Hazards - Plate tectonics & Volcanic hazards Flashcards
(95 cards)
1
Q
what is a natural hazard?
A
-a naturally occuring event which has the potential to cause harm to human life or property
-an event will only become a hazard when it is a threat to people
2
Q
what are the three types of natural hazards?
A
-geophysical hazards ( caused by land processes, majorly tectonic plates )
-atmospheric hazards ( caused by climatic processes and the conditions created because of these, such as weather systems )
-hydrological hazards ( caused by water bodies and movement )
3
Q
what are some examples of geophysical hazards?
A
-earthquakes
-volcanic eruptions
-landslides
-tsunamis
4
Q
what are some examples of atmospheric hazards?
A
-tropical storms
-droughts
-extremes of hot or cold weather
-wildfires
5
Q
what are some examples of hydrological hazards?
A
-floods
-avalanches
6
Q
what is the difference between a disaster and a megadisaster?
A
-a disaster is when a hazard actually seriously affects humans, whereas a megadisaster is when a hazard causes over 2000 deaths, 200,000 people are made homeless, GDP of a country is reduced by 5% or dependence on aid from abroad lasts for a year or more after the event
-e.g. the 2004 Indian Ocean earthquake and tsunami which killed over 230,000 people was a megadisaster
7
Q
what is vulnerability?
A
-how susceptible a population is to the damage caused by a hazard
8
Q
what is Degg’s model?
A
-a venn diagram which shows the interaction between hazards, disasters and human vulnerability
-a disaster will only occur when a vulnerable population is exposed to a hazard as, if the population is not vulnerable, the hazard will not have a significant effect, thus the event will not be disastrous
9
Q
what is meant by resilience?
A
-the ability of those exposed to hazards to utilise the avaliable resources to respond to, withstand and recover from the effects of natural hazards
10
Q
what is meant by risk?
A
-the likelihood that humans will be seriously affected by a hazard
11
Q
what is the hazard risk equation?
A
-hazard ( H ) x vunerability ( V ) / capacity ( C )
12
Q
why do people live in hazardous areas?
A
-hazard events are unpredictable = we cannot predict the frequency, magnitude or scale of a natural hazard event
-lack of alternatives = due to social, political, economic and cultural factors, people cannot simply uproot themselves from one place and move to another, giving up their homes, land and employment
-changing level of risk = places that were once relatively safe may have become far more of a risk over time, e.g. deforestation could result in more flooding from torrential rain associated with tropical storms leading to a greater risk of landslides
-cost / benefit = there are many hazardous areas that offer advantages that in people’s minds outweigh the risk that they are taking, e.g. Californian cities which have a high risk from earthquakes
-perception = people react to the threat of hazards in different ways due to how individuals receive and process information
13
Q
what factors affect people’s perception of hazards?
A
-their economic, social and cultural background
-e.g. wealth, past experience, education, religion and beliefs, mobility, personality
14
Q
how does wealth affect people’s perception of hazards?
A
-wealthier people may perceive a hazard to be smaller as they are less vunerable ( e.g. they have the ability to evacuate with transport access, build stronger houses etc. )
-however, they may also view a risk as greater as there is more risk of property damage and financial loss than someone less wealthy
15
Q
how does past experience affect people’s perception of hazards?
A
-someone who has experienced more hazards may be more likely to understand the full effects of a hazard, so they may view future risks as greater
-however, there are also studies suggesting that people who have experienced hazards are likely to have an optimistic and unrealistic outlook on future hazards ( almost like a ‘lightning never strikes the same place twice’ mentality )
16
Q
how does education affect people’s perception of hazards?
A
-someone who is more educated about hazards may understand their full effects on people and how devastating they can be and have been in the past
-those who are less educated may not understand the full extent of a hazard and may not know to evacuate, prepare etc.
17
Q
how does religion and beliefs affect people’s perception of hazards?
A
-some may view hazards as put there by God for a reason, or being part of the natural cycle of life etc. so may not perceive them to be negative
-in contrast, those who believe strongly in environmental conservation may perceive hazards to be a huge risk to the natural environment
18
Q
how does mobility affect people’s perception of hazards?
A
-those who have limited access to escape a hazard may perceive hazards to be greater threats than they are
-whether they are in a secluded location, or if they are impaired with a disability or illness, those who cannot easily leave an area quickly may feel more at risk
19
Q
how does personality affect people’s perception of hazards?
A
-some people fear hazards and others might think of them as exciting, so the way a person perceives hazard risk depends on that individual person
20
Q
what is the passive response to hazards?
A
-fatalism / acceptance = hazards are uncontrollable natural events, and any losses should be accepted as there is nothing that can be done to stop them
21
Q
what are the active responses to hazards?
A
-prediction = using scientific research and past events in order to know when a hazard will take place, so that warnings can be delivered and impacts of the hazard can be reduced
-adaptation = attempting to live with hazards by adjusting lifestyle choices so that vulnerability to the hazard is lessened, e.g. earthquake resistant buildings
-mitigation = strategies carried out to lessen the severity of a hazard, e.g. sandbags to offset impact of flooding
-management = coordinated strategies to reduce a hazard’s effects i.e. the previous three responses
-risk sharing = a form of community preparedness whereby the community shares the risk posed by a natural hazard and invests collectively to mitigate the impacts of future hazards, e.g. through public education and awareness programmes, evacuation procedures and provision of emergency medical and food supplies and shelters
22
Q
how does the incidence of hazards affect human responses?
A
-incidence = the frequency of a hazard i.e. how often it occurs
-low incidence hazards may be harder to predict and have less management strategies put in place, meaning the hazard is likely to be more destructive when it does occur
23
Q
how does the distribution of hazards affect human responses?
A
-distribution = the areal extent of a hazard
-areas of high hazard distribution are likely to have a lot of management strategies, and those living there will be adapted to the hazardous landscape because it dominates the area
24
Q
how does the intensity and magnitude of hazards affect human responses?
A
-intensity = the power of a hazard i.e. how damaging the effects are
-magnitude = the size of the hazard, usually this is how a hazard’s intensity is measured
-high magnitude, high intensity hazards will have worse effects, meaning they will require more management
25
how does level of development affect human responses to hazards?
-an area with a lower level of development is less likely to have effective mitigation strategies as these are costly and usually require high tech building projects
-however, there are many high income countries that are not as prepared for natural hazards as they should be, meaning they lack the management strategies for an event
26
what does the Park model show?
-how human responses progress during a disaster, which may help planners predict what resources will be needed at each stage
-the steepness of the curve shows how quickly an area deteriorates and recovers
-the depth of the curve shows the scale of the disaster ( i.e. lower the curve, lower the quality of life )
27
what are the stages of the Park model?
-pre-disaster = before the event, the situation is normal
-disruption = during and directly after the hazard event occurs, there is destruction of property, loss of life etc. before people begin to respond
-relief ( hours to days ) = immediate local response i.e. medical aid, search and rescue, and immediate appeal for foreign aid
-rehabilitation ( days to weeks ) = people start to resolve longer-term problems, services begin to be restored, temporary shelters and hospitals set up, food and water distributed, and coordinated foreign aid e.g. peacekeeping forces
-reconstruction ( weeks to years ) = restoring the area to the same or better quality of life, area back to normal e.g. ecosystems restored and crops regrown, infrastructure rebuilt to the same or a higher standard so the area could improve along with vulnerability, and mitigating efforts for future events
28
what does the Hazard Management Cycle show?
-the stages of responding to events, showing how the same stages take place after every hazard
29
what are the four stages of the Hazard Management Cycle?
-preparedness = being ready for an event to occur ( public awareness, education, training )
-response = immediate action taken after event ( evacuation, medical assistance, search and rescue )
-recovery = long-term responses in order to get the affected area back to normal ( restoring services, reconstruction )
-mitigation = strategies to lessen effects of another hazard ( barriers, warning signals developed, observatories )
30
what should be considered when evaluating the effectiveness of hazard models?
-can they be applied to every hazard?
-does the model take any aspects of hazards into account such as level of development?
-could the model be less vague / include more steps that can be applied to all hazards?
-does the model present hazards currently / account for hazards affected by climate change?
31
what is the earth divided into?
-centre = core ( inner and outer )
-mantle
-crust
32
what is the earth's core like?
-made up of dense rocks containing iron and nickel alloys
-subdivided into a solid inner core ( due to pressure ) and a very hot molten outer core, with a temperature of over 5000°C
-this heat is the earth's main source of internal energy: some is primordial heat left over from the earth's formation, and some comes from radioactive decay of elements such as uranium
33
what is the earth's mantle like?
-the thickest layer with a temperature of around 1000-3500°C
-made up of molten and semi-molten silicate rock
-the upper part of the mantle becomes hotter and more fluid ( the asthenosphere ) at depths between about 100 and 700 km
34
what is the earth's crust like?
-the thinnest, outermost layer
-two types of crust = oceanic and continental
35
what is the lithosphere?
-the rocky outer part of the earth
-made up of the crust and the rigid top part of the upper mantle
36
what is the asthenosphere?
-the layer of the earth that lies below the lithosphere, at depths between about 100 and 700 km
-made up of the part of the earth's mantle that behaves like molten plastic despite being solid, which means it can move and deform but very slowly
37
what are the characteristics of oceanic crust?
-6-10 km thick ( thinner )
-density = 3 g/cm^3 ( heavier )
-less than 200 million years old
-mainly composed of basalt: silicon, magnesium, oxygen
38
what are the characteristics of continental crust?
-30-70 km thick ( thicker )
-density = 2.6 g/cm^3 ( lighter )
-over 1,500 million years old
-mainly composed of granite: silicon, aluminium, oxygen
39
what are tectonic plates?
-large sections of the lithosphere which float on the upper mantle and move relative to one another
-plate boundaries / margins are where these plates meet
40
what is plate tectonic theory?
-the earth's crust is made up of several rigid plates moving relative to one another
-this theory emerged from Alfred Wegener's theory of continental drift which suggests that just one giant continent ( Pangea ) existed about 300 million years ago
41
what geological evidence is there for Alfred Wegener's theory of continental drift?
-the jigsaw fit of South America and west Africa
-similar ancient glacial deposits found in South America, Antarctica and India, indicating they were formed together and then moved
-structural faults in rocks in Brazil and west Africa match when the two are compared
-the distribution of mountain ranges that match across continents, e.g. the Appalachian Mountains in North America and the Scottish Highlands
42
what biological evidence is there for Alfred Wegener's theory of continental drift?
-fossils found in India are comparable with fossils in Australia
-fossil remains of the reptile Mesosaurus are found in both South America and southern Africa, indicating they were once joined together
-identical plant fossils have been found in the coal deposits of both India and Antarctica
43
what is the theory of sea floor spreading?
-the ocean floor is moving away from the mid oceanic ridge and across the deep ocean basin, to disappear beneath continents and island arcs
44
what evidence is there for plate tectonic theory and sea floor spreading?
-paleomagnetism = the study of rocks that show the earth's magnetic fields
-as new rock is formed ( by volcanic eruptions ) and cools the magnetic grains within the rock align with the magnetic poles
-our poles switch periodically ( every 100,000 years ) and each time this happens the new rock being formed at plate boundaries align in the opposite direction to the older rock
-as the new rock solidifies it pushes the older rock further away from the plate boundary, creating symmetrical bands of rock with alternating bands of magnetic polarity
45
why is the sea floor spreading?
-new oceanic crust is being created by the solidification of volcanic eruptions ( lava ) at divergent plate margins
-this means that the distance between North America and Europe is increasing at a rate of a few centimetres per year
-however, the earth isn't getting bigger because crust is also being destroyed at convergent plate margins in the process of subduction
46
how do plates move?
-convection currents in the mantle
-ridge push / gravitational sliding
-slab pull
47
how do convection currents cause plate movement?
-heat from the inner core ( from nuclear reactions ) rises through the mantle into the asthenosphere
-hot magma rises because it becomes less dense with heat ( as particles spread out )
-magma is cooler at the top as it is further away from the heat source, so it becomes more dense and sinks back down towards the core where it is reheated and begins to rise again, creating a loop called a convection cell
48
how does ridge push ( gravitational sliding ) cause plate movement?
-at constructive plate margins, hot magma rises to the surface and forms new crust, heating the surrounding rocks, which expand and rise above the surface of the surrounding crust, forming a slope
-as this rock gets older, it cools and becomes denser
-gravity pushes this older, denser lithosphere downslope, away from the margin, which puts pressure on the tectonic plates, causing them to move apart
-shallow earthquakes occur as a result of the repeated tearing apart of the newly formed crust, indicating there is some frictional resistance
49
how does slab pull cause plate movement?
-at destructive plate margins, denser crust ( e.g. oceanic ) is forced under less dense crust ( e.g. continental / oceanic )
-due to the downward gravitational force acting on it, the denser plate sinks into the mantle and pulls the rest of the plate towards the boundary
50
what are the three types of plate margins?
-constructive ( divergent ) = plates move away from each other
-destructive ( convergent ) = plates move towards each other
-conservative = plates move parallel to each other
51
what happens at an oceanic to oceanic constructive plate margin?
-magma from the mantle rises in between the gap left by the two plates separating, creating new land when it cools and forming less explosive, underwater shield volcanoes as ridges along the margin, e.g. the Mid-Atlantic Ridge
-islands are created where underwater volcanoes erupt along mid-ocean ridges and build up to be above sea level, e.g. Iceland
-new land forming on the ocean floor by lava filling the gaps is known as sea floor spreading
52
what happens at a continental to continental constructive plate margin?
-rising magma causes the continental crust to bulge and fracture, forming fault lines
-as the plates keep moving apart, the crust between parallel faults is stretched thinner and eventually drops down to form a rift valley, e.g. the East African Rift System
-shield volcanoes form where magma rises from the mantle and erupts as lava, e.g. Mount Kenya and Mount Kilimanjaro
-eventually the gap will most likely fill with water and become a new ocean
53
what happens at an oceanic to continental destructive plate margin?
-the younger, denser oceanic plate subducts below the less dense continental plate, forming a deep sea trench, e.g. the Peru-Chile trench in the Pacific Ocean
-fold mountains occur when sediment is pushed upwards during subduction along with the edge of the continental crust
-the oceanic crust is heated by friction and contact with the asthenosphere, which melts it into magma
-the extra magma created causes pressure to build up, and pressurised, viscous magma forces through weak areas in the continental plate, causing explosive, high pressure composite volcanoes to erupt through the continental plate
-as one plate moves under the other they can get stuck, which causes pressure to build up and the plates to jerk past each other, causing a large earthquake at the Wadati-Benioff zone
54
what happens at an oceanic to oceanic destructive plate margin?
-the denser plate subducts, forming a deep sea trench e.g. the Mariana Trench, and triggering small earthquakes and volcanic eruptions
-fold mountains occur when sediment is pushed upwards during subduction
-built up pressure causes underwater volcanoes to burst through the less dense oceanic plate
-lava cools and creates island arcs, e.g. the Mariana Islands
55
what happens at a continental to continental destructive plate margin?
-the two plates are similar in density so when they converge neither subducts, which causes both plates to deform upwards and downwards, forming fold mountains e.g. the Himalayas
-there are no volcanoes, but the pressure that builds up between the two plates can cause earthquakes
56
what happens at conservative plate margins?
-the parallel plates move in different directions or at different speeds in the same direction
-no plates are destroyed so no landforms are created
-the two plates get locked together in places and pressure builds up, causing the plates to jerk past each other or to crack and form fault lines, releasing the energy as an earthquake
-e.g. where the Pacific plate is moving past the North American plate many earthquakes occur along the margin and its fault lines, e.g. along the San Andreas fault in California
57
what are hotspots?
-areas of volcanic activity that are not related to plate boundaries and are instead caused by magma plumes ( vertical columns of extra-hot magma that rise up from the mantle )
58
why do hotspots cause volcanoes to occur away from plate margins?
-a rising column of heat that is less dense than the surrounding rock melts sections of the mantle which then rise and burn through weaker parts of the crust, creating volcanoes and islands
59
do magma plumes move?
-no, they stay in the same place but the plates above them continue to move, so volcanic activity decreases as the crust moves away until the volcano eventually becomes extinct
-new volcanoes form in the part of the crust that is now above the magma plume, creating a chain of volcanoes, e.g. the Hawaiian Islands
60
where do most volcanic eruptions occur?
-along constructive or destructive plate margins, or on hotspots
-the Ring of Fire is an area of high volcanic activity located in the Pacific, and the majority of large volcanoes occur within this 25,000 mile belt
61
what is meant by viscosity?
-the thickness of a fluid
62
how does viscosity affect volcanic eruptions?
-low viscosity ( low silica ) magma, e.g. at constructive plate margins, is very runny so gases can escape easily, leading to effusive eruptions
-higher viscosity magma, e.g. at destructive plate margins, makes it more difficult for gases to escape, so pressure builds up and when the eruption occurs it is more explosive
63
what type of magma is formed at constructive plate margins?
-basaltic ( basic ) lava which is very hot and has a low viscosity ( 50% silica ), so it flows easily and quickly
-eruptions of basaltic lava are frequent and go on for a long time, but aren't very violent
-if the margin is on land, as plates pull apart, forming rift valleys, they become thinner and magma from the mantle is able to break through at the surface
64
what type of magma is formed at destructive plate margins?
-andesitic and rhyolitic ( acidic ) lavas which are cooler and more viscous, so they flow less easily
-andesitic and rhyolitic lavas usually erupt intermittently ( every once in a while ) and the eruptions are short-lived
-at subduction zones, where one plate is pulled beneath another, melting of the plate due to pressure and friction forms magma, which rises to the surface as volcanoes
-as the lava is viscous, it forms blockages in volcanic vents, causing pressure to build up and a violent eruption which clears the blockage
65
what type of magma is formed at hotspots?
-basaltic lava which flows quickly, forming volcanoes with gentle slopes ( i.e. shield volcanoes )
66
what is tephra?
-any type of rock fragment that is forcibly ejected from a volcano during an eruption
67
how is vulcanicity measured?
-VEI = volcanic explosivity index, a logarithmic scale running from 0 to 8 which considers how much tephra is erupted, how long it lasts, how high the tephra is ejected etc.
68
what is the frequency of volcanic eruptions?
-some active volcanoes erupt only once every 100,000 years or so, whereas others erupt every few months
-generally, less frequent eruptions are larger in magnitude and more damaging ( explosive )
69
what is the regularity of volcanic eruptions?
-some volcanoes erupt at very regular intervals, whereas others may be dormant for hundreds or thousands of years, then erupt several times in quick succession
-volcanic eruptions are regular in that the eruptions on each type of boundary are similar e.g. eruptions on destructive boundaries will regularly be explosive
70
what is the predictability of volcanic eruptions?
-regularity of eruptions can help scientists to predict when it might erupt again ( e.g. every 10 years )
-small earthquakes caused by the rising magma, an increase in the release of various gases e.g. sulphur dioxide and carbon dioxide, a rise in the level of lava lakes in volcanic craters, and changes in the shape of the volcano or the bulging upwards of surrounding land due to pressure from below etc. can all indicate an imminent eruption, but there is no definite predictions to a volcanic eruption
71
what is the difference between primary and secondary effects / hazards?
-primary hazards = direct result of the eruption, e.g. pyroclastic flows / nuée ardentes, lava flows, volcanic gases, and pyroclastic and ash fallout ( tephra )
-secondary hazards = caused by the primary effects, e.g. lahars ( volcanic mudflows ), flooding, volcanic landslides, tsunamis, acid rain and climatic change
72
what are pyroclastic flows / nuée ardentes and why are they hazardous?
-very hot ( 800°C ), gas charged, high-velocity flows made up of a mixture of gas and tephra
-these usually hug the ground and flow down the sides of the volcano with speeds of up to 700 km/h and travel a long way ( around 10-15 km )
-e.g. the Roman city of Pompeii, Italy was destroyed in 79 AD by such flows from Mt Vesuvius
-as they travel fast and can happen with relatively little warning, pyroclastic flows can cause widespread death and destruction, through e.g. burning and burial under debris
73
what are lava flows and why are they hazardous?
-lava can flow from a volcanic vent down the side of the volcano
-the speed of the flow and distance travelled depends on the temperature and viscosity of the lava, as well as the steepness of the slope
-most flows are relatively slow, so people have time to evacuate areas that will be affected
-however, lava flows are often unstoppable and therefore can destroy anything in their path, including buildings and vegetation, by burning, burying or knocking it down
74
what are volcanic gases and why are they hazardous?
-lava contains gases such as carbon dioxide and sulphur dioxide, which are released into the atmosphere when a volcano erupts
-some of these gases can be harmful to humans and animals if they're breathed in e.g. sulphur dioxide can cause breathing difficulties
75
what is pyroclastic and ash fallout ( tephra ) and why is it hazardous?
-material that has been ejected from a volcano during an eruption and falls back to the ground
-when fallout consists mostly of ash, it's called ash fallout
-fallout consists of material of varying grain size ranging from volcanic bombs weighing several tonnes to microscopic ash particles
-generally, the larger the tephra particles, the shorter the distance from their source ( the volcano )
-large pieces of falling tephra can damage buildings and kill or injure people
-finer material can form a layer up to several metres in thickness, which can kill vegetation, hinder road and rail transport and cause buildings to collapse
-fine ash can be thrown high into the atmosphere where strong winds can blow it around the earth, reducing incoming radiation and cooling the earth
76
what are lahars and why are they hazardous?
-lahars occur when volcanic material mixes with large amounts of water e.g. from rainfall or from ice melted by the eruption
-flows move very quickly ( over 80 km/h ) and can travel for tens of km
-they can bury or destroy natural habitats, settlements and infrastructure e.g. roads and bridges
77
what is flooding and why is it hazardous?
-when an eruption melts glaciers and ice caps, a large amount of water is discharged and serious flooding can result
-e.g. in Iceland in 1996 when the Grimsvotn volcano erupted
78
what are volcanic landslides and why are they hazardous?
-tall, steep composite ( cone-shaped ) volcanoes are weakened by the rise and eruption of lava
-the high velocity and great momentum of landslides allows them to cross between valleys and run up slopes several hundred metres high
-e.g. the landslide at Mount St Helens, Washington in 1980 had a volume of 2.5 km^3, reached speeds of 50-80 m/s and surged up and over a 400 m high ridge located about 5 km from the volcano
79
what are tsunamis and why are they hazardous?
-giant sea waves generated by violent volcanic eruptions in the sea
-e.g. those formed after the eruption of Krakatoa, Indonesia in 1883
80
what is acid rain and why is it hazardous?
-volcanic gases can react with water vapour in the atmosphere, which then falls as acid rain e.g. sulphur dioxide reacts with water to form weak sulphuric acid
-this can damage ecosystems, and can also cause stone and metal to deteriorate, damaging buildings, bridges, statues etc.
81
what is climatic change and why is it hazardous?
-the ejection of huge amounts of volcanic debris into the atmosphere can reduce global temperatures and is believed to have been an agent in past climatic change
82
what are the social impacts of volcanic eruptions?
-primary = people are killed, buildings and infrastructure are destroyed by pyroclastic flows and fallout
-secondary = pyroclastic flows and lava flows can start fires that damage buildings, mudflows and flooding from ice melt can cause further damage and deaths, homelessness
83
what are the environmental impacts of volcanic eruptions?
-primary = ecosystems damaged or destroyed by flows and fallout of volcanic material
-secondary = water acidified by acid rain kills plants and animals, and damages forests by removing nutrients from the soil, volcanic gases contribute to the enhanced greenhouse effect ( global warming ), clouds of ash and volcanic debris reduce the amount of sunlight reaching earth, decreasing temperatures over large areas
84
what are the economic impacts of volcanic eruptions?
-primary = businesses and industries destroyed or disrupted
-secondary = jobs lost, ash clouds prevent aircraft flying and damage crops, damaging the economy of the region and the country, damage to buildings and infrastructure can be expensive to repair, eruptions and the scenery they form can attract tourists, boosting the economy
85
what are the political impacts of volcanic eruptions?
-primary = government buildings and other important areas destroyed or disrupted
-secondary = damage to agricultural land causes food shortages, leading to conflict and political unrest, governments may have to spend money on repairing damage to buildings and roads, rather than e.g. hospitals and schools, so countries may not develop as rapidly
86
what is hazard mitigation?
-anything that is done to reduce the severity or impacts of a hazard
87
what is the difference between short-term and long-term responses?
-short-term responses = occur before, during or immediately after the hazard begins, e.g. evacuating people from areas at risk and providing emergency food supplies
-long-term responses = designed to reduce the impacts of future eruptions by managing the risks
88
how can the impacts of volcanic eruptions be reduced?
-preparedness = monitoring increases the notice of volcanic eruptions so warnings can be given out, education on volcanoes in areas of risk so people know what to do if there is a volcanic eruption, evacuation procedures planned, training response teams to tackle the impacts
-mitigation = direct intervention to the volcano e.g. concrete blocks to steer lava away from areas at risk, strengthening buildings that are at risk of mudflows or ash fallout, evacuation and exclusion zones, mitigating effects on health by having emergency aid and rescue
-prevention = volcanic eruptions cannot be prevented, only the risk to people can be prevented by not allowing people near volcanic hazards e.g. preventing building and development around volcanoes
-adaptation = move away from areas at risk, capitalise on the opportunities of living near a volcano e.g. by farming or working in the tourist industry, change profession so it is less likely to be affected by volcanic hazards
89
how have volcanic eruptions been mitigated against in the past?
-freezing lava in its tracks = in 1973, the inhabitants of Haeimaey, Iceland poured seawater on the front of a lava flow to solidify it before it closed off the harbour, which is critical to the region's fishing industry and a lifeline to the Icelandic mainland
-fighting lava with explosives = Hawaiians used explosives dropped from planes in 1935 and 1942 to try to disrupt lava flows from Mauna Loa that were threatening the town of Hilo, and this created new channels, but the newly formed lava flows soon rejoined the original lava channel so neither attempt was successful
-lava barriers and diversions = shortly after Grindavík's residents were evacuated in November 2023 by Icelandic authorities, construction began on protective barriers for the town and the nearby geothermal power station, and this was successful until a new fissure opened in January, which sent lava into a neighbourhood and destroyed three homes
-draining crater lakes = the Philippine government had authorities dig a 5m-wide channel from the edge of Mt Pinatubo's crater, draining about a quarter of the lake's volume and diverting the excess lakewater into local rivers in an attempt to remove the source of lahars
90
what is an example of a recent volcanic event?
-from January 13 to March 18, 2018, volcanic activity in Mount Mayon, Philippines increased
-Mayon is 2,462 m above sea level
-the most active volcano in the Philippines
-it covers an area of 250 km^2
-although within a national park, it is surrounded by the city of Legaspi and eight other towns
91
what are the physical causes of Mount Mayon?
-the subduction of the Philippine Sea plate underneath the Sunda plate as part of the Pacific Ring of Fire at an oceanic to continental destructive plate margin
-the oceanic crust is heated by friction and contact with the asthenosphere, which melts it into viscous magma, causing explosive composite volcanoes to erupt through the continental plate as the pressurised magma forces through weak areas
92
how does the relief and climate of the region impact volcanic hazard risk?
-Mayon is a composite volcano, which makes it tall and steep-sided, and the climate of the Philippines is tropical maritime, so it is hot, humid and experiences heavy rainfall
-these increase the risk of volcanic hazards such as lahars because volcanic ash and debris have more water to mix with from heavy rainfall, and they will flow faster down the steep sides of the volcano, causing them to be more destructive and reach more people and towns / cities
93
what is the timeline of the 2018 event?
-January 13 = a phreatic eruption began that blasted a steam and ash plume 2,500 m into the air for just over 1.25 hours, ash fell in many of the surrounding towns, alert level raised from 1 to 2, 40,000 residents evacuated from a 6 km radius
-January 14 = 3 more phreatic eruptions, 158 rockfall events recorded, summit crater began to glow, alert level 3
-January 16 = lava flows reached the limits of the 6 km evacuation zone, the province of Albany declared a state of calamity ( a disaster )
-January 22 = a 3 km tall ash column developed, lava fountains, pyroclastic flows, ash plumes, lava bombs and rockfalls were observed, alert level 4
-January 23 = the sound of explosions could be heard, schools and colleges shut, 6 km danger zone expanded to 9 km, 34,000 evacuated, heavy rains were reported, concern over the development of lahars
-early February = some schools and colleges reopened as the explosion slowly subsides
-March = further fall in volcanic activity, alert level dropped to 3 and then to 2 at the end of the month
94
what were the impacts of and the responses to the eruption?
-impacts = 0 died, 86,000 affected, 65,000 stayed in 58 designated evacuation centres, US $3.4 million worth of damages to agriculture ( rice, corn and abaca ), more than 10,000 farmers affected, some roads made impassable by landslides and ash falls, some flights in and out of Legaspi were cancelled
-responses = 74,000 evacuated, Mayon's activity is regularly monitored by PHIVOLCS, Filipino government commited US $1 million for a 'Cash for Work' programme as well as provided hygiene packages for 50,000 families for 10 days and food packs to evacuees for 100 days, army helped to enforce the evacuation, Philippine Red Cross set up first-aid stations and welfare desks to provide psychosocial support, National Council of Churches in the Philippines provided immediate relief assistance to 3,500 families, US government committed over $100,000 to distribute vouchers for families to buy essential items and hygiene kits to help reduce illness in evacuation centres, they also constructed latrines, bathing cubicles and handwashing stations, and promoted safe water and hygiene practices through education
95
what factors affected vulnerability to Mount Mayon's volcanic activity?
-wealth = ranked 15th / 63 countries in income inequality, top 1% of income earners contributed 17% of national income and bottom 50% only captured 14% in 2022
-mobility = half of the households own a motorcycle or tricycle, whereas 11% own a car, jeep or van
-health = life expectancy of below 70 years
-location = 9 km danger zone, 74,000 evacuated, 91,300 students affected
-age = median age of 25.7 years ( UK's is 40.7 ), dependency ratio of 55.7%
-governance = good as Mount Mayon is regularly monitored by PHIVOLCS, a government department dedicated to providing information on hazards, so they were readily prepared for the 2018 event
-education = literacy rate of 99.27%
-level of development = LIC as GNI per capita of $3,950 and GDP per capita of $3,500 in 2022
