Sinkholes seem to appear more often in the news now. The sinkholes tend to be the frequent cause of road tragedies, and they also seem to surprise the authorities. The sinkholes are unpredictable.
Sinkholes appear to be big, come out of nowhere, and are capable of devouring house, people, and anything that come into their area.
But, typically, sinkholes form over a period, requiring a specific condition for the theme to process. It is not quite visible to the naked eye.
Sinkholes are natural depressions, or in simple terms, they are the holes in the Earth’s surface caused by karst processes (when the bedrock of the Earth is soluble enough). Sinkholes often appear in carbonate rocks made of dolomite or limestone.
It can even appear in evaporite rocks underlined by gypsum or anhydrite.
There can be various causes for a sinkhole to form. Let us check what causes sinkholes.
What Is A Sinkhole?
Sinkholes are often known as snake holes, doline, or sometimes swallow holes. The name only suggests holes that sink things in the ground.
The land surface is pretty hard enough to support loads, including loads of trucks, buildings, and other weights. It can be houses, roads, cars, and even human beings. But sometimes, the surface is not stable.
Due to natural or human activity, the surface can sink things deep underground to several meters and anything on the surface.
Sinkholes are cavities or pits in the ground formed by water eroding underlying rock layers, salt beds, or if the rock is limestone or it has carbonate rock. These surfaces can naturally be dissolved by the groundwater circulating through them.
When the rock starts to dissolve, the spaces and caverns develop near that rock, making it more suspectable for sinkholes. The sinkhole collapses suddenly, making a deep hole in the ground. The sinkholes can be very dramatic since the land stays intact for a time until the underground spaces do not spread much.
A sinkhole can range from one meter in depth and width to hundreds of meters. An enormous sinkhole was found in the limestone mountains of Nongle, which is in the Guangxi Zhuang region in southern China.
When measured from the access point of the mountain ridge, the sinkhole in the Guangxi Zhuang region measured 656ft long, 387ft deep, and 328ft broad. The world’s deepest sinkhole was recorded in Chongqing, China which is 662 meters.
What Causes Sinkholes?
A sinkhole can be a result of both natural and human causes. Man-made sinkholes occur when the development of a city is compromised in terms of the structural integrity of the underlying rock.
The buildings, roads, and other infrastructures cause water to stack in certain places and then wash away any layer of rock in the supporting role. In the end, it results in sinkholes.
Let us know what actually causes a sinkhole to form.
More than 98% of sinkholes form due to water. There are several factors for which water is responsible for the sinkhole collapse.
The rocks below the ground surface are mostly made of materials that can dissolve in water, and these materials are limestone and gypsum. When it dissolves these minerals, water can create some open spaces within the rocks.
Such a process is known as weathering, resulting in sinkhole formation. The water below the ground surface gets trapped for hundreds or thousands of years, which causes a natural underground current, and it dissolves the rocks and the forge chasma below the ground.
The topmost layer of the ground tends to grow up to the surface, and then finally, the surface layers get thinner from time to time and ultimately become very weak to support anything above it.
1.2 When Rock Does Not Get Dissolves In Water
These sinkholes appear when the rock below the surface does not dissolve in water. Instead, these rocks are made of tiny grains and can get drained away by the underground water current, which leads to a sinkhole formation.
A three-stories building vanished into a sinkhole that killed almost 15 people in 2010 in Guatemala City. The underlying rock in this region was fragile and had crumbly volcano rock, fine ash, and other debris that erupted from a volcano.
This situation has no connection with the underground water currents; instead, it is all about water movements above the ground.
It is often triggered by heavy rainfall or floods and sometimes even bursts or long-term leaks from the sewer or storm pipes.
When the currents are too strong, the water does not go to its usual place, but it will make a new path for itself. While traveling on the surface, if the water gets ample support from the underground water, the following will result in sinkholes.
Furthermore, the moving water will settle down in one place, and then it will cause the surface to become an impermeable membrane type with water.
1.4 Weather Changes
Often, the sinkholes result from seasonal changes in the groundwater table, freeze, and the thaw of the surface with heavy precipitation, whenever there is heavy rainfall following droughts.
1.5 Hydrologic System Changes
When there are sudden changes in the hydrologic system, like giving more water or taking it in excess, such activities can cause the system to malfunction, which can become temporarily unstable and result in sinkholes.
1.6. Groundwater Gradients Changes
When there is any change in the groundwater gradients, due to the removal and the introduction of water to the new systems, the loose materials in the underground can push out at a fast rate, which causes underground voids and thus forms sinkholes.
2. Human Activities
Several human activities lead to sinkhole formation. In Florida, most sinkholes form due to large underground voids and the surface drainage systems carved with carbonate rocks all around the state.
If the overlying sediments collapse into the voids, then a sinkhole occurs in that place. The drainage system can also collapse, draining water into the rocks, which are weak against such waters. In simple terms, it will form a sinkhole.
For most sinkholes in current times, humans are greatly responsible for sinkhole formation. Drilling, construction, mining, improperly compacted soil for excavation work, broken water or drain pipes, and heavy traffic result in sinkholes.
3. Induced Earthquake
Earthquakes are the most natural occurrence, giving a high probability of sinkhole formation. Earthquakes hit the areas where the weak rocks lie below the surface. However, some induced earthquakes result in industrial and human activity, for which sinkholes occur.
If workers perform careless mining and hydraulic fracking, it can significantly impact that area. The induced impact will affect the stability and the water quality, resulting in a sinkhole.
In August 2012, a massive sinkhole was recovered near the Bayou Corne, 77 miles west of New Orleans, and the sinkhole grew over 34 acres in just four years of span. This sinkhole formed due to the drilling of the ground surface from the Texas Brine Company, which was close to the salt dome’s outer edge.
Sinkhole And Its Types
There are three primary forms of sinkholes, and the geological process determines their formation. It has very few differences. The three sinkholes used are the solution sinkhole, cover subsidence, and cover collapse.
1. Solution Sinkhole
The solution sinkholes are the most common sinkholes found in areas that have exposed bedrock due to continuous erosion of the outer layer by surface water.
The water tends to carry all the small pebbles or rocks with it. Soon, the bedrock of the area eroded, and the particles that were attacked in the spaces left.
Over time, a slight depression is created in the eroded spot, soon forming a hole. The hole formed in the place looks bowl-shaped and can be more extensive.
Often the bedrock happens to suddenly collapse and forms a solution sinkhole. Some solution sinkholes may take a more extended period to develop.
2. Cover Collapse Sinkhole
Cover collapse sinkholes are primarily found in places where the bedrock is mainly covered with the deepest layer of soil and earth. As soon as the bedrock starts to erode, it forms some cracks in the rocky areas around it.
As a result number of weak points are formed in the layers of soil and the strata. Soon, it reaches a point where the weak points of the rocks develop into large holes within the bedrock of the area and fail to support the weight placed above it.
The cover collapse sinkholes happen suddenly, creating large holes in the ground in a few minutes.
3. Cover Subsidence Sinkholes
Cover subsidence sinkholes developed over a long time. Typically, the area whose bedrock is covered with soils and materials, and is not appropriately stacked, faces these sinkholes.
Often places with a considerable quantity of soil, clay, or sand face the occurrence of this type of hole.
When the clay or the sand of this bedrock starts to erode, the materials of this area start permeating between cracks and then settle into spaces left behind. As time passes, such a process creates a cavity on the soil’s surface and not below it.
Formation Of Sinkholes
Sinkholes can be a result of many different causes. It can be caused due to man-made practices, natural causes, and induced erosions.
However, the sinkholes tend to carry the same procedure for their formation. Let us see how the sinkholes are formed.
1. Due To The Effect Of Water
The groundwater can be an overwhelming reason why the land surface collapses and forms sinkholes.
Sinkholes occur commonly in areas that are primarily “karst terrains” and have soluble bedrocks made of limestone and gypsum, having a high probability of forming sinkholes.
This bedrock can easily dissolve in water, creating large underground voids when the bedrock gets exposed to the surface water and gets warned over time.
Some of the holes become ponds since they get filled with water, but they can turn out to be a sinkhole at any point in time. Sinkholes formed in these can swallow vast chunks of land, even rocks, buildings, human beings, and animals.
The cracks formed during erosion, with the small voids created underneath the surface, are generally hollowed out by the surface water. Only the leftover soil remains on top of these karst landscapes.
However, these surface layers can no longer hold once the hole starts to expand. Since the topmost layer can longer hold the weight of the things placed on top of it, and thus it collapses, which reveals the cavern formed underneath.
3. Rainfall After A Drought
When a karst terrain faces a prolonged drought season, the surface of this area gets exposed well enough and gradually loses the strength it holds to keep things intact on top of it.
When drought is followed by heavy rainfall, it causes immense pressure on the surface soil, resulting in houses suddenly collapsing due to sinkhole collapses.
4. Human Activities
Human activity is greatly responsible for the formation of sinkholes. People use drills to make new water wells, create artificial ponds of surface water, divert surface water from a large area, and concentrate it in a single point.
Even activities that include construction, mining, drilling, improper compacting of soil, drainage pipes, broken water, and heavy traffic load can result in sinkholes.
Effects Of Sinkholes
The sinkhole can significantly affect land. However, the effects can vary depending on where and how the sinkholes are formed. Sinkholes can form in both land and water. If formed on land, it can change the area’s topography, thus diverting the stream of all underground water paths.
Some sinkholes commonly occur due to a leak in the underground stormwater pipes. As soon as they collapse, the impact of these accidents can be seen for miles, and the repair of these holes becomes necessary.
However, if they tend to form suddenly in a heavy population area, it can cause a great deal of damage to human life and property.
According to the geological survey, sinkholes occur commonly in Florida since this state has many underground voids and drainage systems carved with carbonate rocks. The drainage systems carved if collapse can put the buildings near it in grave danger.
The toxic chemicals stored beneath the ground come up and can get polluted with groundwater in a few seconds.
Though you can prevent sinkholes from forming due to humans in time, natural sinkholes are bound to occur. People need to maintain the natural water drainage patterns and adequate groundwater pumping and install safe underground systems.
These are the safest ways to ensure that the deep hole in the land surface does not show up in the middle of the city, swallowing everything in its area.
Top 6 Sinkholes All Over The World
Sinkholes can occur anytime and anywhere in the world. However, if the condition of a specific area favors sinkholes, then the land can suffer more sinkholes.
Sinkholes are concentrated in areas with rock surfaces covering sediments. Let us know some of the areas which suffered record sinkholes.
1. Crveno Jorezo, Croatia
It suffered 530 meters of sinkholes and had nearly vertical walls.
2. Great Blue Hole In Belize
The sinkhole in this area looks like a perfectly round hole and lies in the middle of an atoll, which is about 124 meters deep.
3. Sima Humboldt, Bolivia
This area has a developing sinkhole 314 meters deep, and the crater formed is made from some extremely resistant sandstone.
4. Bowling Green, Kentucky
In 2014, in Kentucky, people witnessed a 40 ft wide and 20 feet deep sinkhole. It was opened up beneath the rock surface of the Skydome area of the National Corvette Museum.
This sinkhole had caused eight rare most and one unique Corvette to sink. The vehicles that sank were estimated to be worth far more than a million dollars.
5. Xiaozhai Tiankeng, China
The sinkhole in Xiaozhai is around 662 meters deep and nearly 626 meters wide. This sinkhole is the deepest sinkhole known to date. The term Tiankeng is a local term that means heavenly pit or sinkhole.
The other United States areas with a greater probability of sinkholes are Florida, Tennessee, California, Missouri, Pennsylvania, and Alabama.
6. Guatemala City, Guatemala
The Tropical storm is known to create large holes. So, it happened in Guatemala. The developing sinkhole was triggered by the tropical storm Agatha. Even the city was built in a region where the first few hundred meters of the ground is composed of pumice fill. It is a material that is deposited in past volcanic eruptions.
If the ground beneath your home is not solid enough, you can be a victim of sinkholes. Sinkholes can occur when the water erodes the surface of the earth. Typically, the stability of the ground remains intact if there are gaps in between the surface. Though the water can move the dirt between surface gaps, the stability is not entirely assured.
The water leak in the ground can help excess water to erode the covering sediments. If The water typically drains out the stacking, and if it does, it can create sinkholes in that area. This is why the ground collapses, so leakage is hazardous, and it needs to be sorted immediately.
However, in most cases, the leaks in the surface layer have to be very serious to create sinkholes. Unless the ground under your home has high groundwater flow, it is unusual for a sinkhole formation.
However, you will find some warning signs of an impending sinkhole over your property if it falls due to a sinkhole. So, everyone should know what causes sinkholes and then act according to that whenever humans make infrastructure over their ground.