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