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?

Dissolution sinkholes typically form in areas where the bedrock is composed of soluble rock types such as limestone, gypsum, or salt. Over time, water, often acidic due to the presence of carbon dioxide in the atmosphere, can slowly dissolve these rocks, creating voids or cavities beneath the surface. Additionally, construction activities, especially when the natural land features are altered, can disrupt the balance of forces in the subsurface and lead to sinkhole formation. Surface sinkholes can be particularly concerning when they occur in urban areas or under infrastructure like roads and buildings. They can lead to sudden collapses and damage to property, posing safety risks to people and vehicles. To mitigate the risks associated with sinkholes, especially in construction projects, professional land surveyors like Cadmap conduct detailed surveys to identify potential sinkhole-prone areas. By understanding the geological conditions of the site and detecting any underlying voids or unstable areas, contractors can take appropriate measures to avoid sinkhole-related issues during construction.

Additionally, drainage issues can also contribute to the formation of sinkholes through a process known as subsurface erosion. When water accumulates in the ground due to poor drainage, it can infiltrate underlying layers of soluble rock, such as limestone or gypsum. Over time, this water can dissolve the minerals within the rock, creating underground voids and caverns. As the voids expand, the overlying soil loses support and can eventually collapse into the empty space below, forming a sinkhole. Inadequate drainage exacerbates this process by allowing water to linger in the subsurface, intensifying the dissolution of soluble rock and accelerating the development of underground voids that may eventually manifest as surface sinkholes. Therefore, addressing drainage issues on an individual level by conducting Emergency Drain Unblocking from Express Drainage Solutions (or a similar company) when you need it, is crucial in preventing the potential hazards associated with sinkhole formation.

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. Improving building underpinning and foundations can help with this issue, as underpinning supports the foundation of a structure by transferring the weight of the structure from the foundation, through the unstable soils, to a more stable material below. Underpinning can stabilize or re-level the building’s foundation or close relatively wide cracks in exterior masonry walls that have been significantly affected by settlement distress.

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.