puricarexfiles: SINKHOLES. A sinkhole is a depression in the ground that has no natural external surface drainage. When it rains, all of the water stays inside the sinkhole and typically drains into the subsurface.

Saturday, November 5, 2016

SINKHOLES. A sinkhole is a depression in the ground that has no natural external surface drainage. When it rains, all of the water stays inside the sinkhole and typically drains into the subsurface.

The Science of Sinkholes

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A devastating sinkhole occurred in Florida on February 28, 2013, raising questions and concerns about this incredible phenomenon. Around 20% of the U.S. lies in areas susceptible to sinkhole events, highlighting the need for research and to be informed about this hazard.

What is a Sinkhole?

Geologically, a sinkhole is a depression in the ground that has no natural external surface drainage. Basically this means that when it rains, all of the water stays inside the sinkhole and typically drains into the subsurface.

Sinkholes are most common in what geologists call, “karst terrain.”

What’s that? These are regions where the type of rock below the land surface can naturally be dissolved by groundwater circulating through them.
Soluble rocks include salt beds and domes, gypsum, and limestone and other carbonate rock. Florida, for instance, is an area largely underlain by limestone and is highly susceptible to sinkholes.

When water from rainfall moves down through the soil, these types of rock begin to dissolve and spaces and caverns develop underground. Sinkholes are dramatic because the land usually stays intact for a period of time until the underground spaces just get too big. If there is not enough support for the land above the spaces, then a sudden collapse of the land surface can occur.

Keep in mind though that while collapses are more frequent after intense rainstorms, there is some evidence that droughts play a role as well. Areas where water levels have lowered suddenly are more prone to collapse formation.

Areas Most Susceptible

About 20% of our country is underlain by “karst terrain” and is susceptible to a sinkhole event. The most damage from sinkholes tends to occur in Florida, Texas, Alabama, Missouri, Kentucky, Tennessee, and Pennsylvania.

Different Types and Various Severities

Sinkholes can be characterized into two types.

First, there are cover-collapse sinkholes, which can develop abruptly (over a period of hours) and cause catastrophic damages.

Secondly, there are cover-subsidence sinkholes, which form slowly over time with the ground gradually subsiding or deflating. These types of events can be less noticeable and go undetected for long periods.

Sinkhole collapses can range in size and severity. Sinkholes can vary from a few feet to hundreds of acres and from less than one to more than 100 feet deep. Sinkholes can have dramatic effects, especially in urban settings. They can contaminate water resources and have been seen to swallow up swimming pools, parts of roadways, and even buildings.

Is There a Sinkhole on Your Property?

This is a difficult question, and unfortunately there isn’t a very efficient system to determine this quite yet. It is recommended that people constantly observe their property for things such as small holes in the ground or cracks formed in a structure’s foundation. People can also check to see if they live in areas underlain by soluble rock, and they can do so by checking with county offices, local or state geological surveys, or the USGS.

Even Humans Cause Sinkholes

Houston Water Pump with
Mazaki Automatic Pump Controller

While sinkhole collapses are frequent in karst areas, there are a variety of other circumstances that can lead to such events. Many sinkholes form from human activity. Collapses can occur above old mines, from leaky faucets, when sewers give way, or due to groundwater pumping and construction.

Think about all the changes that occur when water-drainage patterns are altered and new systems are developed. And when industrial and runoff-storage ponds are created, the resulting substantial weight of the new material can trigger an underground collapse of supporting material.

Aquifer systems are another factor in sinkholes. The

Ballast-type Pressure Tanks

sediment above the aquifer system may be delicately balanced by ground-water fluid pressure, meaning that the water below ground is actually helping to keep the surface soil in place.

Groundwater pumping for urban water supply and for irrigation can produce new sinkholes. If pumping results in a lowering of groundwater levels, then underground structures could fail and thus sinkholes can occur.

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