Key Takeaways
- Sinkholes can appear suddenly, but the underlying cavities that form them can take years or centuries to develop.
- Sinkholes can be caused by a variety of factors, including erosion, human activity, and chemical processes such as suffosion.
- Detecting sinkholes before they collapse is challenging due to the difficulty of assessing the condition of soil underground.
- Techniques such as soil sampling, satellite imagery analysis, and seismic waves can be used to identify potential sinkholes, but these methods have limitations.
- Fixing sinkholes typically involves filling them with special resins or concrete, but identifying and addressing the underlying cause is crucial to preventing further damage.
Introduction to Sinkholes
Residents in Melbourne’s north-east were shocked to discover a sinkhole had appeared in their local park, AJ Burkitt Oval, in the suburb of Heidelberg. The sinkhole, approximately 8 meters wide and 5 meters deep, formed overnight, leaving a crater in the formerly pristine oval. While sinkholes can appear suddenly, the holes that form them could be slowly forming over the course of years or even centuries. A cavity might form underneath the earth due to various reasons, including erosion and nearby human activity. In extreme cases, a sinkhole can consume entire buildings, as seen in a 2010 incident in Guatemala.
Causes of Sinkholes
There are several reasons why sinkholes might form, each with its own timeframe. On the longer end of the scale are sinkholes formed by a chemical process known as suffosion, where groundwater dissolves certain kinds of carbonate rock like limestone, hollowing out the earth over thousands of years. This process created the ancient limestone sinkholes seen around Mount Gambier in South Australia. However, sinkholes can form much more quickly if the circumstances are right, such as when soil becomes saturated with water and undergoes liquefaction, becoming weak and prone to collapse. Flowing groundwater can also carry off soil away from the area, creating cavities underground. Human activity, such as digging and tunnel boring, can also contribute to the formation of sinkholes.
Examples of Sinkholes
Several examples of sinkholes have been reported in recent years, including a large sinkhole in Kew in 2020, which was caused by a broken stormwater pipe, and a car-swallowing sinkhole in Port Melbourne in 2014, which was caused by a burst water main. In some cases, soil that is weakened by water is pushed over the edge by human activity, such as nearby tunnel boring machines. Investigators believe that this may have contributed to the appearance of the sinkhole in Heidelberg. In Ballarat, where the terrain is dotted with old mineshafts, sinkholes are a common occurrence, with one resident returning home in 2007 to find his backyard had caved in.
Detecting Sinkholes
Detecting sinkholes before they collapse is challenging due to the difficulty of assessing the condition of soil underground. The ceiling that remains on a sinkhole, even as the ground beneath it is eroded away, makes them difficult to detect before they collapse. Francois Guillard, a senior lecturer in geotechnical engineering at the University of Sydney, notes that predicting where sinkholes will form is difficult due to the complexity of soil conditions. While techniques such as soil sampling, satellite imagery analysis, and seismic waves can be used to identify potential sinkholes, these methods have limitations, and it is difficult to perform this kind of modeling over a wide area.
Fixing Sinkholes
Generally, the way to fix a sinkhole is to fill it back in with special resins or concrete to stabilize the soil. However, identifying the original cause of the sinkhole is paramount in preventing further damage. Geotechnical experts must control underground water flow, which can be challenging, and avoid diverting water to other areas, which can cause the same problem to occur elsewhere. Repair works are set to get underway at the Heidelberg sinkhole soon, and it is essential to address the underlying cause to prevent further damage. By understanding the causes of sinkholes and improving detection and repair methods, we can reduce the risk of these sudden and potentially destructive events.