Geophysical hazards Flashcards
What are the 5 main mechanics of plate movement?
Internal heating
Plumes
Subduction
Rifting at margins
Convection currents
What are the 2 main sources of heat flow within the Earth?
Radiogenic - decay of materials
Primordial heat - heat lost by earth as it begins to cool
Describe convection currents
Hot magma near to the core to the surface heats up, becoming less dense and so moving upwards and spreads out at mid-ocean ridges.
The cold solidified crust sinks back into the earth’s interior because it is heavier and denser than the surrounding material.
This is caused by heat from radioactive decay of uranium and potassium in mantle
Describe the distribution of earthquakes
- occur near plate boundaries
- For example: centre of Atlantic ocean in association with mid-atlantic ridge
- There are many earthquakes around the edge of the Pacific Ocean
- Broad belts of earthquakes
- some anomalies
Describe the human causes of earthquakes
- construction of large dams
- mining
- testing of weapons
Describe the distribution of volcanoes
- found at plate boundaries
- some occur over hotspots
- Pacific Ring of Fire - most active volcanoes
- some occur in the middle of the ocean e.g: Hawaii.
Describe a hotspot
A hotspot is a plume of hot material rising from the deep within the mantle, responsible for volcanoes.
Where are landslides common? Give examples of some regions in the world
- areas with active tectonic processes
- high rainfall
- high population density
Examples:
- Southern Edge of the Himalayas
- Central China
- South West India
What is a recurrence interval or return period?
The expected frequency of occurrence measured in years for an event of a particular size.
Small events have a short return period whereas large events have a high return period.
Units for recurrence interval?
Years
Earthquake frequency and magnitude
The richter scale was used, logarithmic. But now M scale is being used. Moment magnitude scale which measures the amount of energy released.
How is strength of a volcano measured?
- Volcanic Explosive Index
- based on amount of material ejected in the explosion
- height of cloud it creates
- damage caused
Describe vulnerability
The geographic conditions that increase the susceptibility of a community to a hazard
Not only physical effects of a hazard, but also status and property of people
Describe the economic factors that influence vulnerability (5)
Quality of housing
Building styles and codes
Access to technology
Warnings and forecasting
Insurance cover
Describe the social factors that influence vulnerability (4)
Education - high education means more income, better quality housing
Public education about how to deal with events
Awareness of hazards
Gender - many women may feel responsible for children/elderly following an event
How do demographic factors affect vulnerability (3)
Population density
Age - elderly less mobile
Disability
How do political factors affect vulnerability (2)
Nature of society - provision of aid
Effectiveness of lines of communication
Geographic factors affecting impacts of a geophysical event? (8)
- Magnitude and frequency
- Population density
- Type of buildings
- Time of day
- Distance from event
- Types of rocks and sediment
- secondary hazards
- economic development
Definition of risk
A risk is the likelihood of the loss of life, injury, destruction or damage
Factors affecting the perception of risk?
- Experience - the more experience of hazards, the more people become adjusted
- Material well-being: those who are better off have more choice
- Personality
Describe how hazards are characterized (hazard profile)
- Magnitude
- Frequency
- Duration
- Areal extent
- Spatial concentration
- Speed of onset
- Regularity
Describe the trend in geophysical hazards
Remained broadly constant
Earthquakes have killed
more people than all disasters put together
Asia suffered the most
How is susceptibility to hazards increasing?
Population growth is occurring
Higher population density in highly seismic zones
Slums and squatter settlements expand onto high risk areas such as slopes and embankments
How are volcanoes predicted?
Seismometers to record swarms of tiny earthquakes that occur as magma rises
Chemical sensors to measure increased SULPHUR levels
Lasers/GPS to detect physical swelling of volcano
Ultrasound to monitor low frequency waves in the magma resulting from the surge of gas and molten rock
Difficult to predict volcano eruption
How to predict earthquakes?
- Seismometers
- Magnetometer
- Near-surface seismometer
- Vibroseis truck
- Strain meter
- Sensors in wells
- Satellite relays
- Laser survey equipment
How does a seismometer work?
To record micro-earthquakes
How does a magnetometer work?
To record changes in the earth’s magnetic field
How does a near-surface seismometer work?
To record larger shocks
How does a vibroseis truck work?
To create shear waves to probe the earthquake zone
How do sensors in wells work?
To monitor changes in groundwater levels
How do satellite relays work?
To relay data to the US geological survey
How does laser survey equipment work?
To measure surface movement
How to prepare for geophysical hazard adaptation: preparedness
Land-use zoning is an important adaptation
Different land uses may be prevented from locations in a zone that is known to be at risk of a hazard e.g: hospitals should not be built near fault lines
Take out insurance cover against natural hazards. LIC residents cannot afford insurance even if it is available. It is always much harder to justify spending money on an event that might not occur.
New technology can be used to record the swelling of volcanoes and changes in water chemistry. Mobile phones with GPS can be used to inform agencies about geophysical changes.
How to manage landslides?
- Terracing steep slopes
- Drainage of water from slopes
- Building restraining structures such as stone walls
- Erosion control at the base of cliffs
- Diversion of roads away from active areas
How to manage risk for earthquakes?
- Single storey buildings have greater stability than multi-storey
- Basement isolation: mounting the foundations of a building on rubber mounts which allow the ground to move under the building. This isolates the building from tremors
Building reinforcement strategies e.g: building on foundations built deep into underlying bedrock and use of steel-constructed frames that can withstand shaking.
- Land-use planning
Managing earthquakes in pakistan
- Light walls and gables are lightweight structures which are subject to smaller forces and are less likely to fall when the ground shakes
Quake-resistant houses are being built in Pakistan of straw. Compressed bales are held together by nylon netting and sandwiched between layers of plaster
Managing earthquakes in Haiti
In Haiti, heavy concrete roofs collpased on many homes; sheet metal roofs on wooden trusses are more resistant
Small, regularly spaced openings create fewer weak spots in walls. But in Haiti, walls were not properly reinforced
Peru earthquake management
Reinforced walls are made of natural materials such as eucalyptus or bamboo
Walls of some adobe houses have been reinforced with a plastic mesh to prevent collapse.
Earthquake management in Indonesia
- Confined Masonry: brick walls are framed and connected to the roof by corner columns and a crown beam of reinforced concrete. In a quake, the structure moves as a unit
- Shock absorbers: tyres are filled with stones or sand and fastened between the floor and foundation can serve as cheap ground-motion absorbers for many types of buildings.
How to control volcanoes?
- divert lava flows using dry channels or explosives or by pumping water onto the lava front to cool it
- Little can be done to reduce impacts from pyroclastic flows other than to evacuate the area
- GPS can be used to monitor the swelling of volcanoes, could indicate eruption
How to manage the risk of tsunamis?
Sea walls
early warning systems
Walls can only provide a certain amount of protection and will not stop bigger waves.
Cost dictates how high the wall can be built
Describe the rescue-rehabilitation-reconstruction
Rescue = immediate aftermath of a disaster. Sniffer dogs and search and rescue teams
Rehabilitation = refers to people making their homes safe again and live in them again
Reconstruction = fo r some, rehab isn’t possible, so reconstruction is necessary.
RapidFTR created by a student, used to reunite children with their parents in situations.
In exam, write about how there is a different in rehab and reconstruct in HICs and LICs. LICs takes longer than in HICs as government does not have the funds available.
Describe the structure of the earth
4 layers:
- crust - thick continental and thin oceanic
- liquid mantle - constitutes most of it
- liquid outer core
- solid inner core
Describe shield volcanoes
- no explosive activity
- basaltic lava which is runny
- gently sloping sides
- shallower crater
- large circumference
- Mauna Loa - Hawaii example
Describe composite volcanoes
- viscous lava
- alternating layers of lava
- large crater
- steep sides
- active and explosive
- sometimes parasitic cones grow on the sides e.g: Mount Etna
Describe cinder volcanoes
- formed by fragments of solid material which accumulates as a steep conical hill around the vent to form a cone
- Concave
- steep angle of 30-40 deg
- Cinder and ash cones are not very high
- eg: Volcano de Fuego (has a high cone)
- violent eruptions
- lava breaks up into cinders, ash and other fragments
Describe volcanic hazards
Pyroclastic flows:
- Ash and debris that has travelled through the air and fallen to the ground is known as pyroclastic deposits.
- Fine ash particles damage people’s lungs
- Ash is fairly heavy, thick enough for a building to collapse
- Travel at speeds over 500km/hr
Landslides:
Lahars:
- landslide
- debris becomes saturated with rainwater
Volcanic gases:
- C02: Cameroon
Focus is the top or bottom?
BOTTOM - original source of the release of tension
Epicentre top or bottom?
TOP - surface on Earth immediately above earth
