What Causes Sinkholes?

Have you ever been driving along and noticed a large dip in the road? This large dip, or depression, is called a sinkhole, which is caused by underground water infiltrating and eroding the soil. These phenomena are most common in karst-heavy regions – geological areas where the water table is porous, often due to soluble limestone bedrock. Although they are rare in the United States, they still pose a danger to drivers.

We’ve all heard the phrase, “a sinkhole is an open wound in the earth.” If you’ve ever seen one, this comparison becomes obvious. Sinkholes can range in size from a few inches to several yards in diameter, and they can often cause a lot of damage to homes and property depending on their size, location, and depth. Therefore, the phrase can be taken both literally and metaphorically.

How do Sinkholes Occur?

Every now and then, you may notice a sinkhole pop up in your neck of the woods, and since they are generally unknown to the majority of people, it would be natural if they piqued your curiosity. These are surface sinkholes, and although there are many other types, these are the most common and therefore our main topic of concern. A surface sinkhole primarily opens up when a void or cave forms directly underneath it. They can also occur naturally when an underground aquifer is reached or when lava from volcanic activity is forced upwards.

Where Can a Sinkhole Pop Up?

Since soil erosion and voids are the main cause of sinkholes, you might rightfully assume that they mostly affect rural areas, and if you live in a city with concrete foundations, you’re safe. However, stories of sinkholes appearing in urban landscapes have become only too frequent in the past few decades. 

According to data from the U.S. Geological Survey (USGS), sinkholes occur all over the United States, especially in parts like Arizona. According to them, Arizona has the second-highest number of active sinkholes of any state, with more than 2,000 of them. The data also reveals that most other states have at least a few dozen sinkholes, and some, such as Florida, Pennsylvania, and Tennessee, have thousands.

Sinkholes that develop in cities are usually related to underground water issues, such as sewage disposal systems or improper foundations (Mexico City or Jakarta, for example). The most common examples of these can be found in cities in Florida, Texas, Alabama, Georgia, and New York. As you can imagine, a sinkhole in the middle of a city can be devastating.

Noticing the Pattern

Sinkholes are geological faults that form underground. The San Andreas Fault in California is a well-known example of a fault that is capable of generating sinkholes—fortunately, the quakes that trigger them are infrequent.

In most cases, the formation of a sinkhole is very gradual, with enough warning that the damage can be mitigated or minimized. If anyone is paying attention to the saturation levels of the ground, they would notice oversaturation on the surface right before it collapses. However, there are instances where sinkholes appear very suddenly, caused by some sort of last straw that breaks the already burdened camel’s back.

When Can Sinkholes Affect You?

So far, we’ve talked about sinkholes on a larger scale, either in rural areas or cities. And yes, large sinkholes are quite devastating to the environment. However, smaller sinkholes are quite dangerous as well, especially because they can happen on your own property. If the foundations of your house or driveway were built on waterlogged or loose soil, and there is a neglect of proper water disposal procedure, it causes these foundations to weaken. The water has nowhere to disperse, which causes it to oversaturate the ground beneath the house, and when the soil can’t support the weight of the structure above, it collapses and creates a sinkhole right underneath the house. Another thing to be careful about is pipes – damaged or leaky pipes can also potentially lead to smaller sinkholes on your property.

When a sinkhole occurs, the ground’s unique shape is essentially destroyed, and any surface water or underground water sources and drainage systems, such as railroad tracks or sewers, can be affected. After seeing the significant structural damage sinkholes can cause and the threat they pose to land, homes, and people, it is clear why it’s important to know how to identify and prevent sinkholes from forming.