Sinkholes are a hole in the ground, common in karst terrain, which is caused by erosion as the limestone is being dissolved by water. Karst terrain are those areas where the rocks below the surface are of types that are easily dissolved in water, including salts beds, gypsum, limestone, and other carbonated rock. When rain falls, the water slowly moves down the land surface and it begins to dissolve these rocks.
Eventually, it results in underground caverns and spaces. As these underground caves grow larger and larger, the land surface above them will suddenly sink in creating what we call sinkholes. With not enough support for the land surface, sinkholes happened usually in a dramatic way after staying intact for a while.
Studies show that 20% of America is susceptible to sinkholes. Most damages might be found in Florida, Texas, Alabama, Missouri, Kentucky, Tennessee, and Pennsylvania. Florida has many sinkholes activity going because it basically stands in karst terrain with the highest activity on its west central side. Other parts of the world like Guatemala and Egypt also experience sinkholes. Recently, huge sinkholes have appeared in China and other countries as well. Due to its sudden and extreme occurrence, it is best to be ready and aware of its signs.
1. Types of Sinkholes
Geologists have classified sinkholes into three different types: dissolution or solution sinkhole, cover-subsidence sinkhole, and cover-collapse sinkhole. Dissolution or solution sinkhole gradually forms as water from rain slowly dissolves the bedrock and eventually depression forms.
It is generally not dangerous, but sudden drain can happen when it has become a pond. Cover-subsidence also happens slowly in areas where sand covers its bedrock. The sand slowly filters down into the openings and gradually causes the land surface to sink in. Further depression is caused by continued erosion.
Cover-collapse is the most dangerous type of the three. It happens in areas where the bedrock is covered by a layer of clay, thus the dissolving happens under this layer. The dangerous part is the ground continues to crumble from beneath, leaving a thin layer of the surface. When this thin layer finally collapses, it suddenly opens up a sinkhole that swallows anything on top.
2. Droughts and Heavy Rainfall Result In Sinkholes
There are two main sinkholes triggers: heavy rainfall and drought. Heavy rainfall causes some added weight above the cavity which will cause the water to filter in and slowly dissolve the rocks below.
On the other hand, drought might cause overpumping of water supply from wells or even drilling of new wells. This will eventually result in a sudden change in water level causing the emergence of a hollow part in the ground. These hollow parts will eventually lead to sinkholes as the absence of support for the land surface above.
3. Hurricanes and Sinkholes Goes Hand In Hand
Hurricanes would cause extreme weather conditions which usually leads to huge rainfall. Bigger rainfalls means more water is present. Especially when a drought was followed by this hurricane, sinkholes most definitely would take place.
The weight of a large amount of water on the earth’s surface may cause collapse due to the cavity that exists. Also, large masses of water caused a sudden disturbance to the ground water level which will try to fill in the voids in the porous limestone layer, thus sinkholes are very prone to happen if the ground below can’t sustain the surface well.
4. Sinkholes Or Earthquakes
Sometimes earthquakes might also cause depression on land and you might be confused whether it is a sinkhole or just the aftermath of the earthquake. Thus, it is important to ask professionals to observe your house when you notice a presence of depression.
Earthquakes might cause a drop due to the shiftings. It is important to note that sinkholes might be a secondary result of earthquakes. There are cases where several sinkholes appear after an earthquake. It might be caused by the limestone bedrock being hit or continuous water flow due to broken underground water facilities.
5. Sinkholes Warning Signs
SInkholes happen naturally in a sudden state and it is almost impossible to predict them. However, you can always be aware and pay attention to these warning signs which will indicate the presence of sinkholes around you.
If you are living in an apartment building, you can pay attention to structural cracks on walls and floors, muddy or cloudy well water, and if your doors or windows cannot be closed properly. If you are living in landed properties, you can pay attention to whether your fences or other foundations which are previously buried under the ground start to get exposed because the grounds started sinking.
If you have plants or farmland near you and they start to wilt and die, it might indicate that the essential water is drawn away by a sinkhole. Formation of small ponds, circular pattern of ground cracks, areas with bare soils, and trees starting to slump or fall also indicate sinkholes. Lastly, if your plumbing and electrical service is interrupted due to the damage in the utility lines also indicates presence of sinkholes.
6. Sinkholes Early Treatment
Early detection of sinkholes allows you to do something about it to stop it from sinking at all or sinking even more. Sinkholes may appear in different parts of the house and each part requires different treatments to it. Before doing anything, you need to know the cause of it before deciding on anything.
The basic idea is you need to fill in the hollow portion just below the land surface level in order to prevent future sinkholes. Just like treating your teeth cavity, you need to inject grout into the hole and rebuild the foundation.
However, different filing techniques are required for different locations. If the ground has sunk and the depth is more that your chest level, it is better to call for professional help since it might be dangerous.
7. Qattara Depression
One of the most famous sinkholes in the world is the Qattara Depression located in Egypt. Unlike usual sinkholes, this huge sinkhole is caused by the wind which causes salt erosion to happen and eventually eat away all the bedrock causing a giant sinkhole to happen. It is today the second lowest point in Egypt and the largest sinkhole in the world.
8. Xiaozhai Tiankeng
You have known the largest sinkhole in the world, now you need to know the deepest in the world. It is the Xiaozhai Tiankeng located in Fengjie County, Chongqing, China. It is made due to the collapse of limestone bedrocks since the area is made of pure limestone.
It might have been formed thousands of years ago, but it was just discovered in 1994. The depth is between 511 and 662 meters and during a rainy season there will be a waterfall. Underneath it is the Migong river and you can find 1285 plant and animal species living in this sinkhole including the clouded leopard.
9. Underwater Sinkholes
Sinkholes could also occur on sea level. Previously, the water level was not as high as it is now. Thus, sinkholes or caves are formed slowly over time due to the erosion of rocks.
As the water level rises, these sinkholes and caves are filled with water and make these blue holes. They got its name due to the dark,navy blue color it has which is significantly different from their turquoise-colored surroundings.
10. Beware of Blue Holes
When you are diving, you might discover the blue holes. Well, diving in the area seems fine, but things can go wrong. Blue holes are mostly very deep and without you realizing it, you will be diving too deep. It will be dangerous for inexperienced divers and if you have no proper preparation or guidance for it.
At some point, the nitrogen narcosis will take hold causing you to be unable to think clearly and you will start entering a toxic oxygen state. Proper training and research is necessary to dive safely.
11. Home To Alligators
Some of us might be curious about what is found inside the sinkholes. If you are thinking of exploring one, keep in mind to explore these sinkholes when they are in a dry state. These sinkholes or caves during the rainy season might be a place where alligators are. Just like what you can find in the “Deep Hole” located in Myakka River State Park in Sarasota, Florida.
12. Man-Made Sinkholes
Sinkholes are a natural phenomenon that might happen over time. However, human activities might also have induced its emergence. For example, city development which compromises the structural integrity of the underlying rock.
Constructions of roads, buildings, etc. may lead to water collection in a certain area which could cause some supporting rock layers to be washed away. This is why it is important to have a well thought plan before building or developing a city.
13. Sinkholes Increases Each Year
Studies show that there is an increase in sinkholes throughout the year. As global warming becomes an issue today, it also causes an increase in sinkholes for about 1-3% for every 0.1 degree celsius rise in the temperature. Global warming causes extreme weather where heavy rainfalls and flooding could happen. A large body of water is the recipe for sinkholes.
14. Effect of Sinkholes
The presence of sinkholes might change the general topography of the area and it will divert the stream direction of underground water. Since water is one of our basic needs, it might lead to a major problem. It will also affect the quality of the groundwater especially regarding its chemical properties. This includes the water you find in streams, lakes, wetlands, etc.
15. Japan Fix Sinkholes In Two Days
A huge sinkhole happened in early 2016 in the city of Fukuoka, Japan. It took the Japanese only two days to fix the whole mess. The sinkhole happened in one of the busy intersections of the city’s business district and swallowed five road lanes. How fast the Japanese were able to fix this city shows that they have an efficient and advanced technology to tackle the mess.
The aftermath of sinkholes might be devastating in addition to the trauma it may cause due to its sudden occurrence. Even so, we can always be alert and ready. If you know that you are living in areas with karst terrain, you might want to have your lands checked from time to time because early detection is key to a successful prevention.
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