First things first … what are sinkholes? Basically speaking, a sinkhole is created when a void is created under the top layer of earth. This void grows in depth and width until the top layer of soil can no longer support itself and caves into the void, thus creating sink holes.
What exactly causes sinkholes?
We’ve established that the sinkhole opens up when the immediate sub surface material shifts to another location and leaves a void. Sinkholes can be created naturally or by the actions of man. But that’s only the beginning of the story.
What causes the shift?
There are three main situations that cause sinkholes:
If the rocks below the surface are made of materials that dissolve in water, such as limestone or gypsum.
Over hundreds or thousands of years, the water trapped beneath the surface causes natural underground currents that dissolve the rocks and forge chasms under the ground. As this occurs the top of the chasm gradually grows towards the surface and, eventually, the surface layer getting thinner and thinner, until it becomes too weak to support what is above it and falls in.
- When the rock under the surface doesn’t dissolve in water, but instead is made of grains that are small enough to be carried away by underground water currents. For instance in Guatemala City, the underlying rock on which a three story building was built on, was predominantly weak crumbly volcanic rock, fine ash and other debris that had erupted from a volcano, the three-story building vanished into the sinkhole when the underlying material shifted,
The third situation has nothing to do with underground water currents, it’s all about water movements above-ground. They are triggered by intense rainstorms or floods, and burst or long-term leakage from sewer or storm-water pipes.
You’ll notice in all these examples, the water can’t go where it used to, so it finds a new path.
Where do sinkholes form? Sinkholes form mainly in limestone.
Limestone areas in a tropical, moist climate are much more likely to form sinkholes than those in dry climates. However, since they can be natural or man-made, Pennsylvania, Texas, Florida, Alabama, Tennessee, and Missouri, are experiencing sinkholes that appear from nowhere with little to no warnings. This threat obviously gives constant worry for anyone living around the areas where sinkholes are known to exist and the unpredictability of when or where in may occur makes the concern that more frightening.
Methods of mining have been directly linked to the sudden onslaught of sinkholes where few if any existed before. A sinkhole can range anywhere between a slight depression in the ground right up to an enormous hole reaching down half a Kilometer (1640 feet). The world’s current deepest sinkhole is in Chongquig, China, reaching down 662 meters (2171 feet).
Since there is no natural surface drainage, once water gets into a sinkhole it can’t get out via the surface, thus must drain downward, into the subsurface layers creating an ever deeper hole. Such an occurrence, of an abandoned mine creating a swirling water erosion created a huge sinkhole in the backyard of an Ipswich Brisbane neighborhood.
Sinkholes: Staying above the Abyss
The best method to avoid the catastrophe of being engulfed by a sudden opening of a sinkhole is being knowledgeable of the early warning signs and being aware of your surroundings. For instance, if the area is known to be prone to sinkholes it may be a wise idea to not build or buy a home in that area.
What are the warning signs?
In many cases sinkholes don’t form suddenly, they build up slowly over many months or even years. Its the last stage, when the formation of the hole or basin is at the very surface, that’s sudden. Here are signs that might indicated you have a slow-burning sinkhole on your hands:
Fresh cracks in the foundations of houses and buildings
Cracks in interior walls
Cracks in the ground outside
Depressions in the ground
Trees or fence posts that tilt or fall
Doors or windows become difficult to open or close
Rapid appearance of a hole in the ground
- Dying or wilting vegetation in a circular form
A sudden collapse of a sinkhole is nearly impossible to escape unless you happen to be located at the very edge of the hole and lucky enough to grab hold of something substantial enough to stop your fall. Or the depth of the sinkhole is only a few feet, as not all sinkholes open to the center of the earth. So what can you do to help avoid being swallowed alive?
- Hire a Professional … If you are located in states or areas prone to sinkholes and wish to build or buy a home or business, hire a professional geologist to do tests in and around your property. It’s not an ironclad guarantee, but it’ll stack the odds in your favor.
- Double Check Repairs … In certain cases, it is possible to repair a sinkhole. If you are considering buying property with a repaired sinkhole, make sure a licensed engineer certified the repair. Demand all documentation and data on the repair and if possible, have another licensed engineer review the documentation for accuracy. I couldn’t tell the difference between a quality repair report or a forged one. Could you?
- Talk to Your Insurance Company … It’s best to do this before purchasing a property. Make certain the insurance company will insure against sinkhole disasters and the cost of such coverage. Having full insurance coverage, but at $1000 a month fee, is all but the same as not having insurance … for normal people anyway. See if there are any prior qualifications such as a certified engineer buy-off.
Warning Signs Review:
There is usually some sort of sign that a sinkhole is developing, not always, but usually. It’s important to take notice of these signals and know what they mean.
Be on the Lookout:
- Constantly check for unusual ground and plant depressions in and around your property. These telltale signs are:
- If a sinkhole is in the process of forming the structures on top of it can give a hint to its existence: for example, slumping or sagging fence posts, and trees that start to lean. More subtle signs can include doors and windows that don’t close properly.
- Heavy rains can trigger the collapse of a sinkhole that had been slowly forming earlier. When rainfall collects in an area where water previously did not collect, that is another sign that the land is subsiding.
Bad enough that sinkholes could be forming under your feet in normal rains. Bring a hurricane to the region and it could feel like not only the sky is falling, but the ground is falling as well.
When the earth falls out from under your feet, it may not be a sinkhole at all, but rather an earthquake. When the Alaskan earthquake struck on March 27, 1964, Fourth Avenue dropped 20 feet below normal level as the result of the shifting fault-line.
When sudden seismic shaking occurs near the coast don’t wait for a tsunami warning siren, head to higher ground.
Blue holes along low-lying coastlines are the remnants of sinkholes formed during past ice ages when sea level was 300 to 400 feet lower than today. As sea level rose, the sinkholes became flooded, forming vertical caves. The deep blue color of the hole contrasts with the lighter white carbonate sands of the surrounding seafloor and the water is home to many varieties of marine species.
Scuba diving in a blue hole can be dangerous as the depth is difficult to judge with just your eyes. Divers must vigilantly check their depth gauges to make sure they don’t exceed their safety limits.
Sinkholes are an anomaly of nature that was no more of a danger to man than being struck by lightening, but that has changed recently. The ever increasing encroachment on nature by man and the damage that creates, both unintentional and mostly intentional, has completely changed the earth’s composure. New and destructive methods of mining and drilling for fossil fuels have restructured the earth’s crust in a matter of years, that which took a million years to establish.
You don’t need to know all the reasons, new and old, for the eruption of sinkholes, but you must be aware of their increased activities and the new areas which they have suddenly sprung up. Fortunately, few lives have been lost to sinkholes, however, losing a lifetime of valuables to a sudden catastrophe can make you wish you were dead.
Be mindful of the signs of sinkholes and act accordingly and you should be alright, physically anyway.