Managing Natural Hazards Flashcards
Structure of Earth
- Crust
- Upper Mantle
- Mantle
- Outer Core
- Inner Core
Describe the Crust
- Solid
- Oceanic Crust- thinner & denser (under oceans)
- Continental Crust- thicker & less dense (under mountain chains)
- Fractured into large tectonic plates that are slow and in constant motion
Describe the Mantle
- 84% of Earth’s volume
- Upper Mantle below the crust & is mostly solid- moves like melted plastic around plate boundaries
- Lower mantle is hotter & denser
- Temp & Pressure increases with depth
Define plate boundaries
Edges of tectonic plates
What is the lithosphere?
Topmost part of the upper mantle & crust
Explain the movement of tectonic plates above
Semi-liquid rock in the upper mantle is heated by the core & lower mantle
It rises towards the lithosphere
Descends into giant convection currents which drive the movement
Describe the Core
- Extreme temp derived from the radioactive decay of material from 4.5 billion years ago
- Layer of liquid iron above
Explain Earth’s magnetic field
The layer of cool iron allows the iron and nickel to move in convection currents
This movement creates the field
4 main types of plate boundary
- Constructive/ Divergent
- Destructive/ Convergent
- Collision
- Conservative/ Transform
Define Constructive/ divergent plate boundaries
When 2 PLATES ARE MOVING AWAY and a new crust is formed in submarine volcanoes when magma rises
Define Destructive/ Convergent plate boundaries
When dense OCEAN CRUST CONVERGES WITH CONTINENTAL crust, it is pushed down into the upper mantle at subduction zones
As it descends it melts, causing magma to rise and form volcanoes & ocean trenches
Define collision plate boundaries
Continental crust (same density) collides with others and plates are pushed upwards forming fold mountains
Define conservative/ transform plate boundaries
Plates do not slide, instead friction is built up and released using earthquakes
How do earthquakes form?
Tectonic plates are stuck due to friction
Pressure builds over time
Releases and huge shock waves of energy travel outwards along the surface, causing things to shake
Loss of life depends on a range of factors
- Depth of earthquake focus
- Geology of area
- Size & Magnitude
- Vulnerability of population
Measurements of intensity
- Mercalli intensity (1-12)
- Richter magnitude (1-8+)
Impacts of earthquakes
- Loss of life
- Damage to buildings
- Destroyed infrastructure
- Water-borne diseases (cholera)
- Landslides
- Tsunamis
How do volcanoes form?
They form at constructive and destructive plate boundaries as well as magma hotspots
Strength of eruption measure
Volcanic Explosivity Index (VEI)
Impacts from eruptions
- Lava flows
- Gas clouds (CO2 & nitrous oxide)
- Volcanic bombs
- Loss of life
- Loss of farmland and habitats
Reduce earthquake risk beforehand
- Large scale earthquake drills
- Retrofitting old buildings
- Educating population
- Local govts have detailed emergency management plan
- Mapping faults
Reducing earthquake risk during the event
- Send signals/ warnings to people
- Seismometers send signals to medical, fire, rescue stations
Reducing earthquake risk after event
- Search and rescue operation
- Meeting immediate needs of survivors
- Clean up, demolish, repair, planning
- Rebuild, reconstruct, replace
Reducing volcanic eruption risk before the event
- Evacuation plans
- Gas levels can be monitored
- Hazard risk maps
- Volcano shelters
- Education
Reducing volcanic eruption risk during the event
- Evacuation
- Ongoing monitoring for lahar
- Local air traffic will be diverted
- Resettlement
Reducing volcanic eruption risk after the event
- Rescue from damaged buildings
- Clear the ash-fall
- Permanent abandonment of some settlement
Why do volcanoes erupt?
Magma collects in magma chamber
Pressure increases causing fractures
Magma is less dense than surrounding solid rock so rises
Erupts on the surface through a volcano as lava, ash and gas
Define epicentre
Point on the Earth’s surface directly above where an earthquake occurs
Ways volcanoes are described
- Still active and erupting frequently
- Dormant (temporarily inactive but not extinct)
- Extinct
Difference between types of volcanos
- Dome :
Thicker, more vicious lava - Fissure:
Lava out of a thin, long vent - Shield:
Runny lava
Stratovolcanos
Lava dome with ash
Contain gases that increase explosivity
Components of an earthquake-proof building
- Identification no. for helicopters
- Open areas for evacuation
- Weights on roof to counteract shock waves
Define lahar
Mix of rainwater and ejected volcanic materials
Opportunities from Volcano eruptions
- Calderas form- agriculture employment
- Volcanic ash is highly fertile for soil
- Tourist treks & bike rides
- Fishing, water sports, irrigation, drinking source
- Minerals that are mined- volcanic ash
- Produce electricity (geothermal power)
- Volcanic rock statues
