- A sinkhole is a hole in the earth's surface caused by the erosion of the ground layer beneath, according to the United Nations Platform for Space-based Information for Disaster Management and Emergency Response (UN-SPIDER). This hole grows over time and can have a diameter ranging from one to 600 meters.
- The world-famous Boracay Island has 815 sinkholes, causing a risk to structures in the island.
- A sinkhole is difficult to foresee because it occurs suddenly without showing any indication.
- The majority of natural sinkholes are frequently caused by erosion – either physical or chemical erosion. A United Nations agency explained that physical erosion can be caused by water runoff eroding the rock material.
- Chemical erosion, also known as chemical weathering, can be caused by acidic liquids dissolving soluble rock material. Common soluble rocks are limestone (including chalk), rock-salt (halite), and gypsum, according to the British Geological Survey website.
- An earthquake may also trigger a sinkhole. In October 2013, nearly 100 sinkholes collapsed in Bohol due to a strong 7.2 magnitude earthquake that jolted the area.
- The largest and deepest sinkhole in the world is Xiaozhai Tiankeng, located in China, a BBC travel story published in November 2022 said. The sinkhole is about 660 meters deep and 130 million cubic meters in volume.
Apparently that is a possibility with the recent report that 815 sinkholes were discovered in Boracay Island, a place which attracts thousands of visitors.
The number of sinkholes in that island have increased in the last four years: from 789 in 2018, 801 in 2019, and 814 in 2020, and 815 from 2021 to 2022.
OVER 800 SINKHOLES – A TOTAL OF 815 SINKHOLES WERE DISCOVERED IN BORACAY ISLAND, A POPULAR TOURIST ATTRACTION IN AKLAN PROVINCE. (TARA YAP/MANILA BULLETIN)
The increase in the number of sinkholes puts the popular beach destination in Aklan province at risk.
That’s according to Mae Magarzo who said in a Manila Bulletin story that there will be danger if the island exceeds its capacity, and structures will collapse in a matter of time. Magarzo is the chief geologist of Mines and Geosciences Bureau (MGB) in the Western Visayas region.
Magarzo added that a sinkhole is difficult to foresee because it occurs suddenly without showing any indication.
A sinkhole is a hole in the earth's surface caused by the erosion of the ground layer beneath, according to the United Nations Platform for Space-based Information for Disaster Management and Emergency Response (UN-SPIDER). This hole grows over time and can have a diameter ranging from one to 600 meters.
Sinkhole effects
UN-SPIDER explained that a sinkhole in urban places could result in infrastructure damage, partial or entire collapse of structures, evacuation and displacement of local communities, huge economic losses, and fatalities in some rare cases.
In addition, it said sinkholes occurring in nature could cause changes in the regional topography, local flora and fauna, as well as the path of subsurface waterways.
How do sinkholes form?
UN-SPIDER said both land and ocean floor surfaces are susceptible to sinkholes, which may be a result of natural occurrences and anthropogenic or manmade activities.
The majority of natural sinkholes are frequently caused by erosion – either physical or chemical erosion.
UN-SPIDER explained that physical erosion can be caused by water runoff eroding the rock material. Chemical erosion, also known as chemical weathering, can be caused by acidic liquids dissolving soluble rock material. Common soluble rocks are limestone (including chalk), rock-salt (halite), and gypsum, according to the British Geological Survey website.
That explains why Boracay Island is prone to developing sinkholes. Magarzo said the ground of the island is mostly composed of limestone.
An earthquake may also trigger a sinkhole. In October 2013, nearly 100 sinkholes collapsed in Bohol due to a strong 7.2 magnitude earthquake that jolted the area.
Aside from earthquakes, MGB said in a digital flyer that sinkhole collapses may be a result of heavy rainfall, lowering of the water table, coral reef subsidence, “ponding of subterranean river,” and gravity.
Deepest sinkhole in the world
The largest and deepest sinkhole in the world is Xiaozhai Tiankeng, located in China, a BBC travel story published in November 2022 said. The sinkhole is about 660 meters deep and 130 million cubic meters in volume.
Meanwhile, a Smithsonian Magazine story published in August 2016 said that the Dragon Hole or Longdong sitting in South China Sea is the deepest blue hole, or underwater sinkhole, in the world. The sinkhole measures 987 feet deep.