Sinkhole Open Up On Land
Posted on 17. Jun, 2010 by thanate in Sinkhole
Sinkhole or swallow hole is a natural depression or hole in the earth’s surface caused by karst processes. The chemical dissolution of carbonate rocks. Sinkholes may vary in size from less than 1 to 300 meters both in diameter and depth, and vary in form from soil-lined bowls to bedrock-edged chasms. They may be formed gradually or suddenly, and are found worldwide. These terms are often used interchangeably, though many distinguish between features a surface stream flows into and features with no such input.
Photo: Telstar Logistics
Only the former are described as sinks, swallow holes or swallets. A sinkhole on a glacier is called a moulin or a glacier mill. On the surface, sinkholes may develop progressively as subtle, bowl-shaped depressions, or they may collapse suddenly into steeply sided, water-filled craters. The shape of the sinkhole, and the speed that it forms, depend on the size of the subsurface cavity and the thickness of the overburden.
The mechanisms of formation involves natural process of erosion or gradual removal of slightly soluble bedrock such as limestone by percolating water, the collapse of a cave roof, or a lowering of the water table. Occasionally a sinkhole may exhibit a visible opening into a cave below. In the case of exceptionally large sinkholes, such as Cedar Sink at Mammoth Cave National Park, USA, a stream or river may be visible across its bottom flowing from one side to the other.
The sinkholes are common where the rock below the land surface is limestone, carbonate rock, salt beds, or rocks that can naturally be dissolved by circulating ground water. As the rock dissolves, spaces and caverns develop underground. These sinkholes can be dramatic because the surface land usually stays intact until there is not enough support. Then, a sudden collapse of the land surface can occur.
Sinkholes can be human-induced and new sinkholes have been correlated to land-use practices, especially, from ground-water pumping, construction, and development practices. They can also form when natural water-drainage patterns are changed and new water-diversion systems are developed. Some sinkholes form when the land surface is changed, such as when industrial and runoff-storage ponds are created; the substantial weight of the new material can trigger an underground collapse of supporting material, thus, causing a sinkhole.
SINKHOLES and the AQUIFER
Sinkholes originate beneath the surface when groundwater moves through the limestone and erodes large voids, or cavities, in the bedrock. When water fills a cavity, it supports the walls and ceiling, but if the water-table drops, the limestone cavity is exposed to further erosional processes that eventually result in the collapse of the cavity, causing a surface indenture, or sinkhole. The sinkhole becomes a primary site of recharge, where surface water can enter the aquifer and replenish the groundwater supply.
To avoid the destruction of property and the contamination of groundwater, it is important to monitor potential sinkhole formation. Although a sinkhole can form without warning, specific signs can signal potential development:
- Slumping or falling fenceposts, trees, foundations, etc.
- Sudden formation of small ponds
- Wilting vegetation
- Discolored wellwater
- Structural cracks in walls, floors, etc.
WHAT TO DO if a SINKHOLE DEVELOPS on your PROPERTY
- Notify your local Water Management District
- Fence or rope the hole off
- Keep children away!
- Protect the area from garbage and waste
- Contact your homeowners insurance company
Lastest sinkhole news; Sinking land has developed into a huge 80-metre diameter hole on a school playground in Ningxiang county, Hunan province in southern China.
Sinking land has created an enormous hole in front of an elementary school and swallowed an entire playground in Ningxiang county in China’s Hunan province, the Associated Press reports. The sinkhole started to yield in mid-January, at first forming a hole twenty meters in diameter.
Intense springtime rainfall has since accelerated the hole’s expansion, which has, in turn, caused damage to area buildings. According to local officials, many families living nearby have already been evacuated, with government subsidies provided.
At least eight additional sinkholes have formed in various Chinese regions in the past few weeks, sparking fears among residents that the holes could be an early indication of other seismic activity in the country. The official said families living in nearby buildings were evacuated and had received a subsidy of 300 Yuan.
Sources: huffingtonpost.com, plants.ifas.ufl.edu, wikipedia.org
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