Ground Subsidence

Question 1

True or False: Surface or Ground Subsidence is both sporadic and incremental event

Answer 1

True; Sudden Collapse - sporadic; Slow Subsidence - incremental

Question 2

Defined as the lowering of the land surface due to
sinkhole development

Answer 2

Surface Subsidence and Collapse

Question 3

Subsidence due to _______ collapse in karst is
one of the most dangerous geohazards due to its
extreme unpredictability

Answer 3

Sinkhole

Question 4

Water in the atmosphere can dissolve small amounts
of carbon dioxide (CO2
).
This results in rain water having a small amount of

___________ when it falls on the Earth’s
surface.

Answer 4

Carbonic acid (H2CO3)

Question 5

Mining activities that remove material from below
the surface can result in collapse if precautions are
not taken to ensure that the there is adequate
support for the overlying rocks. Give 2 example of these mining actuvities

Answer 5

Salt mining and Coal Mining

Question 6

This decreases if fluids are withdrawn from below the surface, resulting in the
removal of support and possible collapse

Answer 6

fluid pressure

Question 7

What are the two most important fluids that occur beneath
the surface

Answer 7

water (in the form of groundwater),
and petroleum (in the form of oil and natural gas)

Question 8

In the Wilmington oil field of Long
Beach, California, subsidence was first
recognized in 1940 due to withdrawal of
oil from the subsurface. The area
affected was about 50 km2. Near the
center of this area, the surface subsided
by up to ________.

Answer 8

9 meters

Question 9

This subsidence event that has occurred in Wilmington oil field of Long
Beach, California costed over __________.

Answer 9

$100 Million

Question 10

It means depression in the landscape.

Answer 10

Dolines

Question 11

Other words for “Dolines”

Answer 11

Sinkhole, swallet, and swallow hole

Question 12

What are the several processes that form dolines?

Answer 12

surface solution, cave collapse, piping, subsidence, and stream removal of superficial covers

Question 13

What are the five-fold classification of dolines?

Answer 13

1. Solution Dolines
2. Collapse Dolines
3. Suffossion Dolines
4. Subsidence Dolines
5. Alluvial stream-sink dolines

Question 14

These dolines start where solution is concentrated around a favorable point such
as joint intersections. The solution lowers the bedrock surface, so eating out
a small depression.
The depression traps water, encouraging more solution and depression enlargement.

Answer 14

Solution Dolines

Question 15

These dolines are produced suddenly when the roof of a cave formed by
underground solution gives way and fractures or ruptures rock and soil.

Answer 15

Collapse Dolines

Question 16

These dolines form in an analogous manner to subjacent karst-collapse dolines, with a blanket of superficial deposits or thick soil being washed or falling into
widened joints and solution pipes in the limestone beneath.

Answer 16

Suffossion Dolines

Question 17

These dolines form gradually by the sagging or settling of the ground
surface without any manifest breakage of soil or rock

Answer 17

Subsidence Dolines

Question 18

These dolines form in alluvium where streams descend into underlying calcareous rocks. The stream-sink is the point at which a stream disappears underground.

Answer 18

Alluvial Stream-Sink Dolines

Question 19

What is the diameter of the collapse dolines at the water table in Wood Buffalo National Park, Alberta, Canada. The dolines are created by collapses through dolostone into underlying gypsum.

Answer 19

40–100m

Question 20

Types of Sinkholes based on Tihansky (1999):

Answer 20

Solution sinkholes
Subsidence sinkholes
Collapse sinkholes
Pipe sinkholes

Question 21

It has small lake in closed depression in limestone, due to an impervious clay floor or to intersection of depression with the water table.

Answer 21

Solution sinkholes

Question 22

It has lowering of the surface of the ground because of removal of support. Caused in karst
areas by subterranean solution or collapse of caves

Answer 22

Subsidence sinkholes

Question 23

It is a closed depression formed by
the collapse of tie roof of a cave

Answer 23

Collapse sinkholes

Question 24

It is a vertical cylindrical hole - attributable to solution, often without surface expression, filled with
debris, such as sand, clay, rock chips, and bones

Answer 24

Pipe Sinkholes

Question 25

CAUSES OF SINKHOLE COLLAPSE

Answer 25

• Gravity
• Lowering of water table
• Heavy rainfall (sinkhole flooding)
• Ground movement due to
earthquake
• Ponding of subterranean river
• Subsidence in coral reef

Question 26

Give atleast 4 signs of a sinkhole

Answer 26

Cracks in the Ground
Depressions or Pits
Sinking or Tilting Trees
Sudden Appearance of Holes
(based on Slide 26 sa ppt ni Sir)

Question 27

It means splitting into chips or fragments where fragments
of a material (spall) are ejected from a body due to impact and
stress.

Answer 27

Spalling

Question 28

Predicting and Mitigating Subsidence Hazards:

Answer 28

• Generation of subsidence susceptibility maps
• Borehole studies
• Ground Penetrating Radar Surveys
• Mapping of tension cracks and subsidence features
• Regulate groundwater extraction
• Fluid injection
• Grouting

Question 29

True or False: Ground Subsidence is also considered as a mass wasting process.

Answer 29

False

Question 30

Subsidence is related to _______________ which is the weight of the overlying rock and sediment bearing down on subsurface materials.

Answer 30

overburden pressure