Geophysical Hazards Flashcards
what is the structure of the earth from outside to in
- thin rigid crust, composed of the continental crust and thinner oceanic crust
- underneath is a flowing but solid mantle that makes up 82% of the volume of the Earth
- Deeper still is a very dense and very hot core:
-> outer core is liquid
-> inner core is solid
These concentric layers become more dense in the centre, and are controlled by temperature and pressure
what is the asthenosphere?
the layer underneath the lithosphere
what is the plate tectonics theory
the theory that the outer shell is divided into several plates that glide over the mantle, called the continental drift -> first proposed by scientist Alfred Wegener in 1912
where does the earth’s heat come from?
The flow of heat from the Earth’s interior to the surface comes from 2 main sources:
- Radiogenic -> radioactive decay of material in the mantle and the crust
- Primordial heat -> the heat lost by the Earth as it continues to cool from its original formation
what are the 3 mechanisms related to plate movement?
- subduction
- plume
- rifting
how to convection currents operate
- hot magma rises through the core to the surface
- and spreads to the mid-ocean ridges
- the cold solidified crust sinks back because it is heavier and denser than the surrounding metal
- the cause of the movement is radioactive decay of uranium and potassium in the mantle
what is subduction?
subduction refers to the plunging of one plate below another
what is the process of subduction
- oceanic lithosphere plates collide with another plate - whether is continental or oceanic
- The oceanic plate is a lot denser than the continental
- the subducting plate is forced to subduct and creates a subduction zone
what is a plume?
refers to a small area of unusually high heat flow. Plumes can cause movement (the outward flow of viscous rock from the centre) that may create a drag force on the plated causing them to move. Most occur on a plate boundary, such as the Hawaiian Hotspot
what is rifting?
Rifting occurs at constructive plate boundaries, where magma rises and pushes two plates away from each other, for example, the North American and Eurasian plates are moving away from each other.
what is believed to be the main cause of rifting?
hotspot activity
where are volcanoes located?
most are found usually over plate boundaries, however, there are some exceptions, i.e. volcanoes in Hawaii form over hotspots
where in the world are they distributed?
most around the Pacific Ring of fire
what are the 3 different types of volcanoes?
- shield
- composite
- cinder
how do shield volcanoes form?
what do they look like?
are they explosive?
example
- formed from very hot runny basaltic lava
- shield volcanoes are formed with gently sloping slides, shallow crater and a large circumference
- they build up with no explosive activity or ejected fragments
- e.g. Hawaii
how do composite volcanoes form?
what do they look like?
are they explosive?
example
- most common -> formed by alternating eruptions of fragmented material followed by lava outflows/pyroclastic flow
- has slopes of 30º near the summit and 6-10º near the base, and was layers of lava with a crater on top
- sometimes explosive and erupts after a period of inactivity
- e.g. Mount Etna, Italy
how do cinder volcanoes form?
what do they look like?
are they explosive?
example
- formed by fragments of solid material which accumulate as a steep conical hill around the vent to form a cone
- shape depends on the nature of material
- usually concave as material spreads out near the base and has a steep angle of 30-40º
- violent eruptions -> lava ejected into broken rocks and fragments into the atmosphere
- e.g. Big Cinder Butte, USA
what are the 2 types of eruptions
- lava eruption
- pyroclastic eruptions
what is a lava eruptions - silica rich + example
when the ocean meets the continents, silica-rich sediments are absorbed and cause the lava to become more viscous. It blocks vents until enough pressure has built up to break the open.
I.e. Japan
what is a lava eruption - basaltic lava + example
Silica content in a lava eruption makes the difference between continuously erupting or those that erupt infrequently but are violent when they erupt
I.e. Hawaiian eruptions are low in silica. Runny basaltic flows down volcano sides and gases escape easily -> Involve a central vent
what is pyroclastic eruption - strombolian + example
- explosive eruptions that produce pyroclastic flow
- commonly marked by a white cloud of steam emitted from the crater
- frequent gas explosions blast quantities of runny lava into the air, and when these settle and cool they form the cone of the volcano
i.e. stromboli volcano, Italy
what is pyroclastic eruptions - Plinian eruption
- extremely violent characterised by huge clouds of pulverised rock and ash that are kilometres thick
- gas rushes up through sticky lava and blasts ash and fragments into the sky in huge explosions
- Gas clouds and lava can also rush down the slopes
- part of the volcano may be blasted away during the eruption
what are primary hazards
the direct impact of an eruption i.e. lava flows, ash fallout, pyroclastic flows and gas emissions
what are secondary hazards
may be due to the way the ejected material reacts and changes i.e. ash may join with rainwater to form mudflows and create glacial flooding
what are the 2 types of landslides
- debris avalanche
- lahar
what are debris avalanches + example
shallow landslides, saturated with water, that travel rapidly downslope as muddy slurries. They occur around the same time as an eruption
i.e. mount st helens, USA
what are pyroclastic flows? + example
this is when ash and debris have travelled through the air and fallen to the ground. This fine ash can damage people’s lungs, it can also damage buildings as it is too heavy
i.e. Unzen Volcano, Japan
what is the recurrence interval or return period
the expected frequency of occurrence in years of an event of a particular size.
Small events occur more frequently than larger ones
which volcanoes erupt more frequently?
less explosive eruptions occur more frequently (Hawaiin), larger more explosive volcanoes erupt less often (plinian eruptions)
how can we predict volcano eruptions?
- seismicity recording earthquakes and thermal monitoring which occur as magma rises
- GPS - ground deformation
- monitor gas emissions
how do we measure the size of the volcanic eruptions?
- using the volcanic explosivity index (VEI) to describe and compare the size of volcanic eruptions
- uses a scale from 0 (non-explosive) to 8 (explosive)
- log scale -> increases by a factor of 10
what factors do the VEI use to measure the magnitude of a volcano?
- the amount and height of volcanic material ejected
- how long the eruption lasts
- qualitative descriptive terms
what is the richter scale?
a logarithmic scale that measures the power of an earthquake. Earthquake of 5 on the Richter scale is 10 times more powerful than an earthquake of 4
what is the moment magnitude scale
measures the amount of energy released and produces figures similar to the Richter scale. For every increase of 1 of the M scale, the amount of energy released increases by over 30
what are the factors that the Moment magnitude scale measures
- resistance of rocks
- size of seismic waves
- area of the fault surface broken by the earthquake
- amount of slippage/rock movement
what is a hazard risk
when people or property are at risk
what causes places to be at risk from geophysical hazards
behavioural school of thought:
- people put themselves at risk, e.g. living at the foot of steep slopes
Structuralist school of thought:
- stresses constraints on poor people prevailing social and political system of the country
- poor people living in unsafe areas, e.g. on steep slopes of volcanoes, or on floodplains, because they are prevented from living in better areas
- there is a link between environmental hazards and underdevelopment and economic dependency in many developing countries, e.g. hurricane Katrina’s impacts were greater on the poor
what are the process of vulnerability
- root causes (ideologies, gender norms, wealth, power, limited access to resources and structures)
- dynamic pressures (lack of local institutions, rapid population growth)
- unsafe conditions (dangerous locations, unprotected buildings)
what are the economic factors of vulnerability
- levels of wealth influence the quality of housing people live in
- many people have no option but to live in shanty towns
- people may have less adherence to building codes and construction styles
- poorer countries may lack the technology to warn people of upcoming natural hazards
what are the social factors of vulnerability
- people with better education generally have higher incomes and can afford better-quality housing and vehicles
- public education has helped reduce the number of deaths in Japan
- awareness of hazards
- gender: women are usually carers for children or parents and may feel responsible for them during an event
what are the demographic factors of vulnerability
- population density: larger urban areas pose a higher hazardous risk
- older people are more prone to risk
- migrants may be unaware of hazards present in the country
- people with disabilities with more vulnerable
- cultural factors: influence public response, i.e. the extent of trust in the government
where is the Anak Krakatau volcano located?
-> this volcano is an island and caldera in the Sunda Strait (between the islands of Java and Sumatra) in the Indonesia province of Lampung
-> it lies of the Pacific Ring of Fire on the convergence of the Pacific, Eurasian and Philippine plates
when did Anak Krakatau erupt and what happened?
December 22nd 9:03 pm, 2018
what happened in the anak krakatau eruption?
> A 64-hectare chunk of the volcano slid into the ocean following the eruption. This displaced the water, pushing out waves in all directions
how vulnerable are the populations affected by the anak krakatau eruption?
-> Most people lived on the coast in remote areas, with roads that were not as navigable
-> Many had small shops and worked in local hotels, which have been destroyed
-> Lack of disaster-resistant infrastructure
what are the social impacts of the krakatou eruption?
-> 437 dead
-> 15,000 injured
-> no tsunami warning was delivered
-> 600 homes, 60 shops and 420 vessels were damaged
-> International Red Cross sent aid workers to help evacuate injured people, and bring clean water and shelters to those in need
what are the economic impacts of the anak krakatou eruption?
-> damage to coastal tourism facilities
-> damage to coastal defences, infrastructure and roads
-> damage to coastal fishing communities
what are the environmental impacts of the anak krakatou eruption?
-> coastal farming areas were inundated with salt water rendering the areas useless for agriculture
-> sea turtle populations were harmed
-> all biodiversity on anak krakatau were wiped out by the eruption
what are the political impacts of the anak krakatou eruption
-> Indonesia tsunami warning network has not been operational since 2012
what is the case study for a volcanic eruption in LIC
Anak Krakatou eruption, Indonesia
what is the case study for a volcanic eruption in an HIC?
Eyjafjallajökull Eruption 2010
where is the Eyjafjallajökull volcano located
on one of Iceland’s smaller ice caps located far south. It lies on convergence zone of both North American and Eurasian plates - constructive plate boundary
when did the Eyjafjallajökull volcano erupt?
20th march 2010
how did the eyjafjallajökull erupt?
as the volcano erupted, a 2.5km wide caldera beneath the ice cap caused the melting of a large amount of ice, leading to flooding in the south of Iceland. Volcanic ash rose 10km high, and south-easterly winds carried it to the Faroe Islands, Norway and Scotland. All explosive activity ended by the 23rd of May, however, the eruption was officially declared over on the 20th of October, 2010
what were the social effects of the eyjafjallajökull eruption?
- no fatalities were recorded
- some reports of respiratory issues among residents
- 500 farmers evacuated from surrounding areas
what were the economic effects of the eyjafjallajökull eruption?
- a thick ash layer had fallen on some Icelandic pastures making it wet and compact, and therefore hard to harvest or farm
- flights were grounded to Reykjavik, disrupting the import of supplies as well as the flow of tourists
- ash was carried into heavily used airspace over northern and central Europe
what were the environmental effects of the eyjafjallajökull eruption?
- Ash covers pasture and impacts biodiversity
- Ash particles in the atmosphere temporarily increase levels of albedo
- flash flood and rapid heating of river water, caused by rapidly melting ice sheet, raced downstream causing widespread damage to the river channel and banks
what were the political effects of the eyjafjallajökull eruption?
- a high proportion of flights within Europe were cancelled creating the highest levels of air travel disruption since the Second World war
- the civil protection department was deployed to control access from vulnerable communities
what are the volcanic hazards
- jokulhlaup
- pyroclastic flows
- lava
- tephra
- ash/gas
- lahars
what is a jokulhlaup
a flood of meltwater from underneath an icecap or glacier
what causes a jokulhlaup
when a volcano erupts underneath the ice and melts the ice so that it forms a lake, where it is dammed by ice, eventually, the warm water will have a great enough volume to lift the ice away. When this happens the water burst from underneath the ice, carrying with it moraines and blocks of ice
what is an example of a jokulhlaup
Iceland
What are the effects of a jokulhlaup
- change the route of river channels
- washes away bridges and roads
what is pyroclastic flows
a dense mixture of superheated ejected material and poisonous gases (up to 1000ºC) moving rapidly down the sides of a composite volcano (at around 700 km/h)
what causes pyroclastic flows
when a part of the volcanic cone collapses or with thick lava flow. this hazard occurs with explosive eruptions of molten or solid tephra
what is an example of pyroclastic flows
Montserrat (1997)
what are the effects of pyroclastic flows
- anything in the pyroclastic flows way is destroyed
- it leaves behind thick layers of volcanic deposits that may cause secondary hazards such as river flooding
what is tephra
all types of ejected material
what is lava
molten magma that has reached the earths surface
what causes lava
while it is still at very high temperatures, it is in a liquid state and flows. But it depends on which volcano type and how viscous the lava will be. Basaltic = less viscous (runny), Composite = more viscous (thick)
example of lava
Hawaii
effects of lava
burns everything in its path -> destruction to property and human life
what causes tephra
in an explosive volcanic eruption, solid and molten rock material are ejected carried by ash
what is an example of tephra
Iceland
what are the effects of tephra
- falling of tephra can cause roof collapse
what is ash
steam usually containing other gases escaping from geothermal active areas
what causes the ash from volcanoes
geothermal active areas
what are the effects of ash
- reflect radiation from the Sun back into space, cooling the Earth
- gases such as sulphur dioxide can mix with water to form acid rain, which may corrode infrastructure or affect vegetation
- fluorine gas -> can contaminate farmland or water supplies
- can cause an increase in respiratory diseases
- Ash high in the atmosphere can disrupt the flight paths of aeroplanes because of the potential failure of jet engines
what is an example of ash
Mt Pinatubo created 20 million tonnes of sulphur dioxide that rose to 32km
what are lahars
water mixed with volcanic deposits flowing rapidly along existing valleys
what causes lahars
caused by either heavy rainfall or through the melting of snow and ice due to the heat from an eruption at high altitude
what is an example of a lahar
A lahar buried a town in Colombia from Nevado del Ruiz volcano in 1985
what are the effects of lahars
- can sweep away buildings/people because they are very fast moving
how can we predict a volcanic eruption (7), name 3.
- scientific predictions are used to provide precise statements on the time, place and size of a future event
- effective warning systems depend of technology and communication systems and peoples ability to interpret them
- seismometers, to record swarms of tiny earthquakes that occur as the magma rises
- chemical sensors to measure increased suplur levels
- Lasers/GPS to detect physical swelling of the volcano/crater
- Ultrasound, to monitor low-frequency waves in magma resulting from a surge of gas and molten rock
- Observations of the volcano
are volcanoes easy to predict
- earthquakes are the most difficult to predict and forecast
what aspects of a volcanic eruption is hard to predict
- the timescale (duration of eruption)
- when the volcano will erupt
what are the adaptations against volcanoes (3)
how can we prepare?
- land use zoning: densely populated buildings (hospitals/fire services) should not be built close to fault lines or in areas at risk of landslides
- insurance cover against hazards: however, many either cannot afford hazard insurance or find it much harder to justify spending money on an event that might not occur
- new technology (i.e. to record the swelling of volcanoes)
how do we manage volcanoes
- drones: using drones to survey the area, minimising human damage
- GPS monitoring: to measure ground deformation and swelling
- Volcano diversion: the diversion of roads away from active areas or over them in the form of bridges
what are the 3R’s and what do they stand for?
These are the short-term, mid-term and long-term responses after an event
- rescue: saving people so they can survive despite having only minimum life necessites (saving people, getting water, etc)
- rehabilitation: restoring the function of public services, a process that takes place over 1 or 2 years
- reconstruction: rebuiling the public system, economic system, infrastructure and governance functions -> predicted to take 2 to 5 years
what is the focus of an earthquake
point at which the plates release their tension or compression suddenly
what is the epicentre of an earthquake
marks the point on the surface of the Earth immediately above the focus of the earthquake
what is worse: a deeper or shallow epicentre
a shallower ones because the seismis waves have to travel a shorter distance to get to the surface, whereas, the seismic waves from a deeper earthquake can be absorbed by the rock above it
What is a shallow focus/earthquake
- Occurs relatively close to the ground surface
- Greater potential to do damage as less of the energy released by the earthquake is absorbed by overlying material.
What is a deep focus/earthquake
Occur at the considerable depth under the ground
- Travel further to reach the ground, more enrgy absorbed so less impact
What are the different waves we experience in a earthquake?
P waves (primary)
S waves (secondary)
L waves (surface love)
Rayleigh waves
What are primary waves (p -waves)
- Compressional waves: vibrates in the direction they are travelling (longitudinal)
- Fastest moving waves and reach surface FIRST
- Travel through both solids and liquids
- Only damaging in the most powerful earthquakes
What are secondary waves (s-waves)
Move in a sideways motion at 90 degress to the direction of travel (transverse)
- Slower than p waves and are 60% of the speed of p - waves
- ONLY travel through solids
- Do more damage than p - waves
What are surface love waves (L waves)
Slowest waves that cause the most damage as they travel near the surface
- Come shake the ground at right angles to the direction of the wave and some have a rolling motion that produces vertical ground movement.
What are rayleigh waves?
Cause the ground to move up and down
- Travel slowly through the crust and cause the msot damage along with surface love waves
How do earthquakes occur at a plate boundary?
- As oceanic crust slides into hotter fluid mantle, it takes time to warm up. As slab descends, pressure builds up and increase stress on rocks which then distort and cracks, relaesing energy eventually creating earthquakes
Why do some earthquakes occur so deep?
Subduction is relatively fast so by the time crust has cracked it has slid several hunred kilometers into the mantle so earthquakes occurs deeper
What does the size of the earthquake depend on?
- Thickness of the descending slab
- Rate of movement
What is a constructive plate boundary?
Can earthquakes occur there?
Are they powerful?
- Plates move away
- Yes due to moving of plates
- Not very powerful due to no subduction zones
What is a destructive plate boundary?
Can earthquakes occur there?
Are they powerful?
- Plates collide
- Yes due to subduction of oceanic plate
- Very powerful due to quicker subduction
What is a conservative plate boundary?
Can earthquakes occur there?
Are they poweful?
- Plates slide past each other
- Yes due to tension build up
- Can be explosive to release of pressure and energy
What are some human triggers of earthquakes
Construction of large dams
Fracking and mining
Testing of nuclear weapons
How has the construction of large dams triggered earthquakes
- Due to increased load on previously stable land
e.g. Colorado river was dammed by the Hooover dam and the increased load of water reactivated long-dormant faults int he area causng 6000 minor ewarthquakes over the next 10 years, though none casued damage
How has fracking triggered earthquakes
- A process where water containing certain chemicals is injected at very high pressure into rocks inorder to open them up and release natural gas withing ht rocks. In 2011, fracking led to a 2.3 magnitude earthquake in Lancashire, UK.
Biggest one was in Canada of 4.4 magnitude, fracking earthquakes rarely cause damage and arent really felt by people
How has testing of nuclear weapons triggered earthquakes
- Underground nuclear testing e.g. since 1966, France has carried out over 80 underground nuclear explosion tests on the Polynesian isalnd of Moruroa, where more than 120,000 people live. In 1966, a 120,000 tonne nuclear device was detonated, producing radioactive fallout.
what is disaster risk
expressed as the likelihood of loss of life, injury or destruction and damage froma disaster in a given period of time. It is recognised as a consequence of interactions between a hazard and characteristics that amke people and places vulnerable and exposed
what factors might affect disaster risk
name 3
- construction
- urban planning
- education
- disaster risk management
- increasing population means increased exposure
- high levels of inequality
what is the LIC case study for earthquakes
Haiti 2010
what and why was the magnitude so great and what was the cause of the 2010 haiti earthquake
magnitude: richter 7 -> the earthquake had a shallow depth
cause: caused by the rupture of the Enriquillo-Plantain Garden fault, which had been locked for 250 years, gathering stress
name 3 social effects of the haitian earthquake
- 1.3 million people made hoemless due to collapsed or unsafe housing
- 300,000 injured, where treatment is difficult due to several hospitals collapsing
- 222,000 deaths caused by collapsing buildings, a small tsunami and the cholera epidemic in the preceeding weeks
name 3 economic impacts of the haitian 2010 earthquake
- airport and port damage = decrease in imports and exports as well as a slowdown in the rescue and response from overseas
- businesses destroyed and vast sums of moeny for the rebuilding process - money that Haiti did not have
- 30,000 commercial building collapsed leading to a loss of trade for an already crippled economy
what are the 3 environmental impacts of the Haiti earthquake
- deforestation and forest clearance to make way for temporary camps
- small scale pollution by the leakage of oil, due to the rupture and damage to industrial facilities
- pollution of water supply = cholera epidemic
what are 2 political impacts of the haiti earthquake
- appeals for aid were immediately requested, but the American red cross quickly ran out of supplies and turned to public food donations
- Haiti’s justics system became a disarray, with very few people being able to be processed and arrested or brought infront of a judge at all
how does the population density link to the location of the epicentre of the earthquake
- the epicentre was located closest in the Port au Prince region, where most of the population is located -> 300,000 people were affected by this most extreme area, and 2 million affected in violent shaking areas
how has haitis building design and distribution have increased levels of vulnerability
haitis crowded buildings and poor earthquake-proof infrastructure, is a major afctor that caused the collapsing of multiple house and residential areas
what does haiti need to do now to help restore its society? and what are the domicans scared is going to happen?
Rebuilding Haiti’s homes, schools, roads and
other infrastructure will take between $8 billion
and $14 billion. Many Dominicans fear a ood
of illegal migrants into their country due to the
poverty in Haiti unless reconstruction is swift and
effective.
what is the HIC case study for earthquakes + magnitude
Alaska (USA) - 2018 + richter 7
what caused the alaskan 2018 earthquake?
when the pacific plate subducted beneath the north ameriacn plate, converging at a rate of 57mm per year
name 3 social effects of the 2018 alaskan earthquake
- no fatalities reported
- several damage to buidlings and houses
- 46,000 people were left without electricity
name 3 economic impacts of the 2018 alaskan earthquake
- trans alaskan oil pipeline temporarily shut down the flow of oil
- $30 million damages to Anchorage (city)
- $25-$50 million damages to school district
name 2 environmental impacts of the alaskan earthquake
- liquefaction occured in some areas (liquefaction occurs when the shaking causes loose or sturated soils to lose their strength, causing them to act like a liquid rather than a solid. This can result in significant damage to buildings and infrastructure)
- no oil leaks from pipeline
name 1 political impact of the 2018 alaskan earthquake
- Anchorage mayor declared a state of emergency for his city, requested both state and federal assistance
what is the distribution of population density in Alaska
- mean population of 12-133 people per square area in the south of Alaska
what is the relationship between the epicentre of the alaskan earthquake and the population density of the country
- the shallow epicentre is located in Anchorage as well as the largest mean number of people per square mile
what are the additional risks to coastal communities in this areas (Alaksa) strong ‘megathrust’ earthquakes
Some parts of the coast are a lot more vulnerable to tsunami inundation (tsunami flooding) than others, and citizens in these locations will have to move to higher ground extremely rapidly once the earthquake waves subside.
what is a megathrust earthquake?
- earthquakes that occur at covergengent plate boundaries, where one tectonic plate is forced underneath one another
what do the alaskan officials say to due before, during and after an earthquake
- before: complete your disaster mitigation (disaster supply kit, turning off gas, electricity and water, etc)
- during: drop-cover-hold on, drive away from underpass and bridges
- after: check for injuries and evacuate from collapsed buildings
what 3 geomorphological hazards can earthquakes create
- tsunamis
- liquefaction
- landslides
where are earthquakes most dangerous + named and explained example
- where people are not educated on preparation techniques and where buildings are not earthquake-resistant
- i.e. in Cairo (1992), many poorer people in villages and inner city slums were killed and injured when their mud-walled houses collapsed. Similarly, richer people were killed by collapsing concrete buildings - that were sometimes built without planning permission
how do we predict earthquakes?
- scientific predictions are used to provide precise statements on the time, place and size of the future event
- forecasts
- effective warning systems
how do we prepare for earthquakes
- better forecasting and warning
- improved building design and location
- establishing emergency procedures
how to monitor earthquakes. Name 3:
name 3:
- small-scale ground surface changes
- ground tilt
- changes in rock stress
- anomalies in the earth’s magnetic field
- clusters of small earthquakes
- small scale up-lift
what is the seismic gap theory
- it states that over a prolonged period of time, all parts of a plate boundary must move by almost the same amount
- so if 1 part has not moved and the others have, then the part that hasn’t moved is likely to move next
why are the oarfish important to predicting earthquakes
- In Japanese folklore, the oarfish are the messengers of earthquakes. When an earthquake is intended to occur, dead oarfish wash up on beaches. This is because earthquakes release carbon monoxide that kills deep-sea creatures like oarfish.
How can we reduce the impact of earthquakes (4)
- earthquake prediction
- building design
- flood prevention
- public information
examples of earthquake-vulnerable structures and why they are bad
- vertical rods -> do not allow movement during earthquake = bad
- inflexible joints in pipes = usually carry gas or sewage and can break during an earthquake
- Bay bridge = upper structures can collapse easily onto lower bridge structures
examples of earthquake-resistant structures and why they are good
- golden gate bridge = can sway with earthquakes
Flexible joints in pipes = less prone to breakage during earthquake - structure with spiral rods = stronger structure against earthquakes
what are some methods to create earthquake-resistant housing in LICs (3)
- Light walls and gables -> Lightweight structures are subject to smaller forces and are less likely to fall during earthquakes
- Reinforced walls -> Natural materials (bamboo/eucalyptus) have been reinforced with plastic mesh to prevent collapse
- cheap shock absorbers -> made with tyres filled with sand and fastened between floor and foundation
how can we control earthquakes
- We can alter the fluid pressure deep underground at the point of greatest stress in the fault line, where a series of small and less damaging earthquake events may be triggered. This could release energy that would otherwise be built up
- A series of controlled underground nuclear explosions might relieve stress before it reaches critical levels
How do we control tsunamis
- generally managed through sea walls
- and early-warning systems
what is a disadvantage of seas walls for tsunami control
- Walls can only provide a certain amount of protection and will not stop bigger waves
- cost constraints dictate the height of the wall that can be built
what is a megadisaster
an event that kills more than 100,000 people
What are the megadisaster patterns globally
- increase in megadisasters in 2000s (could be because we have better prediction of them)
what type of disaster cause the greatest deaths and which one affects most people
- earthquakes cause the greatest deaths (750,000)
- Flooding affects most people (2.4 billion)
what type of disaster occurs most regularly
- flooding
- storms
which geophysical hazard affects most people
Earthquakes and tsunamis
What is the percentage of death difference between HIC and LIC
- HIC: 13% deaths
- LIC: 33% deaths
20% difference in deaths, where % of disasters are less prevalent in LICs, evidencing how much they were impacted by disasters
What aspects affect the frequency and intensity of disastrous events?
- increasing population
- increasing urbanisation -> more urban places are being built that expand onto fault lines, such as in Tehran (a megacity built on an active fault line)
- Vulnerable areas -> building on places that are more earthquake unstable
- environmental degradation (destruction of mangrove swamps in Sri Lanka = increased vulnerability of coastal communities to the 2004 tsunami)
What are the impacts of extreme events?:
- social
- economic
- environmental
social:
-> thousands of deaths
-> disease/famine
economic:
-> Economic crises (people ask for money from insurance that they had to create for them)
-> loss of businesses
environmental:
-> climate stress and pollution
-> has led to the introduction and development of international organisations (Kyoto protocol)
what is mass movement
the movement down slope of any weathered material at a range of speeds, resulting in a destruction of property and/or loss of life, and is often triggered by human activity
what can cause mass movements (6)
-> angle of the slope
-> nature of the material (strength of the material compared to the force acting on it)
-> amount and type of vegetation
-> water (rainfall)
-> human activity (deforestation destabilises the ground)
-> climate
what are the 2 key effects of gravity on downslope movement
- move material downslope
- Acts to stick the particles to the slope
how does water affect mass movement
Water lubricates particles and might fill spaces between the particles, therefore forcing them apart under pressure
how does pore pressure affect mass movement
it will greatly increase the ability of the material to move
what is slope failure cause by?
- reduction in internal resistance or shear strength (the strength to resist the downward movement of the slope) of the slope
- increase in shear stress -> the forces attempting to pull a mass downslope
