains are
volcanoes and can be characterized by the type of lava and eruptive history. Other mountains are shaped by
glacial processes and can be characterized by their
glaciated features. Still others are typified by the
faulting and
folding of the Earth's crust, or by the collision of
continental plates via
plate tectonics (the Himalayas, for instance). Shape and placement within the overall landscape also define mountains and mountainous structures (such as
butte and
monadnock). Finally, many mountains can be characterized by the type of
rock that make up their composition. More information on mountain types can be found in
List of mountain types.
Geology
Image:Himalaya_annotated.jpg|thumb|right|The Himalayan mountain range with Mount Everest.
rect 58 14 160 49 Chomo Lonzo
rect 200 28 335 52 Makalu
rect 378 24 566 45 Mount Everest
rect 188 581 920 656 Tibetan Plateau
rect 250 406 340 427 Rong River
rect 333 149 409 186 Changtse
rect 550 284 677 303 Rongbuk Glacier
rect 478 196 570 218 North Face
rect 237 231 346 267 East Rongbuk Glacier
rect 314 290 536 309 North Col north ridge route
rect 531 79 663 105 Lhotse
rect 582 112 711 130 Nuptse
rect 603 232 733 254 South Col route
rect 716 165 839 206 Gyachung Kang
rect 882 147 967 183 Cho Oyu
rect 1 1 999 661 Press hyperlinks (or button to enlarge image)
desc bottom-left
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
terrain. The major mountains tend to occur in long linear arcs, indicating tectonic plate boundaries and activity. Two types of mountain are formed depending on how the rock reacts to the tectonic forces – block mountains or fold mountains.
The compressional forces in continental collisions may cause the compressed region to thicken, so the upper surface is forced upwards. In order to balance the weight, much of the compressed rock is forced
downwards, producing deep "mountain roots". Mountains therefore form downwards as well as upwards (see
isostasy). However, in some continental collisions part of one continent may simply
override part of the others, crumpling in the process.
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. This occurrence is fairly common. 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. These areas often occur when the regional stress is extensional and the
crust is thinned.
The
mid-ocean ridges are often referred to as undersea mountain ranges due to their bathymetric prominence.
Where rock doesn't 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, more compressed rock of the synclines.
Further Information
Get more info on 'Mountains'.
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