Tectonic processes and hazards

WHY ARE SOME LOCATIONS MORE AT RISK FROM TECTONIC HAZARDS?

• All tectonic hazards are caused by the Earth's internal heat engine. Radioactive decay of isotopes in the Earth's core and mantle generate huge amounts of heat which flow towards the Earth's surface.This heat flow generates convection currents in the plastic mantle.
• Most tectonic hazards occur at or near tectonic plate boundaries.
• Not all tectonic plate boundaries are the same and this has an impact on the type and magnitude of tectonic hazards. Plate boundary type depends on two factors:
• 1. Motion: whether the plates are moving apart (divergent), colliding (convergent) or sliding past each other (conservative or transform)
• 2. Plate type: whether the tectonic plates are oceanic or continental. Oceanic plates make up the ocean floor and are high density, basaltic rock but only 7-10km thick. Continental plates make up the Earth's landmasses and are much thicker at 25-70km but made of less dense, granite rock.

Divergent boundaries

• Oceanic-oceanic (e.g. Mid-Atlantic Ridge at Iceland) - rising convection currents bring magma to the surface resulting in small, basaltic eruptions, creating new oceanic plate. Minor, shallow earthquakes
• Continent-continent (e.g. African Rift Valley/Red Sea) - caused by geologically recent mantle plume splitting a continental plate to create a new ocean basin. Basaltic volcanoes and minor earthquakes

Convergent boundaries

• Continent-continent (e.g. Himalayas) - The collision of two continental landmasses creating a mountain belt as the landmasses crumple. Infrequent major earthquakes distributed over a wide area
• Oceanic-oceanic (e.g. Aleutian Islands, Alaska) - One oceanic plate is subducted beneath the other, generating frequent earthquakes and a curving (arc) chain of volcanic islands (violent eruptions)
• Oceanic-continent (e.g. Andean Mountains) - An oceanic plate is subducted under a continental plate, creating a volcanic mountain range, frequent large earthquakes and violent eruptions

Conservative boundaries

• Oceanic-continent (e.g. California, San Andreas fault zone) - plates slide past each other, along zones known as transform faults. Frequent, shallow earthquakes but no volcanic activity

• Some volcanic eruptions are described as 'intra-plate'. This means they are distant from a plate boundary at locations called mid-plate hotspots. At these locations:
• Isolated plumes of convecting heat, called mantle plumes, rise towards the surface, generating basaltic volcanoes that tend to erupt continually
• A mantle plume is stationary, but the tectonic plate above moves slowly over it
• Over milennia, this produces a chain of volcanic islands, with extinct ones most distant from the plume location

• Earth's tectonic plates move at a speed of 2-5cm per year. There are seven very large major plates, smaller minor plates and dozens of small microplates. All fit together into a constantly moving jigsaw of rigid lithosphere. Each plate is about 100km thick. Its lower part consists of upper mantle material while its upper part is either oceanic or continental crust.
• The theory of plate tectonics has developed because of a number of key discoveries:
• Alfred Wegener's Continental Drift hypothesis in 1912 that postulated that now-separate continents had once been joined
• The ideas of Arthur Holmes in the 1930s that Earth's internal radioactive heat was the driving force of mantle convection that could move tectonic plates
• The discovery in 1960 of the asthenosphere, a weak, deformable layer beneath the rigid lithosphere on which the lithosphere moves
• The discovery in the 1960s of magnetic stripes in the oceanic crust of the sea bed; these are palaeomagnetic signals from past reversals of Earth's magnetic field and prove that new oceanic crust is created by the process of sea-floor spreading at mid-ocean ridges
• The recognition of transform faults by Tuzo Wilson in 1965

Constructive margins

• Mantle convection forces plates apart at constructive plate margins. Tensional forces open cracks and faults between the two plates. These create pathways for magma to move towards the surface and erupt, creating new oceanic plate. Eruptions are small and effusive in character, as the erupted basalt lava has a low gas content and high viscosity. Earthquakes are shallow, less than 60km deep, and have low magnitudes of under 5.0.

Destructive margins and subduction zones

• Mantle convection pulls oceanic plates apart, creating the fracture zones at constructive margins, and convection also pulls plates towards subduction zones.
• Constructive margins have elevated altitudes because of the rising heat beneath them, which creates a 'slope' down which oceanic plates slide
• Cold, dense oceannic plate is subducted beneath less dense continental plate; the density of the oceanic plate pulls itself into the mantle (slab pull)
• Earthquakes at subduction zones occur at a range of focal depths from 10km to 400km, following the line of the subducting plate. This is called a Benioff Zone. 

• The descending plate begins to melt at depth by a process called wet partial melting. This generates magma with a high gas and silica content, which erupts with explosive force.

Collision zones

• The Himalaya mountains are a location where two continental plates are in collision (the Indo-Australian and Eurasian plates).
• As both continental plates have the same low density, subduction is not possible. Instead, the plates have 'crumpled', creating enormous tectonic uplift in the form of the Himalaya and Tibetan Plateau. 
• Magma is being generated at depth, but it cools and solidifies beneath the surface so eruptions are very rare.
• Collision zones are cut by huge thrust faults that generate shallow, high-magnitude earthquakes.

Transform zones

• Conservative plate boundaries consist of transform faults. These faults 'join up' sections of constructive plate boundary as they traverse the Earth's surface in a zig-zag pattern. 
• In some locations, long transform faults act like a boundary in their own right, most famously in California where a fault zone - including the San Andreas fault - creates an area of frequent earthquake activity.
• Earthquakes along conservative boundaries often have shallow focal depths, meaning high-magnitude earthquakes can be very destructive. Volcanic activity is absent.

Earthquakes

• Earthquakes are a sudden release of stored energy. As tectonic plates attempt to move past each other along fault lines, they inevitably 'stick'. This allows strain to build up over time and the plates are placed under increasing stress. Earthquakes are generated because of sudden release of the sress. 
• A pulse of energy radiates out in all directions from the earthquake focus (point of origin).
• Epicentre - the point on the Earth's surface directly above the focus
• Earthquakes generate three types of seismic wave:
• P-waves, or primary waves, are the fastest. They arrive first and cause the least damage
• S-waves, or secondary waves, arrive next and shake the ground violently, causing damage
• L-waves, or Love waves, arrive last as they travel only across the surface. However, they have a large amplitude and cause significant damage, including fracturing the ground surface
• Earthquakes frequently generate large landslides as secondary hazards. 
• Liquefaction is a particular hazard in areas where the ground consists of loose sediment such as silt, sand or gravel that is also waterlogged - often found in areas close to the sea or lakes. Intense earthquake shaking compacts the loose sediment together, forcing water between the sediment out and upward. This undermines foundations and causes buildings to sink, tilt and often collapse.

Volcanoes

• Lava flow - extensive areas of solidified lava, which can extend several kilometres from volcanic vents if the lava is basaltic and low viscosity. It can flow up to 40kmh
• Pyroclastic flow - very large, dense clouds of hot ash and gas at temperatures of up to 600 degrees. They can flow down the flanks of volcanoes ad devastate large areas
• Ash fall - ash particles, and larger tephra particles, can blanket huge areas in ash, killing vegetation, collapsing buildings and poisoning water courses
• Gas eruption - the eruption of carbo dioxide and sulphur dioxide, which can poison people and animals in extreme cases
• Lahar - volcanic mudflows, which occur when rainfall mobilises volcanic ash. They travel at high speed down river systems and cause major destruction
• Jokulhlaup - devastating floods caused when volcanoes erupt beneath glaciers and ice caps, creating huge volumes of meltwater. They are common in Iceland

Tsunamis

• Tsunami are generated when a sub-marine earthquake displaces the sea bed vertically as a result of movement along a fault line at a subduction zone. The violent motion displaces a large volume of water in the ocean water column, which then moves outward in all directions from the point of displacement. The water moves as a vast 'bulge' in open water, rather than a distinct wave.
• Tsunami characteristics are very different from those of wind-generated ocean waves:
• Wave heights are typically less than 1m
• Wavelengths are usually more than 100km
• Speeds are 500-950kmh

WHY DO SOME TECTONIC HAZARDS DEVELOP INTO DISASTERS?

• Tectonic hazards are natural events that have the potential to harm people and their property. A disaster is the realisation of a hazard, i.e. harm has occurred
• Threshold - the magnitude above which a disaster occurs. This threshold level could be different in a developed versus a developing country because of different levels of resilience.
• A threshold level is often used to determine whether the impact of an event is large enough to be considered a disaster, such as:
• 10 or more deaths
• 100 or more people affected
• US$1 million in economic losses
• Hazard risk equation:
• Risk = hazard x vulnerability / capacity to cope
• Some communities have a high capacity to cope and high resilience (the ability of a community to cope with a hazard). This means they can reduce the chances of disasters occurring because:
• They have emergency evacuation, rescue and relief systems in place

• They react by helping each other to reduce the numbers affected
• Hazard-resistant design or land-use planning have reduced the numbers at risk
• The PAR model suggests that the socio-economic context of a hazard is important. In poor, badly governed (root causes) places with rapid change and low capacity (dynamic pressures) and low coping capacity (unsafe conditions) disasters are likely.

• The impacts of tectonic hazards are broadly of three types:
• 1. Social - deaths, injury and wider health impacts including psychological ones
• 2. Economic - the loss of property, businesses, infrastructure and opportunity
• 3. Environmental - damage or destruction of physical systems, especially ecosystems

• Megadisaster - a disaster with unusually high impacts. Millions of people affected and billions of dollars in damage over a wide area
• Earthquake magnitude is measured using the moment magnitude scale (MMS). This is an updated version of the Richter magnitude scale. MMS measures the energy released during an earthquake. MMS uses a logartihmic scale.

• The Mercalli scale measures earthquake intensity on a scale of I-XII. This scale measures what people actually feel during an earthquake, i.e. the intensity of the shaking effects not the energy released. It cannot easily be used to compare earthquakes as shaking experienced depends on building type and quality, ground conditionns and other factors.
• The relationship between magnitude and death toll is a weak one because:
• Some earthquakes cause serious secondary impacts, such as landslides and tsunami
• Earthquakes hitting urban areas have greater impacts than those in rural areas
• Level of development, and level of preparedness, affect death tolls
• Isolated, hard to reach places could have a higher death toll because rescue and relief take longer
• The magnitude of a volcanic eruption is measured using the volcanic explosivity index (VEI). VEI ranges from 0 to 8 and is a composite index combining eruption height, volume of material erupted and duration of eruption.
• VEI eruptions from 0-3 are associated with shield volcanoes and basaltic eruptions at constructive plate margins and mid-plate hotspots. VEI eruptions from 4-7 occur at destructive plate margins, erupting high viscosity, high gas, high silica andesitic magma. 
• No modern human has experienced a VEI 8 supervolcano (one whose impacts would be felt globally, because of a worldwide cooling of the Earth's climate)

• Tectonic events can be compared using hazard profiles. Hazards with the following characteristics present the highest risk:
• High magnitude, low frequency events - these are the least 'expected' as they are unlikely to have occurred in living memory
• Rapid onset events with low spatial predictability - they could occur in numerous places, and happen without warning
• Regional area extent - affecting large numbers of people in a wide range of locations
• Arguably, major earthquakes at subduction zones and collision zones are the most dangerous tectonic hazards. They can have magnitudes of 8-9 MMS, cannot be predicted and could occur along any tens of thousands of kilometres of plate margin.

• There is some relationship between death toll and HDI, such that lower HDI appears to suggest higher death tolls.
• However, other factors such as population density, duration of ground shaking, secondary hazards and response are also important. Generally, low level of development increases risk by increasing vulnerability.

Increasing risk

• Population growth
• Urbanisation and urban sprawl
• Environmental degradation
• Loss of community memory about hazards
• Very young or very old population
• Ageing, inadequate infrastructure
• Greater reliance on power, water, communication systems

Mitigating risk

• Warning and emergency response systems
• Economic wealth
• Government disaster-assistance programmes
• Insurance
• Community initiatives
• Scientific understanding
• Hazard engineering

• In some locations with very low levels of human development (HDI below 0.55) vulnerability is usually high because:
• Many people lack basic needs of sufficient water and food even in 'normal' times
• Much housing is informally constructed with no regard for hazard resilience
• Access to healthcare is poor, and disease and illness are common
• Education levels are lower, so hazard perception and risk awareness is low
• Many low-income groups lack a 'safety net' - either a personal one (savings, food stores) or a government one (social security, aid, free healthcare) - so have few resources after a disaster

• Governance refers to the processes by which a country or region is run. The effectiveness of governance varies enormously and has a significant impact on coping capacity and resilience in the event of a natural disaster
• Meeting basic needs - when food supply, water supply and health needs are met the population is physically more able to cope with the disaster
• Preparedness - education and community preparation programmes raise awareness and teach people how to prepare, evacuate and act

• Planning - land-use planning can reduce risk by preventing habitation on high risk slopes, areas prone to liquefaction or areas within a volcanic hazard risk zone
• Corruption - siphoning off money ear-marked for hazard management or 'kick-backs' and bribes to allow illegal or unsafe buildings increase vulnerability
• Environmental management - secondary hazards, such as landslides, can be made worse by deforestation. The right monitoring equipment can warn of some hazards, e.g. lahars
• Open-ness - governments that are open, with a free press and media, can be held to account, increasing the likelihood that preparation and planning take place

• The nature of tectonic hazard impacts is influenced by a number of geographical factors. These include:
• Population density - highly populated areas may be hard to evacuate and are likely to be hit harder by an earthquake
• Degree of urbanisation - when cities are struck by major earthquakes, death tolls can be high because of the concentration of at-risk people
• Isolation and accessibility - often rural areas are hit less hard than urban areas by the initial impact of a tectonic disaster, but isolation and limited access can slow the rescue relief effort.

• Countries such as Japan, the USA and Chile have:
• Advanced and widespread insurance, allowing people to recover from disasters
• Government-run preparations such as Japan's Disaster Prevention Day on 1 September each year, as well as public education about risk, coping, response and evacuation
• Sophisticated monitoring of volcanoes, and, where possible, defences such as tsunami walls
• Regulated local planning systems, which use land-use zoning and building codes to ensure buildings can withstand hazards and are not located in areas of unacceptable risk

HOW SUCCESSFUL IS THE MANAGEMENT OF TECTONIC HAZARDS AND DISASTERS?

• Tectonic hazards and disasters are not the same, so even though the number of hazard events remains stable the number of disasters has risen.
• Deaths have fallen over time because of better response management, preparation and prediction. Numbers of deaths have fallen especially since 2000, which may be due to vastly improved mobile communications to warn people of disasters
• The number of reported disasters increased then stabilised as improvements in data coverage and the accuracy of databases increased. Most recently, numbers of reported disasters have fallen, suggesting fewer hazard events are becoming disasters
• The number of people affected by disasters continues to rise as populations grow and more people live in risky locations
• 'Mega-disasters' are characterised by impacts extending beyond the country immediately affected. E.g. 2004 Asian tsunami, 2011 Japanese tsunami, 2010 Eyjafjallajokull eruption
• A number of locations are multiple hazard zones. These include California, the Phillipines, Indonesia and Japan. These locations:
• Are tectonically active and so earthquakes are common
• Are geologically young with unstable mountain zones prone to landslides
• Are often on major storm tracks either in the mid-latitudes or on tropical cyclone tracks

• May suffer from global climate perturbations such as El Nino/La Nina
• Prediction - knowing when, and where, a natural hazard will strike on a temporal and spatial scale that can be acted on meaningfully in terms of evacuation
• Despite decades of scientific research earthquakes cannot be predicted - only areas at high risk can be identified (risk forecasting - provides a percentage chance of a hazard occurring), plus areas that are likley to suffer severe ground shaking and liquefaction; this can be used for land use zoning purposes
• Volcanic eruptions can be predicted - tiltmeters and strain meters record volcanoes 'bulging' as magma rises and seismometers record minor earthquakes indicating magma movement. Gas sprectrometers analyse gas emissions which can point to increased eruption likelihood
• An earthquake-induced tsunami cannot be predicted. However, seismometers can tell an earthquake has occurred and locate it, then ocean monitoring equipment can detect tsunami in the open sea. This information can be relayed to coastal areas, which can be evacuated
• The hazard management cycle shows the different stages of managing hazards in an attempt to reduce the scale of a disaster.
• Preparedness - community education and resilience building including how to act before, during and after a disaster, prediction, warning and evacuation tech and systems

• Response - immediate help in the form of rescue to save lives and aid to keep people alive, emergency shelter, food and water
• Recovery - rebuilding infrastructure and services, rehabilitating injured people and their lives
• Mitigation - acting to reduce the scale of the next disaster: land use zoning, hazard-resistant buildings and infrastructure
• The recovery stage depends on:
• The magnitude of the disaster
• Development level
• Governance, because well-governed places will divert resources more effectively to recovery efforts
• External help, i.e. aid and financing to help the recovery effort

Modify the event - before the hazard strikes (long term)

• Land-use zoning - preventing building on low-lying coasts, close to volcanoes and areas of high-ground shaking and liquefaction risk
• Aseismic buildings - cross-bracing, counter-weights and deep foundations prevent earthquake damage

• Tsunami defences - tsunami sea walls and breakwaters prevent waves travelling inland
• Lava diversion - channels, barriers and water cooling used to divert and/or slow lava

Modify the vulnerability - before the hazard strikes (short term)

• Hi-tech scientific monitoring - used to monitor volcano behaviour and predict eruptions
• Community preparedness and education - earthquake kits and preparation days, education in schools
• Adaptation - moving out of harm's way and relocating to a safe area

Modify the loss - after the hazard strikes

• Short-term emergency aid - search and rescue followed by emergency food, water and shelter
• Long-term aid - reconstruction plans to rebuild an area and possibly improve resilience
• Insurance - compensation given to people to replace their losses

• About 70% of all earthquakes are found in the 'RIng of Fire' in the Pacific Ocean
• The most powerful earthquakes are associated with convergent or conservative boundaries, although rare intra-plate earthquakes can occur
• Earthquakes can develop into a disaster, especially when they are both high magnitude and occur in a densely populated area
• Divergent (constructive) - most clearly displayed at mid-ocean ridges. Large numbers of shallow focus and generally low magnitude earthquake events - most are submarine
• Convergent (destructive) - actively deforming collision locations with plate material melting in the mantle, causing frequent earthquakes and volcanoes
• Conservative - where one plate slides past each other. Lithosphere is neither created nor subducted, and while conservative plate margins do not result in volcanic activity, they are the sites of extensive shallow focus earthquakes, sometimes high magnitude
• The places where plates move away from each other are the divergent 'spreading ridges' in oceans. New oceanic crust, which is thinner and denser than the continental crust, is created. The earthquakes seen at these boundaries tend to be frequent, small and typically a low hazard risk because of their geographical position (the ocean) and they do not typically trigger tsunamis

• Locations where plates slide past each other can present more risk, e.g. the San Andreas Fault in California, where the Pacific Plate creates a zone of friction against the North American Plate 
• The plate boundaries that generate some of the largest and most damaging earthquakes are those where two plates are moving towards each other (convergent). Typically when this happens, one plate starts sliding under the other - as the strain builds over time in the subduction zone, the friction between the two masses of rock is overcome, releasing energy. This will produce both earthquakes (e.g. the tsunami-generating ones off Japan in 2011 and Aceh in Indonesia in 2004) and volcanoes, the magma of which are fed by the subducting plate
• Active subduction zones are characterised by magmatic activity, a mountain belt with thick continental crust, a narrow continental shelf and active seismicity
• Volcanoes are found in a number of different tectonic settings:
• Destructive plate boundaries - when a dense oceanic plate collides with a less-dense continental plate, the oceanic plate is typically thrust underneath because of the greater buoyancy of the continental lithosphere, forming a subduction zone. Surface volcanism (volcanoes at the ocean floor or the Earth's surface) typically appears above the magma that forms directly above down-thrust plates. Destructive margins create the most 

explosive type, characterised by a composite cone associated with a number of hazards. These volcanic eruptions tend to be more infrequent but more destructive

• Divergent boundaries create rift volcanoes where plates diverge from one another at the site of a thermally buoyant mid-ocean ridge. These are generally less explosive and more effusive, especially when they occur under water deep in the ocean floor, e.g. the Mid-Atlantic Ridge. Here there is basaltic magma, which has low viscosity
• Hotspot volcanoes are found in the middle of tectonic plates and are thought to be fed by underlying mantle plumes that are unusually hot compared with the surrounding mantle.
• The presence of a hotspot is inferred by anomalous volcanism, e.g. the Hawaiian volcanoes within the Pacific Plate.
• A volcanic hotspot is an area in the mantle from which heat rises as a hot thermal plume from deep in the Earth. High heat and lower pressure at the base of the lithosphere enable melting of rock. This molten material, magma, rises through cracks and erupts to form active volcanoes on the Earth's surface. As the tectonic plate moves over the stationary hotspot, the volcanoes are rafted away and new ones form in their place. As oceanic volcanoes move away from the hotspot, they cool and subside, producing older islands, atolls and seamounts. Over long periods of time this can create chains of volcanoes, e.g. the Hawaiian islands

• The Benioff Zone is an area of seismicity corresponding with the slab being thrust downwards in a subduction zone. The different speeds and movements of rock at this point produce numerous earthquakes. It is the site of intermediate/deep-focused earthquakes
• Locked fault - a fault that is not slipping because the frictional resistance on the fault is greater than the shear stress across the fault. Such faults may store strain for extended periods that is eventually released in a large magnitude earthquake when the frictional resistance is overcome. The 2004 Indian Ocean tsunami was the result of a mega-thrust locked fault (subducting Indian Plate) with strain building up at around 20mm per year

Secondary hazards of earthquakes:

• Soil liquefaction - the process by which water-saturated material can temporarily lose normal strength and behave like a liquid under the pressure of strong shaking. Liquefaction occurs in saturated soils. An earthquake can cause the water pressure to increase to the point where the soil particles can move easily, especially in poorly compacted sand and silt
  

• Liquefaction can cause buildings to settle, tilt and eventually even collapse
• Land adjacent to rivers and sloping ground can present a hazard by sliding under low-friction conditions across a liquefied soil layer - this is called lateral spreading, sometimes creating large fissures and cracks in the ground surface. Results in damage to roads and bridges, as well as telecommunications and other services (gas, electricity, sewerage) which run through upper sectons of the ground
• Landslides are where slopes weaken and fail. As many destructive earthquakes occur in mountainous areas, landslides (as well as rock falls and avalanches) can be major secondary impacts. They rarely occur when magnitudes are less than 4, but are significant problems when they are larger. This can be especially hazardous to people and property as landslides can travel several mles from their source, growing in size as they pick up trees, boulders, cars and other materials
  
• A report on the 2015 Nepal earthquake suggests that the landslides created by this event could have been made worse by summer monsoon rainfall
• Over the last 40 years, around 70% of all deaths caused by earthquakes globally are attributable to the secondary impacts of landslides. In the 2005 Kashmir and 2008 Sichuan earthquakes landslides accounted for around 1/3 of all deaths

• Tsunami is not a single wave but a series of waves, caused by seabed displacement. The first wave in the tsunami is not necessarily the most destructive, so often there is an escalation effect in terms of damage and loss of life. The amount of time between successive waves (wave period) is often only a few minutes but, in rare instances, waves can be over an hour apart. This represents a greater risk: people have lost their lives after returning home in between the waves of a tsunami, thinking that the waves had stopped coming
  
• Around 90% of tsunamis occur within the Pacific Basin, associated with the activity at plate margins. Most are generated at subduction zones (convergent boundaries), particularly off the Japan-Taiwan island arc, South America and Aleutian Islands
• The impact of a tsunami depends on a number of physical and human factors:
• 1) The duration of the event
• 2) The wave amplitude, water column displacement and the distance travelled
• 3) The physical geography of the coast, especially water depth and gradient at the shoreline
• 4) The degree of coastal ecosystem buffer, e.g. mangroves and coral reefs
• 5) The timing of the event - night versus day and the quality of early warning systems
• 6) The degree of coastal development and its proximity from the coast, especially in tourist areas

Primary hazards of volcanoes:

• Pyroclastic flows - responsible for most volanic related deaths. An ejection of hot gases and pyroclastic material, which contains glass shards, pumice, crystals and ash. These clouds can be up to 1000 degrees.
  
• Tephra - when a volcano erupts it will sometimes eject material such as rock fragments into the atmosphere - this is tephra. This ash and larger materials can cause building roofs to collapse as well as start fires on the ground. Dust can reduce visibility and affect air travel
• Lava flows - they pose a big threat to human life if they are fast moving. On steep slopes some lava flows can reach 15m/sec
• Volcanic gases - gases are associated with explosive eruptions and lava flows. The mix normally includes water vapour, sulphur dioxide, hydrogen and carbon monoxide. Most deaths have been associated with carbon dioxide; it is dangerous because it is colourless and odourless and can accumulate in valleys undetected by people

Secondary impacts of volcanoes:

• Lahars - volcanic mudflows generally composed of relatively fine sand and silt material. The degree of hazard varies depending on the steepness of the slope, the volume of material and particle size. They are associated with heavy rainfall as a trigger as old tephra deposits on steep slopes can be re-mobilised into mudflows
  
• Jokulhlaups - a hazard to people and infrastructure, and can cause widespread landform modification through erosion and deposition. These floods occur very suddenly with rapid discharge of large volumes of water, ice and debris from a glacial source.

• Hazard - 'a perceived natural/geophysical event that has the potential to threaten both life and property'
  
• Disaster - the realisation of a hazard, when it 'causes significant impact on a vulnerable population'. The CRED states that a hazard becomes a disaster when: 10 or more people are killed, and/or 100 or more people affected
• There is a complex relationship between risk, hazards and people. This is due to several factors:
• Unpredictability - many hazards are not predictable; people may be caught out by either the timing or magnitude of an event
• Lack of alternatives - people may stay in a hazardous area due to lack of options, e.g. for economic reasons (work), lack of space to move, lack of skills or knowledge
• Dynamic hazards - the threat from hazards is not a constant one, and it may increase or decrease over time. Human influence may also change the location or increase the frequency or magnitude of hazardous events
• Cost-benefit - the benefits of a hazardous location may well outweigh the risks involved in staying there
• 'Russian roulette reaction' - the acceptance of risks as something that will happen whatever you do

• Degg's model shows the interaction between hazards, disaster and human vulnerability. Importantly, disaster may only occur when a vulnerable population is exposed to a hazard

• Hazard-risk formula:
• Risk = Hazard x Exposure x (Vulnerability / Manageability) 
• Resilience - the ability of a system, community or society exposed to hazards to resist, absorb and recover from the effects of a hazard
• Resilience is also about the ability to 'spring back' from a hazard event or disaster shock. According to UNISDR the resilience of a community is determined by the degree to which the community has the necessary resources and is capable of organising itself both prior to and during times of need
• The Disaster Risk and Age Index highlights two important trends:
• 1) Ageing populations   
• 2) The acceleration of risk in a world that is increasingly exposed to a range of hazard types
• Age is a significant factor in people's resilience, with children and elderly likely to suffer much more from a range of hazards.
• Around 66% of the world's population aged over 60 live in less-developed regions. By 2050, this is expected to rise to 79%
• E.g. the Japanese tsunami of 2011 killed 15,000 people and 9500 were either injured or missing. 56% of those who died were aged 65 and over, even though this age group comprised just 23% of the population in the area affected

• The basis for the Pressure and Release (PAR) Model (also known as the Disaster Crunch Model) is that a disaster is the intersection of two processes:
• 1) Processes generating vulnerability on one side, and
• 2) The natural hazard event on the other
• The 'release' idea is incorporated to conceptualise the reduction of disaster: to relieve the pressure, vulnerability has to be reduced

Social and economic impacts of tectonic hazards

• The impacts of earthquakes (and linked secondary effects) are generally much greater than those presented by volcanoes. The concentration of volcanoes in relatively narrow belts means not only that a relatively small proportion of the land area of the world is close to a volcano but also that a relatively small proportion of the human population has direct exposure to volcanic activity. Somewhat less than 1% of the world's population is likely to experience risk from volcanic activity, whereas the figure for earthquakes is estimated to be 5%

• Economic impacts need to be considered more carefully set against the context, eg.:
• Level of development
• Insured impacts versus non-insured losses
• Total numbers of people affected and the speed of economic recovery following the event
• Degree of urbanisation and, linked to this, land values, and the county or region's degree of interdependence
• Absolute vs relative impacts on a country's GDP; higher relative impacts are more devastating
• Many scales for measuring hazards are imperfect in that they typically measure just one or two physical processes that might cause damage. The nature of the impact depends on both the size of the event (size, duration etc) but also the nature of the environment in which it is happening - the impact depends on the degree of physical exposure and human vulnerability of the communities that might be threatened by the event
• Tectonic hazard profile - used to understand the different physical characteristics of different types of hazards. Can also be used to analyse and assess the same hazards which take place in contrasting locations or at different times. Helps decision makers to identify and rank the hazards that should be given the most attention and resources

• One of the difficulties with hazard profiling is the degree of reliability when comparing different event types. It is much more difficult to compare across hazards, as they all have different impacts on society and have varying spatial and temporal distributions. To accurately rank multiple hazards on one scale certain elements of the hazard become inaccurately displayed or must be omitted from the profile itself.
• In developing and recently emerging countries people tend to have less power over their socio-political and physical environments than the more wealthy. As a result, risk vulnerability is greater for them. This can be explained as follows:
• People and communities in developing and emerging countries only have access to livelihoods and resources that are insecure and difficult
• They are likely to be a low priority for government interventions intended to deal with hazard mitigation
• People's basic health and nutritional status correlates strongly with their ability to survive disruptions to their livelihood and normal well-being. There is also a clear relationship between nutrition and disease, which is often evident after a hazard impact (especially when people are forced to find shelter and come into close contact with one another) - people who are undernourished and sick are at greater risk of disease as they have weaker immune systems

There are several elements of development that relate to vulnerability and disaster risk:

• An economic component dealing with the creation of wealth and the improvement of quality of life which is equitably distributed
• A social dimension in terms of health, education, housing and employment opportunities
• An environmental strand which has a duty of care for resource usage and distribution, now and in the future
• A political component including values such as human rights, political freedom and democracy
• Drought, violence and armed conflict may turn natural hazards into disasters. In addition, the incidence and risks of diseases such as malaria and HIV/AIDS may interact with human vulnerability, worsening disaster risks brought about by urbanisation, climate change, violence and armed conflict, and marginalisation
• Low-income households and communities suffer a disproportionate share of disaster losses and impacts:
• Asset inequality - relates to housing and security of tenure, as well as agricultural productivity or goods and services in trading communities
• Inequality of entitlements - refers to unequal access to public services and welfare systems, as well as inequalities in the application of the rule of law

• Political inequality - the unequal capacities for political agency possessed by different groups and individuals in any society
• Social status inequality - has a bearing on other dimensions of inequality, including the ability of individuals and groups to secure regular income and access services
• Urban segregation can generate new patterns of disaster risk - low-income households are often forced to occupy hazard-exposed areas where there are low land values - such places have poor infrastructure and social protection; they are also likely to have high levels of environmental degradation
• People living in such areas often have low resilience as they have little 'voice' in terms of political debate and influence, as well as being socially excluded and marginalised.They are less likely to benefit from the services or measures, e.g. earthquake protection measures, provided for other neighbourhoods
• Weak political organisation and corruption are additional factors that contribute to a more vulnerable population in terms of disaster risk. They are also linked to other factors at both a local and national scale, including:
• Population density; Geographic isolation and accessibility; Degree of urbanisation
• All of this contributes to a country's resilience

• The increase in hazard vulnerability is mostly due to human factors rather than physical factors, as the trends in tectonic hazards reveal a pattern that does not indicate a significant increase  in the last 50 years
• The overall longer-term natural hazard trends, since about 1960, show that:
• The total number of recorded hazards has increased over the last 50 years
• The number of reported disasters seems to be falling, having peaked in the early 2000s
• Number of deaths is also lower than in the recent past, but there are spikes with mega-events
• The total number of people affected is increasing for some hazard and disaster types, especially meteorological and hydrological
• The economic costs associated with both hazards and disasters of all types have increase significantly since 1960

How good are disaster statistics?

• There is neither a universally agreed definition of a disaster nor a universally agreed numerical threshold for disaster designation
• Reporting disaster impacts, especially deaths, is therefore controversial for a number of reasons:

• It depends on whether direct (primary) deaths or indirect (secondary) deaths from subsequent hazards or associated diseases are counted
• Location is significant because local or regional events in remote places are often under-recorded
• Declaration of disaster deaths and casualties may be subject to political bias, e.g. the 2004 Asian tsunami was almost completely ignored in Myanmar but perhaps initially overstated in parts of Thailand, where foreign tourists were killed, and then played down to protect the Thai tourist industry
• Statistics on major disasters are difficult to collect, particulatly in remote rural areas of low human development countries (LHDs), e.g. the earthquake in Kashmir in 2005, or in densely populated squatter settlements, e.g. the Caracas landslides in 2003-04
• Time-trend analysis is difficult. Much depends on the intervals selected and whether the means of data collection have remained constant. Trends (deaths, numbers affected, economic impacts) can be upset by a cluster of mega-disasters, as happened in the 2004 Asian tsunami or the 2011 Haiti earthquake

Tectonic mega-disasters have many key characterisitcs:

• They are usually large-scale disasters on either an aerial/spatial scale or in terms of their economic and/or human impact
• Because of their scale, they pose serious problems for effective management to minimise the impact of the disaster (both in short and long term)
• The scale of their impact may mean that communities, but usually government as well, often require international support in the immediate aftermath as well as during longer-term recovery. This may be at a regional level (2004 Asian tsunami) or globally (Japan 2011). These events can affect more than one country either directly or indirectly
• Tectonic mega-events and disasters are often classified as high impact, low probability (HILP) events
• The consequences of HILP events spread rapidly across both economic and geographic boundaries, creating other impacts (negative externalities), which are difficult to plan for.
• E.g. The Japanese earthquake in 2011 led to a 5% reduction in the country's GDP. There were much wider knock-on impacts for global TNCs, such as Toyota and Sony, which were forced to halt production

• Multiple-hazard zones are places where a number of physical hazards combine to create an increased level of risk for the country and its population
• This is often made worse if the country's population is vulnerable (wealth/GDP, population density etc) or suffers repeated events, often on an annual basis, so that there is never any time for an extended period of recovery. Such places are seen as disaster hotspots
• Large urban areas are often zones of multiple-hazard risk. Cities are centres of economic development (economic cores) as they represent a natural focus for investment and development. 
• They are also frequently centres of growing population as a result of the rapid urbanisation occuring in most developing countries. Many cities have huge areas of unplanned, poor-quality housing where growing numbers of the urban poor live, often located on marginal, potentially dangerous sites such as river banks and steep slopes
• Many rapidly growing mega-cities are located in hazard-prone areas
• With such high densities of people, hazard management in large urban areas is expensive and complex, making disasters inevitable, both socially (high concentration of vulnerable people) and economically (loss of infrastructure)

• Park's Disaster Response Curve can be used as a framework to help better understand the time dimensions of resilience: from a hazard striking to when a place, community or country returns to normal operation
• The model can be used to help plan and understand risk and resilience, as well as to better prepare for future events, e.g. through modification of the responses to the event

Modifying the hazard event

• Micro protection techniques - strengthening individual buildings and structure against hazardous stress
• Macro protection techniques - large-scale protective measures designed to protect whole communities
• For earthquakes, most energy has been focused on public buildings and faciltiies, especailly those expected to remain operational during a disaster: hospitals, police stations and pipelines. Schools and factories were also strengthened so people could shelter in them. 
• Coastal buffers, e.g. mangroves are known to be effective at dissipating energy from tsunami waves 

• Diverting or chilling lava flows, e.g. by spraying lava flows with seawater to slow its movement by chilling

Modifying vulnerability and resilience

• Prediction, forecasting and warnings
• Improvements in community preparedness
• Working with groups and individuals to change behaviours (to reduce the disaster risk), e.g. better land-use planning
• With better technology, prediction, forecasting and warning are becoming increasingly important parts of disaster preparation and management
• E.g. a tsunami warning system (TWS) is used to detect tsunamis in advance and issue warnings to prevent loss of life and damage to movable possessions. It is made up of two components: a network of sensors to detect tsunamis and a communications infrastructure to quickly issue alerts to allow evacuation of the coastal areas
• Governance is important but it has limitations in terms of the affordability of prediction and prevention measures, especially in the management of maga-disasters immediately after the event

• Volcanoes usually do not erupt without warning - warning signs typically take the form of numerous small earthquakes and a swelling of the ground surface, which reflect the passage of magma to the surface.
• It is difficult to predict exactly when activity will take place, especially the timing of a major eruption. Technology in the form of a network of sensors is now being used to help predict eruptions and allow more sophisticated modelling to be undertaken - monitoring may give time for the area under threat to be evacuated
• Looking at data on deaths, the volcanic hazard threat seems to have been successfully mitigated: only 2 eruptions since 1980 have caused more than 1000 deahts
• An exception to this was the Mount Ontake eruption in Japan in 2014 - there was no warning and the VEI 3 eruption killed 56 people, the first deaths in Japan from eruptions since 1991

Modifying the loss

• Insurance to cover the cost of earthquake damage
• Since 2000, the UNISDR estimates the total economic cost of all disasters to be approx $1.3 trillion

• Even in developed economies such as the USA and Japan, insured losses for tectonic events tend to be relatively low, at approx 25-30%, meaning many people are unprotected
• Disaster aid is the result of humanitarian concern following severe loss
• Disaster aid is often criticised - there may be poor or corrupt distributions systems
• Disaster aid - aid flows to countries and victims via governments, NGOs and private donors. In the longer term aid is used for relief, rehabilitation and reconstruction. This type of aid is often appropriate for middle- and lower-income countries
• Government aid - typically used in emerging and developing countries where the disaster mitigation is achieved by spreading the financial load throughout the taxpayers of the country. This may include a national disaster fund and release of funds may require a poltiical declaration
• The World Conference on DIsaster Reduction was held in 2005 in Kobe, Japan, and established a 'Framework for Action' - aiming to promote a strategic and systematic approach to reducing vulenrability and risks to hazards through building the resilience of nations and communitites to disasters
• This was replaced by the Sendai Framework in March 2015
• The framework emphasised the need to tackle disaster risk reduction and climate change adaptation when setting Sustainable Development Goals