What is a Sea Stack?

Mary McMahon
Mary McMahon

A sea stack is a pillar of rock found in the water close to a coastline. Sea stacks are common along many of the world's coastlines, and some have even become quite famous. Like other features found along shorelines, sea stacks are also in a constant state of flux, with new stacks emerging all the time while old ones disappear. Some sea stacks have been known to erode into very unusual and striking formations, making them popular subjects for photographers and painters.

Sea stacks are natural, rocky towers that have been formed along coastlines by erosion.
Sea stacks are natural, rocky towers that have been formed along coastlines by erosion.

A sea stack is caused by the natural erosion of headlands along the coastline. Typically, the ocean wears a hole through the headlands first, creating an arch which slowly expands over time as it erodes. Ultimately, the arch collapses, leaving a sea stack on one side and the headland on the other. Separated from the shoreline, the sea stack will slowly start to erode, ultimately melting away into the water or collapsing.

Some sea stacks started out as small islands that were worn away.
Some sea stacks started out as small islands that were worn away.

Essentially, a sea stack is like a very small island, and in some cases, sea stacks have actually started out as islands which have been worn away. Many migratory birds use sea stacks for nesting and shelter, appreciating their isolation and relative safety. Sea stacks are also popular among rock climbers, since many such stacks pose interesting and fun climbing challenges.

The distribution of sea stacks in an area varies, depending on the kind of rock the headlands are formed from, ambient weather conditions, and the prevailing currents of the water. In some cases, an area may be littered with sea stacks made from very hard stone, while in other instances a shoreline has only a few stacks composed of soft, crumbly materials like limestone and sandstone. Since many headlands are formed from the former ocean floor, some sea stacks also reveal interesting fossil remains as they erode.

Some caution is advised when one is around sea stacks. It is possible for stacks to collapse unexpectedly, to the detriment of anyone who happens to be standing or boating nearby. When climbing sea stacks, it is a good idea to watch out for soft, crumbly rock which could give way under the weight of a climber, and to avoid especially narrow, spindly sea stacks as they can be very fragile. In addition, because sea stacks are used as nesting areas by birds, access to stacks may be restricted by conservation agencies in the interest of protecting the birds.

Mary McMahon
Mary McMahon

Ever since she began contributing to the site several years ago, Mary has embraced the exciting challenge of being a wiseGEEK researcher and writer. Mary has a liberal arts degree from Goddard College and spends her free time reading, cooking, and exploring the great outdoors.

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Discussion Comments


What are some characteristics of all stacks? I would really like to know.


Thanks for the info! I was delighted to find it, as I was working on a poem I wrote some 12-14 years ago when I lived in WA state, near the coast. I'd watched a rain storm moving in from the ocean, and mentioned "the stacks" -- but for the life of me, I could not remember what stacks were.


@ Aplenty- I have been to the Sonoma Coast and I agree that it is beautiful. The article stated that people like to climb sea stacks, but the ones in this area are quite dangerous to climb. The sea arches and sea stacks in the area are all made of shale, making them very unstable to climb. The park service employees warned us about swimming and climbing the rocks, saying they have to rescue numerous people every year. The ranger said they rescue people who get pulled out to sea, beachcombers attacked by seals (sea lions?), and climbers stuck on rocks when the tide comes in a few times a year.


I used to vacation In Bodega Bay in California as a kid, and we would often go to shell beach and Goat Rock Park. Goat Rock is nice in the morning fog, and I assume it qualifies as a sea stack. There are also many other sea stacks, sea arches, caves, and sea cliffs in the area.

It is an awesome place to explore, but I remember swimming to be particularly dangerous. The water is riddled with White sharks, seals, sea lions, rip currents, and kelp beds. The water is also dark and cold (not very inviting to a young child).

Beach combing in the area is fun though. There are plenty of tide pools to explore, shells galore, and tons of washed up seaweed to scare a little sister. I plan on taking my daughter to the same beaches when she is a little older.

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