September 30, 2016

Chinese researchers have learned that a fabled ocean depth known as the Dragon Hole, a huge underwater chasm located in the South China Sea, is the deepest such natural feature in the world. For most of the past year, researchers made risky dives and used sonar scanners and underwater robots and cameras to explore the hole’s murky depths. They eventually found the Dragon Hole to be 987 feet (300 meters) deep. This makes it the deepest blue hole, a kind of vertical underwater cave, in the world’s oceans. The Dragon Hole (also known as the Sansha Yongle Blue Hole) is about 300 feet (100 meters) deeper than the second deepest such feature, known as Dean’s Blue Hole, located near the Bahamas in the Atlantic Ocean. The Dragon Hole lies among the Paracel Islands (also known as the Xisha Islands), about 175 miles (280 kilometers) southeast of China’s Hainan Island.

On July 24, 2016, a research vessel explores the Dragon Hole among the Paracel Islands in the South China Sea. Also known as the Sansha Yongle Blue Hole, it is the world’s deepest such underwater feature. Credit: © Luo Yunfei, VCG/Getty Images

A blue hole is a type of sinkhole, a bowl-shaped depression in Earth’s surface that forms where the ground sinks, collapses, or washes into underground openings. Such features often occur on dry land, where mildly acidic ground water dissolves underground rock. These openings most often develop in a rock called limestone, but sinkholes also form in other easily dissolved rocks. Blue holes form in rock formations that occur underwater. Over long periods, the rock making up the ocean floor can dissolve in the subsurface to form caves or cavities. If the rock forming the cave ceiling collapses, the newly formed hole on the seafloor is immediately filled with water.

Blue holes get their name from their distinctive deep blue color, a sharp contrast to surrounding, shallower, aquamarine waters. Blue holes can be dangerous for divers to explore because below about 300 feet (100 meters), there is virtually no oxygen and very little light. The steep walls of a blue hole extend into the dark depths, and it is often difficult to determine how far down the bottom lies. Blue holes can also host curious life forms, as the researchers of the Dragon Hole learned firsthand. They found 20 fish species that may be new to science.

Local people have known about the Dragon Hole for centuries. It clearly stands out on the ocean’s surface. The Dragon Hole is mentioned in the 1500′s Chinese mythical novel, Journey to the West. Often called Monkey in the West, the novel describes a pilgrimage of a Buddhist monk in the A.D. 600’s. In this story, a character called the Monkey King visits the Dragon Hole, an undersea kingdom ruled by a dragon.

December 10, 2015

December saw flooding in several parts of the world, with separate weather events inundating portions of the United Kingdom and Ireland, southeast India, and the United States Pacific Northwest.

A woman collects drinking water at a residential area flooded with rainwater in Chennai, India, on Dec. 6, 2015. Credit: © Arun Sankar K, AP Photo

Early in the month, Storm Desmond set a record for 24-hour rainfall in the United Kingdom, dropping 13.4 inches (341 millimeters) in the northwestern county of Cumbria on December 5. Desmond was a type of large, swirling windstorm called an extratropical cyclone. The storm pushed an atmospheric river—a channel of intense moisture in the air—over the region, causing heavy flooding in parts of northern England, northern Wales, and southern Scotland, as well as central Ireland. The floods damaged thousands of homes and killed two people.

The city of Chennai, in southeast India, received 15.6 inches (397 millimeters) of rain over a two-day period in early December. The drenching followed a record-setting November that produced 47.1 inches (1196 millimeters) of total rainfall. The rains caused flooding throughout the state of Tamil Nadu, causing the deaths of more than 200 people and forcing thousands of others from their homes.

In the United States, both Portland, Oregon, and Seattle, Washington, received a month’s worth of rain over just a few days in early December. Heavy rains led to mudslides, sinkholes, and flooding in the Pacific Northwest, leaving thousands of homes without electric power and killing two people.

Additional World Book articles:

• Heavy Rains Trigger Massive Flooding in Australia – A Behind the Headlines article
• Storm Triggers Massive Flooding Along Australia’s East Coast – A Behind the Headlines article
• Worst Flood Ever in Alberta, Canada – A Behind the Headlines article
• Unprecedented Weather Extremes Reported – A Behind the Headlines article
• Study Links Global Warming to Some Extreme Weather Events – A Behind the Headlines article
• “Biblical” Rains Across Colorado’s Front Range – A Behind the Headlines article
• Florida Sinkhole Swallows Resort Villa – A Behind the Headlines article
• Florida Sinkhole Eats Boat and Swimming Pool – A Behind the Headlines article
• Death Toll Rises from Massive Landslide in Washington State – A Behind the Headlines article
• Storms Kill 31 in Southern states of U.S. and Mexico – A Behind the Headlines article
• Historic Flooding in South Carolina – A Behind the Headlines article

August 12, 2013

A 15-foot- (4.5-meter-) deep crater opened last night beneath a resort villa near Clermont, Florida, about 10 miles (16 kilometers) west of Disney World. Dozens of people staying at the 3-story, 24-unit villa managed to escape unhurt before it collapsed into the 60-foot- (18-meter-) wide sinkhole. Guests at the resort called for help before the collapse, reporting that they were hearing cracking noises and had windows blowing out.

A sinkhole is a bowl-shaped depression created when the ground collapses into an opening in the underground rock. This sinkhole formed during a flood, damaging homes and allowing contaminated floodwater to drain into groundwater supplies. (© James A Hyatt)

Sinkholes are common in Florida, which lies atop a system of limestone caverns that are subject to water erosion. Over time, the underground water dissolves the limestone, but the surface of the ground stays intact. Eventually, the void collapses, creating a sinkhole.

In February, a man asleep in bed was swallowed live when a sinkhole opened beneath his house in a Tampa suburb. His body was never recovered.

A solution cave, such as the one shown here, is formed in limestone when water dissolves sections of the rock. Many of the cave's features develop from minerals deposited by the water. (World Book diagram by Bruce Kerr)

Additional World Book article:

• Guatemala 2010 (a Back in Time article)