Subsidence Patrick Kahn GEOG 366

Subsidence The downward (vertical) sinking of earth materials.

It is caused by: 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 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 Areas underlain by limestone or dolostone. Susceptible to dissolution by acidic rainwater (carbonic acid) H 2 O + CO 2 = H 2 CO 3 (carbonic acid in water) Areas underlain by jointed rock are especially vulnerable.

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. 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 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

Sinkholes 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, Occurred in a single day. It was sealed and converted to an urban lake.

Other Karst Disappearing Streams Karst Springs Tower Karst

Disappearing Streams

Karst Springs

Tower Karst

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

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 Lancaster: 6 feet Davis: 4 feet Santa Clara Valley: 12 feet Houston, TX: 9 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 mi 2 of Houston has sunk at least one foot. The Houston ship canal has sunk 10 ft. Cause: groundwater withdrawal.

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.

Two important areas of subsidence: 1. Sacramento-SanJoaquin Delta 2. 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 Soils which shrink in dry periods and swell during wet periods. Causes differential movement which damages foundations. Clay-rich

Expansive Soils

Check the soils report for your area.

Tectonic Subsidence Land subsidence due to earthquakes Fault movement Crustal deformation

Tectonic Subsidence

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

Permafrost

Extent

Permafrost

Mine in permafrost

Permafrost

Deflation of Magma Chambers Lava tubes may collapse much like caves Common in Hawaii

Lava Tube Collapse

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

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

Sinkhole lakes

Florida has most sinkholes in nation

Caves 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 Park’s longest (~20 miles)

Crystal Cave Tourist Cave

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

Mineral King 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