Deck 9: Sinkholes, Land Subsidence, and Swelling Soils

Question 1

How would you recognize a karst landscape?

A) Karst forms very rough deposits of calcium carbonate on various kinds of rock outcrops.
B) Karst forms a rather smooth, flat surface on limestone because of extensive solution by acid rain.
C) Karst has an extremely ragged surface dissolved on the surface of limestone bedrock.
D) Karst forms dune-like rounded hills of windblown dust.
E) Karst is the smooth surface formed on soft shales when salty sea spray reacts with them.

Answer 1

C

Question 2

What weather conditions are most likely to foster the formation of sinkholes?

A) dry weather, because that dehydrates the soil, causing shrinkage and collapse
B) freezing weather, because freezing water expands, causing stresses that force fractures apart to collapse
C) dry weather, because that lowers the water table so the cavern roofs are not supported and may collapse
D) wet weather, because there is ample water to dissolve out caverns
E) wet weather, because the pressure of water in a cavern causes stress that can weaken and collapse the roof

Answer 2

C

Question 3

Which of the following does NOT lead to formation of sinkholes?

A) strong pumping of groundwater for crop irrigation in dry weather
B) pumping groundwater for spraying on crops to prevent freezing
C) construction of a heavy building over a limestone cavern
D) pumping waste fluids into the ground for disposal
E) drilling for groundwater

Answer 3

D

Question 4

Why does Venice,Italy,have canals for gondolas and boats instead of normal streets for cars?

A) It was built on soft muds of a lagoon, and the heavy buildings settled into the mud.
B) The smectite soils in muds under it lead to lateral spreading and subsidence under the load of buildings.
C) The low ground next to the lagoon was a difficult place to provide a good road foundation.
D) Since the city was built about 1,600 years ago, the sea level has risen.
E) Extraction of groundwater below the city caused subsidence of the city below sea level.

Question 5

A roof made of what kind of material collapses to form a cover subsidence sinkhole?

A) sandy and permeable sediment
B) evaporate deposits of salt and gypsum
C) solid limestone with a few fractures
D) porous limestone with lots of fractures
E) swelling soil

Question 6

Where in North America are sinkholes most prevalent and why?

A) in Michigan, because outcrops of limestone are widespread and it is surrounded by the Great Lakes
B) in Washington state, because of all of the rain west of the Cascades
C) in metamorphic rocks of the Canadian Shield, because of all of the lakes
D) in Florida, because it is almost all limestone and has abundant groundwater
E) in Colorado, because layers of sedimentary rocks under the Great Plains bend up to the surface there

Question 7

Other than limestone,what other types of rocks are soluble and can form cavities that collapse?

A) salt and shale
B) shale and bauxite
C) salt and gypsum
D) kaolinite and smectite
E) smectite and gypsum

Question 8

Which of the following areas has NOT seen major subsidence from groundwater withdrawal?

A) San Joaquin Valley of California
B) Las Vegas area
C) Houston area, Texas
D) Charleston, South Carolina
E) Venice, Italy

Question 9

Which of the following statements about sinkhole formation is incorrect?

A) Cover collapse is a way that a sinkhole can form.
B) Permafrost thaw is a way that a sinkhole can form.
C) Large caverns generally form in limestone just below the water table.
D) Cover subsidence is a way that a sinkhole can form.
E) Sinkhole formation depends on the presence of soluble sedimentary rocks like limestone.

Question 10

What are the main characteristics of soil above a limestone cavern that leads to the formation of a cover collapse sinkhole?

A) thin enough that it can trickle through limestone cracks into a cavern below
B) sandy and loose enough that it can trickle down into cracks in limestone
C) coarse-enough grains that surface water can percolate down into cracks above a limestone cavern
D) fairly well cemented so it can maintain the roof of a cavern
E) thick, clay-rich, and cohesive enough to develop a large cavern before it collapses

Question 11

In the United States,sinkholes,subsidence,and swelling soils cause total dollar damage at which of the following levels?

A) more than earthquakes and volcanoes
B) more than hurricanes but less than floods
C) more than forest fires but less than floods
D) more than floods but less than landslides
E) less than hurricanes, floods, or landslides

Question 12

What causes caverns in limestone?

A) Hard grains of quartz sand carried in underground streams erode the soft limestone.
B) They form when rocks above collapse into the limestone.
C) Limestone readily dissolves in seawater, so the caverns formed originally at sea level.
D) Groundwater in limestone is somewhat caustic, so over many years, it dissolves limestone.
E) Rainwater dissolves carbon dioxide to make weak carbonic acid that dissolves limestone.

Question 13

What causes sinkhole collapse? Where is the cavity that it collapses into,and how does that cavity form?

A) A limestone cavern dissolves out with acid rain; a sinkhole forms when its roof collapses.
B) Soil above a limestone cavern percolates down into the cavern, leaving a soil cavity above. That cavity may collapse to form a sinkhole.
C) An underground river erodes a wide area; a sinkhole forms if its roof collapses.
D) The roof of a gold or copper mine collapses to form a sinkhole.
E) Families of moles or gophers dig large underground chambers that can collapse to form sinkholes.

Question 14

What is karst and how does it form?

A) Karst is the ragged surface dissolved on the surface of limestone bedrock formerly buried under soil.
B) Karst is windblown dust deposited in areas of dune-like hills.
C) Karst is the deposit of calcium carbonate that precipitates on rocks in soil when groundwater evaporates.
D) Karst is the cold wind that blows off the North Atlantic Ocean at times in late fall.
E) Karst is the product of reaction between acid rain and limestone in the ground.

Question 15

Caves and caverns most commonly develop in:

A) granite.
B) sandstone.
C) shale.
D) limestone.
E) schist.

Question 16

Which is NOT a method for recognizing the presence of swelling soils?

A) They are extremely slippery when wet.
B) They form a popcorn-like surface when dried out.
C) They stick like gum to the bottom of your shoes when wet.
D) Since they deform elastically, the ground feels spongy or bouncy underfoot.
E) They deform concrete foundations and walls.

Question 17

Under what weather conditions are sinkholes most likely to form?

A) low pressure under the eye of a hurricane
B) especially dry season
C) especially wet season
D) El Niño
E) freezing weather

Question 18

Why are there so many small lakes and springs in western Florida?

A) Since the water table is essentially at the surface, any low area is filled with water.
B) Limestone caverns and sinkholes filled with water because of the high water table.
C) Groundwater rising through the limestone bedrock dissolves it as it reaches acid rain at the surface.
D) Many of them are old limestone quarries, abundant there because of cheap transportation near the Gulf.
E) A swarm of asteroids peppered the area a few thousand years ago; the holes have since filled with water.

Question 19

What is in water in the ground that helps it dissolve limestone?

A) nitric acid from nitrogen in the air combining with rainwater
B) carbonic acid formed from carbon dioxide in air combining with rainwater
C) nothing-pure water has nothing in it, so it can dissolve more
D) oxygen-the reactivity of oxygen oxidizes the calcium of limestone
E) sand-the grains are much harder than limestone, making it more abrasive

Question 20

What causes swelling soils to swell?

A) When they get wet, water enters the clay mineral structure to cause swelling.
B) The presence of abundant kaolinite clay takes water in between its layers.
C) When water in clay-rich soil freezes, the soil swells.
D) When an earthquake shakes wet soil, more water can get between the grains to cause swelling.
E) Landsliding of a mass relieves pressure on soil, permitting it to expand.

Question 21

What material causes swelling soils?

Question 22

How can you recognize the presence of swelling soils?

Question 23

What causes permafrost thaw? What are several problems associated with it? What is one way to overcome permafrost thaw?

Question 24

Your friend just got back from vacation and wants to know if you can help him understand why the place he visited looked so weird.He describes the landscape as being uneven,with lots of depressions,and some ragged parts.What type of landscape is this? How does this type of landscape form? If your friend was on vacation in the United States,where are some of the places he could have been?

Question 25

What aspects of construction can lead to the formation of sinkholes? Why?

Question 26

What agricultural behavior is likely to lead to formation of more sinkholes?

Question 27

What is in water in the ground that helps it dissolve limestone? Where does that substance come from?

Question 28

Discuss the four causes of land subsidence described in the text and one case study of each cause.

Question 29

What is bad about swelling soils?

Question 30

What are two main mechanisms of ground subsidence?

Question 31

In the case of Mexico City,Mexico,land subsidence due to unsustainable groundwater pumping caused many problems because the area is highly populated.Discuss two of these problems.

Question 32

What specific area of the western United States is noted for almost 9 meters of subsidence due to agriculture? Specifically what caused the subsidence?

Question 33

Venice,Italy,is noted for numerous water canals instead of paved streets for cars.Why doesn't it have many typical streets? Explain briefly.

Question 34

What type of ground settling process is common in high latitudes?

Question 35

Name three of the eight states with the largest areas of ground subsidence,including sinkholes.