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Karst formation sinkholes in Florida.
This document defines karst and explains what karst 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.
The presence of karst formations help predict 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.
What is Karst? What is the Role of Karst in Florida or other Sink Hole Formation?
In Florida, the underlying basis of sinkholes is the presence of porous limestone layer below (often thin) topsoil. Karst is any land with sinkholes,
springs, and streams that sink into subsurface caverns.
When to hire a geotechnical engineer for sinkhole or soil testing
What is a Sinkhole?
A sinkhole is
created surface materials collapse or are dissolved into an underground cavern or stream. 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 (sediments or
organic matter that rest on the limestone bedrock). 
The term sinkhole is applied by engineers to the following geological features
Bedrock voids (most difficult to detect, but least likely of imminent collapse)
Depressions in the top-of-bedrock
Sloping voids in the soil column
Zones of wet, soupy soils (mud filled voids in the soil column)
Clay seams (mud filled voids in bedrock)
Actual surface collapse features
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.
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.
Source: USGS - [Excerpting from References 1 and 2]
Characteristics of Sinkholes:
originate beneath the surface
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
the water table drops
the limestone cavity is exposed to erosion
the cavity collapses
causing a sinkhole to develop, possibly suddenly
Four types of sinkholes, all beginning with a solution cavity 
Solution sinkholes - surface depressions, not complete collapse
Cover-subsidence sinkholes - loose, overlying sand slides into solution cavity
Collapse sinkholes - roof of an underground channel suddenly collapses, forming a steep-sided cavity
Cover-collapse sinkholes - thick layer of sand over clay over limestone. Limestone dissolves, clay keeps
the sand from collapsing-in, then suddenly fails, leading to sudden and very
violent collapse: the most dangerous. An example of collapse sinkholes is the collapse of underground mines which can lead to a fracture and collapse of the ground surface above.
Three general types occur in Florida: collapse, solution, and subsidence 
most common type of sinkhole in Florida
Where the overburden is thick soil and heavy clay
Deep, steeply-sided holes
Frequently triggered by fluctuations in the water-table. As water levels fluctuate, the
roof of the cavity is stressed and weakened.
When the water-table drops too far, the cavity walls are unsupported and the ceiling becomes too weak to hold
the heavy overburden. Eventually, the ceiling collapses and a sinkhole is
formed. If the water-table rises, the collapse sinkhole can fill with water, and overflow like a spring.
An off-set sinkhole will have an upstream and downstream conduit as water flows into the sink and siphons underground. If the water-table
drops below the sinkhole, it will remain dry and accumulate sediments and vegetation.
overburden is thin or absent
Forms slowly and continuously
Surface of the limestone bedrock is broken down by erosion from wind and surface water
Bowl-shaped depression, or solution sinkhole
Chemical and physical processes erode the rock
overburden is thin at subsidence sinkholes
subsidence sinkholes form slowly
at subsidence sinkholes dissolving limestone is replaced by sand granules that fall into the depression and fill the holes
subsidence sinkholes form a concave depression
subsidence sinkholes may be only a few feet in diameter and depth
(the development of the cavities in the limestone is retarded since they are filled with clay and sand)
As the sediments fill the depression, they restrict the flow of water through the bottom and the hole
begins to retain water.
as water accumulates, a lake is formed
Sinkholes and Lake Formation
A circular lake indicates that the lake evolved from a collapse sinkhole. A
shallow circular lake results from impermeable sediments washing into a
subsidence sinkhole. If a lake rests above groundwater level, it is above a
Sinkholes and Urban Development
Sinkhole formation is aggravated and accelerated by urbanization. Development
increases water usage, alters drainage pathways, overloads the ground surface,
and redistributes soil. According to the Federal Emergency Management Agency,
the number of human-induced sinkholes have doubled since 1930, insurance claims
for damages as a result of sinkholes has increased 1200% from 1987 to 1991,
costing nearly $100 million.
To avoid the destruction of
property and the contamination of groundwater, it is important to monitor
potential sinkhole formation.
Were some sinkholes made from the glaciers? Especially in Florida?
Were some sinkholes made from the glaciers? Especially in Florida? - J.K., Florida
Rely: Probably not
We have not found a direct association between glaciers and sinkholes, especially in Florida, though in other geographic zones one can state a potential relationship between groundwater movement, rivers, and sinkholes.
So a short answer is that while one could make a speculative argument that water flowing through and removing fines of glacial till in alluvial valleys could play a part in certain sinkhole formations, a predominance of karst-based sinkholes argues against a role of glaciers in sinkholes, at least in north central Florida.
A more detailed look at the relationship between glaciers and sink holes:
Different types of sinkholes: first let's recap how sinkholes form. A contemporary or active sinkhole is formed typically in karst systems as groundwater dissolves minerals creating openings that then subside or collapse.
Cech comments on glaciated terrain and the role of glaciers in deposited sedimentary layers of glacial material and in some cases material that contained groundwater. Paraphrasing:
During glacial activity, (the most recent deglaciation began 15,000 years ago) underlying terrain was scraped, carved, cut as the glacier ice sheet base pushed ice and rocks along , depositing ice and rocks as the ice retreated. This material is glacial till, [Cech p. 112] comprised of boulders, gravel, sand, and silt. During melting some of these smaller particles were further moved by the glacial outwash.
Cech, also himself referring to Charles Lyell [1797-1875] notes that there is a relationship between the valleys or glacial till-filled valleys (in some cases hundreds of feet thick) and later groundwater movement. As he puts it
Rivers that flow through an alluvial valley are often hydraulically linked to groundwater. This physical connection creates opportunities for surface water in a river to recharge groundwater or for groundwater to replenish flows in a river as baseflow. The direction of water movement between groundwater and surface water is dependent on gradients, climactic conditions, and water volume ... - Thomas V. Cech 
So there is a potential relation between rivers and groundwater in some locales that may be traced back to glacial activity.
But to move from there to a closer tie between an active sinkhole and the glaciers seems to me a bit more difficult. If we exclude sinkholes associated with collapses due to mining or similar subsidences, and focus first on the most common sinkhole formation: karst topography plus water, the mechanism that results in a sinkhole is the dissolution of limestone below ground.
Cech and others explain that low pH rainwater entering the groundwater system dissolves (reacts with) the carbonate limestone, opening conduits through the aquifer. When enough limestone has been removed the surface collapses. Thus the two most common sinkholes (especially in north central Florida) are caused by either solution (tending to be slow in formation) or collapse sinkholes (tending to be sudden) through karst formations, not the sudden subsidence of a cavern left by glacial activity.
We'd expect sinkhole activity to increase when there is a period of less rain, leading to drops in water tables and the leaving of voids that may collapse, and we'd also expect sinkhole activity to increase when there is a period of prolonged heavy rainfall, causing rising water tables and causing further dissolution of the underlying limestone formations.
Sinkoles may also be increased due to local drilling of wells into the existing underground water cavities in the karst, or by pumping groundwater from nearby, or by diverting drainage to areas where karst cavities already exist.
More interesting sink hole types from Cech  p. 109] are
siphon sinkholes that occur in a riverbed when a sinkhole opens in the riverbed causing drainage of a portion of the river's volume
swallow sinkholes that happen when a sinkhole of sufficient size opens in a river bed and is able to capture all or most of the river water volume- the river "goes dry" suddenly
karst sinkholes open within a cave or conduit: water flowing in the conduit removes the overburden soils "... revealing a view into the aquifer. It is a combination of a spring and a sink in the same feature."
Conclusions about the Role of Glaciers in Florida Sinkhole Formations
From these descriptions one might infer that some sinkholes could occur in a valley that was previously filled by glacial till if river water or ground water are able to remove sufficient volume of fine soil particles, clay, or silt, even in an area where karst might not be present.
But in Florida where you'd have trouble finding an alluvial valley, sinkholes associated with karst formations are principally due to the chemistry of karst, plus rainwater, not glacial activity. Karst is limestone, formed in "beach ridges" for example near the border of northern Florida and southern Georgia "at elevations between 42 and 49 meters above mean sea level" - the product of sea life. Opdyke et als point out that
Marine fossils of Pleistocene age are known to occur in beach ridges near the border of northern Florida and southern Georgia at elevations of between 42 and 49 m above mean sea level. No evidence exists for a massive melt-off of glacial ice, which would be required to raise sea level to these elevations. Florida, therefore, must have been uplifted epeirogenically during the Pleistocene. Measurement of dissolved solids in
Florida's springs demonstrates that the karst area is losing a minimum of 1.2 x 106 m3/yr of limestone through spring flow, the equivalent of 1 m of surficial limestone every 38,000 yr. This loss has led to an isostatic uplift of the north-central part of the Florida peninsula of at least 36 m during Pleistocene and Holocene time, which agrees with observed elevations of marine terraces. - Opdyke et als 
Reader Question: Are sinkholes still active in Florida?
Are sinkholes an ongoing problem in Florida or just old history? - Anon 3/3/13
Reply: Sinkhole formation is an ongoning phenomenon in Florida and in many other areas of the world: 2013 Seffet Florida sinkhole fatality report
Anon, while an individual sinkhole may stabilize and stop "sinking", the formation of new, often terribly sudden sinkholes are a continuing event in many areas of the world. On February 28, 2013, a sudden sinkhole opening in Seffner, Florida resulted in a death and nearly the death of a second person. A sudden sinkhole formation caused the bedroom portion of a home to fall into the earth, burying Jeff Bush who was in the home at that time. Other occupants of the home escaped injury, but as the New York Times reported in early March of 2013, the home and areas around it were marked off by engineers out of concern that ther "fluid mass" of earth in the area might at any moment engulf the rest of the structure.
The Times reported experts on the scene describing the Seffner Florida sinkhole as a particularly dangerous formation that in its first 24-hours had increased in size to 20 feet deep and 30 feet wide and was still expanding.
"Sinkholes are so common in Florida that the state requires home insurers to provide coverage against the danger" the Times reorted, continuing to describe a 400-foot Florida sinkhole that developed in 1981 and noting that more than 500 sinkholes have been reported in Hillsboro County - the location of the Seffner Florida 2013 sinkhole catastrophe.. 
What we have not found (and continue to research) about the 2013 Seffert Florida sinkhole is whether or not there were early warning signs (SINKHOLE DETECTION, WARNING SIGNS) that might have saved Mr. Bush.
(Apr 23, 2012) A. Mazzara said:
Can my home be inspected for sink hole danger entirely from the outside, or must I give my house keys to the inspector? My goal is to add a sink hole rider on my homeowners policy/
The answer is yes, no, it depends.
If you live in an area where sinkhole dangers involve large collapses and are due to soil or geological conditions that are widespread, a geotechnical engineer can take soil borings to see what the conditions are near the home, will have information about nearby collapses, and can inspect the site for some of the obvious signs of sinkhole activity we describe in these articles, such as leaning fenceposts.
An outside inspection of the house itself, presuming you have an accessible basement or crawl space, would not permit a complete inspection of the foundation and basement slab where more localized signs of settlement or shifting soils might be detected.
So it also depends on your insurance company and their policies. If I were the insurer, I would not write a policy without first inspecting the building for signs of pre-existing movement. Such movement might show up as cracks or walls out of plumb, and might in fact have nothing to do with sinkhole activity. Both you and the insurer can benefit by avoiding a future argument about when cracks appeared and what caused them if the inspector has a thorough base-line inspection report from the start of the policy.
So I'd welcome the inspector indoors and in fact if s/he doesn't want to look inside I'd worry that the inspection was not very thorough.
Companies identify themselves as sinkhole damage repair experts in Floria are listed at SINKHOLE DAMAGE REPAIRS or select a topic from closely-related articles below, or see our complete INDEX to RELATED ARTICLES below.
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Diagnosing & Repairing House Structure Problems, Edgar O. Seaquist, McGraw Hill, 1980 ISBN 0-07-056013-7 (obsolete, incomplete, missing most diagnosis steps, but very good reading; out of print but used copies are available at Amazon.com, and reprints are available from some inspection tool suppliers). Ed Seaquist was among the first speakers invited to a series of educational conferences organized by D Friedman for ASHI, the American Society of Home Inspectors, where the topic of inspecting the in-service condition of building structures was first addressed.
Design of Wood Structures - ASD, Donald E. Breyer, Kenneth Fridley, Kelly Cob een, David Pollock, McGraw Hill, 2003, ISBN-10: 0071379320, ISBN-13: 978-0071379328 This book is an update of a long-established text dating from at least 1988 (DJF); Quoting: This book is gives a good grasp of seismic design for wood structures. Many of the examples especially near the end are good practice for the Californa PE Special Seismic Exam design questions. It gives a good grasp of how seismic forces move through a building and how to calculate those forces at various locations.THE CLASSIC TEXT ON WOOD DESIGN UPDATED TO INCLUDE THE LATEST CODES AND DATA. Reflects the most recent provisions of the 2003 International Building Code and 2001 National Design Specification for Wood Construction. Continuing the sterling standard set by earlier editions, this indispensable reference clearly explains the best wood design techniques for the safe handling of gravity and lateral loads. Carefully revised and updated to include the new 2003 International Building Code, ASCE 7-02 Minimum Design Loads for Buildings and Other Structures, the 2001 National Design Specification for Wood Construction, and the most recent Allowable Stress Design.
Defects and Deterioration in Buildings: A Practical Guide to the Science and Technology of Material Failure, Barry Richardson, Spon Press; 2d Ed (2001), ISBN-10: 041925210X, ISBN-13: 978-0419252108. Quoting: A professional reference designed to assist surveyors, engineers, architects and contractors in diagnosing existing problems and avoiding them in new buildings. Fully revised and updated, this edition, in new clearer format, covers developments in building defects, and problems such as sick building syndrome. Well liked for its mixture of theory and practice the new edition will complement Hinks and Cook's student textbook on defects at the practitioner level.
Straw Bale Home Design, U.S. Department of Energy provides information on strawbale home construction - original source at http://www.energysavers.gov/your_home/designing_remodeling/index.cfm/mytopic=10350
More Straw Bale Building: A Complete Guide to Designing and Building with Straw (Mother Earth News Wiser Living Series), Chris Magwood, Peter Mack, New Society Publishers (February 1, 2005), ISBN-10: 0865715181 ISBN-13: 978-0865715189 - Quoting: Straw bale houses are easy to build, affordable, super energy efficient, environmentally friendly, attractive, and can be designed to match the builder’s personal space needs, esthetics and budget. Despite mushrooming interest in the technique, however, most straw bale books focus on “selling” the dream of straw bale building, but don’t adequately address the most critical issues faced by bale house builders. Moreover, since many developments in this field are recent, few books are completely up to date with the latest techniques. More Straw Bale Building is designed to fill this gap. A completely rewritten edition of the 20,000-copy best--selling original, it leads the potential builder through the entire process of building a bale structure, tackling all the practical issues: finding and choosing bales; developing sound building plans; roofing; electrical, plumbing, and heating systems; building code compliance; and special concerns for builders in northern climates.
Sinkholes and Sudden Land Subsidence References, Products, Consultants
"A Hole in the Ground Erupts, to Estonia's Delight", New York Times, 9 December 2008 p. 10.
History of water usage in Estonia: (5.7 MB PDF) jaagupi.parnu.ee/freshwater/doc/the_history_of_water_usage_systems_in_estonia.pdf
"Quebec Family Dies as Home Vanishes Into Crater, in Reminder of Hidden Menace", Ian Austen, New York Times, 13 May 2010 p. A8. See http://www.nytimes.com/
"Quick Clay", Wikipedia search 5/13/2010 - http://en.wikipedia.org/wiki/Quick_clay
Florida DEP - Department of Environmental Protection, & Florida Geological survey (http://www.dep.state.fl.us/geology/default.htm) on Florida sinkholes: Effects of Sinkholes on Water Conditions Hernando County, Florida, Brett Buff, GIS in Water Resources, 2008, Dr. David R. Maidment, Photos - Tom Scott, Florida Geographic Survey - Web Search 06/09/2010 - http://www.dep.state.fl.us/geology/geologictopics/jacksonsink.htm
and - http://www.dep.state.fl.us/geology/geologictopics/sinkhole.htm
Lane, Ed, 1986, Karst in Florida: Florida Geological Survey Special Publication 29, 100 p.
Foundation Engineering Problems and Hazards in Karst Terranes, James P. Reger, Maryland Geological Survey, web search 06/05/2010, original source: http://www.mgs.md.gov/esic/fs/fs11.html Maryland Geological Survey, 2300 St. Paul Street, Baltimore, MD 21218
"Frost Heaving Forces in Leda Clay", Penner, E., Division of Building Research, National Research Council of Canada, Canadian Geotechnical Journal, NRC Research Press, 1970-2, Vol 7, No 1, PP 8-16, National Research Council of Canada, Accession number 1970-023601, Quoting from original source
The frost heaving forces developed under a 1 ft. (30.5 cm) diameter steel plate were measured in the field throughout one winter. The steel plate was fixed at the ground surface with a rock-anchored reaction frame. heave gauges and thermocouples were installed at various depths to determine the position and temperature of the active heaving zone. The general trend was for the surface force to increase as the winter progressed. when the frost line approached the maximum depth the force was in excess of 30,000 lb (13,608 KG). Estimates of the heaving pressure at the frost line ranged from 7 to 12 psi (0.49 to 0.84 KG/cm) square during this period. The variation of surface heaving force was closely associated with weather conditions. Warming trends resulting in a temperature increase of the frozen layer caused the forces to decline.
Leda clay slopes in the Ottawa valley are vulnerable to catastrophic landslides. More than 250 landslides, historical and ancient, large and small, have been identified within 60 km of Ottawa. Some of these landslides caused deaths, injuries, and property damage, and their impact extended far beyond the site of the original failure. In spectacular flowslides, the sediment underlying large areas of flat land adjacent to unstable slopes liquefies. The debris may flow up to several kilometres, damming rivers and causing flooding, siltation, and water-quality problems or damaging infrastructure. Geologists and geotechnical engineers can identify potential landslide areas, and appropriate land-use zoning and protective engineering works can reduce the risk to property and people.
Deposits of Leda clay, a potentially unstable material, underlie extensive areas of the Ottawa-Gatineau region. Leda clay is composed of clay- and silt-sized particles of bedrock that were finely ground by glaciers and washed into the Champlain Sea. As the particles settled through the salty water, they were attracted to one another and formed loose clusters that fell to the seafloor. The resulting sediment had a loose but strong framework that was capable of retaining a large amount of water. Following the retreat of the sea, the salts that originally contributed to the bonding of the particles were slowly removed (leached) by fresh water filtering through the ground. If sufficiently disturbed, the leached Leda clay, a weak but water-rich sediment, may liquefy and become a 'quick clay'. Trigger disturbances include river erosion, increases in pore-water pressure (especially during periods of high rainfall or rapid snowmelt), earthquakes, and human activities such as excavation
After an initial failure removes the stiffer, weathered crust, the sensitive clay liquefies and collapses, flowing away from the scar. Failures continue in a domino-like fashion, rapidly eating back into the flat land lying behind the failed slope. The flowing mud may raft intact pieces of the stiffer surface material for great distances.
Kochanov, W. E., 1999, Sinkholes in Pennsylvania: Pennsylvania
Geological Survey, 4th ser., Educational Series 11,
33 p., 3rd printing April 2005, Pennsylvania Department of Conservation and Natural Resources / Bureau of Topographic and Geologic Survey, DCNR Educational Series 11, Pennsylvania Geological Survey, Fourth Series, Harrisburg,
1999 - web search 06/05/2010, original source: http://www.dcnr.state.pa.us/topogeo/hazards/es11.pdf - Quoting from the document introduction: The first 18 pages of this booklet contain an explanation of how sinkholes
develop. In order to tell the sinkhole story, it is important to discuss
a number of related geologic disciplines. The words used to describe sinkholes
and these disciplines may be a bit unfamiliar. However, general explanations
are given throughout the booklet to help clarify their meanings.
Key words are printed in bold type for emphasis. The more important
ones are defined in a Glossary that begins on page 29.
The remaining sections, starting with “Sinkholes in the Urban Environment”
(page 18), deal with sinkholes and their impact on our environment.
This includes recognition of subsidence features and sinkhole repair.
Thanks to reader Y.Z., Whitestone, NY for discussing a back yard collapse 4/1/2010
 Sarah Cervone, [web page] data from the APIRS database, Graphics by Ann Murray, Sara Reinhart and Vic Ramey, Vic Ramey is
the editor. DEP review by Jeff Schardt and Judy Ludlow. The web page is a
collaboration of the Center for Aquatic and Invasive Plants, University of Florida, and the Bureau of Invasive
Plant Management, Florida Department of Environmental Protection contact: firstname.lastname@example.org [A primary resource for this article
 Center for Cave and Karst Studies or the
Center, both at
Vanity Fair - web search 06/04/2010 http://www.vanityfair.com/online/daily/2010/06/what-caused-the-guatemala-sinkhole-and-why-is-it-so-round.html
Sinkholes, [on file as /vision/Sinkholes_Virginia_DME.pdf ] - , Virginia Division of Mineral Resources,
Virginia Department of Mines, Minerals and Energy, www.dmme.virginia.gov Virginia Department of Mines, Minerals and Energy
Division of Mineral Resources
900 Natural Resources Drive, Suite 500
Charlottesville, VA 22903
Sales Office: (434) 951-6341 FAX : (434) 951-6365
Geologic Information: (434) 951-6342
divisionmineralresources.shtml - Web search 06/09/2010
Wikipedia - web search 06/04/2010 - http://en.wikipedia.org/wiki/Guatemala_City
Sink Hole & Related Engineering References
Newton, J. G., 1987, Development of sinkholes resulting from man's activities in the eastern United States: US Geological Survey Circular 968, 54 p.
Sinclair, W. C., 1982, Sinkhole development resulting from ground-water withdrawal in the Tampa Area, Florida: U.S. Geological Survey Water-Resources Investigations 81-50, 19 p.
White, W. B., 1988, Geomorphology and Hydrology of Karst Terrains: Oxford University Press, New York, 464 p.
Williams, J. H. and Vineyard, J. D., 1976, Geologic indicators of subsidence and collapse in karst terrain in Missouri: Presentation at the 55th Annual Meeting, Transportation Research Board, Washington, D.C.
Barry F. Beck, A. J. (1999). Hydrogeology and Engineering Geology of Sinkholes and Karst. Rotterdam, Netherlands: A. A. Balkema.
Beck, B. F. (2003). Sinkholes and the Engineering and Environmental Impacts of Karst. Huntsville, Alabama: The American Society of Civil Engineers.
Beck, B. F. (2005). Sinkholes and the Engineering and Envrionmental Impacts of Karst. San Antonio, Texas: The American Society of Civil Engineers.
Tony Waltham, F. B. (2005). Sinkholes and Subsidence, Karst and Cavernous Rocks in Engineering and Construction. Chichester, United Kingdom: Praxis Publishing.
Whitman D., G. T. (1999). Spatial Interrelationships Between Lake Elevations, Water Tables, and Sinkhole Occurence in Central Florida: A GIS Approach. Photogrammetric Engineering and Remote Sensing , 1169-1178.
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