Beware of Sinkholes
Sinkholes tend to take you by surprise. They form so gradually that when they occur, you are truly taken aback. Sometimes they are up to 2,000 ft. in diameter and depth. Other times, they only reach 3.3 feet. There are sinkholes all over the world.
What types of land are prone to sinkholes? Geologists identified two types, namely:
Evaporites (salt, gypsum, and anhydrite)
Carbonates (limestone and dolomite).
Both types of land are sturdy from the start, but over time they become naturally dissolved by groundwater that filters and travels through them. Additionally:
If there is no natural surface drainage, water will move through the soil and slowly dissolve the rock underneath.
Sinkholes are additionally agitated by earthquakes. One sinkhole was discovered in Cambilan, Catigbian, Bohol after an earthquake. Tsunamis and storm surges also can cause sinkholes.
Sadness for the house that used to be in the middle
Sinkhole in Florida
As earlier said, sinkholes take you by surprise. They are truly unpredictable. Before you know it, unknown underwater caverns hide in the ground beneath your home. My mother’s family home is 247 years old. It rests on a limestone bed and nothing has sunk so far. Nonetheless, I am glad I don’t live there, and I wouldn’t invest my money in it. It is the nature of sinkholes to stay intact for a very long period of time, then suddenly, kapow!
The trouble is grave (pun intended) when those underground gaps get too big. One sinkhole in Florida ate into a swimming pool, the road, and buildings.
Largest sinkhole in Florida
Sinkholes endanger most of the Philippines
In the Philippines, the Department of Environment and Natural Resources (DENR) and the Mines and Geosciences Bureau (MGB) said the National Capital Region is safe, as most of it sits on solid adobe rock. However, there are five places with sinkholes, or with the potential to form sinkholes in the Philippines. They are:
Cebu. Sinkholes were found in Sta. Fe town, Bantayan Island which led to a relocation of families in sitio Dapdap, Barangay Langub. The sinkhole was initially about three feet wide, but continued to grow wider until it reached 40 feet in width and four feet in depth. Another sinkhole in Badian, Cebu, was five meters wide and 10 feet deep. It is believed that the sinkhole appeared because of prolonged strong rains and an earthquake.
Bohol. A 7.2 earthquake in 2013 uncovered 100 sinkholes in Bohol, where most of the land is limestone. The sinkholes were found in Tagbilaran City and the towns of Alburquerque, Baclayon, Balilihan, Batuan, Carmen, Corella, Loon, and Panglao.
Over 100 sinkholes discovered in southwestern Bohol after earthquake
Baguio is one of top seven dangerous areas in Asia for sinkholes.
Baguio City. According to a 2015 report by the Cordillera office, Mines and Geosciences Bureau (MGB), there are at least 157 sinkholes in 14 of the city’s barangays. The Baguio City Planning Office also noted that 24 houses have been built on top of these sinkholes. The report also noted that it is possible more sinkholes exist that have not yet been discovered.
Baguio City also has some seven earthquake faults and many areas that are vulnerable to landslides from continuous rainfall. It is among the 10 areas in the world with the highest occurrence of daily rainfall, plus, it averages five cyclones per three years. This combination is bad (or good?) for sinkholes. The World Bank has listed Baguio among the top seven cities in Asia that are risk-prone.
3. Negros. Just five years ago, in 2013, six people were injured by a sinkhole in the middle of a basketball court in Purok Jalandoni, Barangay Oringao, Kabankalan, Negros occidental. Furthermore, Barangay Mabinay in Negros Oriental was reported in 2015 to have had four sinkholes after an earthquake, which were getting larger with continual rain. Some 22 families live near the sinkholes.
4. General Santos City. In February 2015 a suspected sinkhole was discovered at Purok Tinago in Barangay South Dadiangas, General Santos City. Officials however, said it is only a “coastal subsidence”. The hole measured some 1,980 ft. in depth. Local reports added that the underwater hole continues to eat into the shores and gobble their homes. This led to the evacuation of some 46 families.
On the other hand, it is possible that the “coastal subsidence” is causing the sinkhole, since coralline limestones lie beneath the area’s shoreline.
How to Prevent Sinkholes
Buy the right land. If you haven’t built your house yet, and have not yet purchased land, then make sure the land you buy is not comprised of the soil mentioned at the start of this article. For example, Metro Manila is pretty safe because most of the soil is not vulnerable to sinkholes.
Prevention is better than cure. Some sinkholes are caused by man, especially in urban areas. This is because there are many underground utility systems that can deteriorate over time. To prevent this, maintenance is important as well as infrastructure support.
The older, the worser. Beware of old sewer pipes and sewer mains. These are the most common causes of urban sinkholes. Old pipes get holes which slowly leak water in the surrounding area, causing erosion and making the land beneath your house unstable and hollow. It is aggravated when heavy vehicles drive over the surface road and construction occurs around the area.
However, through GPR (ground penetrating radar) scanning, a sinkhole can be detected early, giving neighborhoods and municipalities time to repair or replace pipes, in this way preventing a sinkhole from occuring.
4. Is your house on a sinkhole? You can look for signs of sinkholes on your property. The most common signs are:
Large, round, sunken holes in your land.
A slow lowering of parts of your property over time.
A drooping or cracking foundation.
Cracks in concrete, pavement, or streets that are not caused by something else.
5. CCTV pipe inspection. It is possible to inspect the condition of your pipes through the insertion of a CCTV that will go down the length of your pipes. If leaks are detected, you will know where they are situated, and this will enable you to replace or repair those areas before they cause erosion to the soil.
One of Mexico's Cenotes
Sometimes sinkholes are nice
Koi, anyone? Some sinkholes have formed lovely natural ponds.
Other sinkholes are harmless. In Mexico, there are “cenotes”, naturally formed sinkholes where groundwater emerged after the limestone bedrock that covered it collapsed.
Some sinkholes are famous, such as the Qattara located west of Cairo, Egypt. At some 50 miles long and 75 miles wide, it is the largest natural sinkhole in the world. On the downside, it has been used in battle as it is filled with quicksand. Well, nothing’s perfect.
Sometimes you can swim in them. Florida’s Devil’s Toilet Bowl is one such swimmable sinkhole.
Florida's Devil's Toilet Bowl
Some are mysteriously awesome. One example are the Sarisarinama holes of Venezuela. They are perfectly round basins with a diameter of 350m and a depth of 350m. Each hole has unique ecosystems with many plant and animals that cannot be found anywhere else on earth.
Some are odd moneymakers. In Oman, tourists flock to Bimmah, a sinkhole that is a swimming park.
3. Some are beautiful, like Mount Gambier in South East Australia (between
Melbourne and Adelaide). It has a lot of unique water channels, caves and caverns. Overall, it is breathtakingly lovely.
sinkhole in Binmah, Oman
Some have history. This is the case with The Devil’s Sinkhole in Texas. Archaeological evidence indicates that this sinkhole was once considered sacred by Native Americans. You can even collect stuff like stalactites and arrowheads among others in the grounds.
Haunted Ghost Towns, anyone? Some sinkholes have resulted in beautiful, abandoned ghost towns like Centralia, Pennsylvania which was attacked by an underground fire fueled by rich coal underneath the town. The fire has been burning for over 45 years now and some predict it may last for 250 years. There are also unpredictable sinkholes.
Everything has an up and downside. Who knows what will come of the unique ecosystems that evolve around them. For me, I think these ecosystems, if they prove to be valuable to mankind, would be more beneficial if they formed in ways that will save (not sink) the earth.
NOTE: This article was featured in the November, 2018 edition of Enrich Magazine, a publication that is distributed in five countries.