Questions & answers such as what is a sinkhole & where do they occur?

This article series explains what sinkholes are and why sudden subsidences or sinkholes occur, describes their effects on buildings, and gives building and site inspection advice useful in identifying areas where there is an increased risk of sink holes at properties.

Page top photo: a sinkhole opening up in Florida.

Sinkhole & Subsidence FAQs

These questions & answers about subsidences and sinkholes were posted originally

at SINKHOLES & SUBSIDENCES - be sure to review that information.

How do I know if a sinkhole is forming at a pond near my home in Florida?

I live in Florida in a home located 25ft.from a pond. We are below street grade level and get all the rainwater from 3 converging streets.

The water goes by both sides of the house and into the pond. Last Fall the excessive rain took 6ft. of my entire back yard and moved it out into the pond.

The grass in my backyard has turned brown. I am told that it's because the pond water has made its way to the house and created a fungus by rotting the roots.

Am I looking at a potential sinkhole here that could take the house? On 2019-02-12 by Don Struhar

Reply by (mod) -

I don't know, Don.

Sinkholes are common in many areas of Florida - check if your area is one of them by consulting your local building department
also

see SINKHOLES in FLORIDA

The fungus story doesn't add up in my experience but then we don't know what contaminants are in that surface runoff.

Root rot is of course possible.

I'm worried that sand and pebbles near our pool may be a sinkhole forming near our Chicago home

I'm observing a pile of sand with small pebbles on the same part of the patio which is
Old Chicago brick which is adjacent to the bull nose of the pool. There is a drain two feet away in the pool which led someone to think it may be a return pipe to the pool. There is no sand in the pool though.

When I sweep it up, it reappears in the same spot within a day or so. There is one brick that is minimally depressed. The sand spans one foot by two feet at minimum. Does this sound like anything? On 2017-04-01 by Tricia

Discussion by (mod) -

Honestly I don't understand your situation, but it sounds to me as if you may have a leak in your pool piping system

Followup from Tricia

GM
Thank you for your response.
The reason I don't think it's cool piping is because there's no stand in the pool. It is on the patio decking right in the same area which is adjacent to the pool. I asked a pool man what he thought and he felt since there was no sand in the pool it couldn't be piping

I guess my question to you would be is sand a sign you have seen before in instances of a sink hole. In reading, I have not heard it mentioned. Ty

Explanation by (mod) -

I understand there may be no sand inside your swimming pool but it would be coming for there to be sand under patio blocks or as part of backfill around a swimming pool. I think that at this point you need to try to relate what you're seeing to the operation of the pool equipment.

For example if all of your pumps are off no water is circulating no drain is draining and the soil appears again anyway then we would indeed be looking for an exterior source.

If you live in an area where sinkholes are common that can be a concern but I rather doubt that a sinkhole would cause a pile of sand to appear at the surface of a pool patio.

 

Worried about a sinkhole: investigation exposed us to radon?

There is a possible sink hole on the exterior of a business property. The insurance company is sending out an inspector to inspect each individual suite in the building

This inspection requires 2-3 hours per suite and a period of that time the suite has to be completely evacuated due to them shooting radon.

What is this and are there any dangers for those entering the suite after it is completed? On 2016-08-02 by Pat Morris

Clarification by Mod

Testing for radon does not pose a risk to building occupants, though I am doubtful that radon testing is in the slightest an adequate sinkhole investigation.

 

Question: earthquake and subsidence concern in Virginia

I live in an area where after the earthquake (in Virginia) the ground constantly shakes. I live in an apartment complex on the second floor. I find it unusual that the apartment shakes. It starts off as a rumbling and then shakes like a wave. Then it stops for a brief second and then it starts to tremble followed by a wave.

This continues for about 24 hours a day. I placed a glass of water on a table and/or the floor to see if there is a sign of this trembling/wave like movements. Right now, it is faint. (Oct 12, 2011) T. H.

Reply:

T.H. The August 23 2011 Virginia earthquake was 5.8 magnitude.

You can read about it at the USGS website. Omori's law (with later updates) defines the rate of aftershocks following an earthquake. If you are still feeling building movement that has not dropped to a background level then aftershocks from your earthquake are indeed continuing.

A 3.0 aftershock was reported in Louisa VA just today 12 Oct 2011. So depending on where you live your report may be no surprise, though if it has not already been, it should also be reported to the USGS.

See details at Sinkholes in VIRGINIA

 

Do sinkholes appear around trees during hurricanes?

I would like to know if there have ever been sinkholes that develop around a large tree during Hurricanes after the tree was hit by a lighting bolt. and
if so, where might I read more on the subject. (Aug 1, 2012) William Swieczwski

Reply:

William, lightning strikes and sinkholes are pretty independent events.

However we have seen trees or tree roots "explode" when a tree takes a lightning hit - the energy vaporizes sap in the tree or its roots, causing a steam vapor explosion that can not only split a tree but can blow roots and some soil out of the ground.

Lightning strikes send such a huge amount of energy into objects that lots of strange things can occur - we've seen a hit follow tree roots under ground, across a yard, up an iron entry stair rail, over to metal siding - at which point aluminum rivets in the siding corner trim melted and siding parts fell to the ground; at the same property moisture under a garage slab vaporized, sending the slab and automobile up through the garage roof.

A burst water main resulting from a storm can also cause soil subsidence or a local "sinkhole"

But these are not sinkhole events.

See LIGHTNING PROTECTION for TREES

and LIGHTNING PROTECTION SYSTEMS home

How do I Report or ask for help with sinkhole activity in Southern Maryland?

Who do I contact regarding possible sinkhole activity in Southern Maryland? (Sept 12, 2012) Angela Smith

Who can I contact to inspect a possible sinkhole in my yard. Live in Reisterstown, MD. (Mar 12, 2013) Annie Eckert

Reply:

Start with your local building department or if there is an obvious sinkhole, your fire and emergency services 911

If your home is being affected you will probably need to hire a local geotechnical engineer.

First check with your building department or if younger actually seeing a sinkhole

Or sudden subsidence, keep away and contact emergency services.

See this What To Do If You Suspect a Sinkhole in Maryland - from MGS, the Maryland Geological Survey department that gives steps to follow if you suspect sinkhole activity:

Ultimately you may need a geotechnical engineer

Who approves Sink hole and flood control in Live Oak Florida?

In the City of Live Oak, Florida 46 water surface drain holes for flood control 100 feet to over 1000 feet deep with most about 400 feet deep were installed with grant money and numerous wells installed for water usage in 1.5 square miles. Is this safe?? I perceive this has caused the many sinkholes. Who approved these?

385-362-2337 or 13577 CR 136 West Live Oak, FL 32050=6367 I am 81 years old and this appears to be just common sense and I would like to explain to our Gov. Rick Scott and the FL Insurance Department. (Dec 16, 2012) John Chambliss

Reply:

John, thanks for the very interesting question - sorry but it's beyond my expertise; we could research it and will do so if needed, but first, perhaps you can ask to see a copy of the engineering report that your city must have obtained when deciding to dispose of floodwaters using wells.

I know that in some areas of Florida there has indeed been an effort to re-inject water into grounds previously drained specifically to try to reduce subsidence and return swamplands to operation. Let me know what you find.

See this information on SINKHOLES in Suwannee River Area of Florida, provided by the Suwannee River Water Management District.

Worried about these Sinkholes in southwest Florida

I live in southwest Fla. I have 2 depressions in my yard, 1 in the front that is circular and shows signs of an inward slope.

The second is in the back over where the well used to be (we went to city water). I hear a lot of "popping" noises at night, like they are coming from the attic. I used to hear water rushing noises at night when i lay in bed and sometimes it sounded like dirt falling under the house and crashing below.

This morning i heard what it sounds like the floor cracking. Could my house be on a sinkhole? I'm afraid to call the insurance company, that they will drop me (state farm) and i want to sell it very shortly. Thanks (Feb 28, 2016) jmcinfla

Reply:

Yes, from just your e-text, of course, no one can diagnose something as critical as a sinkhole.

But it would be appropriate to contact a local expert such as a geotechnical engineer who can survey your property, make test borings if necessary, evaluate your home for structural damage, tell you if sinkholes are found in your immediate area, and give advice.

Watch out: for safety Meanwhile I would rope off the greater area of anything that looks suspicious to reduce the chances of someone being injured or worse.

Call the Florida Department of Environmental Protection Sinkhole Helpline at 850-245-2118

See these FAQs and Links to More Information about Florida Sinkholes from the Florida DEP

I have a 4 foot sinkhole or depression in my back yard

I currently have a 4ft in diameter depression in my backyard. It was not there a year ago, and slowly appeared this year from late Summer to Fall.

The depression grows thick green grass? I am concerned it could be an under ground spring or mine?

Not sure what my first step would be to find out? I live in North East PA. Thank you (Dec 20, 2012) Lisa Macchia

Reply:

Ask your local building department for help.

Also contact the Pennsylvania Department of Environmental Protection (PA DEP) where their web page permits you to submit an incident report.

Here are the Pennsylvania DEP Contact Telephone Numbers - you'll see that the state DEP is divided into regional offices.

How can I tell if this a sinkhole versus settling?

Thank you for the info. I live in a karst area with sinkholes confirmed within a mile or two of my home. There's a creek a quarter mile away and the lot slopes fairly sharply. Our 20 y/o home has many of the sinkhole "signs."

Excessive cracking in concrete in half the house (driveway, basement floor, garage, front porch.)

There's also stair step cracks in the concrete block wall in the basement and a growing half inch separation in one area. Cracks through tile and ceiling in a 2nd floor bathroom, pops and creaking, a strange water spot that appeared but never got worse, can't open our screen porch door, rain leaking in under basement door.

I can't tell online if these things could be "just" settling or a sinkhole. Is there a way to tell?

I know the final determination needs to be by an engineer.

Finally, I have felt earthquake-ish "bouncing" occasionally over the past several years on the two upper floors. Is this something that happens with sinkholes? (Mar 1, 2013) sinkhole vs settling

Reply:

For help inspecting a building for signs of settlement or sinking including over a possible subsidence or sinkhole

See SINKING BUILDINGS

A depression never fills up in our yard - is it a sinkhole?

We have about a 4 ft diameter depression very near our house that I have been adding dirt to for about 20 years. It always sinks about an inch or so.
Are we candidates for a sinkhole? (Feb 17, 2014) Depression that never fills up

Reply:

Possibly; you don't say where you live, how often you've added fill, nor how much: it could be a rotting pile of tree stumps and branches, or it could be something deeper and bigger _ I can't guess.

Depending on the geology of where you live, sinkholes will be more or less common.

Are there sink holes around sand mines in Florida?

Are sinkholes more common around old sand mine areas? Residences are being built on sand mine areas here in Florida.

Reply:

Shelly,

Certainly sinkholes occur around various types of mining activity for several reasons including removal of soil and disturbance by mining operations.

In Florida it's the underlying karst formations (not sand) that explains most sinkholes. (May 31, 2014) Shelly

Sinkholes on Long Island NY after Hurricane Sandy

I live on long island. My house was damaged by hurricane sandy but it is now repaired. I did not have structural damage. I am not sure if this has anything to do with sandy . In my rear yard i have concrete.

The concrete was put down about 12 years ago. The corner of one slab is sinking down . It is about 6 inches down so far. Our water level under the concrete is about 10 feet. I am worried that this might be a sinkhole. What do i do? I have no idea who i should call to inspect it. Grg511@aol.Com (July 30, 2014 Mallano shouted

Reply:

Indeed this sounds like soil settlement under a slab.

but indeed sinkholes DO occur on Long Island. You'll want to check with your local building department and to keep people away from the suspected area until you have an assessment of its safety.

See

• Nolan, Bernard T., Barbara C. Ruddy, Kerie J. Hitt, and Dennis R. Helsel. "Risk of nitrate in groundwaters of the United States a national perspective." Environmental science & technology 31, no. 8 (1997): 2229-2236.
• Todd, David K., and Larry W. Mays. Groundwater hydrology edition. Wiley, New Jersey, 2005.
• Ritter, W. F. "Pesticide contamination of ground water in the United States‐A review." Journal of Environmental Science & Health Part B 25, no. 1 (1990): 1-29.
• Mylroie, John E., James L. Carew, and Audra I. Moore. "Blue holes: definition and genesis." Carbonates and Evaporites 10, no. 2 (1995): 225-233.
• Martinez, Joseph D., Kenneth S. Johnson, and James T. Neal. "Sinkholes in Evaporite Rocks: Surface subsidence can develop within a matter of days when highly soluble rocks dissolve because of either natural or human causes." American Scientist (1998): 38-51.

And Long Island NY as well as any developed area can develop man-made sinkholes.

 

A nearby storm pond has a shallow depression in it under the surface near shore but doesn't appear to be growing in size.

A nearby storm pond has a shallow depression in it under the surface near shore but doesn't appear to be growing in size.

The rainwater collected in this pond percolates through the sandy soil much faster than other nearby ponds. I have observed a lot of air bubbles rising out in this depression as well as the nearby sands.

Could this be a sinkhole and about to manifest itself? What is the explanation for the air rising from the pond depression? (July 2, 2015) Rich Phelps s

Reply:

Rich

You haven't indicated where you are located so we don't know if you are in a known sinkhole prone area or not. Until you have the area examined by a local expert or at least your building department,

Watch out: keep people away to avoid the risk of someone being injured or killed by falling into a hole.

Houston Texas sinkhole concern

I live in the Houston area zip 77036 and between two bayous (half a mile from each.) Although we have had flooded streets over the 50 year period since the house was built, our home has not flooded. The foundation was repaired about 20 or 30 years ago.

The past three or four years the walls, ceiling and doors show signs of another foundation problem which I cannot afford to fix. I'm concerned Because the area around the perimeter of the house where the prior foundation piles were place the cement and ground have sunken half a foot to a foot. The detached garage floor has salt deposits and is cracked. The patio, driveway and front sidewalk are covered with black mildew, more so than my neighbors.

The back yard is not level. The ground is "bumpy" and hard to walk on even though it is covered with St. Augustine grass.

I usually have a lot of ants in the yard and around my garden, but this year I haven't seen a single ant bed or even a single ant crawling ! Houston is going through a drought right now and although I want to water around my foundation base, I hesitate to because it may cause more sinkage. Are these signs of a possible sink hole on my property? (Aug 6, 2015) Anonymous

Reply:

Anon:

This sounds serious enough that you need an on-site inspection by an expert, to assess damage to the home, the cause and effects of settlement, the repair costs, and most importantly to obtain an idea of both the safety of the home (risk of collapse) and of the urgency of repair.

I would not arbitrarily water around a foundation before I knew for sure what was going on, as you may make matters worse.

You want help from a geotechnical engineer, or at the least, a foundation repair company who has experience and expertise with foundation damage repair in your immediate area.

Georgia Sinkhole concerns - rectangular depression

I live in Albany GA (Southwest GA) and while sink holes here are not unheard of, you would hear of one opening up in a 4-5 year time period. When I moved in my house in 2000 and there was a small rectangular depression of 4x6 feet in dimension and approx. 2 feet deep in one section.

After several years it never got larger and neighbors indicated the previous owner didn't have a small pool that they were aware of. Sometime in 2008 or 09, we placed decorative stone around the depression and filled it in with dirt and made a flower bed.

Now, the depression has gotten bigger and deeper the stones are beginning to lean inward. Before I enlarge the flower bed, should I be concerned of a sinkhole or is this something different? (Aug 9, 2015) Joe in SOWEGA

Reply:

Joe

In my opinion it would be odd for a true sinkhole to show up as a regular, rectangular shape. More likely you're looking at a collapsing septic tank or similar structure.

Watch out: Since someone falling into such an opening could die, it still makes sense to keep people away until you've had an excavator explore and if necessary open and then fill the hole.

See SEPTIC & CESSPOOL SAFETY

Joe in SOWEGA said:
Thank you for your answer .... I agree with your assessment that it would be odd for a sinkhole to show up in rectangular shape.

I don't really thing it is a sink hole, however, if it was a depression from buried debris from 20-30 years ago it most likely wouldn't show up rectangular either. My house was built on virgin ground in the middle of pine woods and is nowhere near a septic tank.

Though I prefer not to excavate the area since this has taken several get this big, I wonder if filling with layers of dirt packing it along the way would be a suitable solution.

Moderator reply:

Right. Rectangular depressions are often septic tanks, cisterns, old foundations, and on occasion buried appliances.

Certainly you can add fill; the risk is that adding fill over a rusting, collapsing cover over "something" creates a dangerous condition - more weight and then when someone walks over the area, a collapse, injury, or worse. So if you only want to add fill, I'd also keep people from walking on the area.

Believe me this is not just theory. Through my own brilliance I caused an old abandoned drywell to collapse years ago.

See Sinkholes in GEORGIA for details.

Can earthquake like tremors be an early sign of impending sinkhole?

Can earthquake like tremors be an early sign of impending sinkhole? (Jan 6, 2016) Kelly

Reply:

Yes, see Sinkholes in GEORGIA for details of tectonic plate movement and stretch zones that can include sinkhole formation.

Also see SINKHOLE DETECTION, WARNING SIGNS

What's a warning sign for sinkholes

What is a warning sign for sinkholes? (Mar 10, 2016) athi

Reply:

SINKHOLE DETECTION, WARNING SIGNS gives twenty sinkhole warning signs.

Is this a two and one half foot sinkhole spewing water?

We think we may possibly have a sink hole in our back yard. The hole , as of now, 2' deep, 212' long, and 20-24" wide.

We live in the middle of town, and have owned the property since 1981. We have noticed, what seems to be, water, and, or air spewing. Can you shed any light on this situation, please.

The hole is not 212' long, it is 2. And. 1/2 ' long. (Apr 4, 2016) Judy

Reply:

Well that got much smaller - whew! Still I can only guess what forms a 2.5" diameter 24" deep hole; if it's not straight I'd suspect an animal at work but when you ad water spewing there is most likely a leak in a water main.

Watch out: keep people away, LEAVE IT ALONE and call your plumber and water department. If you mess around the spew may turn into a geyser or someone could fall into a dangerous hole.

...

Continue reading at SINKHOLES & SUBSIDENCES - topic home, or select a topic from the closely-related articles below, or see the complete ARTICLE INDEX.

Or see these

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• SINKHOLES & SUBSIDENCES - home
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  • SINKHOLE DETECTION, WARNING SIGNS
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• SINKING BUILDINGS

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Questions & answers or comments about sinkholes and their effects on buildings.