What are sinkholes?
A farmer may view them as naturally forming holes that
occasionally open up in the fields. Some people see sinkholes
as sites for dumping trash.
In urban areas, the sudden appearance of a sinkhole is a
hazard that can disrupt utility services, hamper transportation,
and cause severe damage to nearby structures.
A sinkhole is a subsidence feature.
Subsidence is the downward movement of surface material;
it involves little or no horizontal movement. Subsidence occurs
naturally due to the physical and chemical weathering of certain
types of bedrock.
Subsidence can also occur as a result of ;
• Underground mining,
• Excessive pumping of groundwater or
• Subsurface erosion due to the failure of existing utility lines.
All of these examples of subsidence can produce surface
features that appear similar, but not all are naturally occurring.
Some are solely the result of human activities.
• Protect the planet
• 25% of earths water is from
• 10-15% of earth is classified
• Land usage planning
Source: State of Florida Hydrology Department
What is a karst aquifer?
• A karst aquifer can be defined as any body of rock composed of soluble
material through which groundwater flows and dissolves its own pathways.
• Floridan Aquifer = karst
– Rock is soluble
– Lots of rain/recharge to dissolve rock
– Caves and conduits Indian Springs, Florida
The process of limestone dissolution over a large area results in a
distinct landscape that is called karst topography.
Karst topography includes features such as sinkholes, surface and
closed depressions, and caves.
Causes of Sinkholes
The ground beneath our feet is not as much of a
solid structure as we think it is.
• Humans are also responsible for the formation of sinkholes. Activities like
drilling, mining, construction or drain pipes, improperly compacted soil
after excavation work or even heavy traffic can result in small to large
• Water from broken pipe can penetrate through mud and rocks and erode
the ground underneath and cause sinkholes.
• Sometimes, heavy weight on soft soil can result in collapse of ground,
resulting in a sinkhole.
• Areas that have a bedrock made of limestone, salt deposits or carbonate
rock are most susceptible to erosion and the formation of such holes.
Types of Sinkholes
Sinkholes resulted from a variety of mechanisms, but they
have been classified into three broad categories:
• Solution sinkholes
• Cover Collapse sinkhole
• Cover Subsidence Sinkhole
Source: Causes, Effects and Types of Sinkholes Conserve Energy Future
1) Solution sinkholes
• Most commonly seen in areas that have a very thin cover of soil on the
surface, exposing the bedrock below to continual erosion by water.
• As the water percolates through the bedrock, it carries away small parts
of the rock with it.
• As the bedrock erodes, particles collect in the spaces it leaves. Over a
period of time, a small depression is formed. It is at this point where the
• The hole is usually bowl shaped and can be quite large. Sometimes the
bedrock may collapse all of a sudden to form such a solution sinkhole
and other times it happens over time.
2) Cover Collapse sinkhole
• These take place when the bedrock is covered by a deep layer of soil and
earth. Once the bedrock begins to get eroded, crack start forming in the
rocky areas around it.
• When this happens, a number of weak points begin to form in the layers
of soil and strata above it.
• Finally, it comes to a point when the weak points become a large hole
within the bedrock that cannot support the weight above it.
• The cover collapse usually happens in a sudden manner and can create
large holes in a matter of minutes.
3) Cover Subsidence Sinkhole
• In this case, the hole is formed over a period of time. The bedrock here
is covered by soil and materials which are not well knitted together.
• Areas that have soil comprising largely of clay or sand often face the
occurrence of this hole.
• Once the bedrock starts to erode, the clay or sand starts permeating
through the cracks and settles into the spaces left behind.
• Over time, this creates a cavity on the surface of the soil and not under
Effects of Sinkholes
• When they are formed on land, they can change the general topography
of the area and divert streams of underground water.
• If they form suddenly in areas with heavy population, they can cause a
lot of damage to human life and property.
• Some holes are formed due to the leak in underground storm drains and
• When they collapse, the damage can be seen for many miles due to the
repairs that become necessary.
• They can be dangerous to the foundations of the building. Toxic
chemicals beneath the earth can come up and may pollute the
• Sinkholes occur commonly in Florida as the state has many
underground voids and drainage systems carved from the carbonate
• Cockpit karst
Arecibo Radio Astronomy Observatory, Puerto Rico
Cockpit karst is a form of karst in which
the residual hills are chiefly
hemispheroidal and surround closed,
lobed, depressions known as dolines or
"cockpits" each of which is drained to
the aquifer by one or more sinkholes.
Case histories of sinkhole occurrence reveal that sinkholes occur only in
certain parts of Pennsylvania. By examining these records, learn that
sinkholes are found in areas underlain by carbonate bedrock. Large areas of
central and eastern Pennsylvania are underlain by this type of bedrock.
William E. Kochanov (1999)
What is Carbonate Bedrock?
Includes limestone, dolomite, and marble. Limestone and
dolomite are sedimentary rocks, and marble is a metamorphic rock.
Although sinkholes are associated with all of these carbonate rock
types. But, limestone will be used as the primary source.
Occurrence of Sinkholes
Global distribution of carbonate rocks (mainly limestone)
Bit about Carbonate sediment
• Carbonate sediment is commonly found in relatively shallow
subtropical and tropical oceans around the world.
• Ocean-dwelling organisms such as corals, clams, and algae use the
various elements within seawater to form a hard, rigid skeleton
composed of the carbonate mineral calcite.
• When these organisms die, their skeletons accumulate on the ocean
floor as sediment.
• Movement of this sediment by wave action and ocean currents breaks
the sediment into smaller pieces and transports it from one place to
• The sediment can be further reduced in size by the action of burrowing
and grazing organisms.
• The sediment is ingested by these organisms, available nutrients are
removed, and the undigested portion of the sediment is returned to the
How Does Carbonate Sediment Become Rock?
Unconsolidated sediment needs something to hold the grains together in
order for it to become rock. Limestone is the result of carbonate sediment being
cemented together, generally by the mineral calcite. This cement can be produced
by chemical reactions that take place in the fluids that move through the pore
spaces of the sediment after deposition. Cementation is likely to occur when fresh
water, as opposed to ocean water, moves through the sediment.
How did the limestone get there if it was formed in the
During the earth’s history, the continents
and the oceans have changed in shape and
Shallow seas covered all of Pennsylvania in
past geologic time and produced layer
upon layer of carbonate sediments.
These sediments were lithified (turned to rock), and
the layers were later uplifted, tilted, fractured,
folded, and twisted by the forces unleashed during
the formation of the Appalachian Mountains.
Chemical Composition of Carbonate Bedrock?
• The chief constituent of limestone is the mineral calcite.
• The chemical composition of calcite is calcium carbonate (CaCO3). The
rock dolomite is similar to limestone but has dolomite as the dominant
• Chemically, limestone is considered a base. A base is the chemical
opposite of an acid.
• If an acid is added to a base, the two chemicals will counteract one
another, until the acid has been neutralized by the limestone.
Which is an ACID that reacts with these materials??
What makes rainwater acidic?
Carbonic acid is a weak acid and reacts with limestone and dolomite. In fact, it is
the main acid that dissolves carbonate bedrock.
• They are commonly circular in outline, but they can also be
elliptical, linear, or irregular in shape.
• A tunnel or throat may be visible within the hole.
• If a sinkhole occurs in an urbanized area, utility lines may be
• The size of a sinkhole depends on how much material has been
flushed down the drain and on the size of the pipes.
• Initially, sinkholes have steep or nearly vertical sidewalls.
• Portions of the sidewalls can break off over time and fall into the
• Land use
• Existing and planned land treatment
• Sinkhole drainage area
• Dimensions of the sinkhole opening
• Safe outlet for diverted surface water
• Environmentally safe disposal of sinkhole “clean out” material
• Availability and quality of filter material
• Sinkholes may be natural conveyances of organic material and
nutrients important to cave fauna.
• Safety of equipment and operators and laborers during installation
West Virginia Department of Environmental Protection, Division of Water and Waste Management,
Groundwater Protection Program, 2005
Mitigation designs serve to allow the filling of sinkholes while
maintaining recharge to the aquifer, reducing potential contamination
threats to groundwater, and eliminating safety hazards at sinkhole entries.
Vegetated Buffer Area
• Installed around the sinkhole to improve runoff water quality by filtration
and adsorption of contaminants.
• Within the sinkhole drainage area and should begin at the treated
• The buffer will be a minimum of 25-feet wide measured from the rim of
• This width should provide filtering for some distance outside the
sinkhole because surface water runoff may be temporarily held
before reaching the treated sinkhole.
• The sinkhole and surrounding buffer area will be fenced.
• Livestock will be excluded from the vegetative buffer except when
grazing would be beneficial to maintenance of the buffer.
• Appropriate erosion and sediment control measures should be used to
reduce the amount of sediment entering sinkhole.
Case Study - I
THE EFFECT OF SINKHOLES ON LEAKAGE OF
WATER FROM THE SARABCHENAR DAM,
Journal of Environmental Hydrology, Volume 13, Paper 1, January 2005
• The study area is a part of the
Zagros folded zone and is
situated in the northwest of
Lorestan Province, Iran.
• The mean annual rainfall is 550
• The earth dam was constructed in 1997 in order to control floods for
the city of Khoramabad (the capital of Lorestan province) and
irrigation of the lands of Sarabchenar village.
• The height and the total area of the dam and its lake are 15 meters
and 22 hectares respectively.
• The dam was designed to store 1600000 cubic meters.
• But soon after the construction several sinkholes developed along
the lake of the dam, and water storage never reached the estimated
• Due to the inflow of sediments and mass wasting, the dam is
gradually being filled, and at present it is not used for the intended
GEOLOGY OF THE AREA
• Asmari-Shahbazan (white limestone) of Oligocene age, Kashkan
(reddish conglomerate, marl and sandstone) of Eocene age.
• Tal-e-zang (fine grained and fossiliferous limestone) of upper
Cretaceous-Paleocene age and Amiran (gray conglomerate with
interbedded red sandstone) of upper Cretaceous-Paleocene age
• The Tal-e-zang is seen as small mounds in contact with Amiran
Amiran formation (conglomerate
with inter-bedded sandstone ).
The Amiran formation surrounds the
study area in the southern part. The
highest point is at an elevation of 1700
meters above the sea level.
• At the contact of Amiran and Tal-e-zang (some authors believe it as
Tarbur formation) several sinkholes (ponors) with different diameters
and a depth of about 2 meters have developed.
• The largest sinkhole has an elliptical (saucer) shape with a diameter of
12 meters in the eastern part of the dam.
• Solution, jointing and collapse features are seen on the fine grained
limestone at the foot of the Amiran Formation
Two of the sinkholes
Development of joints and
solution in Tal-e-zang.
Runoff, and the Springs which originate from the Amiran Formation and
Recharge the dam.
The runoff recharges the lake of the dam in the western and the eastern part.
The total discharge of the runoff during high rainfall is 20 liters per second.
The streams become completely dry during periods of no rainfall.
THE PEYAZEH SPRING Peyazeh spring, which is like an artesian spring
and emerges at the contact of Amiran and Tal-
THE SARABDUREH SPRING
• Southwest of the dam at a distance of
about 18 kilometers
• Asmari (limestone) formation
The mean annual discharge is
220 l/s. During the rainy season the spring
THE Q SPRING
The spring is situated southeast of the dam
at a distance of about 28 kilometers and
emerges from the marly limestone of lower
In order to trace the effect of leakage from the sinkholes to the
springs of Peyazeh (5 kilometers east of the dam), Sarabdoureh (18
kilometers from the dam) and the Q spring (23 kilometers from the dam)
• Eight kilograms of uranine was injected in two of the sinkholes after two
days of heavy rainfall in October 2004 through a pvc pipe of 4 inches in
Location of the sampling points Injection of uranine in the largest sinkhole
•Samples were taken at different hours and analyzed by the Kharad
•The effect of uranine was observed after 5 hours in the Peyazeh spring
and 2 days later in the Q spring.
•The average maximum concentration of uranine in the Peyazeh and Q
springs were 41 and 12 ppb respectively.
•The low concentrations of tracer are the result of dilution due to large
quantities of groundwater flow and absorption by clay materials in the
The absorption of Uranine by the
sinkholes can be seen as a red spot
•Sinkholes are formed at the contact of the Amiran and the Tal-e-zang
•Due to the solubility of the Tal-e-zang and the development of joints and
collapse of limestone, sinkholes have been formed.
•Sinkholes are the main avenues for water loss from the dam and there is a
direct connection between the sinkholes and the Peyazeh spring.
•The Q spring is recharged by the Khoramabad river and it is due to this
reason that uranine is seen in the spring.
LIDAR PROCESSING FOR DEFINING SINKHOLE
CHARACTERISTICS UNDER DENSE FOREST COVER: A
CASE STUDY IN THE DINARIC MOUNTAINS
Case Study – II
M. Kobal a, I. Bertoncelj b, F. Pirotti c, *, L. Kutnar a
a Slovenian Forestry Institute, Slovenia
b National Institute of Biology, Slovenia-
c CIRGEO Interdepartmental Research Center of Geomatics, University of Padova, Italy
The International Archives of the Photogrammetry, Remote Sensing and Spatial
Information Sciences, 2014 ,Volume XL-7, 113-118
• Leskova dolina, is in the Dinaric Mountains of southwest Slovenia
(center of area approximately located at Longitude = 14.46°,
Latitude = 45.62° in WGS84 datum).
• The karst geology on the site is characterized by numerous sinkhole
sand limestone outcrops.
• Soils are predominantly from limestone parent material.
• Mean annual precipitation of 2150 mm and mean temperature is
• Lidar data was acquired between 400 and 600 m relative flight
height using a Euro-copter EC 120B helicopter and a Riegl LM5600
laser scanner using 180 kHz pulse repetition rate (PRR).
Sinkhole detection and extraction
• Sinkholes were detected using the lidar-derived DTM.
• The initial step is based on a water flow simulation process. It is
defined by four steps:
(i) watershed delineation,
(ii) confining of higher rank sinkholes and
(iii) extraction of non-karstic sinkholes.
• To calculate characteristics they converted raster representation of
sinkholes to vectors and the following basic morphometric
characteristics were extracted and recorded stratified by rank:
• Diameter, width, area, depth, volume, orientation
• The rotating callipers method was used to delineate minimum
bounding box for a set of points thus defining a convex polygon of a
• The maximum width of a convex polygon was defined as diameter
of a sinkhole and minimum width of a convex polygon was defined
as width of a sinkhole.
• Volume was calculated as the sum of differences between the
maximum elevation within the sinkhole and the elevation of each
cell of a DTM within a sinkhole.
• Orientation was calculated as an azimuth of a line, connecting the
two farthest points within the sinkhole.
• A total of 2660 sinkholes were detected within the study area using
the lidar-derived DTM with the cell size of 1 × 1 m.
• Majority (2095) were 1st rank sinkholes (density: 40.16 km-2),
• 473 sinkholes of 2nd rank (density: 9.07 km-2)
• 79 sinkholes of 3rd rank (density: 1.52 km-2)
• 12 sinkholes of 4th rank (density: 0.25 km-2)
• One sinkhole of 5th rank (density: 0.02 km-2).
• Mean width and length of sinkholes increased with the sinkhole rank
from 26.1 m at 1st rank to 367.6 m at 4th rank, 33.8 m at 1st rank to
576.0 m at 4th rank, respectively.
• Maximum depth of sinkhole ranged from 39.2 in 1st rank to 48.4 m
in 4th rank, while sinkhole in 5th rank reaching depth of 52.8 m.
• Forest-management, the Dinaric fir-beech forests are among the
most important production-forests for timber products; their
ecological and nature-conservation aspects are also significant.
• The mitigation of climate-changes impacts on Dinaric fir-beech
forests in this sensitive karst area is also associated with the
distribution of sinkholes and other karst terrain characteristics.
• In all forest management actions, the distribution, orientation, depth,
and shape of sinkholes have to be taken into account.
• Information about sinkholes is pertinent to planning for future
land development and for the protection of private and public
• It also provides a fascinating story for those who are interested
in learning more about geologic conditions and earth
Ahmadipour, M., 2005, Effect of Sinkholes on Leakage of Water from the
Sarabchenar Dam, Southwest Iran, Journal of Environmental
Hydrology, 13: 1.
Kochanov, W. E., 1999, Sinkholes in Pennsylvania: Pennsylvania
Geological Survey, 4th ser., Educational Series 11, p- 33.
Kobal, I., Bertoncelj , F., Pirotti , L. Kutnar., 2014, Lidar prcocessing for
defining sinkhole characteristics under dense forest cover, The
International Archives of the Photogrammetry, Remote Sensing a
nd Spatial Information Sciences, 7: 113-118
Chen, J. and Xiang, S., 1991, Land Subsidence (Proceedings of the Fourth
International Symposium on Land Subsidence), IAHS Publ. no.
Roberto, S. and Ira, D. S., 2002, Development of collapse sinkholes in areas of
groundwater discharge, Journal of Hydrology, 264: 1–11.
Vincentzo, F., Antonio, F., Mario, P. and Agata, S., 2012, Sinkhole Evolution
in the Apulian Karst of Southern Italy: A Case Study, with some
considerations on Sinkhole Hazards, Journal of Cave and Karst Studies,
West Virginia Department of Environmental Protection, 2005,
Sinkhole Mitigation Guidance, Division of Water and
Waste Management, Groundwater Protection Program., Pdf.