A sinkhole is a depression in the ground that does not have natural external drainage. Sinkholes are caused by water erosion or by a form of collapse of the surface layer. Sinkholes are commonly in karst terrain. These are regions where the rocks below the land surface can be naturally dissolved by groundwater circulating around them. Soluble rocks, such as limestone and other carbonated rock are the types of rocks that are naturally dissolved.
This means that when it rains, the rainfall will stay inside of the sinkhole and will typically drain into the subsurface. The rainfall moves through the soil and soluble rocks will begin to dissolve, creating underground spaces and caverns.
Land that has soluble rocks dissolving from the rain will typically stay intact for a period of time until the underground caverns get too large. Lack of support above the spaces will cause a sudden collapse of the land surface.
Sinkholes can also be human-induced. Groundwater pumping and construction and development practices can cause sinkholes. If natural water drainage patterns are changed and new water diversion systems are developed sinkholes can occur. When the land surface has changed, the weight of the new material can activate an underground collapse of supportive material, which will cause a sinkhole.
A sinkhole can be stopped if it is caught on time. Inserting grout into a developing sinkhole can save the structures above if they are caught promptly enough.
Three Types of Sinkholes
The most common type of sinkhole is known as a collapse or cover-collapse sinkhole. These are typically the sinkholes that will suddenly open to swallow a car. This type of sinkhole occurs suddenly, however, the erosion that causes them to happen has likely been taking place for weeks, months, or even years before, underground.
The top of the cover-collapse sinkhole is usually a soft overburden, made out of soil with clay in it. A small cavern forms underneath the soil, over a period of time. Sediment takes advantage of the cavern and starts spilling into it, this is called spalling.
As the spalling progresses, the underground cavern will fill with more sediment, which will hollow out space under the overburden. Ultimately, the overburden will become so thin that it collapses into the cavern below, creating the sinkhole.
Solution sinkholes are another type of sinkhole. These sinkholes are commonly seen in areas that have a thin cover of soil on the surface, which exposes the bedrock underground to continuous erosion by water. As the water saturates through the bedrock, it will carry small parts of the rock with it. As the bedrock erodes, particles will collect in the caverns it leaves. A small depression is formed over time. The sinkhole forms at this point. Sometimes the bedrock will collapse suddenly to form the solution sinkhole and other times it will happen gradually.
Cover subsidence sinkholes are holes that are formed over a period of time. The bedrock is covered by soil and other materials that are not meant to mend together. Areas that have soil that are made up largely of clay or sand often face the occurrence of this hole.
When the bedrock starts eroding, the clay or sand starts pervading through the cracks and settles into spaces left behind. This will create a cavity on the soil’s surface and not under it.
What are the Effects of a Sinkhole?
Depending on where and how a sinkhole is formed, there will be varied effects. Natural sinkholes occur on land and in the ocean. If the sinkhole forms on land, they can change the topography of the area and deter streams of underground water.
If the sinkhole forms suddenly in areas that have a heavy population, they can cause damage to human life and property. Some holes will form because of a leak in the underground storm drains and sewer systems. When the hole finally collapses, the damage can be seen for miles due to repairs.
Sinkholes can be dangerous to building foundations. Toxic chemicals beneath the surface can come up and may pollute groundwater.
Natural sinkholes cannot be prevented. However, sinkholes caused by humans can be prevented in time. Maintaining the underground systems and plumbing are practices that can ensure that a sinkhole does not occur.
Homes, office buildings, cars, and humans are among the many things that a sinkhole can greatly damage. The repairs are sometimes impossible, as sinkholes can cause fatalities and loss of property as a whole.
Does Location Affect Sinkholes?
The formation of underground cavities occurs where certain rock types are susceptible to dissolution in water. Because of this, dangerous sinkholes can occur. The rock types that cause these disastrous sinkholes are evaporites.
Evaporite rocks consist of salt, gypsum, and anhydrite. Evaporite rocks underlie about 35 to 40 percent of the United States.
Carbonated rocks include limestone and dolomite. These karst landscapes underlie about 40 percent of the United States east of Tulsa, Oklahoma.
According to the United States Geological Survey (USGS), 20 percent of U.S. land is vulnerable to sinkholes. Sinkholes are well-known to occur in Florida. The state is known for frequent rainfall and marshy lands, which is usually identified with sinkholes. Florida is also notorious for having many underground spaces and drainage systems impressed from the soluble rocks.
Alabama, Kentucky, Missouri, Pennsylvania, Tennessee, and Texas are also states where sinkholes are prominent. This is because these states are filled with karst terrains.
The east coast does not have a ton of karst from evaporite or carbonate rock land, which is why there are not as many sinkholes in that region of the country. However, that does not mean that sinkholes never happen. Recently, in New Jersey, there was a sinkhole that opened up and was about 30 feet deep. Sinkholes are not uncommon anywhere.
Not only are sinkholes common on land, but they are also common in the ocean. Water-filled sinkholes are called “blue holes.” Blue holes occur in caves or in the ocean. Deep-sea divers find the blue holes to be their playground. A popular blue hole is Dean’s Blue Hole, located in the Bahamas. and is 663 feet deep.
There are sinkholes in the Khammouan Mountains of Laos and the Mamo Plateau in Papua, New Guinea. Venezuela is known to have the largest sinkholes, formed in sandstone. Sinkholes formed by sandstone also occur in China and Mexico.
The deepest water-filled sinkhole is 1,112 feet deep. This can be found at the Yucatan Peninsula and Tamaulipas in Mexico.
The world’s deepest sinkhole that is known is called Xiaozhai Tiankeng, also known as the Heavenly Pit. The Heavenly Pit is located in China. This sinkhole is 2,054 feet long, 1,762 feet wide, and between 1,677-2,172 feet deep. The sinkhole has been there since ancient times. There is actually a staircase that tourists can climb to discover what the sinkhole looks like. Rare animals and 1,285 species of plants have been found in the sinkhole.
The Qattar Depression in the Matruh Governorate in Egypt is among the deepest natural sinkholes to exist, lying below sea level at 436 feet. The average depth of a sinkhole is 200 feet. The bottom of the depression is covered with salt pans, sand dunes, and salt marshes. The length of the sinkhole is 186.4 miles. The extremely large sinkhole was created by winds blowing the salt bed down to the water table.
Naturally occurring sinkholes form in karst terrains, but they can happen anywhere that has a soluble subsurface rock. Essentially, sinkholes are possible almost anywhere in the world, whether it be in water or on the ground.
I Live in Sinkhole Alley: What Should I Do About Sinkholes?
Since Hurricane Irma hit there have been 400 sinkholes reported in Florida. Most recently, a sinkhole developed on Interstate 75, in Ocala, Florida. As a precaution the highway was shut down. Floridians and everyone else should be very aware that sinkholes can happen at any moment in time.
If you live in Sinkhole Alley you absolutely need to know the signs and what to do in case of a sinkhole. Sinkhole Alley is located in the western-central area of Florida. The counties of Pasco, Hernando, and Hillsborough make up what is known as “Sinkhole Alley.” This section of Florida sits on top of thousands of underground caves, which explains why there are so many sinkhole occurrences.
Cover-collapse and solution sinkholes are the most common types of sinkholes to occur in Sinkhole Alley.
Below are things you need to think about if you live in this area.
Signs of Sinkhole Activity in Sinkhole Alley
- Hard to close windows and doors
- Cracks in the walls, floors, slab, or ground surface
- Sloping in driveways are uneven.
- Doors and windows have cracks in the corners.
- Lawn is shifting
- Soft or spongy spots in yard
- Yard is sinking
- Cracked steps leading away from the house
- Leaning trees, fences, or other structures that should stand up straight.
- Puddles suddenly forming where soil was previously dry
- An appearance of a “chimney hole” – deep vertical hole with steep sides.
- Circular patches of wilting vegetation
Pay attention to your neighbors’ homes. If it seems like your neighbors have any of the above signs, you may want to call a professional to assess your home.
Remember, do not panic if there is suspected sinkhole activity. Instead, follow these steps:
- Call your insurance company.
- File a claim.
- Hire a professional to assess your property. The insurance company will deny or accept the claim you have made.
- After the claim is approved, get necessary repairs as soon as possible before it becomes worse.
- Consult with a soil testing firm or engineering company. To be sure if you have a sinkhole, you need to obtain results of a test by a licensed engineer with a professional geologist consultant. You will need to make it clear with your insurance company that your insurance policy will cover the geological assessment.
If your property is on a sinkhole there are safety precautions that you should take:
- Keep away! If you suspect that a sinkhole exists on your property it is best to stay away from it. Make sure all family members are away from the area.
- Leave your house immediately. First, you must determine if the hole is impacting your house. If it is, you need to leave the home and stay out.
- Block off the area. Make it clear that no one should go near your property.
- Monitor sinkhole for signs of growth and for further structural damage.
- Avoid dumping anything into the sinkhole. If anything is dumped into the sinkhole there could be possible contamination of groundwater. Wait for specific instructions from the local government agency and the insurance company. The last thing you want is to be liable for any damages.
It is mandatory, in the state of Florida, that insurance companies provide homeowners insurance coverage that includes damage from “catastrophic ground cover collapse.” It is also required to offer sinkhole damage coverage, and in general it appears in a proviso that comes at an additional cost.
The Florida Department of Environmental Protection is working with NASA on technology that could monitor changes in Florida’s terrain and will hopefully predict sinkhole areas before they occur.
Unfortunately, sinkholes are a part of life in Florida, especially for those of you who live in Sinkhole Alley. If you find yourself in one of the sinkhole areas and believe you may have sinkhole damage or might have a sinkhole in the future, make sure you take the right safety precautions and steps.
People all over the world should be aware in case of a sinkhole. Remember to check with the insurance company that there will be coverage if there is a sinkhole. The signs of a sinkhole, safety precautions, and steps to take when dealing with a sinkhole are not only meant to be followed by Florida residents.
Finally, be aware of your surroundings at all times. Sinkholes, while not always life threatening, can be damaging. Do what you can to prevent them.
If you have a sinkhole on your property and you need help with an insurance claim, reach out to Bulldog Adjusters in order to find out how we can help streamline the insurance claim process and handle the hassle for you!