(Teacher)
Sinkholes are a problem across the globe, especially in urban areas. Sinkholes can cause damage to roads, collapse structures, and destroy property. The biggest way to prevent a sink hole is to learn what factors are included in the formation a sinkhole is, how a sinkhole forms, and wheatther or not the sinkhole was naturally formed or if humans created the situation that caused the sinkhole in the first place. While it is not possible to actually prevent natural sinkholes, there are several ways that sinkholes which are created from human activity may be prevented, or at least controlled. This paper will attempt to explain how both natural and a man-made sinkholes occur, the possible factors that contribute to the formation of sinkholes that are in an urban area, and possibly attempt to suggest a way to reconsider human caused sinkholes by reducing certain types of urban development which contributes to the formation of sinkholes.
Sinkholes can be human caused or naturally occurring. The naturally occurring sinkholes are a direct result of the circulation of underground water and natural erosion that is caused by the flowing water. Natural sinkholes occur over time and have almost no real noticeable warning signs before the ground opens up and causes the soil to swallow whatever is on top of the earth. This is a generalization of course. There are some warning signs such as leaning trees, falling fences, and small landslides that may occur hours or even days before the onset of a sinkhole.
According to information on the Conserve Energy Future website, “The ground beneath our feet is not as much of a solid structure as we think it is. The ground is made from dirt, along with many rocks and minerals. There is water continually seeping in between the mud, rocks and minerals, as it makes its way down to the ground water reservoirs. As this happens, the water slowly erodes the rocks and minerals.” ("Causes, Effects And Types Of Sinkholes - Conserve Energy Future") An increase in water flow will erode the soil more quickly and as the soil continues to wear away, it will create a cavern. This empty space allows the ground above it to collapse. This is the process that occurs during the stages of a sinkhole formation.
A sinkhole creates a depression above ground that has been created by the lack of natural drainage underground. Basically, when it rains, the water soaks into the soil or surface topsoil until it can no longer hold the water and it creates a sinkhole. When this occurs in karst terrain, which is a geological term for the type of soluble rock that is below the topsoil and can be dissolved through an overabundant amount of rain or type of water oversaturation.
According to the United States Geological Survey, “These [karst terrain] are regions where the type of rock below the land surface can naturally be dissolved by groundwater circulating through them “. ("The Science Of Sinkholes | Science Features") Typically, the karst terrain includes soluble rocks like limestone, gypsum, salt beds, sandstone, decomposed granite, and carbonate rocks. Areas such as these are susceptible to sinkholes. Not only does an overabundance of water create a sinkhole, areas that have had a previously healthy aquifers and are now in drought are also highly susceptible to sinkhole occurrences from the deep hollow caverns that remain after an aquifer has been emptied. (Roach)
When an overabundance of rain falls, the water moves down through the soil, the soluble rocks begin the process of dissolving. When enough of the rock has dissolved to create a cavern, a sinkhole can form. These caverns can stay in place for a while, until the ground above can no longer support itself.
In urban areas, this could be accelerated by road or building construction vibrations, consistent rumbling of traffic, or an oversaturation of lawns. For example, this oversaturation of the surface topsoil and old storm drains that had been leaking. These factors led to the recent series of sinkholes on Highway101, just outside of Harbor, Oregon along the Pacific shore. According to news sources, “The startling chasm, which started out less than a foot across in mid-December, suddenly turned into a monster 80 feet in diameter on Jan. 28, after an inch and a half of rain caused a culvert to fail and triggered a landslide nearby.” ("Giant Sinkhole Eats Highway In Oregon: Dnews") This event closed the highway for a couple of weeks, while it was being repaired. Previously the highway had been held together because the ground above the sinkhole may have been woven together by roots and pipes, until suddenly the weight of the surface became too much for the topsoil below the pavement. The result is a sudden collapse of the ground as it drops into the cavernous hole. This sinkhole in Oregon also caused a landslide, and it may be important to note that the road was built on sand and did not have an adequate base of rock, gravel, or boulders. Which are important for solid road construction along the ocean.
There are two types of sinkholes. The first one is the cover-collapse sinkhole that develops quickly, over a few hours, and will cause severe damage to life, property, and the land around it. As was the case with the sinkhole in Oregon, mentioned above. These are typically caused by a sudden onset of heavy rainfall when the ground, that is already saturated and can no longer stick together.
The second type is a cover-substance sinkhole that forms slowly over a period of time, like a few weeks, a month or more, and sometimes even years. According to Francisco Gutierrez, “Subsidence sinkholes may cause severe damage to man-made structures and the occurrence of catastrophic collapse sinkholes may lead to [the] loss of human life. Dissolution and subsidence processes involved in the development of subsidence sinkholes are controlled by a wide range of natural and anthropogenic factors.” (Gutiérrez) This means that this type of sinkhole will show signs of an eminent collapse by providing a few subtle but important clues, such as the soil will be mushy, the ground will slowly sink, and there will be a sign of the soil becoming deeper and forming a deeper depression. Unless an individual is very in tune with the land around him or her, it would be very difficult to detect this type of sinkhole warning sign.
Some sinkholes may be small, such as the ones that occur in roads and may look like potholes, or the sinkholes can be very large and swallow up hundreds of acres. Sinkholes vary in depth as well. Sinkholes can range from just inches to a hundred or more feet in depth. Sinkholes have been known to take out any structures that sit above it, swallow parts of roads, and engulf entire fields.
The Conserve Energy Future website says that, “Areas that have soil comprising largely of clay or sand often face the occurrence of this hole. Once the bedrock starts to erode, the clay or sand starts permeating through the cracks and settles into the spaces left behind. Over time, this creates a cavity on the surface of the soil and not under it.” ("Causes, Effects And Types Of Sinkholes - Conserve Energy Future") Many times a sinkhole will contaminate groundwater aquifers and surface water sources nearby, depending on the factors involved. This is especially true if the sinkhole is caused by storm drains that carry water from the road, raw sewage that was on its way to the sewer treatment plant, or agricultural runoff.
Unfortunately, there does not seem to be an effective measuring technology that has been invented yet, which is capable of detecting a sinkhole before it begins. Except observations by homeowners, building maintenance, and road crews to spot cracks or slowly sinking ground, it is nearly impossible to detect a sinkhole forming before it does damage.
However, it is possible to study the geological structure of the bedrock or rocks contained beneath any specific area that is proposed for a construction site before anything is planned to be built or plans to be built on a possible sinkhole area. According to the United States Geological Survey website. “By mapping the nation, the USGS contributes important geologic and topographic information needed to understand karst regions and local areas. Detailed geologic mapping helps to define areas of soluble rock at the surface and in the subsurface, thus educating the land planners, policy makers, and the public about sinkhole risk.” ("The Science Of Sinkholes | Science Features") Knowledge is the best prevention, so this is perhaps the most efficient way to prevent structure damage and the loss of life and property that goes with the nature of sinkholes. However, it does not seem like developers take the geological structure of the proposed building site under consideration before a structure is built. It is in this author’s opinion that developers only seem to contemplate if the earth can be moved efficiently or not, and that is about the extent of the geological consideration.
In addition to the factors that create naturally occurring sinkholes, human activity has been a frequent cause of cataclysmic urban sinkholes. Many of the urban sinkholes are caused from the construction vibrations of structures being built. Also included are human activities such as, individuals overwatering the yards of both residential and commercial green areas, or perhaps a leaky residential water pipe, broken storm drainage pipes, or an outside water faucet. Sometimes a sewer or a residential water line will leak and cause the groundwater to eat away at the soil around it, then a new sinkhole will form. For example, according to the Conserve Energy Future website, “Activities like drilling, mining, construction, broken water or drain pipes, improperly compacted soil after excavation work or even heavy traffic can result in small to large sinkholes. Water from broken pipe can penetrate through mud and rocks and erode the ground underneath and cause sinkholes. Sometimes, heavy weight on soft soil can result in collapse of ground, resulting in a sinkhole. Sinkholes can also form when the land surface is changed.” (Conserve-Energy-Future, 2013)
Sinkholes can become extremely hazardous to humans. For example, although the large sinkhole in Oregon did not cause any harm to humans, Highway 101 and some outlying properties were damaged. However, there have been several occurrences of sinkholes that have swallowed humans. The people died because they were caught during the process of the sinkhole opening and they fell into the hole. However, deaths from sinkholes are rare and only occur when a hole opens up suddenly and swallows a house, cars, and roads.
Sometimes a person will die or be severely injured when a giant sinkhole occurs in the middle of a busy urban area, like the extraordinarily large sinkhole that occurred in Guatemala in the spring of 2010 after the Tropical Storm Agatha on May 30th. According to reports, an entire high rise building was swallowed up and left a gigantic hole in the ground. However, this particular event was partially because of human activity and partially caused by the specific soft and porous geological volcanic rock type and the arrangement of the surface area beneath the city. According to the Discovery News website: “The lion's share of the city is built on pumice fill — ash flows made up of loose, gravel-like particles deposited during ancient volcanic eruptions. In places, the debris is piled over 600 feet thick, filling up what would otherwise be a v-shaped valley of faulted bedrock. For those peering into the deep dark depths wondering what might be at the bottom, it's either more pumice fill or bedrock.” (DNews, 2016) This means that it is very likely that any structures that are built on top of the pumice fill will become unstable as the ground beneath the structures continue to wear away. Pumice is an unstable and lightweight volcanic rock that is able to float on the surface of water. It can be crushed easily, and when the weight of a large structure is on top of it, the stone is able to crumble into small bits and consequently this may create a cavern. The most likely result is a sinkhole that will be formed without the help of swirling natural aquifers filled with underground water storage.
When and if the industries that tap aquifers change the natural flow of water usage, it can also change the water drainage system that nature has built without human interference. For example, industrial runoff can create unnatural saturations of the land that is not naturally accustomed to an overabundance of water. This type of situation can create large sinkholes. The reason that it could become a problem is because the land will likely collapse under the weight of such a change. For example, each gallon of water weighs about 7.5 pounds, and an industrial pond is not natural, the most likely effect is that the pond will weigh too much for the ground to hold and eventually collapse under the substantial burden.
There have been many instances of large sinkholes which have opened up across the globe, however, it seems that there have not been any reported catastrophic sinkholes similar to the incident in Guatemala reported since. At least there have not been an incidents of giant urban sinkholes. Human made sinkholes are most likely the most damaging and the most preventable. For example, in Carlsbad, New Mexico two large sink holes opened up in the town. The sinkholes are the result of man-made salt mines that were dug under the highway, a church, and several other buildings in the area. After the sinkholes opened, an investigation occurred which resulted in the salt mine company going to court. The eventual result was that the mining company was fined one million dollars, for causing the sinkholes and although the company had acquired proper permits and were mining appropriately under those permits, they created an unstable surface by drilling several tunnels under the town and too close to the topsoil layer. As a result, the company went bankrupt. According to the Carlsbad local news. “The Carlsbad I&W Brine Well was created as a solution mine operated by the company at the current location almost continuously from 1979 to July 2008, but the mine was forced to close after its process of injecting fresh water into the ground to dissolve the salt and extract brine caused a liquid-filled underground cavern to form.” (Carlsbad Current Argus, 2016) The result of their mining practice was yet another brilliant human action to make money now, not caring about what the end result would be. New Mexico is not known for a generous amount of rainfall, so not only was the mining company injecting the freshwater into the ground to dissolve the salt, it was taking that fresh water from the local aquifer.
Aquifers are another factor in sinkhole creation. The ground above the natural aquifer can be a delicate ecosystem that is balanced only with the pressure of a full and healthy aquifer system. According to the United States Geological Survey, “aquifer systems are another factor in sinkholes. The sediment above the aquifer system may be delicately balanced by ground-water fluid pressure, meaning that the water below ground is actually helping to keep the surface soil in place. The action of humans pumping for urban water supply and for irrigation can produce new sinkholes. If pumping results in a lowering of groundwater levels, then underground structures could fail and thus sinkholes can occur.” ("The Science Of Sinkholes | Science Features")
The water in an aquifer helps to keep the ground above it firmly set in place and continues to maintain a mostly solid state. However, when it has been pumped out for an urban water source, such as for homes or an agricultural supply such as farms, and the aquifer is not able to regenerate quick enough, sinkholes can occur. For example, in the San Juaquin Valley of central California, humans have pumped out too much of the aquifer, and not enough rain has fallen to refill the water reserves underground, and the whole valley is sinking. This is another example of a possible gigantic sinkhole in the making. Who knows how deep it will go.
This giant California sinkhole that is now called the San Juaquin Valley, may become a large lake or inland sea, if people keep pumping water out, especially for agriculture. Once the water is used for watering the crops, the crops keep and use most of the water, so very little of it goes back into the aquifer. The result is that the aquifer is drying up and wells are going dry. For example, a well drilling company that operates out of Fresno, California, spends more time drilling existing wells deeper to help agriculture than it does drilling new wells. According to an article in NBC News online, “in one area of the San Joaquin Valley, accelerated groundwater pumping is causing the land to sink about a foot a year, said Michelle Sneed, a hydrologist with the U.S. Geological Survey in Sacramento. What's more, she said, the subsidence is permanent due to the geology of California's aquifers.” (Roach) This means that the entire central California valley, which takes up most of the center of the state, is slowly becoming a giant sinkhole. Although the agricultural community is aware of the problem, they continue to pump water out and continue to contribute to the sinking issue. In this case, although the public is aware of the problem of draining the natural aquifers and sinking the valley, they do not seem to care about improving the situation.
In conclusion, sinkholes are hazards that are caused by nature and humans. Naturally occurring sinkholes seem to typically occur away from where there is an abundance of human activity, such as in the forest or near wetlands. Basically anywhere away from the city and where it rains heavily. When a sinkhole occurs in the forest, it will bring down trees, and sometimes cause a landslide. Sometimes these sinkholes can become ponds or deep caverns that may trap unsuspecting animals.
Human caused sinkholes can swallow homes, cars, buildings of any type, and much more. These are caused by either too much water saturation, drainage systems that are unable to handle the heavy rainfall or the drainage of a natural aquifer. Sinkholes caused by human activity seem to be much larger than the sinkholes that occur in nature.
The creation of many sinkholes that are caused by human activity can be attributed to factors such as, personal financial gain and an apparent lack of respect for Mother Nature and the natural systems that the Earth has already created. As long as someone is making money through the use of the water, then the financial gain in the present is seemingly worth far more than the possibility of preserving the planet for generations to come.
Human caused sinkholes can be prevented if humans would choose to take action to avoid an impending formation of sinkholes. This could be accomplished through much better planning when deciding how to utilize the aquafer resources. Also an idea for improving on agriculture practices could be the wise use of water resources through conservation. Developers could learn to make educated decisions when planning urban development projects. Additionally, it would be beneficial for everyone to have the foresight to prevent human caused sinkholes. For example, humans can stop draining the aquifers. Humans can also avoid drilling holes for mines that go under the land. Humans can avoid drilling where the holes may cause a cavern that might harm anyone. Perhaps humans can also avoid building structures or roads in an area that is geologically known to have rocks that dissolve in water. Sinkholes that are caused by humans are preventable.
Works Cited
Conserve-energy-future.com. N.p., 2016. Web. 20 Apr. 2016.
"Causes, Effects And Types Of Sinkholes - Conserve Energy Future". Conserve-Energy-Future. N.p., 2013. Web. 19 Apr. 2016.
"Don't Call The Guatemala Sinkhole A Sinkhole : Dnews". DNews. N.p., 2016. Web. 20 Apr. 2016.
"Giant Sinkhole Eats Highway In Oregon : Dnews". DNews. N.p., 2016. Web. 19 Apr. 2016.
Gutiérrez, Francisco. "Sinkhole Hazards". Naturalhazardscience.oxfordre.com. N.p., 2015. Web. 19 Apr. 2016.
Howard Perlman, USGS. "Sinkholes, From USGS Water-Science School". Water.usgs.gov. N.p., 2016. Web. 19 Apr. 2016.
"NM Lawmakers Look To Fix Carlsbad Sink Hole". Carlsbad Current Argus. N.p., 2016. Web. 20 Apr. 2016.
Roach, John. NBC News. N.p., 2014. Web. 19 Apr. 2016.
"The Science Of Sinkholes | Science Features". Usgs.gov. N.p., 2016. Web. 19 Apr. 2016.
