We have heard horror stories about homes and cars being devoured by the earth in Florida but what about Pennsylvania? The top seven states in the United States of America that experience sinkholes are Florida, Texas, Alabama, Missouri, Kentucky, Tennessee, and Pennsylvania.
Pennsylvania’s Department of Conservation and Natural Resources (DCNR) considers sinkholes one of the state’s serious geologic hazards with 7-percent of the state’s 44,000 square miles sitting on sinkhole-vulnerable land.
What is a sinkhole?
A sinkhole is defined as a pit in the ground that immerges when water gathers without drainage. As water seeps below ground, it can dissolve rock forming caverns. Sinkholes are particularly present in areas where the rock foundation is made of water-soluble rocks such as salt, gypsum, limestone or dolomite.
Most of the time, sinkholes form gradually over hundreds of years, however, occasionally there are instances where a collapse of the ground is sudden.
Types of sinkholes
Geologists categorize sinkholes into three distinct types. The first is a dissolution or solution sinkhole. This is the least dangerous type of sinkhole. The solution sinkhole is formed when water from rain or runoff leaks through openings in the rock layer. The water wears away at the soft rock layer causing a depression to slowly establish.
The solution sinkhole normally produces ponds if the indentation gets lined with natural filler such as rock or soil. These sinkholes take years to occur, are small in appearance and are generally not a threat to humans.
The second category of sinkhole is a cover-subsidence sinkhole. These sinkholes occur in areas where sand covers the bedrock layer of the ground. As the sand filters down into openings in the rock segment, the land begins to sink steadily. Cover-subsidence sinkholes are fairly uncommon, take a while to appear and may not be seen frequently since they are smaller and go unnoticed for long periods.
The most dangerous type of sinkhole is a cover-collapse sinkhole. These are the sinkholes that make national news. They are sudden and can strike anywhere where water can carve a cavern underneath the bedrock layer. When the weight is too heavy for the cavern to support, the ground drops without any notice, swallowing up any structures on top.
Cover-collapse sinkholes may develop abruptly, some over a course of a few hours, leaving behind disastrous damage.
There are often warning signs before a sinkhole collapse.
- The ground may slump noticeably, causing fence poles or trees to shift and lean.
- A structure such as a home or commercial building may begin to display small cracks in the foundation.
- Water may be collecting in areas of a yard where it did not gather previously.
- You may also see a “chimney hole” or “chimney sinkhole.” These are deep vertical holes with steep sides.
If you see one of these chimney holes or any other sign of a sinkhole near your property, please report it to the Department of Environmental Protection agency near you by clicking here.
Sinkholes around Pennsylvania
Is this (a) sinkhole or (b) groundhog den entrance?
(Hint, go a)
Sinkhole eats driveway and starts on home:
What can happen on a new development; fixable. Trenches were dug for new construction, it rained and water found the sinkhole throat:
Typical homeowners’ insurance policies do not cover sinkholes or damage caused by a sinkhole. To protect your property from the shifting ground, it is always a good option to have more coverage for the uncertainties in life. Obtaining sinkhole insurance may be as an additional coverage rider on the homeowners’ policy through the insurance agency and can be an extra fee.
If you wish to have a second opinion before getting an additional policy for sinkholes, a structural engineer can help determine if you are in a high-risk area for sinkholes. Sinkholes occur throughout a majority of Pennsylvania and the Pennsylvania Department of Conservation and Natural Resources has been plotting all known sinkholes and surface depressions on an interactive map. To see if there are any “hot spots” in your area, click here.
The professional and talented folks at Yingst Engineers, can help pinpoint where the weakest point in your home’s structure is and investigate for looming sinkholes on your property. If you suspect that there is a structural concern with your home, contact one of our Professional Engineers to schedule an evaluation before a small problem becomes more serious.