Sink Holes Ground Water and Petroleum Extraction Permafrost Thawing and Expanding Clays

Sinkholes

a) Describe the conditions that lead to sinkhole formation.

According to the Missouri Department of Natural Resources, a sinkhole, or doline, can be formed in a number of different ways. Erosion is a common cause of sinkhole formation. Erosion issues such as debris shrinking, migration of debris into openings in bedrock, and even the upward movement of debris can be conditions leading to sinkhole formation (Foose). Sinkholes tend to occur in bedrock areas that contain limestone. However, any type of sedimentary rock base is prone to sinkhole formation. Thus, gypsum and salt beds are common areas that are sinkhole prone because of the high solubility of the salt bed. Likewise, bedrock with a high proportion of carbonates can dissolve easily. As Baryakh and Fedoseev point out, karst is particularly sensitive to sinkholes. Basically, the conditions that lead to sinkhole formation involve just the right combination of soluble bedrock and local water content, flow, or behavior. Acid rain foments the water issues that lead to dissolution of geological surface material causing sinkholes.

The most basic way a sinkhole is formed is when surface ground collapses in, when underground limestone caves give way. A collapse of an underground cave (usually limestone too) can cause the sinkhole. In fact, the conditions that lead to sinkhole formation are directly related to the behavior of groundwater. If the geological composition of the soil and bedrock are such that water can dissolve it, then a cavity can be created. The result is a hole or depression that can fill with more area groundwater or surface water quickly. Human factors such as the overpumping of ground water can also contribute to or cause the formation of sinkholes, as can changes in the diversion of local water systems. This is in fact what took place in the Central Arizona Project, outlined in "Sinkholes, Land Subsidence, and Swelling Soils." The size of sinkholes varies, both in terms of depth and breadth.

b) Describe several consequences related to groundwater and petroleum extraction.

When groundwater or petroleum are extracted from the earth, the result is land subsidence. Although land subsidence can take place due to other causes, extraction of ground water and petroleum is a common cause. The results can be disastrous to the local area and community. Increased rates of flooding and submerging of wetlands can take place due to too much water or petroleum extraction and related land subsidence ("Sinkholes, Land Subsidence, and Swelling Soils"). As a result, salt water can intrude on local wetlands, filling in the gap created by the subsidence and extraction. The ground itself can fail and lead to sinkholes. Commercial damage includes the destruction of drain and municipal water and waste water pipes, because the ground has been compromised due to the extraction and subsidence. Broken pipes can therefore cause hygiene problems in the area. Additionally, there are public safety concerns that are related to groundwater and petroleum extraction such as the unevenness of the surface leading to tilting buildings ("Sinkholes, Land Subsidence, and Swelling Soils").

Another consequence related to groundwater and petroleum extraction is the impact on local aquifers. The chemical and geological composition of the aquifer may be changed, Moreover, as water is extracted from the aquifer, the porousness of the ground is changed from being very porous allowing for the formation of the aquifer, to being not so porous and preventing the aquifer from filling up again (Poland and Davis). It can be hard to gain back the aquifer after its porousness has been compromised. This is because once the granules become more compacted due to the withdrawal of water, expanding them again can be nearly impossible ("Sinkholes, Land Subsidence, and Swelling Soils"). Therefore, areas that once relied on aquifers for water supplies will experience diminished water supplies (Poland and Davis). The only way to prevent loss of aquifer is by ceasing the extraction of groundwater and petroleum in that area but the problem is occurring throughout the United States ("Sinkholes, Land Subsidence, and Swelling Soils").

c) Describe several consequences related to permafrost thawing.

Permafrost, according to the United States Environmental Protection Agency, is permanently frozen soil or rock surface. It is common in most subarctic regions, such as Alaska and Northern Canada. When the permafrost thaws, sinkholes can easily form. But there are more extensive problems related to thawing permafrost. Thawing permafrost can also result in irregular land, leading to leaning buildings and unsafe foundations for the buildings. Trees may fall over when the permafrost thaws, causing damage and even casualties. Beneath the surface, any pipes can easily be damaged due to the permafrost thawing. Infrastructure damage can be astounding, was with large-scale projects like the Trans-Alaska oil pipeline ("Sinkholes, Land Subsidence, and Swelling Soils").

The thawing of the permafrost can also lead to a feedback loop, in which a little thawing causes more due to the release of carbon from the initial thaw. Most permafrost will have some carbon molecules trapped inside. This is especially true when the permafrost is located in peat-rich areas. The melting of the permafrost releases the carbon molecules, and carbon dioxide. Especially in peat-rich areas, the release of the carbon is also accompanied by the release of methane gas. This double release of carbon dioxide and methane gas contributes further to global warming and results in more permafrost areas thawing, and so on for the feedback loop.

When permafrost thaws, it also alters the characteristics of the local geology and plant life. Permafrost bonds together mosses and other elements. When it melts, those elements are no longer bound together. The ground settles where it was once firm, leading to frequent landslides and rock fractures. This compromises the integrity of the ground surface. There are other large-scale consequences of melting permafrost. For example, the melting ice in the permafrost contributes to rising sea levels.

d) Describe several consequences related to expanding clays.

Expanding clays and swelling soils can have disastrous consequences. Some of the consequences are similar to those that take place due to both sinkholes and melting permafrost. For example, swelling clay leads to ground irregularities, which in turn lead to the compromised building structures like foundations of homes. Expanding clays and swelling soils can cause expensive damage to the walls and structures of all buildings. Moreover, the expanding soils can lead to costly damages to asphalt and road working surfaces.