Mountain pass

A mountain pass is a navigable route through a mountain range or over a ridge.

Because mountain ranges can act as formidable barriers, these routes are essential for travel. They play a vital role in human history. People use them for trade and for military expeditions. They also support the migration of both humans and animals. When a pass is at a lower elevation, it is often called a hill pass.

Geologically, a pass is formed through specific natural processes. It may appear between two volcanic peaks. Often, erosion from wind or water creates a gap in the landscape. A pass can take many different shapes. It might be a very short path with steep slopes leading to the top. Alternatively, it could be a valley many kilometers long. In some long valleys, the highest point might only be found through surveying.

In geography, a pass is defined by its topography. It often utilizes a gap, a saddle, a col, or a notch. A topographic saddle is similar to a mathematical saddle surface. In this shape, a saddle point marks the lowest point along a ridge. This point is also the minimum high point between two valleys.

On a topographic map, you can identify passes by looking at contour lines. These lines form an hourglass shape. This shape indicates a low spot situated between two higher points.

Passes serve many practical purposes for travelers and engineers. They provide a route between two mountain tops with a minimum of descent. Because of this, many tracks meet at a single pass. This makes them convenient routes for traveling between a summit and a valley floor. Many roads and railways are built through these gaps. In some rugged areas, engineers bore tunnels under mountainsides. For example, the Eisenhower Tunnel bypasses Loveland Pass in the Rockies. This allows for faster traffic flow throughout the year.

Geography and politics are often linked through mountain passes. If a national border follows a mountain ridge, the pass is typically on that border. These locations may host customs stations, border controls, or military posts. A major example is the border between Argentina and Chile. This border runs north-south along the Andes mountains. It is the third-longest international border in the world. This massive border includes 42 different mountain passes.

Different cultures use unique terminology to describe these features. In the United States, the term "pass" is common in the West. In the southern Appalachians, people use the word "gap." In New England, the word "notch" is frequently used. In Europe, the term "col" comes from Old French. In Japan, they are known as tōge.

In Scotland, the Gaelic term is bealach. In Wales, the term is bwlch. In the Lake District of England, some use the word hause. A hause specifically refers to the highest part, often a flattened plateau.

High-altitude passes require special considerations for survival and travel. In the Himalayas, passes are often denoted by the suffix "La." Some of these are extremely high. The Taglang La reaches 5,328 meters. The Sia La is even higher at 5,589 meters.

Some passes above the tree line face problems with snow drift in winter. Engineers sometimes build roads a few meters above the ground to help. This design allows snow to blow off the road more easily. Some of the highest motorable passes are the Mana Pass and the Marsimik La. The Palakkad Gap in India is notable for being the widest mountain pass in the world.