Concept and nature of natural hazards
3.1.5.1 The concept of hazard in a geographical context
Nature
A perceived event which causes loss of life and damage to properties, damage to the environment and disrupts human activities
Primary
Secondary- landslides and tsunamis
Disaster- great loss of life and destruction
Forms
Geophysical- earths core processes- volcanoes and earthquakes
Atmospheric- energy from sun drives processes in atmosphere- solar radiation- wildfire, tropical storms- changing- carbon budget, decreasing output
Hydrological- energy from sun drives processes in the hydrosphere- flooding
and potential impacts of natural hazards
risk- determined by hazard x vulnerability/ resilience
vulnerability- potential for loss, risk of exposure to hazards combined with inability to cope with them
why stay? Lack of alternatives, benefit- willing- volcanoes tourism, changing levels of risk
vulnerability causes- wealth and level of technology , education and topography
Hazard perception and its economic and cultural determinants
Fatalism- nothing can be done
Eg- Haiti economic- one of poorest nations in world, subsistence farming- poor income, cant afford to build houses that will last seasonal rain
Cultural- voodoo- god determines when people die, hope in afterlife, live 16 times
Adapatation- respond by preparing.
Eg- LA- economic- largest economy in usa, $5 mil on earthquake proof building
Culture- resilient community, religious beliefs- optimistic
Fear- so vulnerable- move away
Characteristic human responses – fatalism, prediction, adjustment/adaptation, mitigation, management, risk sharing –
and their relationship to hazard incidence, intensity, magnitude, distribution and level of
development.
The Park model of human response to hazards
Collects info on the impact of the hazard on the quality of life and the impact of the management in the relief, rehabilitation and reconstruction stages on quality of life.
Use to evaluate how much quality of life was affected and how resilient and vulnerable the place is.
The Hazard Management Cycle.
Collects info on the hazard management actions in a place and the timing of management relative to the hazard event- pre, during, post
- preparation to reduce vulnerability- learn from past
Use to evaluate community preparedness and have they learnt from previous event.
Both-
+ learn from past events, guide for air and reconstruction, improve resilient, evaluate success
- countries have varying capacity to prepare, prep can be overwhelmed by scale of hazard- Japan tsunami 2011, prep can be overwhelmed by human factors- typhoon Haiyan
3.1.5.2 Plate tectonics
Earth structure
Centre- core- dense rock containing iron and nickel, solid inner and very hot molten outer
Mantle- thickest layer- molten/semi molten- upper and more fluid- asthenosphere
Lithosphere- upper mantle and crust
Outer- crust
Oceanic- less thick, younger, heavier
Continental- thicker, older, lighter
and internal energy sources
Primordial- heat lost from earth as it continues to cool from original formation.
Radiogenic heat- heat produced by radioactive decay.
Most heat is found in a liner pattern in the centre of the Atlantic, Indian and Southern Ocean
Lowest heat concentrated in large land masses
Plate tectonic theory of crustal evolution:
Tectonic plates; plate movement gravitational sliding; ridge push, slab pull; convection currents and seafloor spreading.
Continental drift-1910s- Alfred Wegner- todays continents are formed from the splitting of Pangaea (one large continent)
+ geological evidence- fit of south America and west Africa, biological evidence- fossils found in India and Australia are compatible.
- can’t explain how continents move
Sea Floor spreading-1940s- creation of new land at mid ocean ridges- spreading ocean plates away from centre.
+ magnetic strips due to palaeomagnetism mirrored exactly either side of mid ocean ridge.
- can’t explain how space for new land is created and the speed of plate movement
Subduction- 1960s- if land is created at mid-ocean ridge, then it must be destroyed at the ocean margin.
+ huge oceanic trenches where large areas of ocean floor are pulled downward.
- speed of plate movement is faster than can be explained
Convection currents- 1980s- the circulation of magma due to thermal convection currents makes the crustal plat move.
+ unequal temp at surface indicates where hotter magma is rising, and cooler magma is sinking.
- not be proven- can’t access mantle
Ridge push- the pushing force that plates experience as they slide down the raised asthenosphere underneath Mid Ocean Ridges.
Slab pull- denser oceanic plate sinks into mantle at subduction zones.
Gravitational sliding- constructive margins have elevated altitudes because of the rising heat between them which creates a slope- oceanic plate slides into
Destructive (convergent)
Plates move towards each other.
Oceanic + constructive= oceanic plate is forced under continental, as it sinks plate melt due to friction in the subduction zone
Constructive (divergent)
Two plates move away from each other.
Magma rises through the asthenosphere tot eh surface, as this newly formed rock gets older the gravity causes it to slide away from the ridge.
Conservative
Two crustal plates slide past each other, and the movement of the plate is parallel to the plate margin.
No volcanic activity- San andreas fault
Characteristic processes: seismicity and vulcanicity.
Associated landforms:
young fold mountains- destructive plate boundary, The movement of the two plates forces layers of sedimentary rock upwards into a series of folds.
Earthquakes, landslides, and volcanoes
Eg- Himalayas
rift valleys - A rift valley is a linear shaped lowland- formed because of the pulling apart of the lithosphere- constructive plate.
earthquakes, volcanoes
eg- west Atlantic rift
ocean ridges- constructive, magma rises as plates move away from each other- less dense
earthquakes, volcanoes eg- mid Atlantic rift
deep sea trenches- destructive, point at which the oceanic plate is subducted and melts
earthquakes and volcanoes
eg- Mariana trench
island arcs- destructive- magma rises at melting zone- volcanic arc
earthquakes, volcanoes, landslides
Mariana islands
Volcanoes- constructive magma rises where plates move away from each other through the main vent
Magma plumes and their relationship to plate movement.
Localised heating causes at plume of magma to rise through he mantle and eats into the crust
Where lava breaks through- volcanoes form
As plates move the volcanoes moves until eventually becoming extinct
Volcano leaves hot spot tracks where islands can form
Eg- the Hawaii island chain- 6,000km chain of volcanic islands
Limitations- cant be applied to all volcanic activity