Sinkholes; Made by nature or humans?
Abstract
Sinkholes seem to swallow the earth and everything sitting on the surface. Some sinkholes are small and have relatively no effect on humans or property. Some sinkholes are very large and will leave ga[ing holes in the landscape. Sometimes these large sinkholes will devour a road and cause harm to the humans who live, work, and travel where the sinkhole is located. For example, a series of sinkholes and a landslide occurred simultaneously in Harbor, Oregon. This sinkhole was a combination of nature and human activity. Many sinkholes are caused by human activity that nature decides to undo. Humans think they are so clever when they build roads and install water lines through the earth. Humans usually do not replace the same soil they take out, when they build roads or install water pipes. Instead, those clever humans put sand, gravel, and often loose rock in place of the tightly packed earth that was originally in the hole that they dug. The unfortunate result of this human activity is typically mother nature getting revenge in the form of a sinkhole that ends up destroying homes, businesses, and roads. Silly humans.
Sinkholes: Made by nature or humans?
The scientific explanation for a sinkhole is not nearly as creative as the abstract statement, but it is interesting how many of the sink holes that have been recorded over the last century, in and around cities, are typically caused by human activity. Construction of new buildings requires a sewer system, water lines, and other utility connections that are usually underground. These utilities require holes or long ditches, which are dug up and replaced by new soil, sand, or gravel that is not usually packed as tightly as nature had created before the human activity occurred. (Waltham, Bell, & Culshaw, 2007)
Natural sinkholes are formed by several different bedrock and groundwater systems. There are at least three different natural sinkholes which are formed through the process of saturation, separation, and release of saturated and disturbed soil below the surface. According to the United States Geological Survey (USGS) website, sinkholes are “a depression in the ground that has no natural external surface drainage.” This means that as the rainfall increases, so does the level of water inside the cavern that will become the sinkhole. Usually the water will erode rocks and minerals that are porous and water soluble. For example, the rock could be sandstone, gypsum, or decaying granite. The easier it is for water to wear the rock down, the easier it is for a cavern to form under the surface. (USGS, n.d.)
Humans typically experience the sinkhole suddenly, as the surface land will seem intact before the sinkhole appears. This is because the water underground has been working hard to create a hole that becomes the sinkhole. Ground water can flow like an underground creek, river, or pool. The water will circulate through soluble rock, such as gypsum, limestone, or sandstone. The active water will dissolve the rock and create a cavern or empty space. When the ground above is too heavy, vibrates from traffic or construction, or a heavy rainfall has saturated the surface soil, a sinkhole will open up, taking everything that was sitting on the surface with it. Sometimes the sinkhole will swallow trees, pavement, or even houses and buildings. Whatever was resting on the surface will suddenly fall into the hole. It is important that humans remember how unstable the ground benieth their feet, truly is. (USG, n.d.)
Although rain impacts the severity of a sinkhole, it is likely that drought may also play an important role in the severity of a sinkhole. For example, if an area typically receives rain then does not have any for several years, the lack of groundwater can create pockets of unstable dry ground. When traffic or an earthquake occurs, the ground can open up because there is nothing holding it together. Wet rock and packed sand will expand but dry rock and sand will contract, leaving plenty of space for a vibration to effect the stability of the surface, causing the land to sink or slide. The San Joaquin Vally, in California is sinking, according to reports at NASA’s Jet Propulsion Lab. Some areas are sinking about 2 inches annually. This could mean big trouble for those folks living there. The whole valley might become a huge sinkhole, or at least a series of them. (USGS, n.d.)
Geologists at USGS estimate that about 20 percent of the United States is unstable and susceptible to sinkholes. Most of this area is on or near natural bodies of water, such as the oceans, lakes, and swamps of coastal states. Some of the lands susceptible to sinkholes are near crude oil and natural gas reserves. This is because if the reserves are taken out of the ground, there is nothing to fill the void and the ground becomes unstable. The result is a sinkhole. The USGS website shows that the areas which are most vulnerable to sinkholes in the United States, are the areas where fossil fuels are minded or puped out of the ground. These sinkholes would never happen if humans were not causing the voids in the earth. (Silverman, n.d.)
Part of the San Joaquin Valley, in California is sinking because humans have used up almost all of the groundwater reserves. Because the groundwater reserves had kept the ground at a specific elevation, the ground was stable. However, the dried up space that no longer keeps the rock in a saturated and expanded form, is shrinking. This means that it is likely the reduction in elevation will cause the ground to sink below sea level and a giant lake will likely form from either mountain sourced rivers flow into the valley or the Pacific Ocean making its way inland. Either scenario is possible. Essentially, the San Joaquin Valley will become one giant sinkhole. This is a human caused environmental disaster. (USGS n.d.)
Sometimes the effects of human caused sinkholes will take a long time to develop. Poor planning, improper maintenance, and misuse of the surface land may be large factors in the appearance of a sinkhole. For example, if roads are built with insufficient base materials or natural water drainage is unaccounted for, the natural routes from water drainage can cause unstable materials under a road to dissipate. This erosion will cause a sinkhole to form under the pavement and collapse the road. Hopefully, no damage to life or property occurs when the collapse occurs. (Kiger, 2016.).
Oregon seems to have a history of sinkholes, most of which are caused by humans. These human-caused sinkholes typically occur under roads and in newer construction areas such as housing and business. Most of the time the construction plans include considerations for the most appropriate way to deal with surface water, like natural streams that occur during rainstorms or seasonal ponds. However, sometimes something in the planning process goes awry and certain considerations that should have been incorporated are left ignored or they are not followed appropriately. One of the considerations that typically occurs, is the overflow for storm drainage systems under roads, where sand is the base underlayment and the road has a large amount of traffic. This scenario is especially true along highway 101, on the Oregon Coast. (Hernandez, 2016).
A series of sinkholes and a landslide occurred on and around highway 101, in Harbor, Oregon near Brookings. Thankfully, no one was harmed and no buildings went down the hole. However, plenty of road sank and exposed the truth about the construction of the highway. From photos, it is easy to tell that the road was built on sand with a very thin layer of gravel under the asphalt. Storm drains were not enough to contain the 1.5 inches of rain that Harbor received in a short amount of time, which added to the problem. The water pipe failure quickly washed the sand base away, causing a sinkhole to form within hours. Then the road, parking lot, and the side of a hill fell, causing traffic to stop. Workers from the Oregon Department of Transportation put up roadblocks and rerouted traffic, which helped keep people safe. (Hernandez, 2016).
Throughout Oregon, there are many stories just like the sinkhole in Harbor. A large sinkhole opened on Interstate 5, near Roseburg. Unfortunately, someone died during that event, and several vehicles were devoured by the sinkhole. In Portland, Oregon many sinkholes have appeared in roads. Some of those have swallowed cars and one was large enough to ingest a semi-truck. Most of the sinkholes in Oregon have been caused by human activity, such as water pipes bursting after a heavy rain. However, sometimes after a heavy rain, the groundwater pushes to the surface and creates a sinkhole. (Hernandez, 2016).
Sometimes natural aquifers are too full to continue holding the groundwater they contain, and they push the extra water to the surface. When this occurs, the sinkhole is typically in a residential area, a park, or in nature somewhere. Those types of sinkholes sometimes cause damage to property and wildlife and usually accompany a landslide after several days of heavy downpour. An informational graphic, on the next page, was found on the Conserve Energy Future website shows the process of how a sinkhole is created in an urban setting. Through the graphic it is easy to understand how humans can have a devastating effect on the aquifer level and how that effect may create a cave that eventually collapses, which causes a sinkhole. It is a great explanation for how sinkholes are created by human activity.
Graphic by Rinkesh. (2013).
As you can see by the graphic, several factors can attribute to a sinkhole. The sinkholes near homes can cause loss of life and property and are perhaps the hardest to predict. Of course, the picture is only a ficticious example of the textbook sinkhole forming. Sinkholes actually look much more terrifying than the drawing shows. What the drawing fails to show is a car hanging, a human scared, and the fence falling in the hole, or perhaps a tree or two. Sinkholes can be prevented, especially in urban areas or near roadways. The problem is human caused, so humans must be the ones to fix and prevent the problem. The sinkholes that occur under roads may be preventable through wise planning. Some newer road construction on Interstate 5, near Medford, Oregon shows wise planning that allows rain runoff to collect in specially designed roadside ponds, which are lined with a base of large granite boulders, smaller granite rocks, and filled with smaller pea-sized gravel. Finally, the runoff pond is covered with soil, grass seed, and a few bushes to help the runoff area become a small ecosystem. Many new road construction areas along Interstate 5 are using the same method to control storm waters and avoid sinkholes from developing. Overflow areas for temporary flooding waters are important for the prevention of sinkholes caused by a rainstorm filling aquafers.
Many sinkholes that develop because of poor planning before the roads are constructed. These types of sinkholes may be preventable. Proper planning, appropriate use of base materials, and the process of paving the road in a way that allows water to drain off, are all good ways that could help avoid the formation of sinkholes. Other issues that may be addressed are the appropriate size and drainage for water lines that go under roads. Through the use of environmental impact reports that imply the best use of construction to improve the materials used, help the ecosystems impacted, and allow the greatest advantage to the natural balance of the area which is proposed for construction are all important factors in the prevention of human caused sinkholes. Perhaps mother nature will not need to take revenge after all.
References
Rinkesh. (2013). Causes, Effects and Types of Sinkholes - Conserve Energy Future. Retrieved March 21, 2016, from http://www.conserve-energy-future.com/causes-effects-and-types-of-sinkholes.php
Kiger, P.J. (Feb 1, 2016). Giant Sinkhole Eats Highway in Oregon. DNews. Retrieved March 21, 2016, from http://news.discovery.com/earth/giant-sinkhole-eats-highway-in-oregon-160201.htm
Silverman, J. (n.d.). How Sinkholes Work. How stuff works. Retrieved March 21, 2016, from http://science.howstuffworks.com/nature/natural-disasters/sinkhole.htm
Hernandez, T. (Jan 29, 2016.). Landslide, sinkhole close down US 101 in southern Oregon coast. Retrieved March 21, 2016, from http://www.oregonlive.com/pacific-northwest-news/index.ssf/2016/01/landslide_sinkhole_close_down.html
USGS. (n.d.). Retrieved March 21, 2016, from http://www.usgs.gov/blogs/features/usgs_top_story/the-science-of-sinkholes/
Waltham, T., Bell, F. G., & Culshaw, M. (2007). Sinkholes and subsidence: karst and cavernous
rocks in engineering and construction. Springer Science & Business Media.
