Sinkhole: A Natural or Man-made Phenomenon?

In a recent news report, it was announced that a sinkhole suddenly opened up in Guangzhou in China on January 28, 2013. The ground under a building gave way, sending other buildings into the pit. Thankfully no one was injured during the incident. According to reports, the hole measured 3,200 square feet, with a depth of nearly 30 feet. It was also reported that the hole is continuing to expand.

The sinkhole appeared near the site of a subway construction area. It is a good thing that the workers noticed that the ground was sinking and were able to evacuate about 300 people who were in the buildings that were swallowed by the sinkhole. The authorities have yet to determine if the construction of the subway was the cause of the sinkhole.

Similar incidents
This is not the first time that sinkholes suddenly appear. Last year, May 2012, a sinkhole opened up in downtown Guatemala, sending a three-story building into its depths. There was another sinkhole that opened up almost in the same area on April 2007. The sinkhole that occurred in a neighborhood in Guatemala on February 2007 was larger and deeper. More than a dozen homes were swallowed by the 330-feet deep sinkhole that time. In September 2009, the front part of a fire truck responding to a burst water pipe situation went into a sinkhole right in the middle of a street in Los Angeles, California. A shallow sinkhole opened up in a neighborhood in Dunedin, Florida in April 2007. Several other incidences of sinkholes suddenly opening up have occurred in different parts of Florida for years, which according to geologists is a common occurrence in the state.

In 2008, a massive sinkhole appeared in Daisetta, in Liberty County, Texas. Two other sinkholes opened there in 1969 and in 1981. The one that opened in 2008 was the largest in the area, with a length of 600 x 525 feet and a depth of about 150 feet. This gaping hole had swallowed trees, vehicles, poles and equipment for the oilfield. The collapse of the salt dome on which Daisetta sits is blamed for the sinkhole.

Causes of sinkholes
Often, it is the erosion of the underground salt beds or the sedimentary rocks such as dolomite and limestone, which are soluble that triggers the opening up of sinkholes. When groundwater flows through the rocks overtime, the rocks weaken and crumble, cause caverns under the ground. Pressure from above and the movement of the ground underneath cause the upper layers of ground to weaken, crack or crumble and eventually sink, causing gaping holes above ground. They could also occur when sewers and water mains break, or when abandoned mines collapse.

Tourist attractions
Some sinkholes become tourist attractions, like the Sima Martel and Sima Humboldt in Venezuela and the 662-meter deep Xiaozhai Tiankeng in China. Those that form in islands and coral reefs are called “blue holes” and one great example is The Great Blue Hole located in Ambergris Caye in the country of Belize. The deepest blue hole in the world is located in Long Island in the Bahamas, called Dean’s Blue Hole. It is filled with saltwater and 663 feet deep. Its entrance is below sea level, which differentiates it from Italy’s Pozzo del Merro which is deeper, at 1,286 feet and Mexico’s Zacatón, which has a depth of 1,099 feet. These blue holes have become favorite dive spots of international diving enthusiasts.