Risks Associated with
Subsidence and Uplift
Vertical Movements of
the Earth’s Crust
Introduction
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Small scale vertical movements
Human induced or aggravated
Occurring on time-scales of a few
decades
Causing substantial economic losses and
societal disruption
Subsidence and Uplift
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Subsidence: The lowering of the land surface
due to
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Creation of cavities in solid rock by mining,
combustion of coal or dissolution of soluble
material
The removal of fluids (water or oil) from the pore
spaces of unconsolidated or poorly consolidated
sediments
Uplift: changed land conditions due to
expansive soils
Causes of Vertical Movements
•Loss of water in organic soils
•Dissolving of subsurface
limestone rock
•First-time wetting of formerly
dry, low-density soils
•Natural compaction of soils
•Underground mining
•Withdrawal of ground water and
petroleum
Relation between subsidence and collapse
Fluid withdrawn results in bed compaction
Enlarging solution cavities causes collapse
Collapse of mine can cause subsidence or collapse
Subsidence
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Underground mining is the most widespread
cause of subsidence by direct removal
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Coal- Illinois, North Dakota, others
Salt- Kansas and New York
Copper- Ducktown, TN
Removal causing changes in local or regional
groundwater system either by natural or
anthropogenic causes
Copper Basin, TN- Burra Burra Mine
Differential Compaction due to the Compaction of Soils
The high-rise buildings are built on piers in bedrock
The smaller buildings are built on slab foundations st
on soils, in time they settle and damage results
Chemical Weathering
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Role of Acid
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Hydrogen ions in water
pH=-Log[H+] Acid/Base
Carbonic Acid
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H2CO3
CO2 + H2O -> H2CO3
H2CO3 -> H+ + HCO3- (in water)
Solution weathering- Karstic Features
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Calcite (in limestone) dissolves in acidic water
fluted (channeled) rock surface
caves
Effects of Groundwater Action
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Karst topography-Caves
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Rock usually limestone
Dissolves by weakly acidic water
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rainwater pH 5.5 and carbonic acid from humus
Water + carbon dioxide + calcite  calcium ion + bicarbonate ion
Precipitation (dripstones)  solution (caves)
H2O + CO2 + CaCO3  Ca2+ + 2HCO3-
Dripstone- Speleothems
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stalagtite
stalagmite
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Flowstone
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Sinkholes
in a Cavern
System
Winter Park, FL
Subsidence vs. Collapse Sinkhole
Collapse Sinkholes
Collapse sinkholes are the most dramatic of the three
sinkhole types; they form with little warning and leave
behind a deep, steeply sided hole. Collapse occurs
because of the weakening of the rock of the aquifer by
erosion and is often triggered by changes in water levels
in the surficial and confined aquifers.
1
Stage 2
Stage 3
Subsidence Sinkholes
The progression of a subsidence sinkhole is shown below.
Rainwater percolates through overlying sediments and
reaches the limestone, dissolving the rock and gradually
wakening its structural integrity. Gradually subsiding
sinkholes commonly form where slow dissolution takes
place, mostly along joints in the limestone. These
sinkholes tend to form naturally and are not greatly
affected by human activities.
1
Stage 2
Stage 3
Stage 4
KARST
Sinkhole in Winter Park, FL
Balancing Withdrawal &
Discharge of Groundwater
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Pumping in a quarry or other man-made
hole or;
Overpumping of g.w. for supply can
results in:
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Falling water table
Ground subsidence
Subsidence of land
caused by extraction
of groundwater in the
San Juaquin Valley, CA
The land sank 9m or
30 ft in 52 years
Santa
Clara
Basin, CA
GW w/d
Caused
1.2m
Bet.
1960-1967
Greater Houston-Galveston
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Groundwater withdrawn by industry
Petroleum
Between 1906-1978 a total of 2.5m of
subsidence
Greater Houston Area
*
NASA
Seabrook and Bayport, TX
Greater Houston-Galveston
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Withdrawl of fluids, particularly coastal
aquifers, has caused subsidence
fissures, cracks, significant structural
damage and flooding
NASA has constructed a hurricaneresistant facility to warehouse their
moon rock collection
Venice, Italy
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Venice is subject to flooding by high tides in
the Adriatic Sea
Between 1952-1969 Venice was sinking due to
subsidence
Subsidence is caused by groundwater pumping
from 5 aquifers which reduce pore-water
pressure and the fine grained sediment began
compacting
In 1997 proposals for gas exploration has
increased the concerns
Coal Mining
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If the mine workings are near the surface (few 10’s
of meters) the overlying rocks maybe too weak to
support their own weight and eventually they will
collapse into the mine below
This generates a series of collapse pits
2 methods of coal mining
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Room and pillar…leaves behind a support system,
however if the mine is shallow it can cause collapse pits
Longwall mining…the resource is removed completely as
mining advances, in an active mine a hydraulic shield
supports the roof. This leaves behind uniform subsidence
Subsidence pits at the
Surface from collapse
Of the mine workings at
depth
Room and pillar mining
Leaving pillars to support
surface does not work well
because flooding of the
Mine weakens the support
System. Coal is porous
Coal Mining Related Damage
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In areas of Kentucky, Pennsylvania and W.
Virginia surface drains, culverts, underground
pipes are damaged by subsidence. Ponding
and flooding can occur.
Subsidence can disrupt GW flow, draining them
and drying up wells and springs. Fractured
aquifers may lose artesian pressure and
become vulnerable to contamination.
Underground fires
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Carbondale, PA burned for 33 years
Can cause emission of CO and CO2 to atmosphere
through fissures
Mitigating Mine Subsidence
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Subsidence can be mitigated by filling
the void below using mine waste or sand
can be pumped through drill holes at the
surface.
Development can be curtailed or only
allowed after the mining operations are
completed them the foundations of the
structures can be built on the mine floor
Salt Mining
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Salt often mined by solution methods
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Water is injected through wells into a salt deposit, the
salt dissolves and saturated water is pumped out.
The removal of salt leaves a cavity behind and weakens
the support for overlying rocks
In the 1970 an event near Detroit, MI left a pit 120m
across and 90m deep; another in Saltville, VA
produced 75m of subsidence; In 1974 in Hutchinson,
KS a 60m sinkhole with vertical walls formed; in
1980 a lake drained in Louisiana into a salt mine
after an oil drilling rig punched a hole in the mine
Hutchinson, KS 1974
Lake Peigneur, LA
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On Nov. 21, 1980 a drill rig punched a hole through an abandoned
shaft of a still operating multimillion dollar salt mine
The mine was located 430m below the surface of Jefferson Island
salt dome.
The lake drained so fast that 10 barges, a tug boat and an oil
drilling barge disappeared into a whirlpool of water, 25 hectatres
of Jefferson island were also lost including a botanical garden and
a $500K home
The lake immediately began refilling from waters from the Gulf of
Mexico, 9 of the barges popped up to the surface
15million m3 of water entered the salt dome and the mine was
lost
The once shallow lake (1m) was now a deep hole in the bottom
The oil company paid $30million to the mine operation, the
botanical garden and home owners were paid $13million by all
other parties
Salt Mining in Western New
York
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Failure of a room and pillar mine in Retsof Mine
Livingston Co, NY which led to the closure of the
world’s largest salt mine
The salt bed was 300m below the floodplain of the
Genesee R.
On March 12, 1994 a sinkhole developed on flat
farmland, a bridge over a highway failed and the cause
was thought to be a magnitude 3.2 earthquake
Salt Mining in Western New York
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GIS analysis showed that the sinkhole was located
directly above a section of the mine where a new
mining method was employed, one where the
pillar were 20x20 instead of 80x80 ft
The pillars failed leading to a collapse which
produced the seismic event
Immediately following the creation of the sinkhole
water started pouring into the mine, concrete was
poured into the fractures to try to prevent the
water from flowing into the mine but this failed
Subsequently 2 other sinkholes appeared, more
water poured in and started dissolving the pillars,
the mine was abandoned in 1996
Costs of Subsidence
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Sudden events like the Winter Park, FL sinkhole are
rare, but are the easiest to evaluate in monetary
terms… $2 million for losses of permanent structures
Other events are more complex and develop over
long periods of time such as coastal subsidence in
Houston and Venice
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Direct and immediate costs due to permanent flooding
Costs associated with measures to prevent flooding
Costs that will result from future flooding
In 1978 Texas A&M estimated that costs from subsidence
in Houston would be on the order of $ 32 million per
year between 1969-1974
At least 9 sinkholes form in Hernando
County after heavy rain
Monday, June 17, 2002
Associated Press
SPRING HILL —
rain.
At least nine sinkholes formed in Hernando County after heavy weekend
The sinkholes opened late Friday and early Saturday, after about 5 inches of
rain fell overnight. No homes were seriously threatened and no one was injured.
The biggest was about 40 feet wide and 50 feet deep. Officials also had their
eyes on two depressions in a pond that appeared likely to drop.
In Orlando this month, a 150-foot-wide, 60-foot-deep sinkhole threatened
two apartment buildings and forced dozens of residents to evacuate. Last month,
a 10-foot-deep, 15-foot-wide sinkhole collapsed part of Interstate 4 in
Lake Mary, about 15 miles north of Orlando.
And in Hernando County, sinkholes are even more common.
Long periods of drought, followed by heavy rain fall, contribute to the problem.
The area's thin layer of clay to protect the limestone below doesn't help.
During 2001, Hernando County had more than 65 confirmed sinkholes.
Two more sinkholes open in Spring Hill
By MARY SPICUZZA, Times Staff Writer
© St. Petersburg Times
published July 23, 2002
SPRING HILL -- Kathy Davis said she is looking forward to moving into her new home.
And she is not going to let a nearby pair of 15-foot deep sinkholes get her down.
"They're popping up everywhere," Davis said. "I'm not nervous about it. But I'm glad they're not on my
property."
Davis, 56, said she saw the sinkholes after construction workers told her that several nearby trees had
sunk into the ground. She mentioned it to her daughter-in-law, Kimberly Davis, who had just moved in
across the street from her future home.
The Furley Avenue holes are the latest major holes in the Spring Hill area, which seems to be an
especially active area for sinkholes.
Assistant Fire Chief Danny Roberts said workers had enclosed an area of woods near the roadside about
100 feet wide in yellow caution tape. He said that one of the sinkholes appeared to be old but that a fresh
one indicated new activity in the area.
"We've been up there a couple of times checking on it," Roberts said.
Stuart Glover, the president of the Hernando Builders Association, said few builders test for sinkhole
activity before building.
"I suppose someone could test for that," Glover said. "But it's not something most do."
He said he had never seen a sinkhole open near a construction site.
Kathy Davis said she was not thrilled about her neighborhood sinkhole, but she doesn't regret building a
new home.
"From what they tell me, all of Florida is a big sinkhole," she said.
-- Mary Spicuzza can be reached via e-mail at spicuzza@sptimes.com
Responses to Subsidence
Problems: Hazard Mitigation
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Areal Prediction
Intervention
Insurance
Assigning Responsibility
Areal Prediction
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Geologic information in map form including GIS
Areal predicyion over cavities
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Given actual current distribution of subsidence;
subsidence areas in the future can be estimated
by continuous monitoring including GPS
Areal prediction over aquifers that are being
withdrawn
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Available drill-hole data for oil/water fields
GPR: Cross section showing an underground cavity near
Gainesville, FL
Intervention
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Map interpretation
Regulation of source of extraction
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Once cause and effect relationship
established
Legislation creating special boards or laws
to curtail or modify extraction
Insurance
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Protection of the public by making
insurance available
Insurance premium paid reflects level of
risk as established by hazards maps or
site specific insurance
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In Florida state legislature required that all
insurance coverage had a sinkhole clause
Assigning Responsibility
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Establishment of how particular human actions
are responsible for all or part of an observed
subsidence based on cause and effect
Pennsylvania Coal v. Mahon, supreme court
case
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PA tried to regulate coal in 1922 to prohibit mining
in areas where existing structures would be
affected. State lost because they were seen to be
infringing on rights of mine
“Act of God”; were legal establishment of
responsibility has not been established
The Role of Science
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The Panel on Land Subsidence of the U.S. National
Research Council (NRC) (1991) recognized three
information needs:
“First, basic earth-science data and information on the
magnitude and distribution of subsidence [...] to
recognize and to assess future problems. These data
[…] help not only to address local subsidence problems
but to identify national problems. [...] Second, research
on subsidence processes and engineering methods
for dealing with subsidence […] for cost-effective
damage prevention or control. […] And third, although
many types of mitigation methods are in use in the
United States, studies of their cost-effectiveness would
facilitate choices by decision makers.”
Recognition
• Subsidence is sometimes obvious
• Where the frequency of well-casing
failures is high, land subsidence is
often suspected and is often the
cause.
• The formation of earth fissures in
alluvial aquifer systems is another
indication that compaction and land
subsidence may be occurring.
• Other possible indicators of land
subsidence include changes in floodinundation frequency and
distribution; stagnation or reversals
of streams, aqueducts, storm
drainages, or sewer lines; failure,
overtopping or reduction in freeboard
along reaches of levees, canals, and
flood-conveyance structures; and,
more generally, cracks and/or
changes in the gradient of linear
engineered structures such as
pipelines and roadways.
Assessment
Mitigation
• When development of natural resources causes
subsidence, governments sometimes exercise
their power either to prohibit the resource
development or to control it in ways that minimize
damage.
• This may be done through regulation. With
adequate monitoring programs and institutional
mechanisms in place, optimal benefits may be
achieved for both subsidence mitigation and
resource development.