[Geography Notes] on Sinkhole Pdf for Exam

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.

            

     

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.