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Questions and Answers
What natural phenomenon can occur when groundwater abstraction creates a cavity?
What natural phenomenon can occur when groundwater abstraction creates a cavity?
Which factor contributes to ground subsidence during the dry season in areas with clay soil?
Which factor contributes to ground subsidence during the dry season in areas with clay soil?
How does oil and natural gas extraction affect rock layers?
How does oil and natural gas extraction affect rock layers?
What is the typical wind speed classification of a typhoon?
What is the typical wind speed classification of a typhoon?
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What happens to the pressure between rock layers due to groundwater withdrawal?
What happens to the pressure between rock layers due to groundwater withdrawal?
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What are the signs that indicate a typhoon is close to landfall?
What are the signs that indicate a typhoon is close to landfall?
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Which process is a common natural cause of ground subsidence?
Which process is a common natural cause of ground subsidence?
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What role do underground mining activities play in ground subsidence?
What role do underground mining activities play in ground subsidence?
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Which factor contributes to oversteepening of a slope?
Which factor contributes to oversteepening of a slope?
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What process leads to the formation of a void underground when limestone is involved?
What process leads to the formation of a void underground when limestone is involved?
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Which geological hazard is described as settling of the earth's surface below its natural level over time?
Which geological hazard is described as settling of the earth's surface below its natural level over time?
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What effect does adding a landfill or construction on top of a slope typically have?
What effect does adding a landfill or construction on top of a slope typically have?
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Which natural process is a primary contributor to ground subsidence?
Which natural process is a primary contributor to ground subsidence?
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What creates acidic water that can dissolve limestone?
What creates acidic water that can dissolve limestone?
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What is the consequence of acidic water reacting with limestone underground?
What is the consequence of acidic water reacting with limestone underground?
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Which of the following is a characteristic of geological hazards?
Which of the following is a characteristic of geological hazards?
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What is a common result of an incoming typhoon?
What is a common result of an incoming typhoon?
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Which cloud type typically fills the sky about 36 hours before a typhoon?
Which cloud type typically fills the sky about 36 hours before a typhoon?
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What indicates that a thunderstorm may be developing?
What indicates that a thunderstorm may be developing?
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What is one of the impending signs of a thunderstorm?
What is one of the impending signs of a thunderstorm?
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What happens to atmospheric pressure as a typhoon approaches?
What happens to atmospheric pressure as a typhoon approaches?
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What might signify a severe thunderstorm in terms of wind conditions?
What might signify a severe thunderstorm in terms of wind conditions?
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What can happen if a thunderstorm becomes severe?
What can happen if a thunderstorm becomes severe?
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Which of the following is NOT typically associated with an approaching typhoon?
Which of the following is NOT typically associated with an approaching typhoon?
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Which factor is a natural cause of landslides?
Which factor is a natural cause of landslides?
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What is the primary reason for slope failure in oversteepening?
What is the primary reason for slope failure in oversteepening?
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How does vegetation contribute to slope stability?
How does vegetation contribute to slope stability?
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What might artificially increase the risk of landslides on a slope?
What might artificially increase the risk of landslides on a slope?
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What is one effect of prolonged heavy rainfall on slopes?
What is one effect of prolonged heavy rainfall on slopes?
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Which process may lead to overloading of a slope?
Which process may lead to overloading of a slope?
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How does human activity typically contribute to landslides?
How does human activity typically contribute to landslides?
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Which of the following is NOT a cause of landslides?
Which of the following is NOT a cause of landslides?
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Which scenario illustrates natural landslide oversteepening?
Which scenario illustrates natural landslide oversteepening?
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What role does slope angle play in stability?
What role does slope angle play in stability?
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What are the three primary elements needed to sustain a fire?
What are the three primary elements needed to sustain a fire?
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During which stage of a fire is it considered to be at its hottest point?
During which stage of a fire is it considered to be at its hottest point?
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What is a common cause of fires related to electrical systems?
What is a common cause of fires related to electrical systems?
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Which of the following is considered a dangerous stage of fire, even when it is running out of fuel?
Which of the following is considered a dangerous stage of fire, even when it is running out of fuel?
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Which of the following types of fires can be caused by unattended open flames?
Which of the following types of fires can be caused by unattended open flames?
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What is the primary function of a barograph?
What is the primary function of a barograph?
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Which instrument is used to measure the height of the cloud base using time measurement?
Which instrument is used to measure the height of the cloud base using time measurement?
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What does a rawinsonde measure in addition to temperature and pressure?
What does a rawinsonde measure in addition to temperature and pressure?
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How does Weather Surveillance Radar function?
How does Weather Surveillance Radar function?
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Which color indicates a low susceptibility to landslides in rain-induced areas?
Which color indicates a low susceptibility to landslides in rain-induced areas?
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Which instrument uses radar echoes to determine wind speed and direction?
Which instrument uses radar echoes to determine wind speed and direction?
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What does Doppler Radar primarily estimate?
What does Doppler Radar primarily estimate?
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Which weather monitoring tool is equipped with a transmitter for atmospheric measurements?
Which weather monitoring tool is equipped with a transmitter for atmospheric measurements?
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Study Notes
Geological Hazards
- Naturally occurring earth phenomena that can cause danger and disrupt economic and social activities.
- Examples include landslides and ground subsidence.
Landslide
- Downslope bulk displacement of soils and rocks due to gravity.
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Natural Causes:
- Weathering
- Slope angle (steepness)
- Soil profile and its components
- Groundwater activity
- Earthquakes
- Volcanic eruptions
- Extreme rainfall
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Artificial Causes:
- Deforestation
- Adding weight to slopes (buildings, infrastructure)
- Vibrations (traffic, human activity)
- Mining
- Quarrying
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Slope Stability and Equilibrium:
- Slope stability depends on slope angle, slope's load, and slope equilibrium.
- Failure to achieve equilibrium is caused by increased slope angle (oversteepening) and increased slope load (overloading).
-
Oversteepening:
- Happens when a part of a slope is cut, excavated or eroded.
- Happens naturally due to weathering or artificially.
- Weakens the support of the slope's lower section/base on its load.
Ground Subsidence
- Settling or subsiding of Earth's surface below the natural ground surface level.
- Occurs over a long period.
- Less dangerous than other hazards.
-
Carbonate Dissolution and Collapse:
- Slow natural process causing ground subsidence.
- Common in limestone areas.
- Limestone is mainly calcium carbonate.
- Acidic water dissolves limestone, creating voids underground.
- The voids can cause depressions on the surface, potentially creating sinkholes.
Ground Subsidence: Causes
-
Groundwater Abstraction:
- Withdrawal of water from underground sources reduces pressure between rock layers.
- This can cause surface depression ("subsidence").
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Underground Mining:
- Removal of large amounts of underground material can cause subsidence.
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Change of Season:
- Dry seasons cause clay soil to shrink, leading to ground subsidence in areas with abundant clay.
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Oil and Natural gas extraction:
- The process reduces the pressure between layers, weakening support systems for upper layers.
Hydrometeorological Hazards
-
Typhoons:
- Violent tropical cyclones over warm waters (North of equator, Western Pacific Ocean).
- Counterclockwise winds (speed 118-220 km/h; super typhoons >220km/h).
- Signs include increased ocean swell, changes in clouds (cirrus, dark clouds), barometric pressure drop, and abrupt changes in wind speed.
-
Thunderstorms:
- Small-scale storms with lightning and thunder.
- Usually last 30 min. to an hour.
- Potential hazards include strong winds and heavy rainfall (hail, tornadoes).
- Signs include a system of cumulonimbus clouds, dark sky (with tints), lightning and thunder.
Flood and Flash floods
- Flooding occurs when land areas are submerged, often after heavy rainfall.
- Flash floods occur faster, often due to heavy rainfall on already saturated ground.
- Signs of flooding include standing water, rapidly rising water, muddy water, and debris in water.
Fire
- The elements of fire triangle: Oxygen, heat and fuel.
- Stages of fire: Incipient, growth, fully developed, and decay.
- Causes of fires: Faulty wiring, gas leaks, neglected stoves/appliances, and cigarettes.
Tools for monitoring
- Mention various instruments and tools used to monitor different weather conditions including typhoons, floods, and fires to prevent potential hazards or predict the hazard occurrence.
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Description
Test your knowledge on geological hazards, focusing specifically on landslides. Explore the natural and artificial causes, as well as principles of slope stability and equilibrium. Understand how various factors influence the occurrence of this natural phenomenon.
