1. Lecture 29 Subsidence Types

2. Subsidence 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

3. 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

4. In the arid southwest, a visible sign may be fissuring of the earth.

5. Groundwater pumping and land subsidence

6. Amount of subsidence West of Phoenix: 18 feet Las Vegas: 6 feet
Albuquerque: 1 foot
California
Lancaster: 6 feet
Davis: 4 feet
Santa Clara Valley: 12 feet
Houston, TX: 9 feet

7. San Joaquin Valley

8. The future?
Increasing population in the southwest means more groundwater pumping, and continued subsidence, possibly spreading to metropolitan areas where damage will be great.

9. Well head protrusion in Las Vegas.

10. Subsidence…free home remodeling.
Las Vegas

11. Some of the most spectacular examples of subsidence-related earth fissures occur in south-central Arizona.

12. Subsidence in the LA Basin?
Causes
Tectonic activity
Water and oil withdrawal
Examples include
Pomona (water);
Beverly Hills (oil)
San Pedro and Long Beach (probably oil)

13. Groundwater withdrawal, Lancaster

14. Texas: oil related subsidence. Bay waters intruded the oil field.

15. Historic Houston subsidence
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.

17. 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.

18. Two important areas of subsidence:
Sacramento-San Joaquin Delta
Everglades
Continuing organic-soil subsidence threatens agriculture
Affects engineering infrastructure and water transfers
Complicates ecosystem restoration
Threatens the integrity of levees

19. Santa Clara Valley

20. Expansive soils
Soils which shrink in dry periods and swell during wet periods.
Causes differential movement which damages foundations.
Clay-rich

21. Expansive Soils

22. Expansive Soils
Check the soil survey for your area.

23. Tectonic Subsidence Land subsidence due to earthquakes Fault movement
Crustal deformation

24. Tectonic Subsidence
Not to scale! Subsided region can be ~ 100 miles wide!

25. Permafrost Melting of frozen soils Common at higher latitudes
Why not lower latitudes?
Frost heaving (opposite of subsidence) also a hazard

26. Permafrost

27. Permafrost

28. Permafrost
Extent

29. Permafrost

30. Permafrost

31. Permafrost
Mine in permafrost

32. Permafrost

33. Deflation of Magma or Lava Reservoirs
Lava tubes may collapse much like caves
Common in Hawaii
”Caldera collapse”

34. Toba Indonesia

35. Lava Tube Collapse

36. Lava Tube Collapse

37. Links to other Natural Hazards
Earthquakes
How?
Volcanoes
Floods

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

39. Sinkhole lakes

40. Florida has most sinkholes in nation

41. Caves One of the last frontiers for exploration
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
Crystal Caverns

42. Hurricane Crawl Cave
One of Park’s most decorated

43. Lilburn Cave
Park’s longest (~20 miles)

44. Crystal Cave
Tourist Cave

45. Ursa Minor Cave
Park’s newest (non-alpine)

46. Mineral King Best alpine karst in nation Hundreds of sinkholes
~130 cave entrances
Numerous springs and disappearing streams
Not fully mapped until last summer

48. Troglobites
Cave-adapted species