What is a Sinkhole?

Should you be worried about sinkholes

Sinkholes in Florida

First – What is a sinkhole?

A sinkhole is a collapse that can take many forms (sinkholes, depressions, abysses or cenotes); appearing suddenly on the surface of the ground, up to 329ft deep. It can appear on land as well as in the marine environment.

Sinkholes can be progressive or sudden as it has been the case here. There are also Mega sinkholes whose depth get up to 1900ft and can reach half a mile in length.

Know what can happen

The Concern is real

In Florida, there is growing concern about the rapid increase of sinkholes. The sinkholes hit both residential and commercial properties, forming gaping openings in the roadway, farmland, parks, and resorts, etc.

With increasingly “extraordinary” dimensions, it is feared that they will destroy urban neighborhoods, suburbs, schools, hospitals, etc. Their extent varies from a few feet to several thousand square feet. As for their depth, they may exceed 100/350ft. Sinkholes are known to have different shapes including saucers, cones, vertical walls and at times looking like natural ponds.

Sad Stories, sinkholes hit close to home 

Sometime in February 2013, a 20ft deep sinkhole, deep enough to cover a one story building, suddenly appeared under a building in the suburbs of Tampa swallowing and killing a man. Eight residences were evacuated as a preventive measure.

Sinkhole slowly swallows a home

In the same year, another sinkhole of about 49ft by 100ft formed under the house of a man living in Florida. On the night of the ill-fated day, the 36-year-old victim suddenly screamed and called his brother for help when the hole appeared just below his bedroom and engulfed him. His brother and other helpers had to enter the apartment to understand what happened. Indeed, from the outside, the house seemed to be in good shape, completely hiding the enormous hole. Unfortunately, the man could not be rescued, the neighborhood was evacuated entirely, and his remains have never been found.

Similarly, by the middle of 2018, dozens of sinkholes formed in an area of Ocala, Florida, without anyone knowing how to stop their progress. The neighborhood helplessly saw their number double in 24 hours, which resulted in some vehicles being engulfed by the collapses. All that could be done then was for geotechnical engineering experts to be dispatched on site to try and explain this phenomenon

How many sinkholes are there?

In 2014, around 7,000 sinkholes were reported. That is three times more than in 2010 of 2,400. .

 The concern of the Florida communities is justified, especially since the sinkholes are more deadly than before. People have been swallowed up without ever being found.

Besides damage to homes that lead to the displacement of families and at times communities, reconstructions and rebuilding are often made at exorbitant costs to local governments.

Why are such phenomena more prevalent in Florida than elsewhere in the United States or the world? 

According to weather.com, the earth crust of Florida state is composed of carbonate rocks such as limestone which prevents the earth covering the ground from providing a durable, permanent layer.

It should be noted that sinkholes are among the types of karst land-forms – erosion processes related to chemical alteration and dissolution of limestone or dolomite. This explains why, among other things, there are many caves, natural systems of underground drainage, endangered streams, and even tourist sites that have transformed the aftermath of a sinkhole into attractions.

See this clip of “Travel inside a sinkhole”

 

Common types and causes of sinkholes

Some info taken from 

Wikipedia Site – Sinkhole

Solution sinkholes

Solution sinkholes are formed by local chemical weathering of the limestone where water accumulates around a fissure or joint in the rock. This may be underneath the soil or on the ground surface. The hollow that is formed is drained of water through the fissure or joint, but not before it has dissolved some of the limestone. The depression gradually gets enlarged and turns into a sinkhole.

 Collapse sinkholes

Collapse sinkholes occur where the progressive collapse of a cave passage occurs and eventually causes subsidence at the surface level. Sinkholes formed this way exclusively are quite rare, although many sinkholes are in part created by collapse: chemical weathering in a solution sinkhole may cause a part of the wall to become unsupported and unstable, resulting in collapse.

Collapse sinkholes are not rare where limestone is overlain by sandstone and may form quarry-like depressions.

 Suffusion sinkholes

Suffusion sinkholes form where the solution of the limestone has created a depression on the surface of the limestone but under a covering of soil. The unsupported ground subsides into the cavity and leaves a depression in the landscape. These are sometimes referred to as subsidence sinkholes or ‘shake holes.’

 How to find sinkholes – Early sinkhole detection

Some time ago the Florida authorities sought the services of NASA, particularly the use of their InSar technology. The hyper interferometric remote control radar sensor integrated into NASA satellites and drones detects movements and elevations of the ground no matter how small they are.

This sonographer of the earth is already at work in Louisiana to monitor potential collapses along the Gulf of Mexico’s coasts. This type of radar can spot a sinkhole in its early stage of formation because of its unique surface movements.

The InSar is an amazing sinkhole detection tool that has been transformed into the most effective warning system. Its impacts will be immediate. It will, of course, diminish the material damage, but the priority is to prevent the worst from happening, which is the loss of human lives. Another goal is to reduce the number of this category of disasters and, in doing so, to ease the anxiety of the people of Florida.

Can we predict the formation of sinkholes?

The sinkholes represent a severe risk for the safety of citizens in Florida. To detect as much as possible the formation of underground voids and other sinkholes, researchers use various tools such as radars, or seismographs.

The use of these methods requires a particular interest on a specific ground as well as the knowledge of the precursors’ signs of the formation of sinkholes. To this end, the Southwest Florida Water Management District has produced a brochure that lists the various observable signs.

These may include collapsing trees or poles, the formation of small ponds in an area where water was not collected before, the wilting of small circular areas of vegetation, or cracked structures in walls.

 We can also, with less precision, estimate an area in which it is possible that sinkholes appear — for example, taking into account weather events, the composition of basements, and the presence or absence of sinkholes in this area.

 However, this method is not 100% reliable, and despite the efforts made, it is still impossible to accurately predict the formation of sinkholes.

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