Physical Geography - Hazards

Natural Hazard

A potentially damaging physical event that is perceived to be a threat to people, the built environment and the natural environment.

hazard

potential for process to cause loss

disaster

realisation of a hazard potential

Geophysical/geological

Result from the Earth’s internal (tectonic) processes. E.g. Earthquakes, volcanoes & tsunamis

hydrological

Driven by water processes e.g. floods & droughts

atmospheric

Result from the operation of the Earth’s climate, primarily driven by energy from the Sun e.g. tropical storms, tornadoes.

geomorphic

The operation of surface processes, which sculpt the landscape including the mass movement of material. E.g. landslides/avalanches

biohazards

Living organisms which are or cause a threat human health or life. E.g. wildfires, locust plagues

multiple-hazard zones

Places that experience a combination of hazards

human hazards

Driven by human processes or actions e.g. crime, areas with high rates of disease.

World Risk Index

Helps define interaction between natural hazard and vulnerability. Measures degree of exposure to hazard events and combines this with vulnerability.

factors that shape perception

*Location of the hazard

*Proximity to urban areas/settlements

*Population size

*Magnitude of the hazard

*Development of a country

*How often the hazard occurs

perceptions can be influenced by:

• Socio-economic status

• Level of education

• Occupation

• Religion, cultural/ethic background

• family and marital status

• Past experience;

• Values, personality & expectation

Fatalism (acceptance)

Hazards are natural events that are part of living in an area; ‘God’s will’. Action is usually direct and concerned with safety. Losses are accepted as inevitable and people remain where they are.

Adaptation

People have accepted that natural events are inevitable and start to change their behaviour accordingly so that in the event of a hazard losses are kept to a minimum. This is the best option for people and governments.

Prediction

Technology increases and the ways we predict hazards becomes more sophisticated e.g. remote sensing and seismic monitoring on a volcano. An advance in communications allows warnings to reach a greater number of people faster than before.

pressure and release model: root causes

Indicate the underlying causes are the most remote influences. They are a set of well-established, widespread economic, demographic and political processes within a society and the world economy that give rise to vulnerability and affect the allocation and distribution of resources between different groups of people. They reflect the distribution of power in a society, and are connected to the functioning and power of the state.

pressure and release model: dynamic pressures

The processes and activities that transform the effects of root causes into vulnerability. These channel the root causes into particular form of insecurity that have to be considered in relation to the type of hazards facing vulnerable people. These include reduced access to resources as a result of the way regional or global pressures work through to localities.

pressure and release model: unsafe conditions

These are the specific forms in which a people’s vulnerability is expressed in time and space in conjunction with a hazard. This may occur through such processes as fragile local economic conditions, lack of disaster planning and preparedness and a harmed environment.

prevention

 the action of stopping a hazard from happening

prediction

attempting to suggest what may occur in the future eg remote sensing and seismic monitoring, advances in communication to share information and warn people

adaptation/mitigation

 dealing with the effects of hazards through aid, insurance and government action

hazard managment cycle: preparedness

• Education and raising public awareness can reduce the human causes and adjust behaviour to minimise the likely impact.

• Being aware of how to respond to a hazard will speed up the response and recover stages. 

• The level of preparedness is going to be greater in areas of high risk e.g. Japan

hazard management cycle: response

• A more effective emergency plan will lead to a faster, effective response. 

• Assessing the damage during this stage will help the recover stage.

hazard management cycle: recover

• This is when the area is restored to a level of ‘normality’

• Longer term planning for reconstruction starts to take place.

park model of human responses to hazards: relief

The immediate local and possible global responses in the form of aid, expertise and search and rescue.

park model of human responses to hazards: rehabilitation

Lasts weeks or months, when infrastructure is repaired/temporarily repaired to allow reconstruction to begin.

park model of human responses to hazards: reconstruction

Restoring to the same or better quality of life as before the event. Likely to include mitigation.

magma

molten rock, gases and liquids from the mantle accumulating in vast chambers at great pressures deep within the lithosphere. On reaching the surface magma is known as lava.

igneous rocks

rocks formed by the cooling of molten magma, either underground (intrusive) or on the ground surface (extrusive).

intrusive

magma that cools, crystallises and solidifies slowly below the surface is intrusive. It forms coarse-grained igneous rocks, such as granite and dolerite. Vertical dykes and horizontal or incline sills may only become part of the landscape once erosion removes the overlying rocks.

extrusive

lava that is in contact with the air or sea. It cools, crystallises and solidifies far quicker than magma that is still underground. The resulting igneous rocks, such as basalt, tend to be fine-grained with small crystals

Mohorovicic Discontinuity

boundary between crust and mantle

Gutenbury discontinuity

boundary between core and mantle

lithosphere

crust and rigid upper section of the mantle

Asthenosphere

beneath lithosphere, semi molten part of mantle on which plates move. Temperature: between 1000°C and 3700°C

Material: Softer, plastic like rocks compared to the rest of the mantle.

State: Solid

inner core

Temperature: up to 5000°C

Material: Iron-nickel alloy

State: Solid

Size (Radius): 1200km

outer core

Temperature: up to 5000°C

Material: Iron

State: Semi-Liquid

Size (Radius): 2250km

mantle

Temperature: between 1000°C and 3700°C

Material: Silicate rocks

State: A thick liquid. The deeper into the mantle, the denser the material

Size (Radius): 2900km

crust

Temperature: Up to 900°C

continental crust

Material: Sial – silica and aluminium

State: Solid Granitic rocks

Size (Radius): Up to 70km

Density: Less dense than oceanic crust

Age: Over 1500 million years old

oceanic crust

Material: Sima – silica and magnesium

State: Solid Basaltic rocks

Size (Radius): Between 5-10km

Density: More dense than continental crust

Age: Less than 200 million years old

sources of earth’s internal heat

1. Extraterrestrial impacts

2. Gravitational contraction

3. Decay of radioactive elements

4. Latent heat release during mineralogical changes

evidence for continental drift

continental fit

geological evidence

climatological evidence

biological evidence

continental fit

 It is visible that some countries could slot into other countries.

geological evidence

Rocks of the same age and type are found where countries would have fitted together (E.G. East USA and West Europe)

climatological evidence

Many places that no longer have tropical climates have evidence of being in a tropical climate.

biological evidence

Similar fossil formations. Remains of the same animals are found in regions now separated by sea.

ridge push

At constructive plate margins, magma rises to form new crust. The heat from the magma heats the surrounding rocks causing them to expand and rise above the surface forming a slope. The new crust cools and becomes denser. Gravity causes the denser rock to slide downhill. This puts pressure onto the plates causing them to move apart.

slab pull

At destructive plate margins, the denser ocean crust is forced under the less dense continental crust. The sinking of the plate edge pulls the rest of the

plate towards the boundary.

magma plumes

Areas of volcanic activity that are not related to plate boundaries . Hot magma plumes from the mantle rise and burn through weaker parts of the crust. This can create volcanoes and islands . The plume stays in the same place but the plates continue to move , which sometimes causes a chain of islands (such as Hawaii).

volcanoes

• Occur mostly on constructive and destructive plate margins

• Ones not on boundaries are due to magma plumes

measuring volcanoes

• The Volcanic Explosivity Index (VEI) is a logarithmic scale from 0 (smallest) to 8 (biggest).

• The larger the eruption, the less frequently it is expected to erupt.

volcanoe frequency and regularity

difficult to know when they’ll erupt, bigger magnitude eruptions are less frequent, no clear patterns of regularity

monitoring and predicting earthquakes

seismometers and seismograph, tiltometers for ground deformation, magnetometers for movement of magma, hydrological instruments to measure rising groundwater temp/gas content, warning signs eg small eruptions and rock falls

basaltic/basic lava

Hot (12000C) & runny, low viscosity

Low silica content

Flows as rivers of molten rock as takes longer to cool

Keeps its gas content so is more mobile

Produces extensive, gently sloping landforms

Relatively gentle but frequent eruptions

Lava and steam erupted

Found at constructive plate margins e.g. fissures along Mid-Atlantic Ridge e.g. over hot spots –Mauna Loa, Hawaii

andesitic/acid lava

Viscous, cooler (8000C) flows more slowly for shorter distances

Higher silica content

Flows very short distances as soon cools and solidifies

Loses gas quickly so becomes more viscous

Steep-sided, localised features

Less frequent eruptions but are violent because of gas build up

Pyroclastics- ash, rock, gases & steam and lava ejected

Found at destructive margins where oceanic crust is destroyed, melts & rises e.g. subduction zones Mt. St.Helens e.g. as island arcs Mt. Pelee, Martinque

rhyolitic

• High viscosity (sticky) is related to high silica content (65 to 75 per cent). Silica originates from the destruction and melting of plates. 

• Rhyolitic magma traps gas and coagulates up in the vent of the volcano.

• Pressure builds up over time until it is suddenly released in a catastrophic eruption. 

• Lavas have relatively low temperatures of between 650 and 900°C, flow slowly and can damage property. 

• Large explosive eruptions can be highly dangerous.

tephra

large pieces of rock ejected from the volcano

types of volcanoes

fissure, shield, dome, composite, caldera

volcanic hazards

eruption columns and clouds, volcanic gases, lava flows and domes, pyroclastic flows, landslides, lahars, flood basalt, Jökulhlaups

Glacial floods ( jökulhlaups)

when temperatures are high from magma, glaciers or ice sheets at high temperatures quickly melt and a large amount of water is discharged

Nuées ardentes/pyroclastic flows

clouds of burning hot ash and gas that collapses down a volcano at high speeds. Average speeds of around 60 mph but can reach 430 mph

focus/hypocentre

the point inside the crust where the pressure for an earthquake is released.

epicentre

the point on the earth’s surface directly above the focus. The earthquake is stronger here.The closer to the ground’s surface the focus, the more destructive the earthquake is likely to be. This is due to the earthquakes strongest seismic waves reaching the surface.

P waves (primary)

The fastest waves and shake the earth backwards and forwards. They can move through solids and liquids so can move through both the mantle and the core.

S waves (secondary)

Slower and move with a sideways motion, shaking the earth at right angles to the direction of travel. They can travel through the mantle but not the core. They can do far more damage than P-waves.

surface waves

These travel much nearer to the surface and more slowly than P or S waves

but are more destructive.

love waves (L)

The slowest wave, which cause the ground to move sideways and cause the most damage.

Rayleigh (R) waves

Radiate from the epicentre in a low frequency rolling pattern, which make

the ground move up and down.

predicting earthquakes

hard to predict. could look at earthquake progression over time

earthquake mitigation

measuring gas in soil/groundwater, seismographs, mapping to find patters, GPS for ground movements, earthquake drills and proof buildings

measuring earthquakes

main way is the Moment Magnitude Scale (logarithmic - each increase in number is 10x strength of previous number)

tsunami

Mainly caused by under water earthquakes or volcanic eruptions, but can also be caused by landslides into the sea or underwater debris slides.

how tsunamis differ to normal waves

low wave height in ocean, reaches 25m+ at shore, 100-1000km in length, 640-960km/h, are a series of waves with 10-60 mins between each wave

landslides

Earthquakes can cause landslides to occur as the ground shaking can dislodge loose rock, soil or snow.

This can also make it easier for water to infiltrate the ground and the extra weight of the water may trigger a landslide after the earthquake has occurred.

soil liquefaction

If the ground is saturated before the earthquake the shaking can cause the ground to act like a liquid. This means the ground is likely to deform and subside.

It will be made worse by a heavy weight on the ground, e.g. a building.

tropical storms

an intense low-pressure wind system, forming between 5 and 15 degrees latitude and has wind speeds over 75mph

how tropical storms form

moisture and energy from oceans, 26 degree+ sea surface temps, atmospheric instability eg at Intertropical Convergence Zone, coriolis effect (not strong enough at equator) and uniform wind direction

patterns in storm frequency and magnitude

has been an increase in storm frequency (and magnitude and those reaching land) due to global warming, majority of storm aren’t major and don’t reach land

tropical storm predictability

occur in same areas but don’t follow same routes, form at ocean so their movement can be tracked and route predicted, the closer they are the easier to predict, from trends the probability of a storm hitting an area can be predicted

measuring tropical storms

Saffir Simpson Scale (1-5 based on wind speed)

impacts of tropical storms

strong winds (75mph+), storm surges (3m avg height), heavy rainfall (200mm+), flooding, landslides

reducing impacts of tropical storms

• education, evacuation plans, trained emergency services, home adjustments

• hard/soft engineering techniques to reducing flooding eg sea walls, disaster aid, insurance

• can’t prevent tropical storms

• land use zoning - not building near risk areas, building houses on stilts

wildfire

is a name used to describe an uncontrollable rural fire.

• Australia: called bushfires

• North America: called brushfires 

wildfire favourable conditions

thick undergrowth and closely spaced trees, trees containing oil, fine dry materials, prolonged dry periods, strong dry winds, El NIno

causes of wildfires

• natural: no rainfall, lightning, volcanoes

• human: cigarette butts, sparks, BBQs, farmers burning land

wildfire management

• creation of defensive spaces around homes, warning systems

• removing vegetation to limit spread, disaster aid and insurance

• education, Smokey Bear in US

• planning controls to limit building in fire prone areas, non-polluting materials in buildings if they burnt