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 Definition of Karst & Relation of Karst Formations to Sinkhole Collapses
Florida Sinkholes
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InspectAPedia tolerates no conflicts of interest. We have no relationship with advertisers, products, or services discussed at this website.
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.
Green links show where you are. © Copyright 2013 InspectAPedia.com, All Rights Reserved. Author Daniel Friedman.
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.
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
- 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.
See SINKHOLES - IMMEDIATE SAFETY ACTIONS, also see FOUNDATION CRACKS & DAMAGE GUIDE and CESSPOOL SAFETY WARNINGS. Additional septic system safety warnings are at SEPTIC & CESSPOOL SAFETY.
Sinkholes and the Aquifer
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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
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Source: USGS |
Collapse sinkholes
- most common type of sinkhole in Florida
- Happen suddenly
- 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.
Solution Sinkholes
- 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
Subsidence sinkholes
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Source: USGS |
- 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
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Source: USGS |
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
confining bed.
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.
Frequently Asked Questions (FAQs) about Karst Sinkholes
Question:
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[1] 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 [1]
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 [1] 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 [2]
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.. [3]
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.
...
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Technical Reviewers & References
Related Topics, found near the top of this page suggest articles closely related to this one.
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[1] Thomas V. Cech, Principles of water resources: history, development, management, and policy, John Wiley and Sons 2009 ISBN0470136316, 9780470136317
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[2] Opdyke et als, "Origin of the epeirogenic uplift of Pliocene-Pleistocene beach ridges in Florida and development of the Florida karst", N. D. Opdyke1, D. P. Spangler 1, D. L. Smith 1, D. S. Jones 1 and R. C. Lindquist 1, Geology; April 1984; v. 12; no. 4; p. 226-228; DOI: 10.1130/0091-7613(1984)12<226:OOTEUO>2.0.CO;2
© 1984 Geological Society of America
1 Department of Geology, University of Florida, Gainesville, Florida 32611
- [3] "Growth of Sinkhole That Devloured Florida Man Threatens More Destruction", The New York Times, 3 March 2013, p. 27.
- 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
- Thanks to reader Y.Z., Whitestone, NY for discussing a back yard collapse 4/1/2010
- Synonyms and similar terms for sink holes include: shake hole, swallow hole, swallet, doline, cenote, moulin, and glacier mill.
Books & Articles on Building & Environmental Inspection, Testing, Diagnosis, & Repair
 The Home Reference Book - the Encyclopedia of Homes, Carson Dunlop & Associates, Toronto, Ontario, 25th Ed., 2012, is a bound volume of more than 450 illustrated pages that assist home inspectors and home owners in the inspection and detection of problems on buildings. The text is intended as a reference guide to help building owners operate and maintain their home effectively. Field inspection worksheets are included at the back of the volume. Special Offer: For a 10% discount on any number of copies of the Home Reference Book purchased as a single order. Enter INSPECTAHRB in the order payment page "Promo/Redemption" space. InspectAPedia.com editor Daniel Friedman is a contributing author.
Or choose the The Home Reference eBook for PCs, Macs, Kindle, iPad, iPhone, or Android Smart Phones. Special Offer: For a 5% discount on any number of copies of the Home Reference eBook purchased as a single order. Enter INSPECTAEHRB in the order payment page "Promo/Redemption" space.
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- Best Practices Guide to Residential Construction, by Steven Bliss. John Wiley & Sons, 2006. ISBN-10: 0471648361, ISBN-13: 978-0471648369, Hardcover: 320 pages, available from Amazon.com and also Wiley.com. See our book review of this publication.
- Decks and Porches, the JLC Guide to, Best Practices for Outdoor Spaces, Steve Bliss (Editor), The Journal of Light Construction, Williston VT, 2010 ISBN 10: 1-928580-42-4, ISBN 13: 978-1-928580-42-3, available from Amazon.com
- The Journal of Light Construction has generously given reprint permission to InspectAPedia.com for certain articles found at this website. All rights and contents to those materials are ©Journal of Light Construction and may not be reproduced in any form.
- Appliances and Home Electronics, - energy savings, U.S. Department of Energy
- Avongard foundation crack progress chart for structural crack monitoring
- Basement Moisture Control, U.S. Department of Energy
- Building Pathology, Deterioration, Diagnostics, and Intervention, Samuel Y. Harris, P.E., AIA, Esq., ISBN 0-471-33172-4, John Wiley & Sons, 2001 [General building science-DF] ISBN-10: 0471331724
ISBN-13: 978-0471331728
- Building Pathology: Principles and Practice, David Watt, Wiley-Blackwell; 2 edition (March 7, 2008) ISBN-10: 1405161035 ISBN-13: 978-1405161039
- The Circular Staircase, Mary Roberts Rinehart
- Construction Drawings and Details, Rosemary Kilmer
- Crawl Space Moisture Control, U.S. Department of Energy
- 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.
- Building Failures, Diagnosis & Avoidance, 2d Ed., W.H. Ransom, E.& F. Spon, New York, 1987 ISBN 0-419-14270-3
- Domestic Building Surveys, Andrew R. Williams, Kindle book, Amazon.com
- 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.
- Guide to Domestic Building Surveys, Jack Bower, Butterworth Architecture, London, 1988, ISBN 0-408-50000 X
- "Avoiding Foundation Failures," Robert Marshall, Journal of Light Construction, July, 1996 (Highly recommend this article-DF)
- "A Foundation for Unstable Soils," Harris Hyman, P.E., Journal of Light Construction, May 1995
- "Backfilling Basics," Buck Bartley, Journal of Light Construction, October 1994
- "Inspecting Block Foundations," Donald V. Cohen, P.E., ASHI Reporter, December 1998. This article in turn cites the Fine Homebuilding article noted below.
- "When Block Foundations go Bad," Fine Homebuilding, June/July 1998
- Energy Recover Ventilation Systems for Buildings, U.S. Department of Energy
- Energy Savings Methods: Whole House Systems Approach, U.S. Department of Energy
- Historic Preservation Technology: A Primer, Robert A. Young, Wiley (March 21, 2008)
ISBN-10: 0471788368 ISBN-13: 978-0471788362
- Log Homes: Minimizing Air Leakage in Log Homes, U.S. Department of Energy
- Log Homes: Controlling Moisture in Log Homes, U.S. Department of Energy
- Log Homes: Log Home Design, U.S. Department of Energy
- Moisture Control in Buildings, U.S. Department of Energy
- Moisture Control in Walls, U.S. Department of Energy
- Quality Standards for the Professional Remodeling Industry, National Association of Home Builders Remodelers Council, NAHB Research Foundation, 1987.
- Quality Standards for the Professional Remodeler, N.U. Ahmed, # Home Builder Pr (February 1991), ISBN-10: 0867183594, ISBN-13: 978-0867183597
- Natural Ventilation for Buildings, U.S. Department of Energy
- R-Value of Wood, U.S. Department of Energy
- Spot Ventilation for houses, U.S. Department of Energy
- Slab on Grade Foundation Moisture and Air Leakage, U.S. Department of Energy
- 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.
- "Vapor Barriers or Vapor Diffusion Retarders", U.S. DOE: how vapor barriers work, types of vapor diffusion barriers, installing vapor barrier
- Ventilation for energy efficient buildings, Purpose, Strategies, etc.,
- Weather-Resistive Barriers, how to select and install housewrap and other types of weather resistive barriers, U.S. DOE
- Whole House Ventilation Systems, U.S. Department of Energy
- Whole-House Balanced Ventilation Systems, U.S. Department of Energy
- Whole-House Exhaust Ventilation Systems, U.S. Department of Energy
- Whole-House Supply Ventilation Systems, U.S. Department of Energy
- ...
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
also see
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.
- "Geoscape Ottowa-Gatineau Landslides", Canada Department of Natural Resources, original source http://geoscape.nrcan.gc.ca/ottawa/landslides_e.php - quoting from that source:
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
and construction.
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
- [1] 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: varamey@nersp.nerdc.ufl.edu [A primary resource for this article
- [2] Center for Cave and Karst Studies or the
Kentucky
Climate
Center, both at
Western
Kentucky
University
- 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
http://www.dmme.virginia.gov/
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.
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Detecting Sinkholes with Geophysics,
Enviroscan, Inc.,
Lancaster
PA 717-396-8922 email@enviroscan.com www.enviroscan.com 2003
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