What is a Natural Bridge? - Definition & Formation

Instructor: Yuanxin (Amy) Yang Alcocer

Amy has a master's degree in secondary education and has taught math at a public charter high school.

Did you know that there are some bridges that were made from just wind and water? Learn how in this lesson, along with where you can go to see some of them.

What is a Natural Bridge?

What do you think of when you hear the word 'bridge'? Perhaps the famous Golden Gate Bridge in San Francisco, or some other human-made bridge near you?

If so, then you may be surprised to learn that there are bridges that were made without human intervention through natural events. These are called natural bridges, bridges that are naturally made.

The Owachomo natural bridge
natural bridge

How Are They Formed?

If you had a time machine and were able to travel back in time, you'd be able to see how many natural bridges came about. It's not just in a moment though, you'd have to keep jumping forward, as it takes a lot of time. You might see one of these possible natural causes, or a combination.

One way the bridge could have been formed is with water. Think of the Grand Canyon and how the Colorado River slowly carved out that big canyon in a meandering fashion. As rivers flow, they can wash away bits and pieces of the ground that they pass by. Sometimes, they can erode a soft part of the ground underneath a more solid rock formation.

As the river erodes more of the bottom away, it will begin to get lower into the ground. If the rock formation hasn't been eroded when the river gets lower, it will become a natural bridge as it gets exposed. Looking around the Sipapu natural bridge, you can see how the river has carved its way through the area.

The Sipapu natural bridge was formed by river erosion

Another natural cause is from wind erosion. If an area experiences high gusts of wind on a regular and continued basis, then it could slowly but surely knock away little bits and pieces. These would soon add up to a hole that would make the natural bridge.

A third natural cause is cave collapse. If there was a cave underneath the ground and it collapses, it can leave behind a gap. For example, the natural bridges found at the Gifford Pinchot National Forest in Washington were formed from the collapse of lava tubes.

When caves such as these lava tubes collapse, if there is a solid rock formation on top and around, it can leave a gap underneath that will become the natural bridge. Essentially, the cave collapses on both sides, leaving the top intact, thus forming the bridge.

National Monuments

If you want to see natural bridges in person, there are two national monuments you can visit, both in Utah. Of course, there are other natural bridges, but these two national monuments are home to some of the most spectacular ones.

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