This document summarizes different types of land subsidence. It discusses natural subsidence caused by compaction of sediments, shrinking of soils, volcanic processes, earthquakes, and thawing of frozen ground. It also describes human-induced subsidence from fluid withdrawal, mine collapses, and draining of wetlands. Specific types covered include subsidence in karst terrain due to dissolution in limestone areas, sinkhole formation which can be catastrophic or slow, and subsidence caused by groundwater pumping, drainage of organic soils, and tectonic processes like earthquakes. Potential hazards from subsidence are contaminated water supplies and loss of infrastructure, but it can also create new lakes.

1. Land Subsidence
Md Asif Hasan

2. Subsidence
 The downward (vertical) sinking of earth materials.

3. Natural Subsidence is caused by:
 Compaction of recently
deposited sediment
 Shrinking of expansive soils
 Deflation of magma chambers
 Earthquakes
 Thawing of frozen ground

4. 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

5. Karst terrain
 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.

6. Karst plain

7. Sierra Karst

8. Sinkholes
 Come in a variety of
scales.
 Some may be
individuals.
 Others occur in large
numbers forming a
pockmarked plain known
as a karst plain.

9. Cont…
 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

10. Sinkhole at Winter park, Florida, 1981. Occurred in
a single day. It was sealed and converted to an
urban lake.

11. 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.

12. Slow Subsidence
 Less obvious than catastrophic sinkhole formation
 Develops gradually and is typically widespread
 Mapping is critical: InSAR (inteferometric synthetic
aperture radar) uses repeat-pass radar images
from Earth-orbiting satellites to measure
subsidence at sub-centimeter resolution

13. 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

14. Groundwater pumping and land
subsidence
Increasing population means more
groundwater pumping, and
continued subsidence, possibly
spreading to metropolitan areas
where damage will be great.

15. Well head protrusion

16. Subsidence…free home
remodeling.
Las Vegas

17. Tectonic Subsidence
 Land subsidence due to earthquakes
• Fault movement
• Crustal deformation

18. Drainage of organic soils
 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.

19. 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

20. Collapse of dissolving bedrock

21. Disappearing Streams

22. Permafrost

23. Lava Tube Collapse

24. Benefits
 Karst provides unique and seldomly
explored frontier
 Caves contain many rare endemic
species
• Troglobites
 New sinkholes create new lakes

25. Thank You