Did You Know This Is One Way Islands Form?

Islands form in a number of ways. Some are born overnight while others take decades or even centuries to form. How islands form depends a great deal on where the island is located. Islands in coastal regions form as sandbars while those in volcanic areas will form from rock and lava.

Islands are classified in three broad categories – continental, oceanic, and tropical. Continental islands form a part of a larger continental shelf, much of which might be submerged below the surface of the oceanic. Think New Zealand. Oceanic islands are not part of a continental shelf and are most often formed by volcanic activity, such as the Hawaiian islands. Coral reefs form many tropical islands, like those found in the Bahamas. Some islands are also formed out of sandbars.

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Google map of Three Rooker Island and the north tip of Honeymoon Island
Three Rookie Island near Dunedin and Tarpon Springs on Florida’s Gulf coast.

An Island is Born

In the 1970s Three Rooker Island near Tampa Bay on Florida’s Gulf Coast didn’t exist. The 1.5 mile stretch of sea where it now rises was nothing more than shallow water, and an occasional sandbar between Honeymoon Island to the south and Anclote Key to the north.  It didn’t rise from fire and smoke like the new volcanic islands we often hear about in the news or see on YouTube. There was no roiling water, no smoke plumes in the air, no land formation overnight.

Instead, Three Rooker Island slowly emerged like a languid cat waking from a nap. Local currents deposited sands in one place, having taken them from another. In the 1980s, it was a solid sandbar, the youngest member of West Florida’s barrier islands. There is now an even newer one, called North Anclote Sandbar, to the north of Anclote Key. And others forming along channels like the one below at the mouth of the Anclote River.

Mangroves in shallow water might be the beginning of how islands form in some parts of Florida.
Islands along Florida’s coast are tropical islands. Rather than forming from coral reefs, they form from shifting sands like on which mangrove seeds take root.
Mangroves around a waterway.
Mangrove islands, like these, border many of the waterways around Florida. These islands began similar to the one in the previous photo.

How Islands Form from Sandbars

Sandbars come and go, appearing and disappearing at Mother Nature’s whim. Some remain and become barrier islands, one of the most prevalent types of islands in the United States, especially along the Eastern Seaboard and Gulf Coast. These islands, like Three Rooker, most often form as shifting currents pile sediment in one place. Hurricanes and tropical storms create, or destroy, others. Barrier islands protect approximately 15% of the world’s coastlines, and though they are most often associated with more southerly latitudes – think Florida, Georgia, the Carolinas – they can form nearly anywhere, such as Germany’s Norderoogsand.

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Norderoogsand in Germany. Photo: The Telegraph

Thirty years after its formation, Three Rooker Bar is a well-established island. Grasses and trees grow on it. About three quarters of the island is a protected bird rookery. And about one-quarter of it is open for human enjoyment. This doesn’t mean the island doesn’t change. It does. In the past three years a channel has split the island into North and South Three Rooker. Its semi circular shape is more elongated some years than others. But for now, it looks like Three Rooker is here to stay, another link in the chain of islands that buffers the West Coast of Florida.

Final Thoughts on How Islands Form

Next time you’re in Florida on one of her many islands, ask yourself how that island formed. If you’re in the Florida Keys, chances are you’re standing on a coral reef island. But if you’re on Clearwater Beach or any of the other barrier islands, you might be standing on a really solid sandbar!


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    Did You Know This Is One Way Islands Form?Did You Know This Is One Way Islands Form?Did You Know This Is One Way Islands Form?

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    22 Comments

    1. This is so cool! I had never thought about how islands were formed. Three Rooker Bar looks like a fun place to visit as well. I love Florida beaches.

    2. This is so interesting, I actually had zero knowledge of how islands formed before reading this. Thanks for teaching me about the different kinds of islands and how they form!

    3. And here I thought tropical island meant something different entirely! 😉 Thanks for the informative read.

    4. It’s just amazing how the earth works! I have never really thought about how islands are formed. Interesting when you think about the different types of islands like coastal, rock formation from lava, mangroves or made out of corals. Next time I’ll come by a small island I will think of its origin. Thanks 🙂

    5. Howdy! I could have sworn I’ve been to this blog before but after browsing through some of the post I realized it’s new to me. Nonetheless, I’m definitely delighted I found it and I’ll be book-marking and checking back frequently!

    6. It’s so cool to see how things change. And really cool to see an island form in a way which is totally not from volcanic activity. It just springs up out of
      nowhere. Very beautiful looking there too. And amazing that green things already grow there.

    7. I never knew about how beautiful island has
      been formed! Thanks for sharing great
      information! Love learning new while
      traveling! Now I get to remember
      whenever I travel to island.

    8. This was such a cool read. I remember learning about how islands formed in school, but it’s been a few years so I forgot. Thank you for the reminder.
      Now I want to go relax on an island.

    9. I am only familiar with island being form by
      volcanic activities and not other types of
      formation. It would be fun to discover a
      new island and be able to have a great
      hangout place that you can go to on the
      weekends.