A huge sinkhole has opened up in Florida, right underneath a fertiliser plant. The hole appeared directly under a lake of toxic waste, allowing more than 200 million gallons of radioactive water to disappear into the ground. Alarmingly the hole led directly into a huge aquifer that millions of people rely on for their water supply.
Aquifers are underground stores of water. The water moves through holes and spaces within rocks which lie below the Earth’s surface, and this valuable resource can be tapped into by simply digging a well. Aquifers can come in all different shapes and sizes, and the one below the fertiliser plant is huge. It lies underneath the entirety of Florida and extends into the neighbouring states of Alabama, Georgia and South Carolina. This solitary aquifer provides over ten million people with their drinking water.
The sinkhole which opened up at the fertiliser plant was also very large. It measured 13 metres (45 feet) in diameter and quickly swallowed the 215 million gallons of radioactive water which were in the lake. The concern is that the water is now deep within the Earth and has contaminated the valuable water source.
This isn’t the first time that sinkholes have made the headlines in Florida. In 2013, a hole suddenly opened up in the east Tampa suburb of Seffner and swallowed a man while he slept in his bed. His brother heard his screams from the next room as he disappeared into the Earth, but despite his frantic digging, he was unable to rescue him.
Sinkholes may well sounds like some strange nightmare from a creepy horror movie, but they’re actually more common that you might think. Fortunately they can’t appear everywhere; they can only form when the rocks beneath the ground are made of certain types of material, and they also need certain types of weather.
Underneath the soil on the surface of the ground (or sand in Qatar’s case!) is hard rock. This rock, known as bedrock, can be made of a variety of substances. Sometimes it will be made of a glassy rock, formed when the molten earth cooled, other times it may be made of tiny pieces of rock or shells which have been compacted together into a solid substance. These are called sedimentary rocks and it’s these which cause the problems, because some of them have the rather fundamental flaw in that they dissolve in water.
When it rains, water soaks into the soil, and then filters down through the bedrock. Tiny cracks in the rock allow the water to pass through, but as the years pass by, if the bedrock is soluble, the water will slowly dissolve the rock. The cracks will gradually widen, creating empty cavities beneath the surface. The rainwater will then gradually wash the surface soil down into the cavities, weakening the surface.
As time wears on, the soil above the cavity will no longer be able to support itself. The time this takes varies dramatically depending on how thick the soil is above the void, and of what the soil is made. Sand will not be able to support its own strength for long, clay, on the other hand, can hold out for hundreds of years.
The actual collapse is then usually triggered by the weather, either by a drought or a downpour. A drought would see a depletion of the water in the aquifer, water which fills the voids and supports the layer above. The lack of moisture would also cause the ground to become weaker, meaning it may no longer be able to support its own weight.
A torrential downpour, on the other hand, would add weight to the layer of the overlying soil and this could also trigger a collapse. It is probably no surprise that the ground in Florida gave way towards the end of the summer, which is their wettest season. The day that the sinkhole was discovered, August 27, was also a particularly wet day, with very heavy rain.
Although it usually takes thousands of years for caverns to develop under the ground, it’s worth noting that some rocks dissolve far faster than others. Gypsum is the most soluble; if you were to place a block of gypsum the size of a Toyota Landcruiser in a river, it would dissolve completely within about 18 months.
Unfortunately much of Florida’s baserock is made of gypsum, and worrying, much of Qatar’s is as well! In fact, it may surprise you to hear that there are also plenty of sinkholes in Qatar too.
There are estimated to be as many as 9,700 large and small depressions in Qatar, including a number of large sinkholes. The majority are found in the north and central parts of the country, but the largest one, the Musfer Sinkhole, is found just off Salwa Road, and is at least 100 metres deep.
Despite the large number of sinkholes in Qatar, there is no need to panic, it’s very unlikely that you will be swallowed up by the ground on your way to the office. The majority of the sinkholes in Qatar are thought to have been formed hundreds of thousands of years ago, when the climate was very different. Changes in the Indian Summer Monsoon are believed to have periodically made Qatar far wetter and more humid.
Florida, on the other hand, has a tropical climate and is regularly bombarded by torrential downpours. This means the state will always be at risk of sinkholes, and there is no simple fix.