What Is The Difference Between A Caribbean Key And An Island?

The Caribbean is dotted with thousands of islands and keys (or cays). But what’s the difference between an island and a key? Is an island the same as a key? Are they used interchangeably? Inquiry minds want to know, and so did I. So I delved into it and found the answer.

Islands and keys are related but different. A key is a type of island called “coral”. There are five different types of islands including coral, continental, tectonic, volcanic, and barrier. Coral islands are a built-up of tiny sea animals that built up over time and eventually broke the surface of the ocean. 

While researching the difference between an island and a key I came across some fascinating information about island formation. I’m sure I learned this stuff back in middle school but apparently wasn’t very interested then. In addition to the detailed differences between an island and a key, I’d like to share a bit about island formation. You will be amazed!

What exactly is an island?

Island: a tract of land surrounded by water and smaller than a continent – Merriam Webster Dictionary

Scientists think millions of years ago there was one continent that broke off over time into other continents (larger pieces) and islands. 

Continental Islands

So, many islands are “continental”, meaning they were formed by breaking off a continent. They essentially rest on a continental shelf, the solid earth below the land and sloping down to the ocean. 

It might interest you to know that larger bodies of land are called continents, not islands. In fact, did you know Australia is a continent, not an island (surprised me!).

On the other hand, Greenland is an island. In fact, it’s the largest island and about 1/3 the size of Australia – a continent.

Cuba is an example of a continental island, formed from having broken off North America.

Tectonic Islands

Tectonic islands formed islands are created as a result of material build-up from the earth’s plates scraping against one another. When the plates bump into one another, one pushes on top and soil, rocks and other materials get scraped and piled up to the point where they form a landmass. It takes millions of years for enough buildup to form an island.

Barbados is one of the Lesser Antilles island groups thought to have formed tectonically as well as via coral build-up which we’ll discuss in a bit.

Volcanic Islands

Other islands formed as a result of ocean volcanoes erupting. They’re called “volcanic” or sometimes referred to as “oceanic” islands. These islands are high due to the magma, ash and other debris building up into a mountain formation.

Aruba is an example of an island formed from an underwater volcano.

Barrier Islands

Barrier islands are comprised of sediment (sand, silt, and gravel).

None of the Caribbean Islands are barrier islands but I bet you’ve heard of The Outerbanks in North Carolina or Padre Island in Texas! They are both barrier islands.

By the way, have you ever wondered why the Caribbean Sea is so blue? I did too! So I dove into the science and wrote Why the Caribbean Water is so Blue.

Coral Islands

Coral: the calcareous or horny skeletal deposit produced by anthozoan or rarely hydrozoan polyps – Merriam Webster Dictionary

Coral islands, such as ‘Keys” are low, flat islands composed mostly of coral reef. Coral reefs are limestone formations composed of tiny sea organisms and their remains they leave behind when they die. 

Coral growth thrives in warm, shallow water. 

What exactly is a key?

As mentioned, a key is an island. Specifically, it’s an island formed through the build-up of coral. The island IS a coral reef. 

To expand further, a key is a small, low [elevation] island on sand or coral. Since coral growth thrives in warm, shallow water, keys are in fact low islands.

Of course, keys are found in warm tropical regions. They are usually sandy and often surrounded by mangroves (groups of shrubs and trees that grow along the coast).

Popular keys are The Florida Keys and the Great Barrier Reef off of Australia. Since the Florida Keys are in the Caribbean, let’s explore them further.

The Florida Keys

Perhaps the most famous keys in the world, certainly to Americans, are the Florida Keys. The Florida Keys are made up of over 1700 islands off the southern coast of Florida. Since coral reefs are home to amazing sea life, they are a dream destination for scuba divers and snorkelers.

Key Information about The Florida Keys (Pun intended!)

Island Florida Keys
Airport Key West International Airport (EYW)
Archipelago Florida Keys
Best Beaches Smathers Beach, Key West
Calusa Beach, Big Pine Key
Higgs Beach, Key West
Far Beach, Key Largo
Zachary Taylor State Park Beach, Key West
Dry Tortuga National Park, Key West 
Harry Harris Park, Key Largo
Capital Tallahassee (mainland Florida)
Cell Service & Internet Standard US cell service
Climate January: 67°-75°
February: 68°-76°
March: 70°-78°
April: 74°-82°
May: 77°-85°
June: 80°-88°
July: 81°-90°
August: 81°-91°
September: 80°-89°
October: 78°-85°
November: 72°-79°
December: 70°-77°
Country United States 
Currency US Dollar
Getting Around Walking & Bicycles – Your best bet for getting around the islands
Taxi, Uber, Bus, Pedi-cabs, Tour trains & Trolleys
Islands 1700 islands

Largest islands include:
Key West
Big Pine Key (lower keys)
Key Largo
Island Group Florida Keys
Known for Snorkeling, Diving Art & Culture
Language English
Legal Alcohol Age 21
Official Website https://fla-keys.com/
Passport No
Popular Attractions Dry Tortugas National Park and Fort Jefferson Ferry
Fort Zachary Taylor National Park, Key West
Southernmost Point, Key West
Ernest Hemingway’s Home & Museum, Key West
John Pennekamp Coral Reef State Park, Key Largo
Spiegel Grove, Key Largo
Safety Travel Advisory 1 (same as US mainland)
Timezone Atlantic Standard Time
US Ambassador N/A

Next, read: Why the Caribbean Water is so Blue.

What’s the difference between a Key and Cay or Caye?

Keys are also referred to as “cay”. Cay comes from the Spanish word cayo” which means small island. Sounds about right.

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