Y2) TERM 2&3- NATURAL HAZARDS Flashcards
Define ‘hazard’
A hazard is where a geophysical event threatens life and the things that people value (Example: A volcanic explosion in a desert=not a hazard because no one is there)
How might hazards be catagorised?
Hazards are broadly categorised into 4 categories; into tectonic, geomorphological, atmospheric and biological
Where do most tectonic hazards occur?
Tectonic hazards occur largely at tectonic plate boundaries
Where do most atmospheric/biological hazards occur?
Atmospheric hazards often occur in specific bands around Earth:
- Hurricanes= 5-20 degrees of the equator
- Wildfires= areas where vegetation has dried out (often forest edges or places where extreme weather is prevalent
Define ‘risk’
Exposure of people to a hazardous event
Define ‘vulnerability’
Potential for loss
Define ‘perception’
The way in which an individual or group views the threat of an event
Why do people live in hazardous environments?
- lack of alternatives
- changing level of risk
- benefits outweighing costs
- perception of the ability to adapt
- hazards are unpredictable
How might people perceive hazards?
FAF
F- fatalism
A- adaptation
F- fear
How might hazards be managed?
The 3 P’s
- Prediction
- Prevention
- Protection
What is the Sendai framework?
UN based, global cooperative for Disaster Risk Reduction (DRR)
What do ‘hazard models’ show?
These show typical/ generalised approaches/ responses to hazard events. For example: Parks Model and the Hazard Management Cycle
Name the layers of the Earth
From the inside out:
- Core (inner and outer)
- Mantle
- Crust
Or:
- Inner core
- Outer core
- Mesosphere
- Asthenosphere
- Lithosphere
Outline the characteristics of the 2 types of crust
- Oceanic- 6-10km thick, SIlica MAgnesium (SIMA), density of 3gcm-3, basaltic , silica content of 45%, runny lava
- Continental- 35-40km thick, SIlican ALuminium (SIAL), density of 2.6gcm-3, granitic, silica content of 70%, thick lava
What is the first ‘golden rule’ of plate tectonics?
Silica is sticky
State the evidence for plate tectonics
- Geological
- Biological
- Climatological
- Seismic waves
- Magnetosphere
- Sea floor spreading
- Paleomagnetism
Why do plates move?
The plates move slowly due to:
- Basal drag or convection currents- these currents are in the mantle, causing friction (basal drag) on the underside of the plate, dragging the plate along
- Slab pull- the weight of the descending plate dragging the plate along
- Ridge push- updoming at the margin pushes the plate along under the influence of gravity
What are the 3 main plate boundary types?
- Constructive- plates move apart
- Destructive- plates move together
- Conservative- plates move alongside each other
What are ocean ridges?
These form where plates move apart under the oceans. E.g the Mid Atlantic Ridge
What is a rift valley? (horst and graben)
These form where plates move apart under the land. E.g East African Rift Valley
What is a divergent plate boundary?
Plates move apart (constructive plate boundaries), such as the N American and Eurasian plates
What is happening at the Mid Atlantic Ridge?
The N American and Eurasian plates are diverging, resulting in a volcanic ridges found running from N to S the length of the Atlantic ocean- in places, the ridge is high enough that it can be seen above sea level, such as Iceland.
What is happening in the Great African Rift Valley?
The African continent is being ripped in half. The Nubian plate is separating from the Somalian plate resulting in a horst and graben landscape. In a million years time, these grabens could be gone and inundated (filled) with sea water
What are the dimensions of the Great African Rift Valley?
50km wide, 4000km long and 600 meters deep
Why does silica matter?
Silica is sticky.
High silica content will mean that lava is slow flowing and will form steep sided volcanoes which will make them very explosive
Low silica content will mean that lava is fast flowing and will form gently sloping volcanoes which will be effusive (not explosive)
The continental crust has a higher silica content than oceanic, so volcanoes will be more explosive, steeper sided and have a different set of hazards associated with them
What is a destructive plate boundary?
Where 2 or more plates converge or move into each other
Does oceanic crust sink or ‘float’?
Oceanic crust will always sink because it is denser than continental crust is. Continental crust will ‘float’
What are the 3 possible combinations found at typical destructive plate boundaries?
- Oceanic vs Oceanic
- Oceanic vs Continental
- Continental vs Continental
List come landforms found at destructive plate boundaries
Island arcs, ocean trenches, young fold mountains and old fold mountains
Comment on the hazards you might expect at a constructive boundary
Conservative boundaries occur where plates ‘slide’ past each other and no melting occurs so no volcanoes will form and earthquakes will occur
Why is the San Andres Fault famous?
This is famous for earthquakes
How can plate movement be monitored?
Plate movement can be monitored on the ground (tilt meters) or from space (GPS)
Where do hotspots occur?
Hotspots occur in the middle of plates due to plumes of magma within the mantle breaking through the crust in interpole regions (e.g Hawaii)
What could cause earthquakes that isn’t plate tectonics?
- bomb testing
- building collapse
- downwarping of the crust (RIS)
- mineshaft collapse
- fracking
How fast do plates move?
They move at around 5-6 cm per year and some up to 18 cm per year
Why do plates move at different speeds?
They move at different speeds because they are all affected by slightly different processes and convection currents may acct as a brake as well as an accelerator
Explain the difference between lava found at an oceanic vs oceanic destructive plate boundary compared to an oceanic vs continental destructive plate boundary
- Oceanic vs oceanic destructive plate boundary= runny lava (basaltic/andesitic)
- Oceanic vs continental destructive plate boundary= viscous lava (dacitic/rhyolitic)
- This is due to plutons absorbing silica from the overlaying plate. If the overlaying plate is oceanic, the silica content of the plutons will remain low/ if the overlaying plate is continental, the silica content of the plutons will increase
Why is rhyolitic lava more viscous than basaltic lava?
Because there is a higher silica content, making it stickier
Does oceanic crust always sink?
It always sinks because the oceanic crust is denser than the continental crust
Name the 4 types of lava (B….A…..D….R)
B- Basaltic (~45% silica)
A- Andesitic (~55% silica)
D- Dacitic (~65% silica)
R- Rhyolitic (~75% silica)
What’s the difference between a’a and pahoehoe lava?
A’a is slow flowing and spiky, whereas pahoehoe is more fast flowing and smooth looking
Outline the relationship between silica content and lava temperature
The higher the silica content, the lower the lavas temperature will be
What is the VEI?
This is the Volcanic Explosivity Index. This is like the Richter scale but for volcanoes and is measured based on the observed ejecta
What is a ‘Hawaiian eruption’?
These are fast flowing, high temperature and most often effusive eruptions
What is a ‘Plinian eruption’?
These are very explosive
Name 4 primary effects of volcanic eruptions
- Lava flows
- Pyroclastic flows
- Pyroclastic materials (ash, tephra, blocks, bombs)
- Gases
Name some secondary effects of volcanic eruptions
- Lahars
- Tsunamis
- Climate change
- Acid rain
Why does the USA have a special interest in La Palma?
It is a Canary island and could cause a mega-tsunami sending waves of up to 300m towards the East coast of the USA
What is pyroclastic flow?
This is a mix of hot ash, lava fragments and gases. Can move up to speeds of 450 mph and can be 1000 degrees Celsius
What is pyroclastic materials?
These are ash (2mm), lapilli (2-64mm, little stones), volcanic bombs (64mm+) or volcanic blocks (massive volcanic bombs)
What are lahars?
A lahar is made up of water, ashes, debris, mud and pyroclastic material. This creates a mud flow and can move at 60 mph and can be 100 degrees Celsius
How do volcanoes cause climate change?
Volcanoes cause climate change by releasing greenhouse gases such CO2 into the atmosphere
How do volcanoes create tsunamis?
Volcanoes create tsunamis when they generate massive landslides (Lituya Bay // La Palma)
How might we be able to predict an eruption?
Predicting an eruption
- Gases
- Surface deformation
- Phreatic explosion
- Seismic activity
- Return interval
How do you structure a 9 marker?
no intro // 3 x PEEL paras // conclusion
What does “the return interval” mean, in the context of volcanic eruption?
“The return interval” means the amount of time between eruptions, e.g. “This volcano erupts every 50 years…”
Where do most earthquakes happen?
~90% of earthquakes occur mainly at plate boundaries; the most powerful being at destructive plate boundaries
Earthquake depth – which are the most powerful?
Earthquake depth – shallow quakes are the most powerful
What are the 3 types of seismic wave called?
P, S and L waves move the ground in all directions; waves can also be “amplified” by soft rock
List some primary seismic hazards
Primary hazards include – earth shaking, ground rupturing!
List some secondary seismic hazards
Secondary hazards include tsunamis, liquefaction, landslides
How do we measure earthquakes (which scale)?
Earthquakes are measured on the Richter Scale, MMS and Mercalli scale
The impacts of earthquakes depends on what?
The impacts of earthquakes depends on numerous physical and human factors
What is geo-amplification?
Geo-amplification can cause seismic waves to reduce in magnitude (hard rock) or become “amplified” (soft rock)
Comment on the relationship between magnitude and frequency of earthquakes
Magnitude vs frequency of earthquakes: high magnitude events have a low frequency, and low magnitude events have high frequency. Simples
What’s the difference between a mass damper and a tuned mass damper?
Mass damper vs tuned mass damper: mass dampers are a simple mass added to a building to remove it from the resonant frequency of earthquakes to limit shaking; tuned mass dampers also move to compensate for “swaying”
What does “cross bracing” try to do?
“Cross bracing” tries to control how/ and how much a building flexes, to limit the likelihood of catastrophic collapse, or “pancaking”
Explain how a base isolator works?
Base isolators work by putting a “shock absorber” between a building and the ground, so that as the earth shakes, the vibrations are absorbed by the shock absorber (i.e. the “damper”), and the building doesn’t get as damaged.
Summarise Japan’s earthquake management strategies.
Japan’s earthquake management strategies are awesome – if you invented a list of every management strategy you could think of, you’d be correct!
What is a shake table?
A shake table is a large platform, supported on powerful hydraulics, where full partial scale buildings are constructed and subjected to simulated earthquakes, whilst being thoroughly monitored inside and out.
How might a LIC manage earthquake hazards?
LICs might manage earthquake hazards using low-tech solutions, such as tyres for base isolators, water butts for mass dampers, cross-bracing to improve structural integrity, lightweight structures to reduce casualties/ fatalities upon collapse
Explain the formation of a tsunami (use the diagrams below! )
Tsunamis are formed when sea bed uplift occurs, displacing the sea above creating two waves travelling in opposite directions
Describe and explain the process of liquefaction
Liquefaction is where the ground “becomes like a liquid”, and becomes mobile, leading to the subsidence of buildings. Also, as the ground shakes, water is squeezed to the surface, further adding to the subsidence of buildings.
what is the speed of a P wave and what does it travel through
6000m/s
solid
liquid
what is the speed of a S wave and what does it travel through
3000m/s
solid
what is the speed of a L wave and what does it travel through
2500m/s
only found at surface
How does silica affect lava?
Silica is sticky! More silica = more viscous lava; less silica = runny lava. Consider BADR // consider oceanic vs continental materials…
What are the signs that a volcano might erupt?
Signs that a volcano might erupt: surface deformation / gases / seismic activity / phreatic explosion / increased surface temperature / odd animal behaviour…
Summarise one piece of evidence for plate tectonics
Evidence for plate tectonics; continental fit / mid-ocean ridges / palaeomagnetism / magnetosphere / geological (matching rock types) / biological (fossils) / climatological (coal in Antarctica/ glacial striations in Brazil)
Why do plates move?
Plates move due to convection currents in the mantle (basal drag) / slab pull / ridge push
Aseismic engineering – details please!
Aseismic engineering – earthquake-proof-ness! Can be high or low tech / mass dampers / tuned mass dampers / base isolators / cross bracing / reinforced concrete / small windows / escape routes and chutes / anything else?…
List the 4 requirements for a hurricane to form
The 4 requirements for a hurricane to form are: 27oC SST, depth of 50m // Coriolis // a really low, low-pressure system // weak vertical wind shear
How fast does the wind need to be moving to be called a “hurricane”?
The wind needs to be moving at 74mph (120kmh) to be called a “hurricane”
90% of deaths associated with hurricanes is caused by what?
90% of deaths associated with hurricanes is caused drowning
List some hurricane management strategies
Some hurricane management strategies include:
Sand bags
Shuttering
Radar
Lidar
Buoys
Levees
Afforestation
Land use zoning
Media
Stilts
Coral reef maintenance
Structural reinforcements
Aid
Insurance
Cloud seeding
Refrigerated mortuary trucks
Emergency shelters and drills
