Sinkhole & subsidence warning signs:

This article describes the visual signs that a sinkhole is likely or is already developing in an area: sinkhole warning signs.

We discuss: how we inspect a property for signs of sink holes, subsidences, collapses. Types of sink holes, signs of sink holes. Causes of sinkholes. Sink hole damage and risks. When to hire a geotechnical engineer for sinkhole or soil testing

We also discuss what sinkholes are and why they 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.

Guide to Detecting & Diagnosing Sinkholes and Sudden Soil Subsidence or Yard Collapse at Properties

- Daniel Friedman - Florida Suncoast ASHI Educational Seminar - 1 May 2004, updated 2007, 2008, 2014

Portions of this text are extracted, quoted, or paraphrased from references provided; a key resource author was Sarah Cervone at Reference-1.

The bare minimum that a property owner needs to know about sinkholes or any other sudden subsidence of soils at a property is that these conditions might be very dangerous.

Someone falling into a sink hole or into a collapsing septic tank could be seriously injured or even die.

If a suspicious hole, subsidence, or depression appears at a property the owner should rope off and prevent access to the area to prevent anyone from falling into the opening, and then should seek prompt assistance from a qualified expert, geotechnical engineer, septic contractor, excavator, or the like.

How big are sinkholes?

Most sinkholes are 10 to 12 feet in diameter.

A discussion of foundation repair methods such as driven piers, helical piers, or other structural repair methods may seem in order, but if a sink hole is big enough to swallow a home, the first order of business for areas where those problem soils are found (California sinkholes, Florida sinkholes, Pennsylvania sinkholes over mines, Texas sinkholes, often over salt domes and possibly affected by wastewater disposal back into the ground during oil drilling, others) is to recognize the signs that sinkholes have plagued a neighborhood and/or that a sinkhole is possible, probable, or an imminent risk.

Synonyms and similar terms for sink holes include: shake hole, swallow hole, swallet, doline, cenote, moulin, and glacier mill.

Significant to property inspectors, the first signs that a sinkhole was developing in Dasietta Texas was the opening up of cracks in the ground and in the roadway on the morning of the collapse.

Because a sinkhole can develop suddenly and expand rapidly, the sudden appearance of cracks in the earth should be taken as a serious safety hazard at any location, more so in an area where sinkholes are known to occur.

What about cases where a sinkhole collapse may be ongoing or imminent? Recognizing indicators of potential sinkholes can reduce but not eliminate this risk.

This limitation should be stated clearly by any home inspector in an area where sinkholes are known to occur or wherever one is suspected.

If a sinkhole is already visible near an inspected property or if signs of a sinkhole are observed this information should be cited by the inspector as a potential safety concern and significant expense requiring immediate professional action.

Is it a sinkhole or some other kind of soil collapse? Does a soil collapse threaten nearby buildings? Is a soil collapse dangerous?

Examples of other possible buried components that can lead to sudden or gradual soil subsidence, apparent sink holes, and collapses are given below. These, too, can be very dangerous, as we describe in the case of collapsing cesspools or even buried trees and stumps.

But their probable impact on nearby structures may be less than from a classic sinkhole provided the collapse is not already close - within 50 feet - of a building.

Watch Out : excavation or soil subsidence near a building can lead to a dangerous foundation collapse. Here are some other collapsing ground hazards:

• Collapsing cesspools - very dangerous - see CESSPOOL SAFETY WARNINGS
• Dug wells with unsafe covers - very dangerous
• Collapses and soil subsidence over buried trees and stumps - potentially very dangerous, especially to children and pets
• Yard collapses over abandoned drywells, cesspools, septic tanks - very dangerous -
  
  See SEPTIC & CESSPOOL SAFETY.
• Buried swimming pools, vehicles, even old garbage dumps that were later built-over (such as in Hyde Park, New York)
• Abandoned, buried building foundations not completely demolished and filled-in
• Cracks, gaps, ravines opened by earthquakes
• Risk of mudslides and collapsed homes in steep slope un-stable areas such as some areas in California

Note on cesspool collapse hazard - question about sudden back yard cave in

Earlier this evening, after a day of rainfall, our backyard caved in.

Currently there is a hole in the ground about 12x10ft and 6-7 feet in depth.

After the initial collapse, there was some growth in the diameter but that appears to have stabilized. The closest edge is about 6-7 feet away from the actual house.

[Photo at left shows the New York "sinkhole".]

See Sinkholes in New York for details of this case and our advice on what to do about this sudden yard collapse in New York.

Watch out:  Immediately rope off the area of any soil subsidence or suspected old septic tank or cesspool area, and mark it plainly as unsafe so that a wandering neighbor, adult or child, does not go near nor fall into this hole.

It could be quite dangerous.

See CESSPOOL SAFETY WARNINGS for examples of potentially fatal cesspool collapse hazards.

Real Sinkhole Detection and Warning Signs

Visual Indicators of Extra Risk of Sinkhole Formation

Although a sinkhole can form without warning, specific signs can signal potential development: [7]

Site and Neighborhood Observations - ordered from general-area to site-specific to property-specific

• Indications on maps of the locations of likely sinkholes.[8]
• Areas known to be of thin supporting layers of sand and clay soil (look at any local excavation projects) (
  
  Sinkholes develop more frequently north of Tampa Bay where the limestone base is closest to the land surface and the supporting sand and clay layers are thin. [9] )
• Areas known to be soil over salt domes 
  
  See TEXAS SINKHOLES for an example.
• An actual sinkhole is present on or near the subject property (duh!)
• Slumping or falling fenceposts, trees, foundations on or near the property
• Previously-buried fenceposts, foundations, trees, become exposed [because of sinking ground]
• Small rills, gullies, or bare soil areas develop [soil particles being carried away to sinkhole]
• Cracked earth, a circular pattern of ground cracks outlining the sinking area. Sudden earth cracking should be taken as a very serious sinkhole or earth collapse risk.
  
  See TEXAS SINKHOLES or an example.
• Undercut stream banks and fallen trees along a drainage way
• Sudden formation of small ponds [of rainfall forming where water has not collected before]
• Wilting vegetation [small circular areas, because moisture that normally supports the vegetation is draining into a developing sinkhole - wilting is not always a sinkhole indicator]
• Circular or oval depressions in cultivated fields that may or may not pond standing water after rain events
• Areas of cultivated fields which are not being plowed
• Areas of oil drilling or underground mining which remove large volumes of liquids or solids from the earth
• Areas of oil drilling where wastewater produced by drilling is pumped back into the ground may cause dissolution of salt domes and lead to local sinkhole collapses
  
  See TEXAS SINKHOLES for a possible example.
• Gradual, localized ground settlement [does not always indicate a sinkhole]
• Sudden ground openings
• Sudden ground settlement
• Interrupted electrical or plumbing service to a building or neighborhood due to undermined, settled buried mechanical lines.
• Broken water mains or sewer mains can lead to street, sidewalk, and property sinkholes and sudden, very dangerous subsidences

Visual Indicators of Extra Risk of Sinkhole Formation (continued)

Building and Water Supply Observations

• Silt buildup, fresh mud deposits, muddy water [in wells? in a pond or stream?] Muddy or cloudy well water from nearby wells can indicate an early stage of sinkhole development.
• Structural cracks in walls, floors [10]
• Doors or windows that don't close properly [traced to building foundation movement]
• Records of sewer or water main breaks

Temporal Sinkhole Triggers

• Following a period of heavy or prolonged rain (washing-in supporting soils)
• Following a period of drought (lowering the water tables, leaving cavities)
• Following a period of housing development (adding pressure on supporting soils)
• Over pumping existing water supply wells, or drilling of additional wells in an area (lowering the aquifer)
• Diverting surface water from a large area and concentrating it in a single point
• Artificially creating ponds of surface water

Engineering Methods for Detecting Sinkholes

• Soil borings or other direct testing - Borings can be reduced by reconnaissance scannings using the following methods:
• Electromagnetics (EM) and DC Resistivity: detect variations in subsurface electrical properties related to anomalously thick or wet soils (electrical conductivity highs similar to our use of moisture meters in homes), or voids in the electrically conductive clay soil mantle (electrical conductivity lows)
• Spontaneous Potential (SP): detects naturally-occurring minute electrical currents or potentials commonly associated with concentrated vertical water infiltration (Streaming potentials)
• Micro-gravity: detects minute variation in gravity (subsurface voids create missing mass and lower gravity)
• Seismic Refraction: profiles the top-of-rock which may display conical depressions of a type associated with subsidence sinks or deep gouges or cutters which represent sinkhole-prone lineaments.
• Ground-penetrating radar [12]

What to do if a Sinkhole is observed or suspected at a property during a home inspection

This constitutes an immediate potential safety concern. ASHI Standards require you make appropriate notifications.

• Notify all parties: occupants, owners, real estate agents, buyers
• Notify the local Water Management District
• Fence or rope the hole off or arrange for this action to be taken immediately
• Keep children away!
• Protect the area from garbage and waste
• The property owner should be advised to contact their homeowners insurance company
• You may inform the parties that there are engineering firms specializing in detection and evaluation of potential or evident sinkholes
• Record in your report the notifications and actions you took

Sinkhole Warning - How Much Time Do You Have ?

A rapid sinkhole caused by well drilling or other sudden alterations to the terrain may not give any warning signs. Otherwise, the collapse process usually occurs gradually enough that a person may leave the affected area safely.

The final breakthrough leading to a sudden sink hole collapse can develop over a period of a few minutes to a few hours. [13] or select a topic from the closely-related articles below, or see the complete ARTICLE INDEX.

See "Developing your X-Ray Vision - A Promotion Theory for Forensic Observation of Residential Construction - Levels of Fear, and how to use them to find and report significant, hidden problems, https://InspectAPedia.com/home_inspection/Building_Inspection_Techniques.php

Also see The Nature of Vision - Inspecting Complex Systems - When and Why Inspectors "See" or "Don't See" Things Which are Present - InspectApedia.com/vision/Visual_Perception_Errors.php. Comments and content suggestions are invited.

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Reader Q&A - also see RECOMMENDED ARTICLES & FAQs

On 2018-10-21 by Jeannie Nobbley

I think there is a sinkhole

IMAGE LOST by older version of Comments code - now fixed. Please re-post the image if you can. Sorry. Mod.

On 2018-09-15 by (mod) -

X-ray, no.

Ground scanning radar is possible but probably not cost Justified.

If you know there was a water main break close to or under your building that's pretty compelling evidence.

On 2018-09-13 by Stan Watson

How do you determine if a sink hole was created under a garage from a main water break? Evidence of brick failure and outer wall movement appearing at garage. Windows jammed and noticeable movement. Can one X-ray scan the garage floor?

On 2018-09-11 by (mod) -

Possibly.

Certainly I would think that was such a notable event your local building and safety authorities would know about the boom that you described and would have investigated it. Have you asked?

On 2018-09-10 by P Delo

I live in a sinkhole prone area in PA where there is a lot of limestone. We've recently experienced a lot of "booms", some to the point that it has shaken the house. We know other houses in a mile radius also felt it shake their homes. Could this be an indicator of a developing sinkhole?

On 2018-07-01 by (mod) -

We discuss this where you posted the same question on another page. Water can bring frogs and if coming from a burst water line or sewer line could cause a local Southern subsides and a yard or Street. Loosely speaking people refer to those as sinkholes although they're not geologically based.

On 2018-06-30 by Heidi Rection

Would seeing toads in the area that have never been around before be a warning sign?

On 2018-06-30 by Jesse Jackie Late

Hi, I live in a suburb of Minneapolis called Eden Prairie. Lately, we have had rain and flood warnings (in close by areas).I saw two toad lately and we have never had toads before. one of them was really tiny. Could this be a sign of a sibkhole?

On 2018-03-15 by (mod) - electrical resistivity measurements for sinkhole detection

William

A geotechnical engineer consults maps of the local soil and underground features and then might use soil boring to take samples in an area under study.

Aside from local borings, Ground Penetrating Radar or GPR is the most-common method for screening an area for sinkhole formations.

Other experts have used electrical resistivity measurements.

See

• Chalikakis, Konstantinos, Valérie Plagnes, Roger Guerin, Rémi Valois, and Frank P. Bosch. "Contribution of geophysical methods to karst-system exploration: an overview." Hydrogeology Journal 19, no. 6 (2011): 1169.
• Kim, Gisung, Younggoo Han, and Sehun Kim. "A cooperative-sinkhole detection method for mobile ad hoc networks." AEU-International Journal of Electronics and Communications 64, no. 5 (2010): 390-397.
• Kim, Kisung, and Sehun Kim. A sinkhole detection method based on incremental learning in wireless ad HOC networks [PDF] The Korean Operations Research and Management Science Society (2007): 1-6. that offers a publicly available PDF - retrieved de novo 2023/07/16, original source: koasas.kaist.ac.kr/bitstream/10203/18729/1/A Sinkhole Detection Method based on Incremental Learning in Wireless Ad Hoc Networks.pdf
  
• Shim, Woochul, Gisung Kim, and Sehun Kim. "A distributed sinkhole detection method using cluster analysis." Expert Systems with Applications 37, no. 12 (2010): 8486-8491.
• Van Schoor, Michael. "Detection of sinkholes using 2D electrical resistivity imaging." Journal of Applied Geophysics 50, no. 4 (2002): 393-399.
• Zisman, E. D. "A standard method for sinkhole detection in the Tampa, Florida, area." Environmental & Engineering Geoscience 7, no. 1 (2001): 31-50.
  
  

On 2018-03-15 by William Gilbert

What is the best tool for sink hole detection under a house?

On 2017-10-08 by (mod) -

Quianna

Start by taking note of the country, state, province, or city where you live, then search for sinkhole information for that specific area. If you live in an area prone to sinkholes then you may indeed want to hire a geotechnical engineer to consult about your site and home.

If you are not in a natural sinkhole areas then sinkholes can still occur due to underground leaks, subsidence over buried trash, etc. and you still need assistance. But the diagnosis and cure recommended by a local mason experienced in foundation repair may be sufficient. The contractor, in turn, should help you decide if engineering help is needed. We can't make that assessment by a text query.

See SINKHOLES - IMMEDIATE SAFETY ACTIONS

Editor

On 2017-10-08 by Qianna Aragon

Ive lived here for about 11 years and just in the last 4-5 months ive noticed the cement walkway sort of lifting at certain seams then in a couple days id see it now downward at the seams

And i notice this because im a smoker and ive told my boyfriend enough for him to tell me stop im sounding weird then i mentioned it to our landlord ((Wife)) the 3rd time i told her i actually got her to come back and look she agreed but forgot to mention it to her husband((he would have been on it))

Anyways im really scared after reading just 2 articles ofrom google and seeing all the signs...
Im almost certain thats what we have..Come to think of it our neighbors recently took their pool out because it got a crack underground...hmm

How do i go about this if im not theowner of the home
I cant sleep at night..

...

Continue reading at SINKHOLES - IMMEDIATE SAFETY ACTIONS or select a topic from the closely-related articles below, or see the complete ARTICLE INDEX.

Or see SINKHOLE DETECTION FAQs - questions & answers posted originally on this page

Or see these

Sinkhole & Subsidence Articles

• SEPTIC & CESSPOOL SAFETY
• SINKHOLES & SUBSIDENCES - home
  • DEFINITION of SINKHOLES
  • GHOST LAKES & SINKHOLES
  • SINKHOLE DAMAGE REPAIRS
  • SINKHOLE DETECTION, WARNING SIGNS
  • SINKHOLES - IMMEDIATE SAFETY ACTIONS
  • SINKHOLES COURSE - X-Ray Vision?
  • SINKHOLES on KARST FORMATIONS
  • SINKHOLES on LEDA CLAY FORMATIONS
  • SINKHOLE RESEARCH & REFERENCES
• SINKING BUILDINGS

Suggested citation for this web page

SINKHOLE DETECTION, WARNING SIGNS at InspectApedia.com - online encyclopedia of building & environmental inspection, testing, diagnosis, repair, & problem prevention advice.

Or see this

INDEX to RELATED ARTICLES: ARTICLE INDEX to SINKHOLES

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