Subsidence
Patrick Kahn
GEOG 366
Subsidence

The downward
(vertical) sinking of
earth materials.
It is caused by:
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
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Compaction of recently
deposited sediment
Shrinking of expansive
soils
Deflation of magma
chambers
Earthquakes
Thawing of frozen
ground
Human-induced subsidence is caused
by:



Withdrawal of fluids from
subsurface reservoirs
(water, oil)
Collapse of soil and rock
over subsurface holes
(underground mines)
Draining of wetlands
causing the oxidation of
organic soils
Sinkholes and Subsidence


Sinkholes
• Solutional
• Collapse
Subsidence
• Sediment and Soil Compaction
• Collapse soils
• Fine Sediment
• Expansive Soils
• Tectonism
• Permafrost
• Lava Tubes
Karst

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Certain rocks are
water-soluble,
particularly those with
gypsum and salt.
Limestone and other
carbonate rocks need
acidic water for
sinkholes to develop
(karst terrain)
More than 40% of the
humid USA east of
Oklahoma is underlain
by such rock
Sinkhole, Jan 2005, Colorado. On the northern limit of a swarm of sinkholes that extends
to Carbondale. The underlying bedrock is evaporite (e.g., gypsum, anhydrite, siltstone
and halite). Two electric golfcarts, stored under the structure, disappeared into the
sinkhole.
Karst terrain

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Areas underlain by
limestone or dolostone.
Susceptible to
dissolution by acidic
rainwater (carbonic acid)
H2O + CO2 = H2CO3
(carbonic acid in water)
Areas underlain by jointed
rock are especially
vulnerable.
Sinkholes

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Come in a variety of
scales.
Some may be
individuals.
Others occur in large
numbers forming a
pockmarked plain
known as a karst
plain.
Minnesota
Karst plain, Arizona


Many karst areas
underlain by
extensive cave
systems.
In humid regions,
less soluble material
is left behind,
creating tower karst.
Solutional and collapse
sinkholes

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Solutional sinkholes:
•
Form by dissolution as
acidic groundwater is
concentrated in holes
associated with joints.
Collapse sinkholes
•
Most common type:
develop by collapse of
near surface material
into part of an
underground cavern
systems. Can be
spectacular
Hazards?

Easily polluted water supplies
•
•
•

Rapid water flow and little filtration. Point source
pollution drains rapidly to drinking water source.
Three municipal sewage lagoons have collapsed in
southeastern Minnesota, sending millions of gallons of
sewage to the aquifer!
And what about…manure storage areas; feedlot
runoff…
Loss of buildings and infrastructure
Collapse of dissolving bedrock
Florida
Sierra Karst
Sierra Karst
Sierra Karst
Sinkholes
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The sudden and sometimes catastrophic
collapse may be triggered by groundwater
declines caused by pumping
The high solubility of salt and gypsum permit
cavities to form in days to years
Carbonate bedrock: slow process- centuries to
millennia
Human activities expedite cavity formation
Sinkholes in urban areas and
transportation corridors, N. Carolina
Many sinkholes are interspersed
between homes
Going, going….
Sinkhole at Winter park, Florida, 1981. Occurred in
a single day. It was sealed and converted to an
urban lake.
Other Karst
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Disappearing Streams
Karst Springs
Tower Karst
Disappearing Streams
Karst Springs
Tower Karst
Subsidence
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Less obvious than catastrophic sinkhole
formation
Develops gradually and is typically widespread
You can’t tell by looking that the San Joaquin
Valley floor was once 35 ft higher in some
locations
Mapping is critical: InSAR (inteferometric
synthetic aperture radar) uses repeat-pass
radar images from Earth-orbiting satellites to
measure subsidence at sub-centimeter
resolution
Ground subsidence

Can occur owing to
the compaction of
material as
•
•
•
Water is drained from
the soil, often caused
by a reliance on
groundwater supplies.
Organic material
decays
Oil is removed

In the arid
southwest, a visible
sign may be fissuring
of the earth.
Groundwater pumping and land
subsidence
Amount of subsidence

West of Phoenix: 18 feet
Las Vegas: 6 feet
Albuquerque: 1 foot
California
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Houston, TX: 9 feet
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• Lancaster: 6 feet
• Davis: 4 feet
• Santa Clara Valley: 12 feet
San Joaquin Valley
The future?

Increasing population in the southwest
means more groundwater pumping, and
continued subsidence, possibly
spreading to metropolitan areas where
damage will be great.

Well head protrusion
in Las Vegas.
Subsidence…free home
remodeling.
Las Vegas

Some of the most
spectacular
examples of
subsidence-related
earth fissures occur
in south-central
Arizona.
Subsidence in the LA Basin?
Causes
1.
Tectonic activity
2.
Water and oil
withdrawal
•
Examples
include
•
Pomona
(water);
Beverly Hills
(oil), San
Pedro and
Long Beach
(probably oil)
Groundwater withdrawal,
Lancaster
Texas: oil related subsidence.
Bay waters intruded the oil field.
Historic Houston subsidence.
Over 3,200 mi2 of Houston has sunk at least one foot. The Houston ship canal has sunk
10 ft. Cause: groundwater withdrawal.
Drainage of organic soils
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Occurs when soils rich in organic carbon are
drained for agriculture or other purposes.
The most important cause is microbial
decomposition, which, under drained
conditions, readily converts organic carbon to
carbon-dioxide gas and water.
Compaction, desiccation, erosion by wind and
water, and prescribed or accidental burning
can also be significant factors.
Two important areas of
subsidence:
1.
2.
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Sacramento-SanJoaquin Delta
Everglades
Continuing organic-soil subsidence
threatens agriculture
Affects engineering infrastructure and
water transfers
Complicates ecosystem restoration
Threatens the integrity of levees
Santa Clara Valley
Expansive soils

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Soils which shrink in
dry periods and swell
during wet periods.
Causes differential
movement which
damages
foundations.
Clay-rich
Expansive Soils
Expansive Soils

Check the soils
report for your area.
Tectonic Subsidence

Land subsidence due to earthquakes
•
•
Fault movement
Crustal deformation
Tectonic Subsidence
Permafrost
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Melting of frozen soils
Common at higher latitudes
• Why not lower latitudes?
Frost Heaving (opposite of subsidence)
also a hazard
Permafrost
Permafrost
Permafrost

Extent
Permafrost
Permafrost
Permafrost

Mine in permafrost
Permafrost
Deflation of Magma Chambers
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Lava tubes may collapse much like
caves
Common in Hawaii
Lava Tube Collapse
Lava Tube Collapse
Links to other Natural Hazards

Earthquakes
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Volcanoes
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Floods
• How?
• How?
• How?
Benefits


Karst provides unique and seldomly
explored frontier
Caves contain many rare endemic
species
• Troglobites
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New sinkholes create new lakes
Sinkhole lakes

Florida has most
sinkholes in
nation
Caves

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One of last frontiers
Many provide fascinating irreplaceable
features and rare species
• Kentucky
• New Mexico
• Sierra Nevada – Sequoia/Kings Canyon NP
• Hurricane Crawl Cave
• Lilburn Cave
• Ursa Minor Cave
Hurricane Crawl Cave

One of Park’s most
decorated
Lilburn Cave
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Park’s longest (~20
miles)
Crystal Cave
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Tourist Cave
Ursa Minor Cave
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Park’s newest (nonalpine)
Mineral King
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Best alpine karst in
nation
•
•
•
•
Hundreds of sinkholes
~130 cave entrances
Numerous springs and
disappearing streams
Not fully mapped until
last summer
• Who mapped it?
Troglobites

Cave-adapted
species