Lecture 11 - Permafrost

Question 1

Subsidence?

Answer 1

A slow or rapid, nearly vertical, downward movement of Earth’s surface

Question 2

Karst?

Answer 2

A common type of landscape associated with subsidence; resulting from the dissolution of limestone, dolotstone, marble, gypsum, or rock salt by groundwater

Question 3

What causes soil expansion and contraction?

Answer 3

Changes in the water content of the soil

Freezing and thawing

Question 4

What causes sinkholes?

Answer 4

Dissolution produces voids which join to form caves, and then sinkholes

Question 5

Karst plain?

Answer 5

A surface pock-marked with a large number of sinkholes

Question 6

What are the types of sinholes?

Answer 6

• Solution Sinkholes: formed by dissolution of buried bedrock along planes and fractures
• Collapse Sinkholes: collapse of surface or near-surface rock or sediment

Question 7

What causes calcium carbonate to deposit on the sides, ceiling, and floow of caves?

Answer 7

Groundwater seepage

Question 8

Tower karst?

Answer 8

Steep limestone pillars common in highly eroded karst regions (humid tropical regions)

Question 9

Dissapearing streams?

Answer 9

Streams that flow from the surface into cave openings

Question 10

Springs?

Answer 10

Natural discharges of groundwater at the surface (vulnerable to contamination)

Question 11

What are the parameters for permafrost?

Answer 11

Soil or rock must remain cemented with ice for at least 2 years continuously

Question 12

Types of permafrost?

Answer 12

• Continuous permafrost (temp less than -5)
• Discontinuous permafrost (covers 50-90% of ground, temp -4 - -2)
• Sporadic permafrost (covers less than 50% of ground, temp -2 - 0)

Question 13

Active layer?

Answer 13

Top layer of soil which is not continuously frozen, due to changing surface temps

Question 14

Piping?

Answer 14

Particles of silt and sand in the subsurface slowly carried by groundwater laterally to a sping, caused by groundwater creating tunnels as it percolates through loose sediments

Question 15

Fine sediments?

Answer 15

• compacts when pore water is removed
• flooding replenishes it
• common on river delta

Question 16

Collapsible sediments?

Answer 16

• Loess and some stream deposits in arid regions are loosely bound or are water soluble
• water weakens bonds = compaction

Question 17

Organic sediments?

Answer 17

• wetland soils contain large amounts of orgnaic matter and water
• water drains/soil decomposes, soils compact

Question 18

Expansive soils?

Answer 18

Expand during wet periods and shrink during dry periods

• common in clay, shale, clay-rich soil w/smectite
• produces dissication cracks

Question 19

Desiccation cracks?

Answer 19

cracks fromed when all the water is removed from the soil

Question 20

What natural phenomenon has been lowering the coasts of Vancouver Island, Washington, and Oregon?

Answer 20

Earthquakes

Question 21

How does magma cause subsidence?

Answer 21

When a volcanoe erupts, the magma chambers are emptied and the ground sinks

Question 22

Frost heaving?

Answer 22

Upwards well of soil during freezing conditions as ice grows towards the surface
- soils containing silt are susceptible

Question 23

What are the effects of permafrost thaw?

Answer 23

• roads cave in
• airport runways fracture
• buildings crack/tilt/collapse

Question 24

What contributes to the sinking of New Orleans?

Answer 24

coastal flooding and loss of wetlands along the mississipi delta

Question 25

What are some natural service functions caused by subsidence?

Answer 25

• karst regions contain the world’s most abundant water supply
• aesthetic
• scientific resources
• unique ecosystems (aka cave dwellers)

Question 26

What are signs of subsidence?

Answer 26

• cracks
• hummocky grounds
• closed depression