1. How and why do geological disasters occur?

1.1, 1.2 predict effect of plate boundaries on earthquake and volcano types

Divergent boundarie

Earthquakes:

• earthquakes at divergent plate zones are result of injection of upper mantle magma into thin oceanic crust, or the resultant movement of tectonic plates away.

• magma emerges → pushes crust apart = cracks and faults → frictional stress

• as ocean plate is thin, foci rarely >50-70km therefore shallow focus. can also occur in brittle continental crust eg. african rift valley

• 4/5 have Richter magnitude less than 5

• can be used to map divergent plate boundaries with a high degree of accuracy

Volcanoes

• effusive volcanism, most commonly on seafloor. upwelling of magma creates rift valleys

• when upwelling, basaltic lava reaches surface form spherical ‘pillow lava’

• in deeper waters, pressure up to 200x that of sea level. water can no longer boil, gas remain in liquid due to high pressure

Convergent boundaries:

Earthquakes:

• plates collide, usually cold/brittle/dense oceanic plate subducts, fractures and compresses due to increasing temperature and pressure

• friction of plate subduction produces earthquakes at increasing depths beneath overriding plate (Benioff-Wadati zone), with foci as deep as 670 km, produce extremely large scale earthquakes

• 80% occurr around Pacific Ocean Ring of Fire subduction zones

Volcanoes:

• oceanic-oceanic: subducting plate introduces water/sediment to mantle → water breaks silicate mineral chains, cause partial melting of mantle → more viscous magma enriched with gas volatiles (CO2 and water)→ viscous lava reaches surface = lava domes → collapse into ash flows/eruptions → sufficient build up = violent pyroclastic eruptions

• oceanic-continental: oceanic plate subducts, again causing melting → thicker continental plate causes more silica/cooling as rises = more viscous → rarely explote, cause severe ash falls

Transform boundaries:

Earthquakes:

• plates moving past each other in opposite direction

• generally only active in upper 20km = shallow earthquakes, but often high magnitude

• eg. San Andreas fault

Volcanoes:

• N/A

Other volcano types:

Hotspot Volcanoes:

• occur anywhere on earth’s surface

• hotspot = large stationary magma souce deep within Earth that rises as a thermal plume

• produces low silica, effusive, non-viscous lava = pillow lavas in ocean, smooth lava flows on land

• creates new volcanoes: as plate moves, creates a chain

1.3 hazards associated with earthquakes

Ground Motion:

• P (compression), S (transverse, no liquid medium), L waves (surface waves)

• Rayleigh = side to side, Love = rolling wave

• built structures eg building, bridges, roads, dams not usually designed to move. movement of earth in all directions destroys human structures

• greater magnitude = greater intensity of land movement. can trigger land slides, displacement of land and create quake lakes (lake formed after the damming of a watercourse by a landslide caused by an earthquake)

Liquefaction:

• propagation of waves through loose/saturated silty/sandy soils. causes collapse of granular structure

• this places the load of other structures on the incompressible water, meaning they sink into the soil

• structure is now resting on dense fluid and settles unevenly. this can occur to buildings, roads etc

Landslides

• pressure of groundwarer in a slope increase due to intense rain or ground movement

• pressure/weight increases beyond the rest of the slope can support. lateral stresses caused by horizontal slope help overcome this, causing a movement of rock, debris or eath down a slope

• serious risk in mountainous regions such as Papua New Guinea

Fire

• significant upheaval of earth can damage powerlines and gas mains, easily setting structures alight

• damaged water mains also hindered firefighting efforts

Floods

• excessive ground movement can damage dams, reservoirs and levees, causing flooding

• delayed flooding can occur when natural/artificial dams are damaged, but fail some time after the earthquake

Tsunami

• a series of fast, low and long ocean waves that move out from a central area

• in deep ocean, a tsunami can travel up to 950km/hr, may be less than 1 metre high

• as tsunami approach the coastline, they slow but don’t lose energy. this allows the back of the wave to catch up with the front, increasing height to several metres

• most commonly caused by undersea earthquakes, due to fault slips

• propagation (in ocean, tsunami waves cna be 100kms apart but not very tall)→ shoaling (waves approach shallow, slow down, increasing height) → drawback and inundation (water draws back further than normal and is joined by the next inundating wave)

• damage is caused due to flooding, loose materials can be pushed along by water and act as battering rams, flat land near coast most susceptible, inlets and rivers allow surge to move inland

• run up: highest point on land that the tsunami reached (height above sea level)

• max horizontal extent of flooding: how far inland tsunami reached

• eg. sumatra, indonesia 26/12/2004 magnitude 9.1 earthquake, wave height of 50m, 5km inland

1.4 hazards associated with volcanoes eg. ash eruptions, lava flows, lahars, poisonous gas emissions

Tephra:

• ash falls

• explosive eruption: force of hot expanding gases can produce a roiling cloud of gas and ash, rising up to 50km

• larger particles (0.1-10metres) fall within 2km

• prevailing winds can spread fine particles large distances

• sharp/abrasive particles may irritate lungs/eyes of people/animals, destroy engines (economic loss), bury vegetation, close roads, suffocate, contaminate water, reduce visibility, collapse buildings, clog machinery/sewer systems

• ash flows

• caused by collapse of ascending eruption cloud or collapse of a lava dome near top of volcano

• particles and gases act as a frictionless fluid, flowing downhill at speeds exceeding 160km/h

• chemical reactions within cloud release heat

• eg. Vesuvius

Lava flows

• least dangerous of all volcanic hazards due to slow speeds

• can be harmful eg. kilauea, hawaii

• outside of lava cools, keeping inside warm whilst moving

• basaltic/mafic flows eg. from shield volcanoes much faster moving, reach up to 50km from eruption. andesitic often restrained to 5km

• burn stationary structures and vegetation

• cover in layer of hardened basalt

Pyroclastic Flows

• explosive columns of volcanic debris, ash and hot gases (H2O, SO2 and CO2)

• ground layer of fragmented lava and rocks flowing downhill, thick cloud of ash moving above

• travel at up to 100km/hr

• destroy all in path due to high temperatures of volcanic material and hot gases (200-700)

• deadliest of all volcanic events, carry debris of destroyed vegetation and buildings in their wake

• can also be created by collapse of a lava dome

Lahars

• mixture of volcanic material and water that forms a mudflow resembling a river of wet cement

• composition vary from fine sand particles to large boulders

• occur when lava in contact with water sourceseg. crater lakes, rivers, heavy rainfall, dam collapse, glaciers

• can be triggered by rain or seismic activity

• affect communities many kms downstream

• impossible to outrun, deadly. risk severe crush injuries, drowning or asphyxiation

• deposits often acidic due to aerosols in ash clouds (eg. hyrdochloric acid), impacting soils and river

Avalanches

• failure of material due to explosion

• tens of cubic kms of material travel many kms

• debris can descend rapidly into sea, causing volcanic tsunamis

Gas Emissions

• vaired release of gas in all explosions

• water gas and CO2 largest component, CO2 heavier than air, can settle in low areas near volcano. lethal to human and animals in these depressions

• SO2 can combine with water to create sulfuric acid

• Hydrogen sulfide short term exposure can kill

• hydrogen chloride and hydrogen bromide can create acids

• hazardous concentrations of gases only occur 1-2km radius of volcano

• gases can erupt at surface or leak into watersources

1.5 impact of types of magma and impact on explosivity

mafic: contains olivine, pyroxene. found in the mantle eg. mid ocean ridge

felsic: contains potassium feldspar, biotite mica, quartz continental crust. found in continental crust eg. hot spot

1.6 investigate point at which a geological hazard becomes a disaster

geological hazards defined as a risk, chance or probability of something. becomes a disaster when it affects humans and exceeds society’s ability to cope eg. cause signifcant dmage to buildings, infrastructure. effective government can prevent hazards from becoming disasters

2. How do natural disasters such as explosive volcanic eruptions, earthquakes and extreme weather events influence the biosphere and atmosphere?

2.1 compare the eruptions that occurs at explosive and effusive volcanoes in terms of the impact on the biosphere and atmosphere

Explosive Eruption

• classified according to VEI. measures volume of erupted tephra

• phreatic explosion: magma heats water, steam powering the explosion

Biosphere

• ash (containing CO2, hydrochloric acid etc) settles, acidifying streams/water/rain

• carbon dioxide and monoxide can acculmulate in low-lying areas, asphysixating livestock and other animals

• ash can cause blindness, tooth abrasion and digestive problems, prevent birdsreproducing due to nests being covered in ash

• breakdown of volcanic material produce soils that are rich in nutrients eg phosphates, nitrates, potassium and calcium. eg. farmers in Congo found crops have doubled since 2002

Atmosphere

• any eruption of VEI>4 (10-25km) can penetrate troposphere (atmosphere lower layer). VEI=8 (50+km plume) reach stratosphere meaning won’t have winds to disperse

• ash can act as nucleation points, causing vapour to condense = greater rain fall after eruption. can also reflect some of the radiation, creating local cooling

• CO2 and water absorb heat, raising air temp

• sulfur dioxide reacts with water to form sulfuric acid aerosol. freeze, disperse worldwide, reflect, reduce sunlight reaching earth, cooling effect

• HCl and HF actively destroy ozones

• aerosols in stratosphere from mid-range eruptions settle in 5-8months, 12 months for sulfur dioxide to return. dust around 12 months

• after rain removes dust and sulfur dioxide, CO2 continues to warm planet

Effusive Eruptions

• classified by: area covered by the lava, erupted volume, duration of eruption

Biosphere

• gas released can produce acid rain, high fluorine content killed much of the island’s livestock. in 1783, Laki, Iceland killed 20% of human population, experienced unusually cold summer

• sulfur dioxide can produce sulfuric acid = acid rain or freeze as aerosols

• Lava flows can also submerge/burn plant life. can create fertile soil

Atmosphere

• eruptions generally anhydrous

• CO2 common in lava. whilst rarely produce enough force to penetrate high in the atmosphere, gas released can alter gas mix, affecting global temp

• global cooling followedby large temperature rise end-Permian mass extinction intensified by mass release of SO2 during siberian eruption (estimated due to lava encountering water).

• siberian trap release 85 trillion tonnes of CO2. erupting lava passed through extensive coal layers and limestone beds, releasing more CO2. led to intense greenhouse efect

2.2 analyse the effects of a major volcanic eruption on the atmosphere in terms of changing the climate (warming and cooling)

Global Cooling

• explosive eruptions eject large amounts of water vapour, ash and sulfur dioxide into lower stratosphere

• if SO2 mixes with water vapour, form sulfuric acid rain

• eruption with VEI>5, and high proportion of SO2 sulfuric acid reach stratosphere = freeze producing aerosol, reflecting incoming radiation

• ash can remain in the sky in the lower part of volcanic cloud, both increasing albedo

• radiative forcing: any change in solar radiation reaching Earth’s srufave. can alter global climate in short and long term

Global Warming

• eruption release greenhouse cases (water, CO2, CO). CO will oxidise to become CO2

• greenhouse gas molecule absorbs infrared light, vibrate more strongly, collides with other molcules, transfers energy, raising temperature

• water vapour warms lower/middle troposphere

• distribution of CO2 alters warming. if reaches stratosphere, far more likely to be distributed globally. middle to lower troposphere will allow it to mix with rain, form carbonic acid and fall

2.3 investigate one eruption that has had a significant effect on biosphere/atmosphere eg. Mount St Helens

• 2550 metre stratovolcano in USA

• edge of De Fuca plate, subducting under the North America plate

• mid-March 1980 small earthquakes and steam-venting. 27th march, steam explosions created 75 meter crater, smoke began to escape

• by 18th May, thousands small earthquakes had weakened north side= creating fractures and bulge that grew 2m/day

• 18th may, magnitude 5 earthquake collapsed north flank. explosion of VEI 5 erupted, blowing 400m off the top of the mountain

Biosphere:

• tore thousands of trees from 600km^2 of forest

• created giant debris avalanche that covered 80+km^2 and deposited more than 2.3x10^9m of trees, ash and volcanic debris into nearby Spirit Lake

• killed more than 7000 deer, elk, bears plus small animals and birds due to lahars and debris

• elevated sediment levels lasted decades, affected migration of salmon/steelhead trout. 12 million salmon fingerlings died as result of eruption

• 57 people killed, primarily due to asphyxiation

• north of mountain remains sparse despite flourishing green forest on other side

• surrounding agriculatural crops flourished, increased rainfall

Atmosphere:

• withing 15 min of eruption, column of ash, gas and water vapour had risen 24km and begun to expand out

• ash reached north-east of the state in 90 minutes

• continued to inject ash into atmosphere for another 9 hours

• within 2 days, spread to the centre of USA

• within 15 days encircled Earth. ash began to settle, but remained suspended in stratosphere for many years

• low sulfur dioxide content = minimal sulfate aerosol

Assessing the Impact

• most destructive volcano in history of USA

Impact on Human Environment

• 57 people died, many more imjured

• extensive damage to forests, waterways, towns, buildings, bridges etc

• more than 200 houses, 450km of roadway, 24km railway

• fine ash clogged pumps, filters other mechanical equipment

• took several weeks to remove 190 000m^3 of ash from roadways, buildings and airport runways

• total cost around US $1.1 billion

• unemployment rose due to impact on local industries. mental health issues

Impact on weather

• slight cooling of approximately 0.8C across eastern Washington state. due to increased albedo due to ash. altough sunlight couldn’t get in, infrared could not get out, so overall little effect on temp

2.4 evaluate the causes and physical of climatic phenomena on a local ecosystem, including: hailstorms, east coast lows, droughts or floods, bushfires & 2.5 investigate how human activities can contribute to the frequency and magnitude of some natural disasters eg. droughts, floods, bushfires, landslides

Drought

defined by BOM as when rainfall over a 3month period is in the lowest decile of what has been recorded for that region in the past ie. normal precipitation doesn’t occur

Causes:

• drought in Aus happens due to its geography. positioned below a subtropical high pressure belt = gry and sinking air = little rain

• El Nino also a driver. occurs when water in central/eastern tropical Pacific Ocean becomes sbstantially warmer. this warm water moves eastwards, dropping rain over central and eastern Pacific Ocean, rather than Aus.

• El Nino officially declared if temp of eastern Pacific Ocean rises 0.5C over long term average

Physical impact

• no recharge of ponds, lakes, streams

• freshwater bodies maybe reuduced to smaller bodies or completely dry up

• affect living organisms eg fish yabbies snails and plants are stranded with little water, high temps increase evaporation and salinity

• if conditions stagnant, fish/other animals die due to lack oxygen → increased nutrition leads to algal blooms (of blue/green, gold algae)

• this algae toxic to humans/animals. lack of clean water forces animals such as kangaroos, possums, wombats, bilbies and birds elsewhere to access clean water

Impact of humans

• indigenous people learnt patterns of drought and how to live with them

• dammin inland rivers changed flood regime, preventing recharge of groundwater systems

• removal of trees increase run off, reducing infiltration

• shallow dams, as well as water transport channels allows evaporative loss

• agricultural practices that lead to soil compaction (eg. cattle, heavy machinery) reduce infiltration and promote run off

Flooding

part of the natural water cycle. echarge freshwater systems such as rivers and lakes, and infiltrate soil to recharge groundwater

Causes:

• prolonged heavy rain that overwhelms the capacity of the water-holding body

• La Nina: winds over Pacific Ocean are much stronger and puch the warm ocean water west towrds Indonesia. this causes cold water to rise to the surface near South America, making ocean slightly colder and drier. warm water moves west, as do clouds, increasing Australian rainfall

• large storm systems form around moist air masses, move across the country, cause floods over large areas of inland Australia

• cyclones can bring large amounts of moisture from the ocean and cause coastal flooding

• Indian ocean dipole: temperature difference in the two areas of the Indian Ocean. a negative dipole results in higher water temperatures in the east of the ocean and an increase in cloud formation over Australia and strong wet season in the north

• over last 20-30 years increase in occurrence of negative events

Physical impact:

• floods can carry sediments, nutrients and pesticides, posing a threat to marine environments. these flood plume shave a significant impact on seagrass by covering them with silt

• high nutrient concentration can cause algal blooming, reducing sunlight and oxygen reaching marine plants → animals eg dugongs, sea turtles may be unable to find food, leading to disease, malnutrition, death

• can be beneficial eg flooding Lake Eyre resulted in influx of birds and mammals living there. flooding forced rabbits to surface, providing food for eagles/dingoes

coolabahs germinate only after flooding

Impact of humans:

• global warming exacerbate the effects of El Nino and La Nina

• more concrete = increased run off

• large scale deforestation = can’t control flooding

• climate change = global warming rise sea levels

Hailstorms

precipitation that falls in form of ice

Causes:

• tsharply rising air currents in a large cloud carry rain to regions that are cold enough for it to freeze. repeated movements within the cloud coat ice balls with successive ice layers until they become too heavy and fall out of the cloud

Physical impact:

• strip vegetation from trees, extensively livestock and property

East Coast Lows

intense low-pressure systems off the coast of NSW, southern Queensland or north Victoria

Cause:

• deepening low-pressure system that moves off the coast and sits over one of the warm water eddies that has broken off the East Australian Current. a high pressure system needs to be in place over New Zealand, and approaching from the West of Australia

• this causes a steady flow of moist air to move towards the coast. high wind speeds lead to extreme sea conditions, coastal erosion, rainfall along the coast, localised and regional flooding

• in worst cases, east coast low operates for 5 days

• a wave of air 12-15km off the ground moves towards the coast, causing a low-pressure system to develop along its eastern side. interacts with warm coastal water, intensifying the low pressure. if high pressure system from south blocks low, creates a strong pressure difference along the south of the low, causeing stronger winds

Physical impact:

• extensive damage to beachfront infrastructure

• severe coastal erosion, flooding

Bushfires

Natural consequence of living in Australia. Indigenous people had well-established methods of dealing with fire known as firestick farming

Cause:

• below average rainfall, high wind speeds, low humidity

• can start naturally (lightning etc) or by humans

• more likely to occur under El Nino due to increased fuel load

Physical Impact

• burns forests that could take centuries to recover

• loss of plant roots can make soil unstable, erode into creeks/rivers in subsequent wind or rainstorms

• loss of plant life open areas up to competition with introduced species for space/water/light

• animals can be killed or injured by bushfire

• many aus plants adapted to fire eg. Banksia require fire to melt resin and germinate. eucalypts will sprout lignotubers

Human impact

• only 26% of bushfires caused by lightning, others human impact

• can be caused by arcing of overhead cables, arson, negligence, sparks from machinery (eg. grinders) or controlled burns that got out of control

Landslides

aka mass wastings, part of a group of mechanisms that move material down a slope under the force of gravity

Cause

• gravitational force exceeds the strength of materials that make up the slope.

• if slope comprises excess water pressure or movement (seismic) more likely to slide

Physical Impact

• generally smaller scale, crush organisms, block roads etc

Human Impact

• any change in mechanical strength of rocks/soil will increase likelihood

• construction of road on sife of hill eg. Coalcliff, NSW, some rocklayers weak, landslides common after wet weather

• removal of stabilising plant roots, run off water etc

3. What technologies enable prediction of natural disasters and minimisation of their effects on the biosphere?

volcanoes: 3D imaging, seismic data, early-warning systems, ground-movement data, analysis of historical data

technology has involved significantly. can now be predicted weeks in advanced. previously eg. Mt St Helens detected from film seismometer, fed into punch card computer. still anticipated eruption/most of placed to evacuate

earthquakes: ground movement detectors, anomalous animal behaviour, strain meters

the crust is complex and highly variable, making predicting its’ response to stress very difficult to predict. earthquakes can only be predicted with certainty minutes beforehand

east coast lows: temperatures, pressure systems

can develop in 12-24 hours, although meteorologists can see signs up to a week away. intense low pressure systems that may be caused by a variety of weather phenomena at any time of year.

evaluate the technologies used to minimise the effect of natural disasters associated with volcanoes and earthquakes, including building codes, disaster warning systems and education

to minimise the effects of geological hazards on humans, we need to predict the overall risk at a location and, when possible, predict individual events

Building Codes

a set of rules put in place by local, regional or national governments for the construction of new buildings eg. specifying calculation methods and strength values of key structural elements to avoid building collapse. 1997 Australia enforced

Japan:

Japan 1978 earthquake created new ‘shin-taishin’ codes. in 1995 magnitude 6.9, only 0.3% these buildings suffered damage

Taishin: suitable for low rise, thicker beams, pillars and walls, no dampening system

seishin: not required, recommended for high rise. hydraulic shock absorb some of energy. each cylinder elongates and contracts,absorbing much of the earthquake’s kinetic energy

Earthquake Resistant Building:

• Base Isolation: construction on flexible pads, bearings, springs, so base absorbs the shock wave. can also be achieved through fluid-filled pistons. pistons convert movement to compression of oil and heat. pendulum sway opposite direction to building. both counterract natural sway

• Structural Reinforcement: cross-bracing,stiff shear walls around lift shafts, reinforced frames

• Flexible materials: eg.steel and wood allow a structure to bend and deform, absorbing energy of an earthquake without breaking

Volcanic Resistant Building:

• most important decision is Where to build, by analysis of historical data. should be away from valleys that will tunnel pyroclastic flows/lahars

• ash 3x heavier than snow, rooves require 3x reinforcement. 45 degree slant shed majority of the ash, 15 degree retaib. gutters and drains should be avoided where possible

• must be built to withstand seismic activity. reinforced concrete can better withstand wind, earthquakes, rocks and ash fall

• ash and gases rekeased are highly acidicand corrosive. outdoor electronics should be wrapped in plastic, windows should have secure shutters in the case of windborne debris

Disaster Warning System:

coordinated government response provide staged warnings of danger, alert emergency response teams

Japanese volcano warning system:

network of remote monitoring equipment around each active volcano sens real-time data to volcanic observation centres. mobile teams perform measurements on the ground.danger is detected, assessed according to predetermined criteria and a level of the warning system is trigged: 1 (calm) - 5 (evacuate)

Earthquake warning system

P waves detected, used to estimate the magnitude of the earthquake. J-Alert transmits via sirens, loudspeakers, phones, tv and other electronic media. alert triggered by movement, no human oversight, occasional glitch. ShakeAlert 2015 debated USA, what level to alert at

Public Education

necessary for hazard warnings to be effective. 2-day warning necessary for evacuation, only possible for volcano. 30 sec warning for earthquake can still be extremely helpful: allow trains to slow, aeroplanes to stop taxiing, lifts to open, people to move away from dangerous machinery, shelter under desks. this requires an educated, calm public

Japan is a world leader in disaster management, through schools. on 1/9 disaster prevention day, drills held around country to improve coordination between government, volunteer organisations and public

assess the accuracy of technologies used in meteorology to predict and prevent damage to life and infrastructure as a result of natural weather events

international cooperation (Aus, USA, UK, France, Canada and other EU) as well as sophisticated computer modelling and a variety of data imputs has allowed forecasting to become more complex

Satellites: allow detection of tropical cyclones, developing thunderstorms, volcanic ash, fire, smoke, fog and clouds at resolutions of 0.5-2.0km. observed from Japan’s satellites, scan earth every 10 min

Radar: short pulses electromagnetic waves, detect reflection = determine rain and wind speed. allows precipitation maps to be created. optimal range 5-200km

long term climate predictions allow investment in infrastructure eg. rising sea levels, fresh water shortages, fire season. alter construction, emergency service training and landscape design

seasonal forecasts help manage water use, guide agricultural decisions, help utilities prepare for greater use during extreme heat. decisions about undertaking hazard reduction burns. water restriction

weekly weather forecasts avoid infrastructure damage, help people avoid extreme weather events. world bank estimates 7 day warning can prevent 15% infrastructure damage. enable communities and emergency services to prepare eg. for cyclones and to evacuate vulnerable areas. shipping routes altered. allow time to move livestock, vehicles and people undercover.