- published: 01 Jul 2014
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A mountain pass (also gap, notch, col, saddle, hause, bwlch (Welsh), brennig or bealach (Gaelic)) is a route through a mountain range or over a ridge. 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 saddle surface, with a saddle point marking the highest point between two valleys and the lowest point along a ridge. On a topographic map, 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, constituting a drainage divide. Passes may be very short, consisting of steep slopes to the top of the pass, or valleys of many kilometres, whose highest point is only identifiable by surveying.