Mountain pass
, still snowy even in June, has long been a major route through the Alps.
Topographically, a pass has the general form of a saddle between two mountains (the elevation as a function of two position coordinates is mathematically a saddle point). They are often found just above the source of a river, constituting a sort of "bridge" over to the headwaters of a different river. Passes may be very short, consisting of steep slopes to the top of the pass, or valleys of many kilometers, whose highest point is only identifiable by surveying.
Roads have been long been built through passes, and more recently railways. Some high and rugged passes may have tunnels bored underneath, so as allow faster traffic flow year-round.
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 or customs station, and possibly a military post as well. For passes with roads, it is also customary to have a small roadside sign giving the name of the pass and its elevation above mean sea level.
There are thousands of named passes around the world; some are familiar names, such as the Great St. Bernard Pass in the Alps, the Khyber Pass between Afghanistan and Pakistan, and the Khunjerab Pass (15,520 feet) between Pakistan and China.
The word "gap" is more commonly used in the southern Appalachians, while "notch" is more common in New England.
See also:
- List of mountain passes
- Principal passes of the Alps, Ranges, Peaks and passes of the Alps
