Recently, I read a sad true life story narrated by a man from Florida who lost his brother, house and property to a sinkhole. According to him, he heard his brother scream from the bedroom, a scream that was quite unusual for an adult. Immediately he ran towards his brother's bedroom, and to his surprise and terror, his brother, his brother's bed and TV were gone, and all that was remaining in the bedroom was a hole, expanding so fast as kerosene spreads over a surface.
At first, he tried to save his brother by trying to dig at the rubble in the hope of seeing the brother, all to no avail. When the situation became more threatening, Jeremy Bush, and other four people in the house with him including a 2 year old child had to quickly escape from their one story 1970s era home in Seffner, before they get swallowed up along side it.
Picture by Dave Bunnell - wikicommon CC BY-SA 3.0
A sinkhole
Sinkholes are quite deadly and whenever they occur, there is no way to recover from the loss. Unlike disasters wildfire and tsunami in which after the disaster, you still have a land on where to rebuild your home, it doesn't happen like that with sinkhole. When a sinkhole occurs, the land gets destroyed, and if one decides to rebuild, the project would be very costly to finance. In this article, I will be telling us how sinkholes are formed, the types, instances of where and when they occurred and what to do to stay alive if you get caught up in it.
SINKHOLES
Sinkhole is the term used to refer to a hole or a depression found in the ground which is as a result of the collapse of the surface layer. Cenote, sink, shakehole, swallow hole, doline and smaller are also terms used to refer to sinkholes. Most sinkholes are formed as a result of karst processes. Some of these processes includes the suffosion process and the chemical dissolution of carbonate rocks. Sinkholes can be of different sizes (in depth and in diameter) which can be within the range of 1m to 600m. Some sinkholes takes years to form, while some kind of occur suddenly. It is not unusual to find an underground stream or river flowing in the bottom of a sinkhole.
Some sinkhole also reveal a cave beneath. Sinkholes occur mostly in lands were it's underground rocks are carbonate rocks, salt beds or made from soluble rocks like gypsum that are easily dissolved by the water flowing under the ground. They also occur in lands filled with quartzite and sandstone.
The occurrences of a sinkhole is most time a sudden event. This is due to the fact that the surface of the land above ground remains intact till the ground under it is not enough to support it, then at that point it collapses.
FORMATION OF SINKHOLES
There are two major processes in which sinkholes are formed. They are the natural processes and the artificial processes.
Natural processes
As the name entails, these processes are not as a result of human actions but rather, they are caused by nature. These natural processes involved in the formation of sinkholes are based on the principles of erosion and suffosion. In the erosion process, slightly soluble bedrock like the limestone (CaCO3) are gradual removed by the action of percolating water on them. Thus, the bedrock is been worn away gradually till it won't have the strength to carry the weight of the layer on the surface anymore.
The suffosion process is a bit different. In the suffosion process, the major work is done by the ground water. With time, the groundwater dissolves the carbonate cement that acts as a binder to the sandstone particles and as it flows, it carries the particles away. This continues till a void is formed beneath till the surface and it comes crashing down. Other events that causes the formation of sinkholes are the lowering of the water table and the collapse of a cave surface.
Artificial Processes
Humans also have there fair share in the formation of sinkholes. Some of human activities that results to the formation of sinkholes includes the overpumping and extraction of groundwater and other subsurface fluids, salt mining.
I bet you are shocked, but it is true. Man can be too extreme sometimes, milking nature too fast without giving her time to replenish what was taken from her. One of the aftermath of doing that is in the form of sinkhole.
Another common cause is the leakage of water main breaks or sewer collapses from old pipes. It goes without saying that little drops of water wears the great stone. Not minding how little the leak it, it has the potential of causing a sinkhole. Other human activities that trigger sinkholes are vibrations due to drilling, change in weight, mining, and heavy traffic in a location for a long period of time.
Finally, sinkholes can form due to human actions whenever man changes the pattern natural water drainage occurs, or when new water diversion systems are created. But majorly sinkholes are triggered when ever a new weight which is greater than what the land surface can carry is placed on a land surface which has a void already existing beneath it.
TYPES OF SINKHOLE
Sinkholes are often classified into three major types; the dissolution or solution sinkhole, cover-subsidence sinkhole and cover collapse sinkhole.
Dissolution or solution sinkhole:-
In this type of sinkhole, the limestone or bedrock is covered by a little soil or vegetation. Thus, whenever the rain falls, the water from the rain tricks down slowly through the opening in the bedrock and gradual dissolve it. As this continues, depression forms over that area. Dissolution sinkholes can easily turn to pond once the depression gets lined with debris, because the debris traps water inside the depression. Dissolution sinkholes are not so dangerous since their occurrence is not a sudden event but something that happens with time. Those that form ponds are to be feared since that can collapse anytime due to the sudden drainage of water as the protective layer gets loose.
Cover-collapse sinkhole:-
The most dangerous type is the cover-collapse sinkhole. In this type, the covering of the bedrock is a layer of clay. The major work is done by the underground water which gradually dissolves the chamber beneath the earth's surface, this dissolution creates a void which causes ground sediments to keep falling in a bid to close up the void formed. This crumble continues till what is remaining between the Earth surface and the void beneath is just a thin layer. When the layer on top becomes weak, it suddenly collapses and the same time the sinkhole opens swallowing anything on top of it.
Picture by Lupin CC BY-SA 3.0
Limestone pavement
Note
*The chemistry behind this is that, these bedrocks contain calcium carbonate, also known as limestone (CaCO3) and calcium carbonate (CaMg(CO3)2) which are soluble in weak acids. Normally, ground water contain carbonic acid (H2CO3) which it derive from the organic materials in the soil. Thus, these carbonates gets dissolved easily by underground water. *
Cover-subsidence sinkhole:-
The cover-subsidence sinkholes happen in areas where the bedrock is covered by sand. Thus, as the sand moves down through the opening in the rock, it causes the surface of the land to sink. This continues to happen till the depression becomes too noticeable and a sinkhole is formed. This is also a very gradual process, just like in the dissolution sinkhole.
OCCURRENCE OF A SINKHOLE
There is a higher tendency for a sinkhole to occur in a karst landscape than in any other landscape. In fact, it is possible to find more than a thousand sinkholes just within a very little area of a karst landscape. The evidence to this assertion can be verified by the type of rivers found in such areas. Most rivers found in karst landscape are underground since these sinkholes drain up all the waters in that area.
Due to the number of sinkholes in that area, an airborne view of the karst landscape can be liken to a skin with so much scars.
Instances of karst landscapes that fits these descriptions (the sinkhole and all) are the Mamo plateau in Papua New Guinea and the Khammouan mountains situated in Laos. It's is worth noting that the biggest sinkhole that can be found in all sandstones known to man are the sinkholes, Sima Humboldt and the Sima Martel, both in Venezuela.
Sinkholes occur more frequently in Florida than in any other state in United States because of the large amount of limestone existing beneath the ground of Florida, especially in the center of the state for more than 20 million years. The limestone at the edges of the state are not as old as those at the center. Those at the edges are just 120,000 years old, thus the occurrence of sinkholes are more rare in these areas.
Another place prone to sinkholes occurrence is the Murge area in the South of Italy. The process of the formation of the sinkholes in Sistema Zacatón in Tamaulipas (Mexico) is quite unusual. Here the sinkholes are formed by the action of a volcanically heated acidic groundwaters.
Sinkholes are also formed in layers of limestone. There formation is due the high level of groundwater flow which are always as a result of excessive rainfalls. This is what lead to the formation of the great sinkhole that currently exist in Nakanai Mountains, suitated in Papua, New Guinea. Due to this high level of groundwater flow, a very strong underground river can be formed which goes ahead to create a huge void underground. One of the largest known sinkholes formed by this means is the giant sotanos found in Queretaro and San Luis Potosi states of Mexico, and the 662m Xiaozhai Tiankeng sinkhole.
THE EFFECTS OF SINKHOLES
The effect of a sinkhole is dependent of its place of occurrence. When sinkholes occur on land, they greatly change the topography of the land in that area, and they also lead to the diversion of the water moving underground.
Sinkholes are more dangerous when they occur in populated areas, as they lead to loss of lives and properties. Holes that form due to leaks in underground drain pipes and sewage systems can cost millions to repair since the leak damage can be observed for many miles and thus detecting the source of the leak might be a huge task.
Another effect of sinkholes is the release of toxic chemicals that are stored beneath the earth. When sinkholes occur, those harmful chemicals can pollute the underground water, thus making the water in that area undrinkable. These chemicals too can be dangerous to the foundation of the building as it can lead to corrosion and rust of the metals used in the foundation of the building.
MAN AND SINKHOLE
Though the number of people that die from a sinkhole disaster is the least when compared to other forms of natural disaster, it is still an issue of great concern, as the death of one person we love is the same as a million death. In addition to that, the loss of property is another concern, when sinkholes occur, houses get swallowed up completely, veheciles are lost too. In short, the monetary worth of the loss is quite much, and the amount needed to close up a sinkhole ranges around hundreds of million of dollars. In this section, I will be listing out major sinkholes that have occurred in human history and how it have seriously affected man.
Probably the worst, this sinkhole occurred about 5000 years ago a city Ubar, in the Arabian peninsula. It occurred when the underground water system, which was one of the things that made the city flourish crashed. The aftermath was disastrous. The sinkhole formed swallowed completely an entire city (a city as large as Los Angeles), from the beginning of it to the end, killing everyone living in that city. In memory of it, the lost city is been referred to as the "Atlantis of the Sand"
At first the people of the Guatemala City complained of hearing strange sounds from the ground, a sound the couldn't determine the source.
They heard this strange sound for weeks till the catastrophe struck in literally late February of 2007. On that day, a sinkhole of nearly a perfect circle, with a depth of more than 280 feet opened up, swallowing everything on top of it. It was terrible, three people were unfortunate to be standing exactly at that spot, they went down with the hole. The sinkhole was quite life threatening, thus, more than a thousand people have to be evacuated from that area.
A picture by Chensiyuan- Wikicommon CC BY-SA 3.0
An aerial view of Guatemala City
This occurred in March, 1998. Though, at first the cause was yet unknown, the effect was felt through out all the surrounding towns. So many businesses were affected and the sinkhole caused so much traffic. The first person that encountered the sinkhole was very lucky to have survived. He, without knowing drove his Honda straight through the sinkhole. He was quite fortunate to have jumped out of the car before it came crashing to the bottom of the hole. Well, that is it. I am still trying to imagine how he managed to jump out, he's one lucky son of a gun.
Hurricane Agatha Guatemala City Sinkhole
After the sinkhole that opened up in 2007 in Guatemala City, another opened up just 2km away from the position of the first. The depth of the sinkhole is up to 300 feet, and when it fell, it took with it15 people.
This sinkhole can be regarded as the worst to have occurred through out the history of Florida. It's huge negative effect on the economy of Florida can't be exaggerated. This sinkhole occurred when a hole with depth of about the height of a 15 storey building suddenly opened beneath a pile of gypsum stack of about 80 million ton. The effect was terrible, this dumped about 6 million cubic feet of waste and toxic after into Florida's underground layer of water bearing porous stones, were up to 90% of Florida's drinking water was gotten from.
The berezniki sinkhole started in 1986 and since then it has been growing. As of 2012, it has grown 340 yards wide and 430 yards long, with its depth close to 780 feet deep, and as it grew people get displaced from their habitat. The troubling part is that this is more than twice the size in 1986, and at this rate, soon it will consume the whole city.
HOW TO PREDICT A SINKHOLE
Well, am sorry to say this, but currently, there is no way known by man on how to predict a sinkhole before they occur. But that doesn't mean that researches are not being made on how to do that. But there are some preventive measures you can take so as to reduce the probability of a sinkhole forming under your building and swallowing your building. cars and other properties.
The first preventive measure to take is to check out the maps provided by your country for that area the land is located so as to make sure that the land is not located in a high risk area.
The next thing to do is to check out if there is any hole or crack formation in the foundation of your building or other surrounding building.
Also check with the local authorities if soluble rocks like limestone can be found in the land upon which you've built, or intend to build your house. If there is, it should be wise to believe that a sinkhole can happen in the land anytime.
It the land doesn't contain any soluble rock, and is also in the safe region, you can be at least 70% sure that sinkhole can't happen in that area. If not, you better get prepared to evacuate at a moment notice.
HOW TO PREPARE FOR A SINKHOLE
Always have your emergency kits ready, and within reach so as to escape at a moment notice if the need arises. Also have a discussion before hand with your family on where you guys are to assemble in case the family separates while trying to escape a sinkhole.
Insure your property, including your building and cars. Make sure you make a photo of them. They can be of great use when collecting your insurance benefits.
Don't keep all the copies of the insurance proof in the house, make a copy and keep it in banks, they are more safer there.
Avoid excessive extraction of water, milling and other human activities that trigger sinkholes.
HOW TO SURVIVE A SINKHOLE
If you are lucky and managed to get away from a sinkhole before it completely caves in, well, thanks to God. But if it occurs suddenly and you couldn't escape, doing this few things can increase your chances of survival.
As it occurs, cover your head with your arms as best as you can so as not to feel the direct impact of anything that will come crashing on your head. Protecting your head like this can also give you enough room to breath.
As you fall with the house, squeeze your arms and legs together while tucking your knees, as if you are trying to land with a parachute. When you finally hit the ground font fall with your legs, as you might break quite a number of bones by doing that, but rather, when you fall, fall with your side so that the force due to the impact would be spread evenly through your spine and your bone joints.
Make sure that you have a whistle in your emergency kit, as it might help rescuers to find you if you get buried under a pile of rubble. This is more preferable than yelling as yelling requires lot of oxygen. Also have an oxygen supply in your kit.
Always carry a mobile phone with you, so as to inform others that you need help.
CONCLUSION
Even though sinkhole are quite unpredictable, I think man has conquered and won triails more severe than sinkhole. Natural causes of sinkhole are quite more prevailing than human causes, thus, there much occurrence. Right now, man is faced with two major issue, how to prevent sinkholes from occurring and how to discover a way of repairing the land destroyed by the sinkhole.
It is in man's nature to seek for the easy way out, but the truth remains that, if we keep running away from the holes formed and prefer the easy way out, which is to search for another land to develop, our tomorrow won't be funny. The world is increasing in population, and the need for habitat is on the rise as well. Thus, repairing those lands and making them habitable once more is of vital importance.
We can achieve that by fixing of these sinkholes through these two major ways. The first is the compaction grouting, in which concrete grout mix is used to seal up the void and also preventing it from any further dissolution. Another way of sealing of the sinkhole is through the chemical grouting in which polyurethane foam is injected into those areas affected by sinkhole, thus densifying that area. We can also set up pipes and use it as a support for the house to be build on top of the sinkhole. It is kind of pinning the house to the ground. The steel to be used should be a very high standard drilled steel that is coated so as not to be attacked by corrosion or rust.
If man decides to face this sinkhole problem the same way he faced all those problems he overcame, I bet you that sinkhole disaster would soon become a fairy tale.
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