Tectonics and vulnerability Flashcards
Description of constructive margin
-Core heats magma, rises to asthenosphere
-Cannot break through so moves parallel
-Plates are dragged apart
-Ridge push as plates are pushed up in the middle and their weight pushes them apart
-Slab pull where the other end of the plate is on a destructive margin
-Mid Atlantic ridge
Mantle characteristics
870 C
Less to medium density
Upper=olivine Lower=magnesium silicate
Liquid & solid
Outer core characteristics
4400-6100 C
Dense
Iron & sulphur
Liquid
Inner core characteristics
7000 C
Very dense
Iron & Nickel
Solid
Effusive
Runny
Description of destructive margin
-Oceanic plate is subducted (slab pull)
-Fold mountains, as plate concertinas
-Melted rock & gas in subduction zone
-Great pressure so magma rises to make volcanoes, these are explosive
-Many shallow and deep EQs with benioff zone going deep
-Nazca and SA plates
Description of continental collision margin
-Neither subducts so no volcanoes
-Crumple upwards to make fold mountains
-EQs mainly on boundary and are very violent, also intra-plate as plates deform
-The Alps (African and Eurasian)
Description of transform margin
-Plates move parallel
-No subduction so no volcanoes
-Many shallow EQs
-Elastic rebound
-San Andreas Fault
Elastic rebound
Plates get stuck at the margin so start to bend. Snap back to original shape in new locations.
Formation of island chains
-Hotspot in oceanic plate
-Outpouring of basalt makes land
-Plate moves so creates island in new spot
-Hawaii
Causes of intra-plate EQs
-Old weaknesses from previous collisions
-Climate change causing isostatic rebound
(New Madrid fault line)
-Rising sea levels adding weight to crust
Viscosity
Low=runny High=thick
More silica = Higher viscosity
Basaltic lava
Low viscosity
Where lava is heated by core and low in gas
Low magnitude eruptions
Constructive margins
Rhyolitic lava
High viscosity
Where subduction adds silica, gas and water to the magma
Magma has difficulty making it to the surface but creates very explosive eruptions when it does
Ash clouds, pyroclastic flows, volcanic bombs and lahars
Destrucive margins
Earthquake terminology
Focus- Origin point
Epicentre- Point on surface above focus
Seismic waves- Transmit energy from eq
EQ wave types
P - Compression, less damaging, fastest
S - Vertical amplitude, slower
L - Side to side, most damaging, at surface
Liquefaction
Water saturated material becomes loose and water surrounds all grains.
Christchurch, New Zealand
Primary impacts of a volcano
Lava flow
Pyroclastic flow
Gas eruptions
Ash cloud
Secondary impacts of a volcano
Lahars
Landslides
Jokulhlaup
Acid rain
Pyroclastic flow
Formed from collapse of eruption column; lava dome or lava flow. Fluidized by water vapour and gases. Montserrat 1997
Lahar
A slurry of mud, water and volcanic debris, formed when a pyroclastic flow melts snow/ice or there is heavy rainfall
What causes a tsunami (tsunamigenesis)
An impulsive and rapid crustal movement which displaces the water above it to create a series of waves
Shoaling effect
As a wave/tsunami enters shallow water, the velocity diminishes and the height increases
Natural hazard definition
An extreme event that has potential to cause loss of life and damage to property
The pressure release model
Root causes
+Dynamic pressures
+Unsafe conditions
+Natural hazard
=Disaster
Risk = Hazard x Vulnerability
Root causes
Limited access to: power, structures, resources.
Political & economic systems
Dynamic pressures
Lack of: training, local investment, press freedom
Rapid population change/urbanisation
Deforestation
Unsafe conditions
Physical environment
Local economy
Social relations
Factors affecting perception of disasters/hazards
Common or rare event
Media coverage
Death toll
Location/timing
Education
Immediate or delayed impacts
Belief in authority
Why has the number of disasters risen historically
-More people living in danger zones
-More hazards recorded by social media (but less reliable)
-Better monitoring (esp for LICs)
-Better understanding
-More priority of data collection
Nepal vulnerability
-Low GDP/high debt so lack of defence investment and ability to deal with secondary impacts
-Women don’t work
-Isolated communities in mountains
-Monsoons cause landslides
-Unequal education
