Physical Geography: Hazards angel

Causes of hazards

Natural or environmental

Human

Geophysical hazard

Related to the earth (earthquakes, Volcanoes)

Hydrological hazard

Related to water (Tsunami, Storm surge)

Atmospheric hazard

Related to weather (Tornado, Lightning)

Disaster

Realisation of a hazard when it causes damage

Vulnerability

The potential of loss

Types of Vulnerability

Physical (fault lines, high/lowland)

Economic (prediction, prevention)

Social (ability, age, economic status)

Acceptance (fatalism)

people can do nothing to control events, losses have to be accepted.

Domination

Hazards are predictable and can be better understood using research

Adaptation

Mitigating and managing loss and vulnerability

Stage one of the park model

Normal quality of life, Education and preparation is occurring, medical teams ready.

Stage two of the park model

Hazard occurs, QoL drops dramatically, evacuation occurs

Stage three of the park model

Search, care and rescue teams work to reduce/reverse the decline in QoL

Stage four of the park model

Rehabilitation phase, provision of aid in order to return to normal QoL

Stage five of the park model

Reconstruction and economic recovery, review of process occurs

Radiogenic heat

Radioactive decay of uranium-238, thorium-232 occurring in the core

Primordial heat

Heat left over from formation of the earth

Asthenosphere

Liquid magma layer of the mantle that creates convection currents

Lithosphere

Cooler more solid mantle towards the crust that is broken up into tectonic plates

Evidence for plate tectonics

- Continental fit

- Geological evidence (rock)

- Climatological evidence (climate)

- Biological evidence (fossil)

Paleomagnetism

The study of the alignment of magnetic minerals in rock,specifically as it relates to the reversal of Earth's magnetic poles; also the magnetic properties that rock requires during formation. Proves crust is moving

The moho discontinuity

boundary between crust and mantle (seismic waves change their velocity)

Ocean ridges

Plates move apart and magma rises up creating a slight peak under the sea

Rift valleys

Plates moving apart on continental crust, creates a large crack which is solidified but appears deep

Island arcs

as oceanic crust of the sinking plate melts, magma rises through the top plate, over time the flows build up a series of islands

Fold mountains

mountains that form where two plates collide and force layers of rock into folds

Conservative plate margins - facts

- Move in opposite directions or the same direction at a different speed

- Plates get stuck due to pressure and the stress is released

- shallow-focus earthquakes

- San andreas fault.

Constructive plate margins - facts

- Move apart from eachother

- Gap in land is filled with magma causing mid oceanic ridges and sea floor spreading or rift valleys and horst.

- mid atlantic ridge

- east african rift valley

Destructive plate margins (O/C) - facts

- Denser oceanic plate is forced underneath continental

- subduction occurs potentially creating volcanoes

- continental plate is uplifted, forming fold mountains

- Deep sea trenches

- Andes

Destructive plate margins (O/O) - facts

- two oceanic plates move towards eachother, slight subduction occurs and a deep sea trench is formed

- Causes submarine volcanoes, which form island arcs

- Hawaii

Destructive plate margins (C/C) - facts

- both continental plates pushing upwards causes rock to crumble upwards to form fold mountains, material is forced downwards to create deep mountain roots

- Himalayas

Ocean ridges (Constructive margins) and volcanic activity

-Plates move apart and magma rises to the surface, cooling and forming new crust e.g. Iceland (Surtsey)

-Gentle sides, frequent eruptions

- Basaltic lava, shield volcanoes

Hot spots - hawaii

- pacific plate moves nw at 5-10cm per year, leaving an island arc in its path

- forms shield volcanoes above the hotspots, errupting large volumes of basaltic (runny) lava, forming a wide and broad volcano

-as volcano ages, the lava becomes more alkaline and cinder and spatter cones may appear

Volcanic Explosivity Index (VEI)

Runs 1-8 logarithmically, factors in magnitude and intensity. Criticized as it doesn't factor in gas release only loss of lide and lava flow

Basic (basaltic) lava

- Low silica content

- thinner

- Travels faster

- gas and steam escape quickly

- Found at constructive margins and hotspots

-Quiet eruptions from shield volcanoes

Andesitic/Rhyolitic lava (Acidic)

-Higher silica content

-Thicker (higher viscosity)

-Slower travel

-Destructive margins

-Composite volcanoes

- gas and steam escape slowly

-Violent eruptions

Pyroclastic flow

- Ash cloud on top

- Picks up material

- Thin layer of gas underneath, allowing it to act like a liquid

- Can be hot enough to kill instantly

Lahar

mudflow made up of water-soaked volcanic ash and rock

Tephra

Materials of all types and sizes that are erupted from a crater or volcanic vent. Tephra is classified by size.

Inter plate boundary earthquake

-95% of all eqs

- occur along the plate boundary

Intra-plate boundary earthquake

- 5% of eqs

- occur inside the plate

- due to human activities (mining,fracking and dams)

Focus

Where the rock fractures/earthquakes originates

epicentre

Vertically above the focus/ where the earthquake is the strongest.

P-waves

- primary longitudinal waves, travels through liquids

-Fast (reach surface first)

-Travel mantle and core to opposite side of the globe

S-waves

- transverse secondary waves

- high frequency

- travels through liquids

Surface l-waves (love waves)

- lowest

-Causes the most damage

- moves side to side on the surface

- originates from epicentre

Surface r-waves (reyleigh waves)

-Radiate from epicentre and out

-Complicated low frequency rolling motions

- move up and down

-wave motion on surface

Surface waves facts

- most severe to people and property

- rock type has impact, hard rock absorbs them

Richter

- measured from 1-10

- logarythmic (x100 which creates innaccurate perceptions in magnitude differences (7-8 is giant)

- used less.

Moment magnitude scale

- measures total difference a fault has moved and the force needed to generate this movement

- known as movement release of an earthquake

- used worldwide by seismologsts

Modified mercalli intensity scale (MMI)

-measures impact on people and property

- 12 point scale classifies intensity of eq

- moderate eq in densely populated area score higher than extreme eq in unpopulated area.

liquefaction

-Shaking destabilises soil by increasing space between the grains

-water floods into this space causing waterlogged soil which flows like liquid

- buildings and cars get stuck in it

- even after the liquefaction is over, the objects are stuck.

Methods of monitoring

-Satellite surveying/remote sensing

-Radon gas sensor

-water table lebels

-Strain meter

- Laser reflector

-Levelling

-Seismometer

- Gravity meter/ Magnetometer/ Electrical resistivity meter

Prediction of seismic events

accurate short term prediction is impossible.

Over time, an event can be expected due to seismic gap theory

Seismic gap theory

sections along a fault that have been inactive have the greatest potential for an earthquake in the near future

Hazard mapping

Highlights areas that are vulnerable to a natural disaster and help prevent serious damage and deaths. Used in city planning etc

Seismic protection - Modifying built environment

- Aseismic design (stepped profile, reinforcements, swaying)

-Retrofitting older structures (additional outer frames)

-Appropriate technology (Similar effects in LICs, build roof out of corrugated iron)

-Land use planning (Avoiding building on faults)

- Fire prevention (Smart meters cut off gas in eq)

- Tsunami protection (sea walls)

Seismic protection - Modifying human behaviours

- Education (eq drills, awareness of homes hazard risk)

- Planning responses of ems (search training)

-Risk sharing and community preparedness

Seismic protection - Modifying loss by Insurance and aid

-Ensures lack of financial loss

- allows reconstruction

- expensive to individuals, not effective in LICs

Factors needed for storm hazards to form

- Sea surface temperature above 26.5+

- Cluster of thunderstorms merge together

- Light winds to crary the storm

- Low atmospheric pressure

- Rotation of the earth

Characteristics of a tropical storm

- 200-700km in diameter

- area of intense low pressure

- rotating wind system

- move from east to west then north to south

- symmetrical around the edges

- Travel act 20km/h

- windspeed of 100km

Hazards associated with tropical storms

- storm surges ( can extent 100 miles, 20ft high, water is pushed up due to the low pressure zone)

- High winds ( over 300km/h strong enough to blow houses down, heavy debris at high speeds)

- Flooding (sends flood water to other areas outside storm path, destroys crops, flood water is contaminated by sewage, Katrina)

Why and how do storm surges form?

- Tropical storm deposits a large amount of water into the ocean

- Increase in water volume and the low pressure experienced pushes the water up, creating the height. They then hit the shore and travel inland

- Bays and other local topography play a large role by acting as a funnel.

Prediction of tropical storms

- hurricanes are predicted using monitoring and warning systems and so varies from country to country on its effectiveness

- USA and the national hurricane centre (FL) are able to access data from land and sea based recording sites and stationary satellites

-Allows warnings and evacuation routes to be given, this ensures a good understanding of procedure, can reduce financial and personal losses

- In USA 1km of coast evacuated costs $1 million

- Cyclone and hurricanes are unpredictable so only give 12-18 hours of warning

- 1997 - Cox Bazar area of bangladesh evacuated over 300k, leading to less than 100 deaths

Tropical storm prevention

- cannot be prevented

- cloud seeding tries to help by forcing water to be released from clouds, but research discontinued as global energy systems are pressured

Tropical storms protection

- Evacuation can occur

- If not evacuated governmental units, national guard has to step in to prevent looting

- Cyclone/ hurricane drills are practiced

- Land-use planning identifies regions most at risk and development can be limited in these areas.

- Sea walls can be built and houses can be put on stilts.

Define wildfires

- General name for uncontrolled rural fires aka bushfires, brushfires and veldfires.

- Occur on every continent except antartica

Wildfires as a quasinatural hazard

- 90% caused by humans

- can be caused by lightning or extreme heat and dry conditions

Triangle of fire

- Ignition source is required to provide the heat

- Fuel is heated and begins to burn

- Oxidant is used to sustain combustion

Firebrands

- Burning fragments of fuel

- carried ahead of fire front by convection currents and strong winds

- ignites spot fires

- randomness of firebrands and spot fires presents a significant challenge

Flaming front

- Front of the fire where combustion is most present

Spot fires

- Small fires that are formed by firebrands

Convection column

- A vertical, rising column of smoke, ashes and particulates caused by a fire.

What is El Nino?

- Climatic cycle that occurs every 6-8 years

- warming of the pacific ocean off of the west coast of SA

- Can cause drought in areas such as australia

Indian Ocean Dipole

- cyclical event

- impacts countries on indian ocean

- Positive IOP has cooler than normal water in east and hotter than normal water in the west

- tends to be a decrease in rainfall over central and southern Australia

Vegetation impacting wildfires

- Some have less moisture

- More litter

- oil inside eg eucalyptus

- Grassland much less flammable than forests as it has less fuel.

Climate impacting wildfires

- Heatwaves dry out vegetation and provide conditions

- Droughts

- Wind strength (Santa ana in CA) spreads the fire

Benefits of wildfires

- Clears weaker trees and debris, ensuring a healthy forest

- Clears vegetation, allowing room and the sunlight needed for new plants to germinate and grow

- releases nutrients to the soil, encouraging new plant growth

- Destroys insects, parasites and diseased plants

- Fire helps germination by destroying resin surrounding cones

- Everglade national park, suggests that 33 species of trees depend on wildfires for their survival

- Pyrophytic plants have a high moisture content and underground storage structures, meaning they are effectively fire-prroof

eg baobab bark

Surface fires

- fires that typically burn only the forest's underbrush and do little damage to mature trees. Surface fires actually serve to protect the forest from more harmful fires by removing underbrush and dead materials that would burn quickly and at high temperatures.