Permafrost and Subsidence Flashcards
What is subsidence?
The slow or rapid almost downward movement of earth
What is Karst?
Landscape resulting from dissolution of limestone, dolostone, marble, gypsum or sock salt
What does soil expand and contract?
Changes in water content
Freezing and thawing
True or false: subsidence is one of the most widespread and costly natural disasters?
TRUE
What is a karst plain?
Terrain pocketed with lots of sinkholes
What is a collapse sink hole?
collapse of surface sediment
What is a solution sink hole
Caused by breakdown of underlying bedrock on planes or fractures
How are caves formed
A series of subsidence, due to changes in the water table
What is formed by the water responsible for forming caves?
Calcium will deposit on the walls and will form flowstone, stalagmites and stalactites
What is the difference between a stalagmites and a stalactites
stalagmites grow up from ground
stalactites hang from the ceiling
How is flow stone formed?
From water flowing and carving patterns
What is tower karst?
Highly eroded karst regions, common in humid tropical regions
What are disappearing streams
streams that flow from the surface into mouths of caves
What are springs?
discharge of ground water to the surface, very susceptible to contamination
what is permafrost?
Soil that has remained cemented in ice for at least 2 years
What is continuous permafrost
Mean annual temperature is less than -5 degrees
What is discontinuous permafrost?
Covers 50-90% of the landscape, mean annual temperature between -4 and -2 degrees
What is sporadic permafrost?
Covers less than 50% of the landscape, mean annual temperature between -2 and 0 degrees
What is the active layer?
thaws in spring and re freezes in fall
What happens to the ground when perm frost thaws?
It can cause subsidence, when there is a lot of thawing it causes thermokarst
What happens to frost susceptible sediment when it freezes
It expands causing frost heaving
What is piping
Particle of silt and sand carried in groundwater laterally to a spring
What is piping caused by. Where is it common
Groundwater creating tunnels as it moves through loose sediment, in silt and sand sediments
How do fine sediments compact?
By the removal of pore water, common on river deltas
How do collapsible sediments compact?
They dissolve in water or have loose bonds, arid regions
How do organic sediments compacted?
wetland soil contains a large amount of water and compacts when water is drained
What is expansive soils?
Soils that expand when wet and contract when dry, common in clay rich soil containing smectite
What is the link between earthquakes and subsidence
earthquakes can lower ground surface, costal subsidence can cause flooding, magma uplifts volcano during eruption and after the chamber empties surface subsidence
What regions are at risk
landscaped with soluble rocks or permafrost or easily compacted sediment, soils with lots of smectite clay and silt is very securable to first heaving
What are some ways humans cause subsidence
Underground mining, permafrost thawing, withdraw of fluids (oil, natural gas etc.), restriction of deltas via dams etc. draining wetlands, landscaping on expansive soil Ex. addition of plants changes water levels
