Sinkhole Meaning
Sinkholes are pits in the ground that develop in regions where water collects without external drainage. Sinkholes mainly take place as water drains underneath the ground. It can dissolve subterranean caverns, especially in areas where the bedrock is composed of water-soluble carbonate rocks such as limestone or dolomite or the evaporated rocks such as salt or gypsum.
Sinkholes also develop when the roofs of caves demolish. Sinkholes are most commonly funnel-shaped, with the broad end opened at the surface and the narrow end at the bottom of the pool.
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What Happens with the Occurrence of Water Sinkholes?
Groundwater levels descended to record-setting lows as farmer’s had pumped water to irrigate their plants for safeguarding from the cold temperatures. The sinkholes demolished streets, homes, and portions of cultivated areas. Sinkholes differ from shallow holes about 3 feet deep, to pits more than 165 feet deep. Water can clear out through a sinkhole into a cave or an underground channel. When mud or residue plugs one of these underground caves, it fills with water to become a pond or a lake.
Formation of Sinkholes
In a landscape where limestone sits below the soil, water from rainfall gets collected in cracks in the stone. These cracks are known as joints. Gradually, as the limestone dissolves and is transported, the joints broaden until the ground above them becomes shaky and shatter. The shattering often takes place very quickly and without very much warning. Water accumulates in these shattered sections, developing sinkholes.
Example of a Sinkhole
Sinkholes form naturally, especially where there is ample rainfall, and the rock below the surface soil is limestone. For example, a cenote (pronounced as "seh-NOH-tay") is a kind of sinkhole which occurs with the collapse of an underground cave, revealing the water to the surface. Cenotes are very common in Mexico on the Yucatan Peninsula. There are over 2,000 cenotes on the Yucatan of Mexico, and they are an essential source of fresh water for people there. Ancient Mayans had the opinion that cenotes were a corridor to the underworld.
How Quickly Do Sinkholes Form?
Commonly, sinkholes form slowly. Sometimes, though, the collapse is unexpected and immediate. Those unexpected sinkholes are mostly the ones that open up and consume cars, roads and homes.
Types of Sinkholes
Since Florida is subjected to sinkholes, it makes for a good place to discuss some different types of sinkholes and other sinkhole information like the hydrologic and geologic processes that form them. The mechanism of dissolution, where surface rock is soluble to weak acids and suffusion, where cavities develop underneath the land surface, are responsible for approximately all sinkholes in Florida.
1. Dissolution Sinkholes
Dissolution of dolomite or limestone is most intense where the water first comes into contact with the rock surface. Aggressive dissolution also takes place where flow is focused in foregoing openings in the rock, such as fractures, along joints, and bedding planes, and in the zone of water-table oscillation where groundwater is in contact with the atmosphere.
Rainfall and surface water filter through joints in the limestone. Dissolved carbonate rock is transported from the surface and a little depression slowly forms. On exposure to carbonate surfaces, a depression may concentrate upon surface drainage, triggering the dissolution process. Residue carried into the developing sinkhole may plug the ponding water, outflow and developing wetlands. Rolling hills and shallow depressions induced by solution sinkholes are common topographic characteristics throughout much of Florida.
2. Cover-Subsidence Sinkholes
Cover-subsidence sinkholes are liable to form slowly where the covering sediments contain sand and are permeable. In regions where sediments bear more clay or cover material is thicker, cover-subsidence sinkholes are relatively smaller, uncommon, and may go undetected for extended periods.
3. Cover-Collapse Sinkholes
Cover-collapse sinkholes may form suddenly (over a span of hours) and cause devastating damages. They take place in areas where the covering sediments contain a substantial amount of clay. Over time, surface drainage, erosion, and accumulation of sediment reshape the steep-walled sinkhole into a shallower bowl-shaped depression. In addition, the sediments break down into a cavity. As this spalling continues, the cohesive covering sediments develop a structural arch. The cavity relocates in an upward direction by continuing roof collapse. The cavity finally breaches the ground surface, developing abrupt and dramatic sinkholes.
FAQs on Sinkhole
1. What is a sinkhole in the context of geography?
In geography, a sinkhole is a depression or hole in the ground with no natural external surface drainage. It is formed when water erodes soluble bedrock, such as limestone or gypsum, creating underground voids. When the overlying land surface can no longer support its own weight, it collapses or gradually subsides into the cavern below, creating the sinkhole. They are a common feature of karst topography and are also known as dolines.
2. What are the primary causes of sinkholes?
Sinkholes are primarily caused by the process of chemical weathering and erosion of soluble bedrock by groundwater. The main causes can be categorised as natural and human-induced:
Natural Causes: These include the slow dissolution of rocks like limestone and gypsum by slightly acidic rainwater, fluctuations in the water table that remove buoyant support for the surface material, and heavy rainfall that saturates and weighs down the soil.
Human-Induced Causes: Activities such as excessive groundwater pumping for irrigation or urban supply, construction that places heavy loads on the ground, leaking pipes, and altering natural water drainage patterns can accelerate the formation of sinkholes.
3. What are the main types of sinkholes explained in geography?
Geographers classify sinkholes into three main types based on how they form:
Dissolution Sinkholes: Occur where there is little to no soil cover over soluble bedrock. Water from rain and surface runoff slowly dissolves the rock, forming a depression on the surface.
Cover-subsidence Sinkholes: Form where the bedrock is covered by a deep layer of permeable sediment (like sand). As the bedrock dissolves, the sandy sediment slowly fills the voids, causing a gradual sinking of the land surface.
Cover-collapse Sinkholes: These are the most dramatic. They occur where the bedrock is covered by a cohesive material like clay. An underground cavern forms, but the clay layer initially holds. Eventually, the cavern grows too large, and the surface cover collapses suddenly and catastrophically.
4. Why are some regions more prone to sinkholes than others?
Some regions are more susceptible to sinkholes due to their underlying geology. The most significant factor is the presence of extensive soluble bedrock close to the surface, such as limestone, dolomite, gypsum, or salt beds. Regions with this type of geology are known as karst landscapes. In these areas, slightly acidic groundwater can easily dissolve the rock over time, creating a network of underground caves and voids. When these underground structures weaken, the surface is highly prone to collapse, leading to a high frequency of sinkholes.
5. How is a sinkhole different from a pothole?
While both are holes in the ground, a sinkhole and a pothole have fundamentally different origins. A sinkhole is a geological feature caused by the collapse of the ground surface due to subsurface erosion of bedrock. In contrast, a pothole is an engineering failure of a paved surface, like a road. Potholes form when water seeps into cracks in the pavement, freezes and expands, and then thaws, weakening the road material, which then breaks down under traffic.
6. What are the major environmental and structural impacts of sinkholes?
The impacts of sinkholes can be severe. Structurally, they can cause catastrophic damage to buildings, roads, bridges, and other infrastructure, leading to instability and collapse. Environmentally, sinkholes can alter surface drainage patterns and provide a direct pathway for surface pollutants to contaminate groundwater aquifers. This can have long-term negative effects on water quality and local ecosystems that depend on that water source.
7. Can you provide some real-world examples of significant sinkholes?
Yes, there have been many notable sinkholes around the world. For example:
The 2010 Guatemala City sinkhole was a massive, near-perfectly circular collapse that measured about 65 feet wide and 100 feet deep. It was triggered by a combination of factors, including Tropical Storm Agatha and leaking sewer pipes.
The land surrounding the Dead Sea is known for its numerous sinkholes. This is because the underlying rock salt is highly soluble, and as the sea's water level drops, fresh groundwater dissolves the salt layers, causing frequent collapses.
