What is a Blue Hole? Great Blue Hole ~ Dean's Blue Hole ~ The Blue Hole ~ The Blue Cave Korcula~ El Zacatón Sinkhole

The Great Blue Hole Located in Belize
The Great Blue Hole Located in Belize | Source

What is a Blue Hole?

Blue holes, generally located in low-lying coastal areas, can be inland caves or underwater sinkholes. Most blue holes are approximately 330-390 feet (100-120 meters) deep, with a roughly circular entrance having an approximate diameter of 82-115 feet (25-25 meters) across.

The world's deepest blue hole - at 1,100 feet (335 meters) - is located in Tamaulipas, Mexico. This blue hole, the El Zacatón sinkhole, is an inland blue hole.

Blue holes fall into two classifications: anchialine caves (inland blue holes) and submarine caves (ocean blue holes). Although the anchialine caves are inland they also contain saltwater.

Because of the unique water conditions found in blue holes, skeletal remains of extinct as well as still living species are well preserved.

Blue holes are somewhat circular in shape, steep-walled, and can be extremely deep. One Bahamian blue hole exceeds 600 feet (180 meters). These caves can also contain miles and miles of lateral passageways extending in any direction.

Blue holes derive their name from their appearance – the depths of the hole appear a deep dark blue while surrounded by the lighter blue shallows.

There is very little water circulation in a blue hole; and, it becomes anoxic (without oxygen) at the deeper depths. This lack of circulation and lack of oxygen makes a blue hole inhospitable to most sea life; however, bacteria flourishes in this environment.

Most inland blue holes contain both freshwater and saltwater. The freshwater will cover the top of the blue hole with the saltwater filling the lower depths. At the point where the freshwater and saltwater meet, the halocline, a corrosive reaction that is able to eat away at the rock takes place. As the rock is eaten away, lateral passages are created along the side of the vertical wall. Over time, these passages can travel great distances. The Sawmill Sink in the Bahamas has lateral passages that extend over 2,000 feet (600 meters).


Coral found in Great Blue Hole
Coral found in Great Blue Hole | Source

The Great Blue Hole in Belize

The Great Blue Hole, located in the Lighthouse Reef Atoll near Belize City, was discovered by marine conservationist Jacques Cousteau. This circular hole is approximately 1,000 feet (305 meters) across and approximately 400 feet (123 meters) deep.

Huge stalactites and stalagmites formed inside this blue hole during the ice age are a treat for divers from all over the world.


The video below shares a lot of information about the Blue Hole in Belize.

Dean’s Blue Hole in the Bahamas

Dean’s Blue Hole is the deepest sinkhole whose entrance is below sea level known to man. At 663 feet (202 meters) deep, Dean’s Blue Hole, named for a family who owns nearby land, is popular among divers. It is located on Long Island, Bahamas in a bay west of Clarence Town.

The sides of this blue hole are not entirely vertical. At the top, Dean’s Blue Hole is approximately 82-115 feet (25-35 meters). This diameter drops down vertically approximately 66 feet (20 meters) and then widens into a cavern that is approximately 330 feet (100 meters) across.

The Blue Hole near Gozo, Malta

Malta’s Blue Hole is the island’s most popular dive site. This blue hole begins 23 feet (7 meters) below the water’s surface.

Inside the blue hole, 72 feet (22 meters) below the water’s surface, a cave branches off from the hole. By swimming through a short passageway, or chimney, divers enter an additional area within the blue hole containing coral gardens teeming with life.


The video below takes a while to buffer and load, but is well worth the wait. The colors of the soft corals, the calcium deposits, the algae and the cyanobacteria all mixed together are quite stunning. The various fish swimming and grazing on the cave walls along with the polychaete worms, also known as bristle worms, that crawl along the walls at the middle of the video are also a sight to behold. Journey even deeper with the diver and explore dimly lit caverns.


This video of the Blue Hole in Malta also takes a while to buffer. This video shows different sea life than the previous, including a jellyfish, tube worms, and a starfish.

Blue Hole and Canyon in the Red Sea, Egypt
Blue Hole and Canyon in the Red Sea, Egypt | Source

The Blue Hole Near Dahab, Egypt in the Red Sea

The Blue Hole in the Red Sea, just north of Dahab, is known as the “World’s Most Dangerous Dive Site” and has even been nicknamed the "Diver's Cemetery". This blue hole is approximately 427 feet (130 meters) deep. Although the approved recreational diving limit is 131 feet (40 meters), a tunnel located 170 feet (52 meters) tempts many divers to go deeper, some to their death. The entrance to this passageway is difficult to find making it even more dangerous for those who are tempted to go deeper than the 131 feet (40 meter) limit to explore this tempting tunnel. This blue hole and the surrounding area offers an abundance of coral and fish for a diver’s pleasure.

Swimming Through the Arch

The Blue Cave Korcula, Croatia

Croatia’s favorite dive spot, the Blue Cave (Modra Spilja), is not very deep – only 115 feet (35 meters). This minimal depth makes visibility inside the blue hole much clearer. Various types of marine life lining the walls is easily viewed and enjoyed.


Click here to watch a great video of this blue cave.


Watch the video below as a tour group enters and tours the caves.


Above the Water in the Blue Cave Korcula

El Zacatón sinkhole, once considered to be bottomless, is the world's deepest sinkhole.
El Zacatón sinkhole, once considered to be bottomless, is the world's deepest sinkhole. | Source

The El Zacatón Sinkhole

The El Zacatón sinkhole is the Earth’s deepest water-filled sinkhole, and it is also a blue hole. It’s roughly circular opening is approximately 360 feet (110 meters) across. But more amazing, it is 1099 feet (335 meters) deep! That’s more than 3-1/2 football fields deep!

It is from the floating islands of grass (zacate) that El Zacatón received its name. These islands of grass driven by the wind blow across El Zacatón regularly. Some of these islands of grass are quite large.

Until 2007, the pit was considered to be bottomless, and divers have lost their lives trying to find its bottom. Its depth was finally resolved through the use of NASA’s DEPTHX (Deep Phreatic Thermal Explorer) project’s robot.


Other Blue Holes

There are many other blue holes located around the world.

Another Blue Hole (Castalia) of interest, located in Castalia, Ohio, is approximately 75 feet (23 meters) in diameter and approximately 45 feet (14 meters) deep. Although it is filled with entirely freshwater (a spring fed basin), the waters are anoxic and will not sustain fish. This particular blue hole, which had previously been a tourist attraction, is now off limits to the public, but other sinkhole induced blue holes can also be found in the area.



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Copyright © 2012 Cindy Murdoch (homesteadbound)



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Comments 51 comments

lee custodio profile image

lee custodio 4 years ago

probably not this summer... ;-)


homesteadbound profile image

homesteadbound 4 years ago from Texas Author

Too bad. Maybe next summer for both of us. Thanks for stopping by!


Lady Guinevere profile image

Lady Guinevere 4 years ago from West Virginia

Cool places and info. Lots of great information.


homesteadbound profile image

homesteadbound 4 years ago from Texas Author

Lady Guinevere - I am glad that you enjoyed the info! Thanks for stopping by!


alocsin profile image

alocsin 4 years ago from Orange County, CA

I didn't know about this phenomenom. They're quite beautiful. voting this Up and Beautiful.


homesteadbound profile image

homesteadbound 4 years ago from Texas Author

alocsin - thanks so much for the votes. Yes, they truly are beautiful. Thanks so much for stopping by!


greatstuff profile image

greatstuff 4 years ago from Malaysia

Hi homesteadbound. A very well researched article. When I was working in Saudi Arabia, I use to go swimming and fishing in the Red Sea. Even along the coastline, I could see something similar to the blue hole, but a lot smaller. I can imagine the Blue Hole near Dahab, Egypt being the most dangerous. The Red Sea is already a dangerous place, with sharks and sudden sharp drop in the sea bed, so we have to be careful when out swimming , snookering or diving.


homesteadbound profile image

homesteadbound 4 years ago from Texas Author

greatstuff - I love the ocean, but I typically cannot experience it first hand. I have never been able to learn how to swim. When I go on snorkeling trips, I use a tube, but I love the intricate beauty that can be found in the ocean. Thanks so much for sharing your perspective on this subject. It was so good to see you here and so nice of you to leave such a great comment!


Jackie Lynnley profile image

Jackie Lynnley 4 years ago from The Beautiful South

Hey I can swim but not in the ocean, it is all I can do to stand up and there is no way I would go way out in that terrific water...a phobia I guess lol. (or brains)Would love to snorkel one day myself though. Great hub...so interesting. Great to have one for smiles before bedtime, thanks!


TransferAmerica profile image

TransferAmerica 4 years ago from Torrance, CA

Amazing. I have always wanted to explore these. Great hub!


homesteadbound profile image

homesteadbound 4 years ago from Texas Author

Jackie Lynnley - I am so glad you enjoyed this. Although I had to snorkel with an inner tube tethered to a boat, it was an amazing experience. Thanks so much for stopping by!


homesteadbound profile image

homesteadbound 4 years ago from Texas Author

TransferAmerica - In a way, virtually you did just explore these blue holes. Thanks so much for making the virtual journey with me!


molometer profile image

molometer 4 years ago

Totally awesome and beautiful. These videos are stunning. I love diving and would love to visit some of these blue holes.

I have seen a themocline where the water changes temperature which was brilliant. I would love to see the split between salt and fresh water. Sounds fascinating.

Truly awesome hub, well put together, thanks Cindy.

Voted up all buttons except funny and SHARING


MosLadder profile image

MosLadder 4 years ago from Irvine, CA

AWESOME! Bookmarking this to read again. Fascinating topic!


Movie Master profile image

Movie Master 4 years ago from United Kingdom

Hi Cindy, your hubs are always so well researched and interesting, I knew nothing about blue holes, so this one is educational as well!

Thank you and voted up, best wishes Lesley


homesteadbound profile image

homesteadbound 4 years ago from Texas Author

molometer - I am so pleased that you enjoyed this. And it's good to know that you enjoyed the videos. I watched videos for a couple hours to pick out the ones that I did. Thanks so much for stopping by, commenting and voting!


homesteadbound profile image

homesteadbound 4 years ago from Texas Author

MosLadder - Thanks for stopping by, and feel free to do so again, any time!


FloraBreenRobison profile image

FloraBreenRobison 4 years ago

I've never seen any of these or other blue sinkholes in person. The look beautiful. But I cannot swim so the thought of seeing them in person scares me.


homesteadbound profile image

homesteadbound 4 years ago from Texas Author

Lesley - I am so happy to introduce you to the blue holes. I have a few other related hubs I hope to publish in this area also.

Thanks so much for stopping by!


homesteadbound profile image

homesteadbound 4 years ago from Texas Author

FloraBreenRobison - I cannot swim either, but almost everything about the ocean fascinates me. I have snorkled in an inner tube while tethered to a boat. Thanks so much fro stopping by!


Rain Defence profile image

Rain Defence 4 years ago from UK

Wow this is awesome. I never really considered Malta as a dive destination. This has made me want to book a diving holiday!

The sinkholes would probably scare me but I'd love to dive them. On my last diving holiday, some of my favourite diving moments were swimming over the edge of seemingly bottomless abysses. A lot of the good stuff is on the walls of those abysses, so they're great to dive and it's awesome when you can't see the bottom, but know it goes down a long, long way underneath you!

The two divers who tried to dive to the bottom of el zacaton must have been nuts! Just thinking about it gives me goosebumps.

Great hub, Voted up!


Austinstar profile image

Austinstar 4 years ago from Somewhere in the universe

Whoa! I knew about the big blue hole in Belize, but how did I ever miss the El Zacatón sinkhole in Mexico? I thought I had traveled all over that country. True, I don't remember ever going to Tamaulipas. I'll have to Google this. Cool! Thanks!


homesteadbound profile image

homesteadbound 4 years ago from Texas Author

Rain Defence - Wow is right! Since I can't swim I have never been diving, but I can dream. I imagine it is great. I love the ocean and all that is in it. I hope you get to go diving soon. Thanks so much for diving into this hub so enthusiastically!


Rain Defence profile image

Rain Defence 4 years ago from UK

Well you know what, you don't really need to be able to swim well or even really at all to dive. That might sound crazy, but you have all the breathing gear on and flippers, so it's completely different from normal swimming. If you could just master some basic swimming then you'll be good enough to dive. You're never too old to learn!


homesteadbound profile image

homesteadbound 4 years ago from Texas Author

Austinstar - it is always nice to know that I've been able to share some new information with someone. I hope you find what you are looking for and I hope you are able to visit the blue hole. Thanks so much for stopping by!


DonnaCosmato profile image

DonnaCosmato 4 years ago from USA

Wow, these are awesome images and descriptions! I'm really glad to learn more about this topic.


homesteadbound profile image

homesteadbound 4 years ago from Texas Author

I have tried to take swimming lessons about 4 times now, and I just can't seem to get the hang of it. It would be nice though! Thanks so much for caring enough to stop back and comment.


homesteadbound profile image

homesteadbound 4 years ago from Texas Author

Donna - I was pleased to be able to share it with you and have you enjoy it. Thanks so much!


Brett.Tesol profile image

Brett.Tesol 4 years ago from Somewhere in Asia

A really good review of the beautiful phenomena.

My stepmother was once snorkeling around the edge of one of these, not being a very good swimmer she was being careful, but managed to drift off the edge and suddenly she became panicked, splashing around like crazy on the surface! To the observers this was very funny.

Thanks for SHARING.


dinkan53 profile image

dinkan53 4 years ago from India

Beautiful places and cool videos. Good work, enjoyed it. thanks. Rated up and beautiful.


homesteadbound profile image

homesteadbound 4 years ago from Texas Author

Brett.Tesol - These would be very scary (because of depth) for someone who did not know how to swim very well. I assume she was okay. Thanks so much for stopping by and commenting.


RealHousewife profile image

RealHousewife 4 years ago from St. Louis, MO

Awesome Homestead! I was in Mexico about year ago and we went to a Cenote is that the same thing? They are gorgeous but a little bit scary I think!

I watched that movie Sanctum - reminds me of that in some of your discriptions. This is a terrific topic!


homesteadbound profile image

homesteadbound 4 years ago from Texas Author

dinkan53 - I glad that you enjoyed this hub, dinkan53.


homesteadbound profile image

homesteadbound 4 years ago from Texas Author

RealHousewife - A Cenote is a landlocked sinkhole - yes, they are essentially the same. I will be writing about those soon as well, as part of this series I am creating here. I can imagine that anything that big and deep can be scary... and almost other-worldly. I have not seen sanctum but the previews do remind me of this.

Thanks so much for stopping by and commenting.


melbel profile image

melbel 4 years ago from New Buffalo, Michigan

Wow, that's REALLY pretty! I think I would like to go there some day. I have this fear, yet an attraction to incredibly deep water. It would be cool to see something like this.


homesteadbound profile image

homesteadbound 4 years ago from Texas Author

melbel - I think that some of these are surrounded by coral reefs. I know the Great Blue Hole in Belize is. So you could see the hole up close and still enjoy the water and the dive around it. It could be a win-win for you. I hope you get to see it one day! Thanks so much for stopping by!


eddiecarrara profile image

eddiecarrara 4 years ago from New Hampshire

Great hub homesteadbound, I admire the time and effort you put into your work, you produce such interesting and insightful hubs, Thank you.

I have only snorkeled in the Caribbean, I have never had the time to learn scuba diving, but when I do I'll be sure to check out at least one of the blue holes, very mysterious. Not sure If I'll have the ambition to go deep but at least explore the edges. Voted up and interesting :)


homesteadbound profile image

homesteadbound 4 years ago from Texas Author

eddiecarrara - It is good to hear that my hubs are making an impression. I am truly interested in creating a quality product.

Scuba diving could be a very awesome experience. If it is something that you want to do, I hope you are able to do it, and I hope you will be able to visit one of these fantastic destinations. Thanks so much for visiting!


Peggy W profile image

Peggy W 4 years ago from Houston, Texas

Hi Cindy,

This is an amazing hub! The descriptions of the blue holes were informative and the videos are stunning to watch. No wonder people love to scuba dive! I have never done so and probably never will at this point in my life, but getting to see what they experience by watching these videos is pure enjoyment. Up votes and will SHARE!


MP50 4 years ago

Interesting Hub homesteadbound, never swam in a blue hole. Have swam in the blue lagoon Jamacia, this lagoon was a mixture of salt water and fresh water.

Scary place to swim through black and blue water, hot and cold. Apparently no one has ever touched the bottom of this lagoon?

Voted up and SHARED thanks.


homesteadbound profile image

homesteadbound 4 years ago from Texas Author

Peggy W - I am pleased that you enjoyed the hub! I too have never scuba dived, but I would have to learn how to swim first. I love the ocean and all that is in it. Thanks so much!


homesteadbound profile image

homesteadbound 4 years ago from Texas Author

MP50 - That is a scary thought that something is so deep no one has ever touched the bottom. Thanks so much for stopping by!


Sharyn's Slant profile image

Sharyn's Slant 4 years ago from Northeast Ohio USA

Wow Cindy ~ Very cool hub! Great research - always learn something new from you!


homesteadbound profile image

homesteadbound 4 years ago from Texas Author

Sharyn's Slant - So happy to share these awesome blue holes with you. Thanks for stopping by!


sgbrown profile image

sgbrown 4 years ago from Southern Oklahoma

Hi Cindy. I love the hub and the videos are wonderful! Such beauty! There is a "Blue Hole" in Santa Rosa, New Mexico, I believe. I was there many, many years ago! I went with some friends they were scuba diving there. I was not brave enough. Love the hub! Voted up and awesome! Have a wonderful day! :)


homesteadbound profile image

homesteadbound 4 years ago from Texas Author

sgbrown - I am pleased that you enjoyed this hub. I plan to write a hub about land bound blue holes also. thanks so much for sharing!


debbie roberts profile image

debbie roberts 4 years ago from Greece

Hi homesteadbound, I was just browsing the internet for some information on blue holes and you popped up close to the top on the first page of google. Just what I was looking for, thank you.

Interesting hub and just the info I was searching for.

Voted up and interesting.


homesteadbound profile image

homesteadbound 4 years ago from Texas Author

debbie - how fun! So glad that we were able to come full circle and you landed back here. I am pleased that I was able to answer your question. Thanks you so much.


Thomas Raek 4 years ago

Great job Cindy, quite educative i must say. Now i really wanna take a dive in a blue hole lol. i hope it would possible?


homesteadbound profile image

homesteadbound 4 years ago from Texas Author

Here's hoping you get to as well, Thomas! So glad you enjoyed the mini-vacation!


alis 3 years ago

a blue hole off belize

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