Hazards

responding to hazards - fatalism

accepting that hazards are natural events part of living in an area

action is direct + concerned with safety

losses accepted as inevitable

people remain where they are

responding to hazards - adaptation

people accepted that natural events are inevitable

start changing behaviour according so that losses are kept to a minimum

best option for people + governments

responding to hazards - prediction

technology increases + the ways we predict hazards become more sophisticated eg. seismic monitoring on a volcano

advance in communications allows warning to reach a greater number of people + faster

geophysical hazard

caused by land processes, majorly tectonic plates eg volcanoes

atmospheric hazards

caused by atmospheric processes + conditions created from these, such as weather systems eg wildfires

hydrological hazards

hazards caused by water bodies and movements eg floods

factors affecting viewpoints of hazards

• wealth - more wealth may perceive a hazard as smaller as they are less vulnerable, could view as greater due to more risk of property damage and financial loss

• experience - more experience of hazards more likely to understand the full effects, also could be more likely to have an optimistic and unrealistic outlook on future hazards

• education - more educated may understand their full effects + understanding how devastating they can be

• religion/beliefs - may belief God is behind the hazards so may not view them as negative

• mobility - those with limited access to escape a hazard may perceive them as greater threats than they are

mitigation of hazards

strategies to lessen the severity of a hazard eg sandbags preventing impact of flooding

management of hazards

strategies to reduce a hazards effects (prediction, adaptation, mitigation)

risk sharing

form of community preparedness, where the community shares the risk posed by a natural hazards + invests collectively to mitigate the impacts of future hazards

incidence

frequency of a hazard, how often it occurs

intensity

the power of a hazard, how strong it is + how damaging the effects are

magnitude

the size of the hazard, usually how its intensity is measured

pressure and release model - root causes

• underlying causes

• well-established, economic, demographic + political processes within a society

• give rise to vulnerability over time

• affects the allocation + distribution of resources between groups of people

• reflect the distribution of power in a society + are connected to the functioning and power of the state

pressure and release model - dynamic pressures

• processes and activities that transform the effects of root causes into vulnerability

• channel root causes into forms of insecurity that have to be considered in relation to the types of hazards facing vulnerable people

• included reduced access to resources as a result of the way regional/global pressures work through to localities

• eg. lack of training/skills/freedom/ethical standards/investments

pressure and release model - unsafe conditions

• specific forms in which peoples vulnerability is expressed in time and space in conjunction with a hazard

• may occur through processes such as fragile local economic conditions, lack of disaster planning and preparedness and a harmed environment

• eg. fragile physical environment, fragile local economy, vulnerable society, public actions

definition of a natural hazard

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

can cause loss of life, property damage, social/economic disruption

Degg’s model

A natural hazard only becomes a disaster when it causes significant impact on a vulnerable population

World Risk Index

helps define the interaction between natural hazards + vulnerability

measures degree of exposure to hazard events + combines this with vulnerability

measured by degree of susceptibility, coping capacity + ability to adapt in long-term of communities

factors affecting impacts of natural hazards

• location

• proximity to urban areas

• population size

• magnitude of the hazard

• development of country

• frequency of the hazard

Hazard management cycle

• shows how the events of one hazard event inform planning + preparation for the next hazard event

• time of each stage depends on:

  • level of development

  • magnitude of hazard

  • quality of governance

  • aid available

stages of the hazard management cycle model

• response - immediate actions, search&rescue, emergency aid

• recovery - rebuilding economy + infrastructure, restoring services

• mitigation - actions to reduce the impact of the next hazard event eg. flood barriers, setting up early warning system

• preparedness - education to ensure that people are prepared for future hazard events eg. earthquake drills, public awareness campaigns

Park Model of Human Response

• shows how people’s quality of life is affected by hazards

• outlines how people respond to hazard events

• downward curve of disruption varies depending on nature + magnitude of the hazard (high mag+sudden event = steeper/deeper curve)

• upward curve of recovery depends on:

  • preparation + planning

  • development

  • national and international aid

phases of the Park Model

• relief - immediate response including search&rescue, provision of emergency medical aid

• rehabilitation - includes temporary restoration of services/infrastructure eg. temporary schools and shelters

• reconstruction - permanent restoration aiming to provide the same/improved quality of life than before eg. aseismic designs

typical Park Model for lowly developed countries

LDE countries may have a worse initial impact of the hazard event due to lack of preparation and planning

Search and rescue takes longer due to lack of equipment and training or waiting for international assistance to arrive

Recovery + rehabilitation takes longer due to lack of money, corruption, poor governance

Quality life may take longer/may never return to the normal

layers of the earth

crust

mantle

outer core

inner core

magma

molten rock, gases + liquids from the mantle accumulating in vast chambers at great pressures deep within the lithosphere

once it reaches the surface = lava

igneous rocks

formed by the cooling of molten magma, either underground or on the ground surface

intrusive igneous rocks

cooling of molten magma underground

forms coarse-grained igneous rocks eg. granite

vertical/horizontal dykes or incline sills may become part of the landscape once erosion removes the underlying rocks

extrusive igneous rocks

cooling+crystallising+solidifying of magma on the ground surface

solidifies far quicker than magma underground

fine-grained igneous rocks with small crystals eg. basalt

Mohorovičić discontinuity

boundary between the crust and the mantle

Gutenberg discontinuity

boundary between core and mantle

lithosphere

crust + rigid upper section of the mantle

broken up into plates

only the top is the crust, majority is within the mantle

asthenosphere

beneath the lithosphere, semi molten part of the mantle on which plates move

movements powered by heat from core

inner core temp + distance from earths surface

5000°

5000-6370km

characteristics of the inner core

• solid - nickel/iron alloy(80%)/platinum group elements

• radius 1200km

• 2% of Earth’s total mass

• during Earth’s formation, melting caused denser substance to sink towards the centre, less dense migrated to the surface

outer core temp + distance from earths surface

4000-5000°

2900-5000km

characteristics of the outer core

• semi-liquid - nickel-iron alloy, 10% sulphur + oxygen

• radius 2250km

• 30% of Earth’s mass

• density 10-12.3 g/cm³

characteristics of the core

• supply of heat to the Earth

• heat comes from decay of radioactive substances eg. uranium,

• heat is responsible for moving material in the mantle

• outer + inner core cause Earth’s magnetism because the outer core spins whilst the inner core doesn’t

lower mantle temp + distance from earths surface

2000-3000°

1000-2900km

characteristics of the lower mantle

• mesosphere

• solid rock

• 41% of Earth’s mass

• composed of different oxides with increasing iron content with depth

upper mantle temp + distance from earths surface

1000°

base of crust-400km

characteristics of the upper mantle

• lithosphere + aesthenosphere

• semi-molten magma

• 10% of Eath’s mass

• density = 3.25-3.40 gm/cm³

• composition - changes with depth

types of crust

• oceanic crust - thin but dense

• continental crust - thicker but less dense

main sources of Earth’s internal heat

• radioactive decay of elements such as uranium and potassium inside the earth’s core

• heat left over from collisions of asteroids and other small bodies which resulted in the formation of Earth

plate tectonic theory

• the lithosphere is broke into large slabs of rock called tectonic plates

• these move due to convection currents in the asthenosphere

• plate boundaries/margins = edges of plates where they meet

continental drift theory

Alfred Wegener - believed that earth’s continents had once been a single landmass, the continents had gradually drifted apart over millions of years

• movement of tectonic plates due to varying weights of crust

• originally thought that convection currents causes the movements of the plates, but now slab pull is thought to be the primary force

convection currents

circulation of magma within the asthenosphere

magma heated by radioactive processes sin the core and cools at the surface, and so circulates between the two places

slab pull

force contributing to the movement of tectonic plates

as the denser plate subjects, gravity pulls it down into the mantle

subduction zone

formed when two plates move towards each other

ridge push

• at constructive plate margins, magma rises to form new crust

• the heat from the magma heats surrounding rocks, making them expand and rise above the surface forming a slope

• new crust cools and becomes denser

• gravity causes denser rock to slide downhill → puts pressure on plates and causes them to move apart = gravitational sliding

mid-ocean ridge

parting oceanic plates at a constructive plate boundary create a ridge, with new land at the base of the oceanic valley

magma rises to fill gap, accumulates over time to become taller + wider

eg. Mid Atlantic Ridge

rift valley

• forms when diverging plates are beneath land

• as plates move apart, the crust stretches and fractures

• areas of crust drop down between faults to create a valley

• eg. East African Rift Valley

ocean trench

• at destructive plate boundaries

• oceanic crust subducts continental

• creates long narrow deep compression = a trench

• eg. The Mariana Trench

fold mountains

• at destructive plate boundaries

• during subduction, the plates collide and compress/push up sedimentary rock = fold mountain

• eg. The Andes

sea floor spreading

• proof of existence that the sea floor has gradually moved apart at a mid-ocean ridge

• lava cools and solidifies with the minerals lining up with the magnetic field

• direction of the minerals on either side is a mirror image

island arc

• at ocean-oceanic destructive plate boundaries

• convection currents involved in the process

• heavier plate subducts under the lighter one, slab pull causes it to be dragged down into the mantle

• subduction causes melting in the mantle → produced silica rich magma that rises and cools and over time accumulates to form volcanoes above sea level in an arc like shape

• eg. Ryuku Islands south of Japan

destructive plate boundary + landforms/processes created

• plates moving towards each other

• continental-continental = earthquakes + fold mountains

• oceanic-oceanic = earthquakes + volcanoes + island arcs + ocean trenches

• continental-oceanic = earthquakes + volcanoes + fold mountains

constructive plate boundary + landforms/processes created

• plates moving away from each other

• continental-continental = earthquakes + volcanoes + rift valleys

• oceanic-oceanic = earthquakes + volcanoes + ocean ridges

conservative plate boundary + landforms/processes created

• plates moving parallel to each other

• earthquakes

continental-oceanic destructive plate boundary

• denser oceanic plate subducts below continental - leaves ocean trench

• when sediment is pushed up during subduction = fold mountaIn

• ocean crust is melted into the asthenosphere → extra magma created causes pressure to build up

• pressurised magma forces through weak areas in continental plate = composite volcanoes

oceanic-oceanic destructive plate boundary

• heavier plate subducts + leaves ocean trench + fold mountains

• built up pressure causes underwater volcanoes bursting through oceanic palte

• lava cools and creates island arcs

continental-continental destructive plate boundary

• both plates aren’t as dense as oceanic so lots of pressure builds

• older oceanic crust is subducted, but not subduction of continental crust

• pile up of continental crust on top of lithosphere due to pressure between plates

• fold mountains formed from piles of continental crust

oceanic-oceanic constructive plate boundary

• magma rises between the gap left, forming new land when it cools - ocean ridge

• less explosive underwater volcanoes formed as magma rises

• sea floor spreading = new land formed on ocean floor by lava filling the gaps

continental-continental constructive plate boundary

• land in the middle of the separation is forced apart - rift valley

• volcanoes form where the magma rises

• the gap eventually most likely fills with water

conservative plate boundary - any crust

• parallel plates move in different directions or at different speeds

• no plates destroyed so no landforms creates'

• when they move, lots of pressure built up

• oceanic - can displace a lot of water

• continental - fault lines can occur where the ground is cracked by the movement

hotspots

areas of volcanic activity not related to plate boundaries

hot magmas plumes from the mantle rise and burn through weaker parts of the crust → can create volcanoes and islands

the plume remains in place but the plates continue to move → can create a chain of Islands (eg. Hawaii)

magma plumes

upwellings of superheated rock that rise from deep within the Earth’s mantle towards the surface

can break through the middle of a tectonic plate to reach the surface causing volcanic activity and earthquakes far away from plate margins

eg. Hawaiin hotspots

distribution of volcanic hazards

• most active volcanoes at or near plate boundaries

• 75% occur around the Pacific Ocean ‘Ring of Fire’

• also found at hotspots

volcanic eruptions at constructive margins

• eruptions usually small

• usually basaltic lava

volcanic eruptions at destructive margins

• eruptions tend to be explosive

• often andesitic or rhyolitic lava

basaltic lava

• hot (1200°C) + runny, low viscosity

• low silica content

• flows as rivers of molten rock

• keeps gas content → more mobile

• produces extensive, gently sloping landforms

• gentle but frequent eruptions

• lava + steam ejected

• eg. Mid Atlantic Ridge

andesitic lava

• cooler (800°C), more viscous

• high silica content

• flows slowly + short distances

• loses gas quickly → more viscous

• produces step-sided localised features

• less frequent but more violent eruptions due to gas build up

• pyroclastic + steam + lava ejected

• eg. Mt St Helens

Rhyolitic lava

• lowish tempts (650-900°C)

• very vicious and sticky, very high silica

• magma traps gas + coagulates up in the vent of the volcano

• pressure builds over time until suddenly released in catastrophic eruption

• flows slowly + can damage property

• larger explosive eruptions = highly dangerous

magnitude of volcanoes

• measured using Volcanic Explosivity Index

• more powerful = more explosive

• 0-8 scale

• factors considered: how long it lasts, how much material is erupted, how high material is ejected

explosive eruptions

intense, high magnitude eruptions

lower frequency

effusive eruptions

calmer, lower magnitude eruption

higher frequency

frequency of volcanic eruptions

• varies per volcano

• classified as active, dormant or extinct

• estimates 50-60 volcanoes erupt each month

classification of volcanoes eruption

• active - have erupted in living memory

• dormant - have erupted within recorded history

• extinct - will not erupt again

regularity of volcanic eruptions

• each type of boundary are similar

• eruptions on destructive boundaries will regularly be explosive

• sometimes eruptions may be irregular and not fit patterns

predictability of volcanic eruptions

• regularity can help estimate when eruptions will take place

• seismic activity, gases releasing, elevation etc - can indication an eruption

• no definite predictions

tephra

large pieces of rock ejected from the volcano

crater

opening at the top of a volcano

volcanic cloud

gas, steam and ash escaping from the volcano

secondary vent/cone

allows magma to escape from the side of the volcano

lava flow

allows magma to escape from the side of the volcano

ash and lava

build up overtime to form sides of the volcano

main vent

the tunnel in which magma rises to the top of the volcano

fissure volcano

• hollows in existing landscapes are filled to create flat, featureless basaltic plains

• eg. Deccan Traps

shield volcano

• typical of constructive plate boundaries and hotspots

• volcanic cone

• eg. Hawaii and Iceland

dome volcano

• typical of destructive plate boundaries

• pyroclastic flows are common

• eg. Mount Pelee, Caribbean - killed 30,000 within minutes

composite volcano

• alternate layers of lava and ash causes weaknesses that can be exploited by magma

• eg. Mount Merapi, Indonesia

caldera volcano

• occurs when violent eruptions blow out the top of volcanoes summit, emptying the magma chamber so the sides collapse in

• often the caldera is flooded by a sea or lake

• eg, Santorini Greece

Disaster Risk Equation

Risk = Hazard x Vulnerability

eruption columns and clouds

• explosive eruption blasts solid/molten rock fragments + volcanic gases into the air with tremendous force

• volcanic ash in the cloud can post a serious hazard to aircraft

• eruption clouds can extend hundred of miles downwind

• heavy ash fall can collapse buildings

volcanic gases

• emitted during eruptions

• cracks in the ground allow gas to reach the surface, even when the volcano isn’t erupting = fumaroles

• 90%+ of gas emitted is water vapour

• other gases = CO2, sulfur dioxide, hydrogen sulphide, hydrogen + fluoride

• CO2 heavier than air so can get trapped in Lowe areas in concentrations that are deadly to humans and animals

• fluorine is highly toxic in high concentrations

• huge eruptions inject sulfur dioxide gas into stratosphere → forms sulphuric acid → reflects solar radiation and can lower earths surface temp

• also contribute to destruction of ozone layer

pyroclasts

hot broken fragments of rock ejected with great velocity - can be very large

lava flows and domes

• magma that pours/oozes onto the Earth’s surface

• higher silica content = flows slowly

• flows of andesitic + rhyolitic lava flow very slowly as get are thick

• flows of basaltic lava can run fast and easily destroy homes