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The allure of blue holes

04 Jun 2022

By Nethmie Dehigama Since reading an article in a National Geographic magazine many years ago, I have always found blue holes beautiful, mysterious, and fascinating. Blue holes are massive, submerged sinkholes that are open to the surface – which is why they are visible from the air. The existence of these underwater caverns was discovered in the late 20th century by fishermen as well as recreational divers. They are named ‘blue holes’ because they appear to be a darker blue than the water around them. This is because blue holes are generally found in shallow waters, and as we know, shallow oceanic areas are lighter in colour, while the deeper areas appear dark. Blue holes do not just go straight down: they extend into a maze of holes, tunnels, and caverns. These attract expert divers from around the world keen on exploring the uncharted and perplexing territory. They also attract curious tourists. How did they form? Blue holes have developed in areas made of limestone or coral reef, most likely during the last ice age when the water level was much lower. Erosion due to rain or chemical weathering is considered to be the most likely reason for the creation of these sinkholes at the time. The end of the ice age saw these sinkholes completely submerged. Additionally, the chemicals present in blue holes eat away at the surrounding rock, creating mysterious vertical caverns – some over 600 metres in length. The deepest blue hole in the world discovered to date is found in the South China Sea, called ‘Dragon Hole’, and is known to be 987 feet deep. The largest blue hole is The Great Blue Hole in Belize, which is about 354 feet deep and 984 feet across. Biodiversity and conditions Blue holes are also rich hotspots for microbial biodiversity and captivate scientists the world over. There have been many fossils discovered within these holes, as well as important types of bacterial colonies. These bacteria thrive under extreme conditions. Blue holes also have a ‘line’ or a murky zone within it called the halocline, which is generally not visible to the naked eye. Here, dense saline water has mixed with fresh rainwater, and there is hydrogen sulphide gas – a by-product of bacteria and plant debris rotting for aeons. Some divers swimming through this layer have reported having experienced burning skin and nausea. Deep below, there is a build-up of silt, no light penetration, and also no oxygen. This is why the fossils discovered were perfectly preserved without decay. However, at levels where there is some oxygen, types of blind fish, tiny crabs, and shrimp, as well as microbes including ‘extremophiles’ – organisms thriving under extreme conditions – have been found. The vertical caverns also have stalagmites due to the build-up of sediment over the years. This provides a great deal of information on historic atmospheric conditions for researchers. Expeditions Diving into blue holes is quite a difficult task and requires great professional skill and equipment to do so. Unfortunately, these watery locations have seen multiple deaths of divers who have attempted to reach the bottom or explore caves within. The blue hole found in the red sea in Egypt has been nicknamed ‘The Divers’ Cemetery’ because at least 40 divers have died there. Two of the most prominent expeditions happened in 2009 and 2019. In 2009, a team of scientists ventured into the blue holes in the Bahamas. Keith Tinker led over 150 dives there, where they studied how bacteria lived with minimal to no sunlight and oxygen. In 2018, another group of scientists descended into the Belize blue hole. Using two submarines of the latest technology, they mapped the interior of this hole, and also studied the stalactites and the halocline layer. Blue holes you could visit The Great Blue Hole, Belize – this is the most famous blue hole and is popular among recreational scuba divers The Blue Hole of Gozo, Malta – this is a much smaller and tamer blue hole in the Mediterranean Sea Dean’s Blue Hole, Bahamas – this is the second deepest blue hole and is a beautiful, scenic location Blue Hole of Dahab, Egypt – the third deepest blue hole. Here, many divers have died trying to locate the underwater tunnel that goes through the reef Jacob’s Well, Texas – also popular with scuba divers and swimmers. A dozen people are known to have been trapped in the narrow underwater caves here, too. It is certainly on my bucket list to travel to see these awesome natural phenomena, and maybe to even dive into them. The world is truly an intriguing place. Would you want to explore a blue hole? Author bio: Nethmie is a digital marketer, writer, songwriter, and literature enthusiast. She has a BA (Hons) in International Communications. PHOTOS © CAROLINE BJÖRNERÅS, PETE NIESON (SHUTTERSTOCK), MARSHALL PHOTO, BRIAN KAKUK    

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Discover Kapruka, the leading online shopping platform in Sri Lanka, where you can conveniently send Gifts and Flowers to your loved ones for any event. Explore a wide range of popular Shopping Categories on Kapruka, including Toys, Groceries, Electronics, Birthday Cakes, Fruits, Chocolates, Automobile, Mother and Baby Products, Clothing, and Fashion. Additionally, Kapruka offers unique online services like Money Remittance, Astrology, Medicine Delivery, and access to over 700 Top Brands. Also If you’re interested in selling with Kapruka, Partner Central by Kapruka is the best solution to start with. Moreover, through Kapruka Global Shop, you can also enjoy the convenience of purchasing products from renowned platforms like Amazon and eBay and have them delivered to Sri Lanka.Send love straight to their heart this Valentine's with our thoughtful gifts!


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