Ground Subsidence and Karst Subsidence Flashcards
Defined as the lowering of the land surface due to
sinkhole development
Karst subsidence
t or f: Sudden collapse events are rarely major disasters, certainly not anywhere near the scale of the
earthquake, volcanic, tsunami, or landslide disasters
t
t or f: Slow subsidence of areas can cause as much
economic damage, although spread out over a
longer period of time.
t
this is one of the most dangerous geohazards according to mgb due to its extreme unpredictibility
subsidence due to sinkhole collapse
triggering mechanisms for subsidence
carbonate dissolution
removal of solids and mine related collapse
fluid withdrawal
Water in the atmosphere can dissolve small amounts
of _________ which results in rain water having a small amount of _____________ when it falls on the earth’s surface
carbon dioxide (CO2) ; carbonic acid (H2CO3)
carbonic acid plus calcium carbonate prduces
calcium ions and bicarbonate ions (dissolved CaCo3)
examples of mining activities that results in collapse
salt mining (injection of fluid and extraction of brine)
coal mining (room and pillar mining)
If fluids are withdrawn from below the surface, a
_____________ may occur resulting in the
removal of support and possible collapse.
decrease in fluid pressure
two of the most important fluids that occur beneath the surface
groundwater and petroleum (oil and natural gas)
first recognized subsidence due to oil withdrawal
Wilmington oil field of Long Beach, California (1940)
are affected by Wilmington oil field subsidence
50km2
vertical displacement if Wilmington oil field subsidence
9m
reduced area of subsidence (Wilmington) ; what year
8km2 ; 1962
other technical term for sinkhole
doline
the word “doline” derives from the _________ word “____” meaning _____________
Slovene ; dolina ; depression in the landscape
english terms for sinkholes with rather loose connotations
sinkhole, swallet, and swallow hole
several processes that form doline
surface solution
cave collapse
piping
subsidence
stream removal of superficial covers
five-fold classification of dolines
- Solution Dolines
- Collapse Dolines
- Suffossion Dolines
- Subsidence Dolines
- Alluvial stream-sink 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.
Solution Dolines
are produced suddenly when the roof of a cave formed by underground solution gives way and fractures or ruptures rock and soil.
Collapse 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.
suffossion dolines
form gradually by the sagging or settling of the ground surface without any manifest breakage of soil or rock
subsidence dolines
form in alluvium where streams descend into underlying calcareous rocks
Alluvia stream-sink dolines
the point at which a stream disappears underground.
stream-sink
manifestations of a subsidence doline
tilted vegetations
term for coalesced doilines
uvala
small lake in closed depression
in limestone, due to an impervious clay floor or to
intersection of depression with the water table.
solution sinkholes
lowering of the surface of the
ground because of removal of support. Caused in karst areas by subterranean solution or collapse of caves
subsidence sinkholes
a closed depression formed by
the collapse of tie roof of a cave
collapse sinkhole
a vertical cylindrical hole - attributable
to solution, often without surface expression, filled with debris, such as sand, clay, rock chips, and bones
pipe sinkhole
pipe sinkholes are filled with debris such as
sand, clay, rock chips, and bones
causes of sinkhole collapse
- Gravity
- Lowering of water table
- Heavy rainfall (sinkhole flooding)
- Ground movement due to earthquake
- Ponding of subterranean river
- Subsidence in coral reef
how are sinkholes formed?
diagram go
signs of sinkholes in your backyard
topography
ponding of water
tension cracks
orientation of vegetation
Splitting into chips or fragments
where fragments of a material (spall) are
ejected from a body due to impact and stress.
spalling
g=fragments of a material ejected from a body du to impact and stress
spall
predicting and mitigating subsidence hazards
- Generation of subsidence susceptibility maps
- Borehole studies
- Ground Penetrating Radar Surveys
- Mapping of tension cracks and subsidence features
- Regulate groundwater extraction
- Fluid injection
- Grouting
injection of special cement on the subsurface
grouting
signs that an area has karst topography
shard ridges, conical hills
age of limestones in the philippines
eocene - pleistocene
