What is a Sea Arch?

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  • Written By: Diane Goettel
  • Edited By: Bronwyn Harris
  • Last Modified Date: 02 December 2018
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A sea arch is a natural arch or bridge made of stone that has been created when water wears away the underside of a rock, leaving just the top behind. They commonly form where cliffs meet the sea.

Natural arches are created through the process of land, wind, or water erosion, or some combination of these methods. They are often made by the meeting of two types of rock, with the harder substance on the top of the arch, which forms the bridge. When the bottom rock is a softer type of stone, it will erode away more quickly, leaving behind an arch.

A sea arch is created when the natural erosive forces of water break through a slice of rock and leave behind an arch. Water, after all, is one of the most powerful forces on the planet. It has the power to destroy cities, but it also has the power to make stunning sculptures in the earth, such as the Grand Canyon.

Beautiful sea arches exist all around the world. One particularly well known one named "London Bridge" was located near Victoria, Australia, but collapsed into the water in 1990. Others include the Durdle Door and the Stair Hole on the coast of southern England.


These arches are often formed out of former caves. In many instances, a limestone cave full of sinkholes will begin to collapse, leaving behind what was once the mouth of the cave. This former entrance then becomes an arch.

Because each sea arch is the result of erosion, many of them will eventually collapse, like Australia’s London Bridge. Depending on the age and structure of the arch, it may look sturdy and everlasting or frail, about to fall in on itself. As one falls to rubble at the edge of the ocean, however, another will likely take its place when a cave collapses in on itself or a sliver or weak rock finally gives way to allow the passage of wind and water through the stronger arch above.


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Post 6

Sometimes, part of the rock formation will collapse while leaving another part intact. I saw a photo of the London Bridge after it collapsed, but there was still another sea arch out to the side that appeared to be in good shape.

Post 5

@kylee07drg – I do love capturing moments in time with my camera, especially the ones of vulnerable things like sea arches that may not be there the next year. I'm glad that so many people are interested in documenting natural formations like this, because we will have plenty of photos to remember them by when they are gone.

Post 4

I've often wanted to take a boat through a sea arch. I've seen some beautiful ones in movies that I would love to cross under.

I wouldn't be too afraid of a sea arch falling on my head as long as it didn't look too frail. It is made of strong rock, after all, and unless there is a major storm brewing at the time, it isn't likely to collapse all at once.

I would definitely avoid sea arches when a hurricane is approaching, though. The strong wind and waves could cause one to fall, and they could also cause your boat to crash against the surrounding rock.

Post 3

It's tragic that these beautiful formations are just destined to fall apart. It's important to visit things like sea arches while they last and to take plenty of photographs.

Post 2

@ GenevaMech- I have explored the volcanoes national park in the big island. It is one of the most beautiful and surreal places I have ever been. You can see beautiful colorful birds, outlandish trees and flowers, volcanic steam vents, lava tubes, groups of wild boar, endless expanses of lava, and lava covered with vegetation in this park.

I have also seen some of the coolest looking bugs I have ever seen. Glow in the dark spiders, giant spiders that look like yellow and black walking sticks, huge centipedes, and the colorful crab spiders that weave thick webs in dark corners.

Probably my most memorable experiences were hiking across the Kilauea caldera and crater, and walking through the tree fern forests. My family enjoyed watching the hula dancing at the visitor center, and the drive down the chain of craters road.

Post 1

I used to live in the small town of Volcano Hawaii on the big Island. At the end of Chain of Craters Road, which runs through the Hawaii Volcanoes National Park to the coast, are the Black volcanic cliffs and the Holei Sea Arch. The arch is a giant arch that sticks out from the side of the sea cliffs.

The arch must be about 80 or 90 feet tall, and on windy days, you can feel the spray from the waves splashing into the cliffs.

If you ever visit the big island of Hawaii, the Crater Rim Road and Chain of Craters road are must-sees. At the end of the chain of craters road you can enjoy a picnic on top of the sea cliffs. You will be able to gaze at what seems like an endless south pacific ocean.

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