Module 6: Hazards
VOLCANOES
Effusive
 Divergent, oceanic ridge, hotspots (Kilauea, Hawaii)
 Mafic – non viscous, originates deep in mantle
 Lava flows, gas emissions
 Impacts on:
o Biosphere – lava destroys habitats, fertilised soil (andisol)
o Atmosphere – gases in atmosphere for decades. Short term 3-5 years
of cooling. Long term greenhouse gases trap heat and cause warming
Explosive
 Subduction zones (Mt Pinatubo, Philippines)
 Felsic – viscous, shallow mantle
 Ash eruptions, lahars, gas emissions
 Impacts on:
o Biosphere – ash covers everything, changing temperatures, water
contamination, lahars destroy habitats
o Atmosphere – gas/sulfates/ash block incoming solar radiation
Hazards associated with volcanoes
Ash Eruptions
 Product of explosive volcanic eruptions – made of tiny fragments of jagged
rock, minerals and volcanic glass.
o Hard, abrasive and does not dissolve in water.
o Can be powdery and sand-like.
 Plumes of volcanic ash can spread over large areas of sky, turning daylight
into complete darkness and drastically reducing visibility.
 Volcanic ash and gases can sometimes reach the stratosphere (upper layer
of atmosphere).
o Reflects incoming radiation and creates cooling temperatures.
o “Volcanic winters” – in extreme cases the debris blocks out so
much sunlight and global temperatures can cool eg. 1883 Krakatoa
eruption lowered global temperatures by 1.2°C for 3 years.
 Ash can:
o Destroy/disrupt machinery
o Melt inside aeroplane engines
o Contain carbon dioxide and fluorine
o Lead to crop failure and animal death
o Ascend hundreds of km into atmosphere and stay for years
 Pyroclastic flows: explosive eruptions can also create an avalanche of ash,
volcanic gases and rock.
o These can be impossible for humans to outrun.
o They are capable of razing buildings and uprooting trees.
o Up to 1000°C making it frictionless and can move up to 700km/hr.
o Blast and burn everything in their way.
 A benefit: Andisol is a type of soil formed from volcanic ash. Andisols are
generally very fertile and support extensive agricultural development.
Lava Flows
 Lava flows are the least hazardous process and vary depending on their
silica content, temperature, extrusion rate and slope of the land.
 They cover roughly 70% of the Earth and are very common on other
terrestrial planets, covering 90% of Venus and 50% of Mars.
o Pahoehoe: Smooth and continuous lava. Lower effusion rate =
slower. Low viscosity. Basaltic lava only. Thin flows (1-3m)
 Not very dangerous BUT very destructive. You can walk
away from it but you cannot stop what it destroys.
o A’a: Rubbly and chunky lava. High effusion rate = faster. Generally
basalt. Thicker flows (3-20m)
 Composition of pahoehoe and A’a can be the same:
pahoehoe lava can turn into A/a lava if it speeds up. A’a
cannot become pahoehoe.
o Blocky: Even more chunky. Even faster. Very thick flow (20-100m).
Can be andesitic, tephritic. Needs more silica.
o Pillow lava: Usually basaltic or andesitic. Always in water. Rounded
curved shapes.
Lahars
 Lahars are a type of flooding that happens in volcanic eruptions when the
volcano has snow on it, it is raining or if there are rivers/dams nearby.
o 1984 Columbian volcano Nevada de Ruiz – 50m deep. Hit the town
of Amero 100km from volcano at night. 23,000 people killed in
minutes.
Poisonous gas emissions
 Magma contains dissolved gases. As magma rises, pressure decreases and
can cause ozone destruction.
 Sulfur dioxide can get into the stratosphere and block solar radiation
(sulfate aerosols).
 Can mix with moisture in lungs to create H2SO4 (sulfuric acid) and damages
lungs. Can be fatal in high concentrations.
 Can only protect from it by leaving the area or using industrial gas masks.
Prediction and prevention methods
 3D imaging
o Some computer technology can input ground, gas, seismic and historical
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data and generate a 3D model of what is happening inside a certain volcano
and can potentially predict an eruption. Has not been around for long
enough to evaluate effectiveness. It is believed to be fairly accurate, but the
technology can always be improved
Gas sensors
o Gases like sulfur dioxide, carbon dioxide and hydrochloric acid can escape a
volcano before it erupts. Sensors on land, underground and in satellites can
detect these gases and predict a potential eruption. Not very effective: not
every volcano produces gases first and not all gases are a sign of an
eruption.
o Eg. Kilauea eruption, Hawaii 2018. Studying gas sensors and historical data
suggested a likelihood of an eruption. Scientists weren’t certain about the
accuracy or reliability of their data so no earlier warnings were issued
Seismic data
o Record changes on inside
o Harmonic tremors, changes in frequency
Early warning systems
o Allow for preparation and evacuation
o Texts, sirens, radio, media
Ground movement data
o Monitors ground shaking
o Tilt and slope changes indicate bulging
Historical data
o Signs of eruption
o Location, frequency, intensity
o Potential impact zone
CASE STUDY: Mt Pinatubo 1992
Impacts on:
 Atmosphere
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Hydrosphere
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Sulfur dioxide creates sulfate aerosols. These absorb solar radiation,
and which blocks out sunlight and cools the Earth
Lowered average global temperatures by 0.5°C for almost three years
The boost of sulfate aerosols into the atmosphere impacted global
warming by slowing its process slightly
Sulfate aerosols blocking out sunlight caused the oceans to become
colder
Over a few months, the cold layer gradually subducted and created
convection currents
The average water temperatures for the months after the eruption
were lower as a result of the blocked sunlight
Biosphere
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The convection currents created by the cold layer subduction caused a
mix across all depths of water and mixing of nutrients like phosphorous
This was seen in the Red Sea with the forming of algal blooms which
smothered coral and blocked out more light
When temperatures went back to normal within the next few years,
algal blooms died, and reefs gradually became healthy again
CASE STUDY: Krakatoa 1883
Short term impacts
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Sulfur dioxide produced in the eruption shot into the air and created sulfate
aerosols. These absorb some solar radiation which blocks out sunlight and cools
the Earth
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6 cubic miles of rock, ash, dust and debris was shot into the atmosphere,
darkening the sky and creating dense clouds that blocked out sunlight and
lowered temperatures in the immediate area
There was a drop in average global temperatures for several years afterwards by
about 1.2°C
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Increased amounts of rainfall for the next few months was experience all over
the globe, particularly in California with its highest recorded rainfall ever
Long term impacts
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The explosion caused such intense global cooling for so long that it is believed to
have had long term impacts on our current climate, specifically the process of
global warming
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Scientists believe that if the eruption had not happened, global temperatures
and sea levels would be much higher than they are today
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Ocean heat content and thermal expansion was substantially reduced by this
eruption. The cooling of the ocean surface gradually subducted into deeper
ocean layers which caused temporary reductions in ocean heat content, slowing
its heating process on a scale of decades
EARTHQUAKES
Boundaries
 Transform boundaries (rubbing against each other)
 Convergent boundaries (pushing together)
 Divergent boundaries (pulling apart)
 Subduction zones (shallow and deep – convergent)
Types of earthquakes
Tectonic earthquakes
 Convergent: reverse faults – plates pushed up, moving against gravity
 Divergent: normal faults
 Transform: strike-slip faults
Volcanic earthquakes
 Results from tectonic forces which occur in conjunction with volcanic
activity
Collapse earthquakes
 Small earthquakes in underground caverns and mines
Explosion earthquakes
 Result from the explosion of nuclear and chemical devices
Seismic waves
P waves (solids and liquids) and S waves (solids only)
o Love waves, sheer waves, Rayleigh waves
 Measured on the Richter scale and Mercalli scale:
o Richter: magnitude (vibrations)
o Mercalli: magnitude (damage)
Depth
 Transverse boundaries = shallow
 Subduction zones = deep and shallow
Ground movement detectors
 Position and movement of plates
 Measures built-up tension and strain
Building codes
 Used in high risk locations
 What materials can withstand earthquakes
 Ground isolation and insulation
Hazards associated with earthquakes
o Landslides
o Ground shaking/breaking
o Damages infrastructure and land
o Fires
o Soil liquefaction
o Tsunamis
Prediction and prevention methods
 Earthquakes are extremely hard to predict, almost inherently impossible.
Some small (but not great) leads:
o Animal behaviour
o Chemistry of underground water
o Low frequency radio emissions from rocks
 Ground movement detectors:
o Good: measures strain on boundaries and can better prepare high
risk areas
o Bad: cannot predict time, may never actually happen
Other
o Building codes
o Avoidance
o Education
o Early warning systems
o Evacuation
TSUNAMIS
 Most often caused by earthquakes at oceanic plate boundaries
Early warning systems
 Floating buoys provide live data about rising and falling water.
 Sirens and media alerts sent around to threatened coastlines.
 Residents have time to flee to higher ground.
 Systems were not active in the Pacific Ocean in 2004, they are now.
At risk:
 Low lying coastal areas and highly populated communities with
neighbouring subduction boundaries.
 Poorer countries less likely to have warning systems or good public
awareness.
EAST COAST LOWS
 Intense low pressure systems that produce extreme weather
 Quite slow moving/stationary with longer lasting effects and prolonged
periods of heavy rainfall.
 Strong winds affecting waves.
 Formed sometimes with cold fronts/tropical cyclones.
o Interactions between cold front from south and warm water from
EAC.
o Can come down south from tropical cyclones up north.
 Causes: low pressure system sits off NSW, moved there or formed there
 Impacts: severe storms, rain, hail, lightning, floods, wind, coastal erosion,
damaged infrastructure
Hailstorms
 Causes: storms, east coast lows
 Impacts: damage to everything – infrastructure, agriculture
BUSHFIRES
 Despite human’s desire to control fire and forest destruction, it is a process
that has been around for hundreds of millions of years.
 This process aids in fertilising soils, regulating plant distribution and aiding
in biodiversity.
 Bushfires kill weeds which struggle to regrow after fires, though most
native plants will.
 Science has shown an onset of frequent and widespread occurrence of
charcoal (a proxy for past fires) 360 million years ago.
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This is 80 million years after terrestrial plants began to colonise Earth 440
million years ago.
o Consequent of droughts: drier land makes things more flammable.
o Consequent of heatwaves: higher temperatures encourage fire
and withered plants/trees become fuel for fire.