Mountain pass - AbsoluteAstronomy.com

A mountain pass is a route through a mountain range

Mountain range

A mountain range is a single, large mass consisting of a succession of mountains or narrowly spaced mountain ridges, with or without peaks, closely related in position, direction, formation, and age; a component part of a mountain system or of a mountain chain...

or over a ridge

Ridge

A ridge is a geological feature consisting of a chain of mountains or hills that form a continuous elevated crest for some distance. Ridges are usually termed hills or mountains as well, depending on size. There are several main types of ridges:...

. If following the lowest possible route, a pass is locally the highest point on that route. Since many of the world's mountain ranges have presented formidable barriers to travel, passes have been important since before recorded history, and have played a key role in trade, war, and migration.

Mountain passes are analogous to the mathematical concept of a topological

Topology

Topology is a major area of mathematics concerned with properties that are preserved under continuous deformations of objects, such as deformations that involve stretching, but no tearing or gluing...

saddle surface

Saddle surface

A saddle surface is a smooth surface containing one or more saddle points.The term derives from the peculiar shape of historical horse saddles, which curve both up and down....

, with a saddle point

Saddle point

In mathematics, a saddle point is a point in the domain of a function that is a stationary point but not a local extremum. The name derives from the fact that in two dimensions the surface resembles a saddle that curves up in one direction, and curves down in a different direction...

marking the highest point between two valleys and the lowest point along a ridge. On a topographic map

Topographic map

A topographic map is a type of map characterized by large-scale detail and quantitative representation of relief, usually using contour lines in modern mapping, but historically using a variety of methods. Traditional definitions require a topographic map to show both natural and man-made features...

, passes are characterized by contour lines with an hourglass shape, which indicates a low spot between two higher points.

Passes are often found just above the source of a river

Source (river or stream)

The source or headwaters of a river or stream is the place from which the water in the river or stream originates.-Definition:There is no universally agreed upon definition for determining a stream's source...

, constituting a sort of "bridge" over to the headwaters of a different river. Passes may be very short, consisting of steep slope

Slope

In mathematics, the slope or gradient of a line describes its steepness, incline, or grade. A higher slope value indicates a steeper incline....

s to the top of the pass, or valleys of many kilometres, whose highest point is only identifiable by surveying

Surveying

See Also: Public Land Survey SystemSurveying or land surveying is the technique, profession, and science of accurately determining the terrestrial or three-dimensional position of points and the distances and angles between them...

.

Road

Road

A road is a thoroughfare, route, or way on land between two places, which typically has been paved or otherwise improved to allow travel by some conveyance, including a horse, cart, or motor vehicle. Roads consist of one, or sometimes two, roadways each with one or more lanes and also any...

s have long been built, and more recently railways, through passes. Some high and rugged passes may have tunnel

Tunnel

A tunnel is an underground passageway, completely enclosed except for openings for egress, commonly at each end.A tunnel may be for foot or vehicular road traffic, for rail traffic, or for a canal. Some tunnels are aqueducts to supply water for consumption or for hydroelectric stations or are sewers...

s bored underneath to allow faster traffic flow throughout the year.

The top of a pass is frequently the only flat ground in the area, a high vantage point, so it is often a preferred site for buildings. For countries whose borders are delimited by a mountain range, the pass is typically part of the border, and the facilities likely include a border control

Border control

Border controls are measures used by a country to monitor or regulate its borders.The control of the flow of many people, animals and goods across a border may be controlled by government Customs services. Security is enforced by various kinds of Border Guards and Coast Guards...

or customs

Customs

Customs is an authority or agency in a country responsible for collecting and safeguarding customs duties and for controlling the flow of goods including animals, transports, personal effects and hazardous items in and out of a country...

station, and possibly a military post as well, as relatively few soldiers are required to guard a pass. For passes with roads, it is also customary to have a small roadside sign giving the name of the pass and its elevation

Elevation

The elevation of a geographic location is its height above a fixed reference point, most commonly a reference geoid, a mathematical model of the Earth's sea level as an equipotential gravitational surface ....

above mean sea level

Above mean sea level

The term above mean sea level refers to the elevation or altitude of any object, relative to the average sea level datum. AMSL is used extensively in radio by engineers to determine the coverage area a station will be able to reach...

. An example of this is Argentina

Argentina

Argentina , officially the Argentine Republic , is the second largest country in South America by land area, after Brazil. It is constituted as a federation of 23 provinces and an autonomous city, Buenos Aires...

and Chile

Chile

Chile ,officially the Republic of Chile , is a country in South America occupying a long, narrow coastal strip between the Andes mountains to the east and the Pacific Ocean to the west. It borders Peru to the north, Bolivia to the northeast, Argentina to the east, and the Drake Passage in the far...

that share the world's third longest international border, 5300 kilometres (3,293.3 mi) long, running from north to the south through the Andes

Andes

The Andes is the world's longest continental mountain range. It is a continual range of highlands along the western coast of South America. This range is about long, about to wide , and of an average height of about .Along its length, the Andes is split into several ranges, which are separated...

mountains, having a total of 42 mountain passes between them.

As well as offering relatively easy travel between valleys, passes also provide a route between two mountain tops with a minimum of descent. As a result, it is common for tracks to meet at a pass; this often makes them convenient routes even when travelling between a summit and the valley floor.

There are thousands of named passes around the world, some of which are well-known, such as the Great St. Bernard Pass

Great St. Bernard Pass

Great St. Bernard Pass is the third highest road pass in Switzerland. It connects Martigny in the Canton of Valais in Switzerland to Aosta in Italy. It is the lowest pass lying on the ridge between the two highest summits of the Alps, Mont Blanc and Monte Rosa...

at 2473 metres (8,113.5 ft) in the Alps

Alps

The Alps is one of the great mountain range systems of Europe, stretching from Austria and Slovenia in the east through Italy, Switzerland, Liechtenstein and Germany to France in the west....

, the Khyber Pass

Khyber Pass

The Khyber Pass, is a mountain pass linking Pakistan and Afghanistan.The Pass was an integral part of the ancient Silk Road. It is mentioned in the Bible as the "Pesh Habor," and it is one of the oldest known passes in the world....

at 1027 metres (3,369.4 ft) between Afghanistan

Afghanistan

Afghanistan , officially the Islamic Republic of Afghanistan, is a landlocked country located in the centre of Asia, forming South Asia, Central Asia and the Middle East. With a population of about 29 million, it has an area of , making it the 42nd most populous and 41st largest nation in the world...

and Pakistan

Pakistan

Pakistan , officially the Islamic Republic of Pakistan is a sovereign state in South Asia. It has a coastline along the Arabian Sea and the Gulf of Oman in the south and is bordered by Afghanistan and Iran in the west, India in the east and China in the far northeast. In the north, Tajikistan...

, and the Khardung La

Khardung La

Khardung La is a high mountain pass located in the Ladakh region, Jammu and Kashmir, India...

at 5359 metres (17,582 ft) in Jammu and Kashmir

Jammu and Kashmir

Jammu and Kashmir is the northernmost state of India. It is situated mostly in the Himalayan mountains. Jammu and Kashmir shares a border with the states of Himachal Pradesh and Punjab to the south and internationally with the People's Republic of China to the north and east and the...

, India

India

India , officially the Republic of India , is a country in South Asia. It is the seventh-largest country by geographical area, the second-most populous country with over 1.2 billion people, and the most populous democracy in the world...

. The Marsimik La

Marsimik La

Marsimik La or Marsimek La, elevation , is a high mountain pass in the Chang-Chemno Range in northern India about east of Leh, further by road...

at 5590 metres (18,339.9 ft) is a lesser-known pass; it is one of the world's highest motorable passes and lies in India

India

, on the northern-most tip of the Changthang Plateau, near the Chinese border.

There are many words for pass in the English-speaking world. In the United States

United States

The United States of America is a federal constitutional republic comprising fifty states and a federal district...

, pass is very common in the West

Western United States

.The Western United States, commonly referred to as the American West or simply "the West," traditionally refers to the region comprising the westernmost states of the United States. Because the U.S. expanded westward after its founding, the meaning of the West has evolved over time...

, the word gap is common in the southern Appalachians

Appalachian Mountains

The Appalachian Mountains #Whether the stressed vowel is or ,#Whether the "ch" is pronounced as a fricative or an affricate , and#Whether the final vowel is the monophthong or the diphthong .), often called the Appalachians, are a system of mountains in eastern North America. The Appalachians...

, notch in parts of New England

New England

New England is a region in the northeastern corner of the United States consisting of the six states of Maine, New Hampshire, Vermont, Massachusetts, Rhode Island, and Connecticut...

, and saddle in northern Idaho

Idaho

Idaho is a state in the Rocky Mountain area of the United States. The state's largest city and capital is Boise. Residents are called "Idahoans". Idaho was admitted to the Union on July 3, 1890, as the 43rd state....

. Scotland has the Gaelic

Scottish Gaelic language

Scottish Gaelic is a Celtic language native to Scotland. A member of the Goidelic branch of the Celtic languages, Scottish Gaelic, like Modern Irish and Manx, developed out of Middle Irish, and thus descends ultimately from Primitive Irish....

term bealach (anglicised "Balloch"). In the Lake District

Lake District

The Lake District, also commonly known as The Lakes or Lakeland, is a mountainous region in North West England. A popular holiday destination, it is famous not only for its lakes and its mountains but also for its associations with the early 19th century poetry and writings of William Wordsworth...

of north west England, the term hause is often used, although the term pass is also common—one distinction is that a pass can refer to a route, as well as the highest part thereof, while a hause is simply that highest part, often flattened somewhat into a high level plateau.

See also