Above the vast sea, a deep blue round water will suddenly appear. Seen from a high altitude, it looks like the pupil of the sea. Seen from the depths of the earth, it is deep, mysterious, and strange.

Above the vast sea, a deep blue circular water will suddenly appear. Seen from a high altitude, it seems like the pupil of the sea. Seen from the depths of the earth, it is deep, mysterious and strange. This strange nature The landscape is known as the Blue Hole. Since ancient times, people have made many speculations about the blue hole, which have cast a mysterious veil on the blue hole. So, what exactly is a blue hole and what’s inside it?

Author: Bai Hongxin Chen Xiaomei

Picture source: Xinhua News Agency

The legend of the Blue Cave has existed since ancient times

As far back as the ancient Roman era, some people went to explore the Blue Cave, and it was said that "The Blue Cave is a place for contemporary witches to cultivate their health and practice magic power." Base", which makes the true appearance of the Blue Hole unknown and always shrouded in mystery.

In China's Paracel Islands , there is a "Dragon Cave" that is passed down by fishermen orally. Because it is unfathomable, the fishermen are in awe of it and it also has a long legend. Some say that there is a large sea monster in it and should be avoided; others say that it is the "Eye of the South China Sea" because it contains the "Dinghai Divine Pearl", a treasure that holds the sea; others say that this is the location of the "Dinghai Divine Needle". Sun Wukong made a big fuss in the Dragon Palace and pulled out the Dinghai Divine Needle to use as the Ruyi Golden Cudgel, leaving this unfathomable hole.

Of course, these are just legends. Ocean Blue Hole is a rare marine geographical phenomenon on the earth. Compared with the surrounding waters, the water in the blue hole presents a deep blue tone.

How are blue holes formed?

So how are these mysterious blue holes formed? According to Professor Yang Zuosheng of the Ocean University of China, there are currently two types of causes of ocean blue holes, namely the cause of limestone caves and the cause of coral reef growth structures.

The so-called limestone cave means that due to the lowering of sea level during the glacial period, the limestone was dissolved and developed into a large cavity (similar to a cave) in the lower part. When the dissolution cavity became larger and larger, it caused the top to collapse and form a large hole with steep edges. , called sinkhole . After the ice age ended, the sea level rose, and seawater refilled the sinkhole, which became the "blue hole" that everyone sees.

This type of blue hole contains a large number of stalagmites, stalactites, etc., and the cracks are developed, often forming several channels connected to the outside sea water. There is a certain exchange between the water body in the cave and the outside sea water. There may also be limestone walls or cave roofs at the bottom of the cave. A large amount of products fell when erosion and collapse occurred. The famous Belize Great Blue Hole belongs to this type.

The coral reef growth structural model was proposed in the late 1990s, the most typical of which is the Hautman-Abrolhos Coral Reef Blue Hole on the southwestern outer shelf of Australia.

Since the Holocene 10,000 years ago, the coral reefs in this sea area have grown rapidly. Many rapidly growing smaller reefs have formed spine-like protrusions and gathered together, eventually forming an approximately circular hole. The internal water environment of the cave has a significant impact on the growth of corals, while the external water environment is conducive to the growth of corals, gradually developing into a blue hole with larger water depth. There are no stalagmites, stalactites and other products observed in this type of blue hole. There is no channel for exchange with the outside seawater. There is coral sand at the bottom.

What's in the Blue Hole?

The mysterious blue hole has become an adventure destination for diving enthusiasts. World-famous divers have tried the fun of diving in the blue hole. These blue holes have also become very attractive tourist attractions.

Because blue holes are usually hundreds of meters deep and severely lacking in oxygen, they cannot support the survival of most marine life. There is no interference from modern biological activities here, which is conducive for scientists to study ancient fossil remains and other sediments here.

For example, scholars from Rice University and Louisiana State University studied sediment samples extracted from the Great Blue Hole in Belize and found that the age of the samples ranged from 1,000 to 800 years ago, which is consistent with The decline of the Mayan civilization occurred during the same period. Through the analysis of elements (titanium) in the samples, it was found that the number of tropical cyclones during this period was less than before, and droughts were longer than before.

The Yucatan Peninsula where Belize is located is an area with relatively scarce water resources. At that time, the Mayans mostly relied on rainwater stored in limestone pits to survive drought periods. However, long-lasting droughts may have exhausted the stored water. drinking water. After the water crisis, famine, turmoil and war followed, which led to the decline of the Mayan civilization. Therefore, blue holes are called by scientists "the last legacy that preserves the secrets of the universe."

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(Original title: What is the mysterious "Blue Hole")

Source: Beijing Evening News

Editor: tf010