Unit 9: Hazardous Environments Flashcards
Divergent plate margins
Spreading
Constructive
Ridge
Volcanic activity
Convergent plate margins
Subduction
Destructive
Trench
Volcanic activity
Transform plate margins
Later sliding
Conservative
No effect of topography
No volcanic activity
General pattern of earthquakes and volcanoes
Generally follows a linear pattern along tectonic plate boundaries. Earthquakes are common at destructive (convergent), constructive (divergent) and transform boundaries. Volcanoes are concentrated along destructive and constructive boundaries. There are anomalies such as intraplate earthquakes and volcanic hotspots where activity occurs way from plate boundaries due to stresses within the plate or mantle plumes. These highlight the relationship between tectonic processes and surface features
Earthquake concentration along plate boundaries
Most earthquakes occur along tectonic plate boundaries where significant geological activity takes place
Destructive/convergent boundaries for earthquakes
Strong earthquakes are common at destructive boundaries where an oceanic plate subducts beneath a continental plate or another oceanic plate
Constructive/divergent boundaries for earthquakes
Earthquakes at constructive boundaries where plates move apart are less powerful and occur at mid ocean ridges
Transform boundaries for earthquakes
Frequent and sometimes severe earthquakes occur where plates slide past one another
Intraplate earthquakes
Only a small number of earthquakes occur caused by stresses within the plate
Subduction zones and deep earthquakes
The deepest and strongest earthquakes occur at subduction zones where one plate is forced deep into the mantle
Global distribution of volcanoes
Most are located along tectonic plate boundaries
Destructive/convergent boundaries for volcanoes
Common at destructive boundaries where an oceanic plate subducts beneath a continental or another oceanic plate
Constructive/divergent boundaries for volcanoes
Also form where plates move apart creating fissures for magma to rise
Hotspots and intraplate volcanoes
Some volcanoes form away from plate boundaries over mantle hotpots where plumes of magma rise through the crust
Subduction zones are explosive eruptions
Volcanoes at subduction zones often produce explosive eruptions due to magmas high viscosity and gas content forming steep sided stratovolcanoes
Shield volcanoes at divergent boundaries and hotspots
Divergent boundaries and hotspots often create broad shield volcanoes which have gentle slopes and less explosive eruptions
Tsunamis location
Occur mainly in tectonically active regions especially around subduction zones where one plate sinks beneath another. 90% of tsunamis have been in the Pacific. Underwater earthquakes, volcanic eruptions or landslides can displace large volumes of water generating powerful waves
How are island arcs formed
Formed at convergent plate boundaries where two tectonic plates collide and one plate (usually oceanic) is forced beneath the other through subduction. As the subducting plate sinks into the mantle it melts due to high temperatures and pressures creating magma. This magma rises to the surface through cracks in overriding plates forming a chain of volcanic islands. Over time these emerge above the oceans surface creating an arc shaped chain. As the plate descend into the mantle it bends and creates a curvature resulting in a bow-shaped chain of volcanoes
Where are island arcs found
Usually in oceans along subduction zones at convergent boundaries between two oceanic plates or between an oceanic or continental plate
What do island arcs look like
Typically form a curved or arc like shape. Often made up of volcanoes some of which are active giving them a rugged, mountainous appearance. Due to volcanic soil many are covered in dense, tropical vegetation. Near the concave side of the arc there is a deep ocean trench where the subduction occurs
How are hot sports formed
The earths core heats the surrounding mantle causing it to be less dense and rise in a column. As this plume reaches the base of the lithosphere the heat causes partial melting of the overlying rock creating magma. The magma rises through weaknesses in the crust and erupts on the surface forming volcanoes. As the plate moves over the stationary hotspot over time a chain of volcanic islands is formed. Often forms broad shield volcanoes. Do not form at plate boundaries but within tectonic plates
Where are hot spots found
Can be found in the middle of tectonic plates rather than along boundaries. They can occur in oceanic and continental settings
What do hot spots look like
Often form isolated chains of volcanic islands. These are typically shield volcanoes which have gentle slopes and wide bases. The islands get progressively older as they move away from the current active volcanoes. As the islands erode and sink over time some of the them become underwater mountains (seamounts)
How are mid-ocean ridges formed
Form at divergent plate boundaries where two tectonic plates are moving apart. As the plates separate, magma from the mantle rises through the gap creating new oceanic crust. This is sea floor spreading. This magma cools and solidifies at the ridge forming undersea volcanic mountains. Over time this pushes plates further apart expanding the basin
Where are mid-ocean ridges found
Located on the ocean floor where tectonic plates are diverging. They are the longest mountain ranges in the world
What do mid-ocean ridges look like
They are vast, submarine mountain ranges that can extend thousands of kilometres. At the centre of the ridge there is a deep rift valley where the plates are pulling apart. The ridge is a site of frequent volcanic activity as magma rises. Can be home to hydrothermal vents where superheated water and minerals spew from the ocean floor
Tsunamis (primary earthquake hazard)
Large waves generated by underwater earthquakes affecting coastal areas with flooding
Aftershocks (primary earthquake hazard)
Small tremors following the main earthquake causing further damage
Ground shaking (primary earthquake hazard)
The most immediate and widespread effect causing buildings to collapse and triggering landslides
Surface rupture (primary earthquake hazard)
Displacement along the fault line that can crack roads, railways, pipelines and buildings
Liquefaction (primary earthquake hazard)
Occurs when saturated soil temporarily loses its strength and behaves like a liquid causing sinking structures
Economic disruption (secondary earthquake hazard)
Long term effects from the destruction of businesses, transportation and infrastructure
Health crises (secondary earthquake hazard)
Broken sanitation systems and facility damage can cause disease outbreaks and strain healthcare systems
Flooding (secondary earthquake hazard)
Can occur from dam failure, broken water mains or blocked rivers due to landslides or debris
Fires (secondary earthquake hazard)
Damage to gas lines and electrical infrastructure can lead to fires
Social displacement (secondary earthquake hazard)
People may be forced to flee creating refugee crises
Landslides and rockfalls (secondary earthquake hazard)
Triggered by ground shaking or destabilisation of slopes leading to property and infrastructure destruction
Earthquake
A series of seismic vibrations or shock waves which originate from the focus
Focus
The point at which the plates release the tension or compression suddenly
Epicentre
The point on the earths surface directly above the focus
Seismology
The study of earthquakes and seismic waves that move through and around the earth. Seismologists study earthquakes and seismic waves
Seismic waves
The waves of energy caused by the sudden breaking of rock within the earth or an explosion. They are the energy that travels through the earth recorded on seismographs
Shallow vs deep focus
Earthquakes are classified as shallow, intermediate or deep depending on the location of the focus. Shallow focus earthquakes are the most damaging
Focus depth
Shallow = 0-70km
Intermediate = 70-350km
Deep = 350-670km
Intermediate and deep focus earthquakes occur only in subduction zones where cool rocks extend to great depths
Why do earthquakes happen?
Most are casued by the movement of tectonic plates
Reactivation of old fault lines that have been inactive for a long time
Subsidence as a result of deep mining
Pressure on surface rocks from water in large reservoirs
Underground disposal of liquid wastes
Underground nuclear testing and explosions
Mining and fracking
Increased crustal loading
Primary waves
The fastest moving type of wave and the first detected by seismographs. They are longitudinal and pus and pull the ground in the direction the wave is travelling, causing little damage. Can travel through solids and liquids
Secondary waves
Travel slower than P waves in the same direction but shake the ground perpendicular to the direction of wave travel. More dangerous because have a greater amplitude and produce vertical and horizontal motion of the ground surface. Can travel through solids not liquids
Surface waves
Are the slowest waves travelling along the surface of the earth made up of love and rayleigh waves
Love waves
Move back and forth horizontally and cause a lot of damage but can only travel through solids
Rayleigh waves
Cause vertical and horizontal ground motion. Can be the most destructive as they cause the ground to rise and fall as they roll past. Can travel through liquids and solids
Richter scale
Measures the magnitude of an earthquake showing the amount of energy released. It is a logarithmic scale so each whole number increase represents a 10x increase in amplitude and 32x more energy released. Developed in 1935 by Charles Richter used for smaller, local earthqyakes
Moment magnitude scale
A modern system used to measure the size of earthquakes. Considered more accurate than the Richter scale especially for large or distant events. It calculates the earthquakes moment which considers the area of the fault that slipped, the distance it moved and the rigidity of the earths crust measuring the total energy released. Is a logarithmic scale. Works consistently for earthquakes of all sizes and distances. Used for more precise and consistent comparisons worldwide
Mercalli scale
Measures the intensity of an earthquake based on its effects on people, buildings and the environment. Uses Roman numerals I to XII where I represents a tremor that is barely felt and XII shows total destruction. It is subjective as it depends on human observations rather than scientific instruments
Tectonics and the global distribution of earthquakes affecting their impact
Most earthquakes do coincide with major plate margins. A number of earthquakes occur away from plate margins. Certain margins have a greater density of earthquakes. Earthquakes form a narrower spread at some plate margins. Those at destructive margins have a greater spread and affect more than constructive. Those places closer to destructive or transform margins are more at risk. Pressure builds at plate margins which when released causes an earthquake. A greater pressure builds at destructive and transform margins
Causes of mid plate earthquakes
Referred stress release where stress built at a margin is relieved along a mid plate fault
Reservoir construction where increased weight and pre pressure reactivates faults
Water or oil abstraction altering underground pressures
Mining subsidence
Earthquake magnitude and depth affecting their impacts
The stronger the earthquake the more serious its effects except magnitude alone is not responsible for the scale of a disaster. Shallow focus earthquakes cause a greater intensity of surface shaking and the greatest effects. Shallow earthquakes are associated with destructive margins where the subducting plate descends at an angle so stresses near the surface
Nature of bedrock affecting earthquake impacts
Some materials are vulnerable to liquefaction causing building foundations to become unstable and slopes vulnerable to mass movement
Population density affecting earthquake impacts
There is a large overlap between major earthquake zones and high population density. These conurbations are especially vulnerable due to densely packed buildings and raised freeways. 10% of the population are in earthquake zones
Building and structural vulnerability affecting earthquake impacts
Most suffering results from building and structure collapse. In wealthy areas building materials and appropriate designs can minimise deaths but older properties remain vulnerable despite regulations. In poorer areas building design is inadequate and regulations are rarely enforced. In areas with rare earthquakes, precautions are limited so suffering is greater
Extent of earthquake preparedness affecting their impacts
In wealthy areas with common earthquakes much is done to prepare. There are drills and people are informed. Emergency services and supplies are ready to cope with the aftermath. Preparation can reduce the scale of a disaster but could fail to live up to expectations. Poor countries are less prepared due to a lack of money to invest and earthquakes are perceived as infrequent problems when facing struggles of survival
Levels of development affecting earthquake impacts
A poor country with less rigorous building standards and an inability to cope with the aftermath will suffer a greater loss of life, homelessness and livelihood. Richer MEDCs suffer less human loss but greater financial loss as insurance companies and governments fund re building programmes and compensation
What is a tsunami?
A wave or series of waves generated by a sudden displacement of water. They have long wavelengths of up to 100km and there can be up to an hour between waves. They can travel up to 800km/h across the ocean over many thousands of kilometres
Causes of tsunamis
There needs to be a vertical displacement of a body of water in the ocean. This is most commonly associated with earthquakes and volcanic eruptions especially along destructive plate margins where two plates are moving towards each other causing great build up of pressure. They can also be generated by underwater landslides, explosions and cosmic body impacts
What happens as a tsunami approaches land?
Friction with a shallowing seabed slows the wave and causes it to rise and gain in height. Variations in offshore profiles and the configuration of the coastline will significantly affect the height of the wave. The highest tsunamis are due to a narrowing of the coast. Wave refraction will also affect a tsunamis orientation and height
Effects of tsunamis
Waves tear apart homes and businesses
Materials and possessions are buried in mud
Fishing vessels are swept onshore
Diseases can spread rapidly due to a lack of safe water and sanitation
Lack of food and shelter
Fishing communities have no boats and communities dependent on tourists are deserted
Mental effects of deaths of family
Behavioural responses to tsunamis
There can be several hours between an earthquake and a wave reaching land so people have time to respond by moving to safer ground. With increased technology and the use of satellites and computer modelling warnings can be issued. An increased understanding of wave mechanics enables scientists to be precise about the scale of waves. Public awareness and education are important. Local authorities need to have plans for the immediate aftermath such as with stores of emergency supplies and considering compromised transportation
Structural responses to tsunamis
The cost of building seawalls along an entire coastline would be prohibitive and would have a significant impact on coastal systems. Tsunamis being relative rare in any one place makes this impractical
Tsunami warning systems
Advisory: an earthquake has occurred which might generate a tsunami
Watch: a tsunami has been generated but it is over 2 hours from the area. Local officials should prepare for possible evacuation
Warning: a generated tsunami could cause damage so people are strongly advised to evacuate
Factors determining tsunami destructiveness
Wave energy
Shape of coastline
Relief of coastline
Presence of natural defences
Demography
Lack of experience
Lack of or inadequate warning systems and evacuation plans
Types of volcanoes
Shield: large, broad slopes, fluid lava flow
Composite: steep and symmetrical, explosive eruptions
Lava domes: small with steep sides, oozes viscous lava
Cinder cones: smallest, single vent, erupts cinders, ash and rocks
Types of lava
Basaltic
Andesitic
Dacite
Rhyolite
Decreasing mobility so increasing explosivity
Aa and pahoehoe lava flows
Aa lava flows have a rough and jagged surface while pahoehoe flows are smooth, ropy or billowy in texture. Aa flows are typically slower due to higher viscosity whereas pahoehoe flows are faster and more fluid due to lower viscosity. Aa forms when lava cools and solidifies quickly, breaking into fragments as it moves. Pahoehoe forms lava that remains hot and slows smoothly. Pahoehoe is hotter with a higher gas content making it more fluid. Aa is cooler and has less gas contributing to thicker behaviour
Iceland eruptions
Characterised by persistent fissure eruption. Large quantities of basaltic lava build up vast horizontal planes
Hawaiian eruptions
Involve more noticeable central activity. Runny, basaltic lava travels down the sides. Gases escape easily. Occasional pyroclastic activity occurs but is less important
Strombolian eruptions
Characterised by frequent gas explosions blasting fragments of runny lava into the air to form cones. Very explosive with lots of pyroclastic rock. Marked by a white cloud of steam from the crater
Vulcanian eruptions
Violent gas explosions blast plugs of sticky or cooled lava. Fragments build up into cones of ash and pumice. Occur when there is very viscous lava that solidifies rapidly after an explosion. Clears blocked vents and spew volcanic ash in atmopshere
Vesuvian eruptions
Characterised by powerful blasts of gas pushing ash clouds to the sky. More violent with lava flows. Ash falls to cover surrounding areas
Plinian eruptions
Gas rushes up through sticky lava and blasts ash fragments into the sky in an explosion. Violent eruptions create large gas clouds and thick volcanic debris. Gas clouds and lava can rush down slopes. Part of the volcano may be blasted away in the eruption
Active volcanoes
A volcano that is currently erupting, has erupted recently or is likely to erupt in the near future
Dormant volcanoes
A volcano that is not currently erupting but has erupted in the past and may erupt again in the future
Extinct volcanoes
A volcano that is unlikely to erupt again because it has no more magma supply
Primary impacts of volcanoes
Tephra
Pyroclastic flows
Lava flows
Volcanic gases
Ash
Secondary impacts of volcanoes
Lahars
Flooding
Tsunamis
Volcanic landslides
Climate change
Tephra
Solid material ejected from the crater. Vary from large volcanic bombs to fine ash particles
Volcanic bombs
Volcanoes can blast rock fragments and cooling lava bombs at high speed. The blasts and bombs can destroy buildings and kill plants and animals. The bombs do not travel very far but are deadly in the blast zone
Ashfalls
Ash from the volcano can travel long distances in the air and falls over a wide area
Primary impacts of ashfalls
Composed of tiny fragments of rock and glass, blankets regions making air dangerous to breathe and reducing visibility. Inhaling ash can cause respiratory problems especially for those with pre existing conditions. Long term exposure leads to long damage. Can cause building collapse from weight and abrasive nature damages equipment posing risks to transportation or services
Secondary impacts of ashfalls
Contaminated water is unsafe threatening health while coasted agriculture causes soil degradation, reducing crop yields and food supplies. Particles can clog drainage systems causing flooding. Clean up efforts are costly and time consuming
Pyroclastic flows
Very hot and travel up to 450 mph. Gas charged, high velocity flows made up of gases and tephra. Normally hug the ground and travel downhill or spread laterally under gravity. Their speed depends upon the density of the current, the volcanic output rate and the gradient of the slope. A broad term for fast moving currents of hot gas, ash and volcanic material that flow down the slopes of a volcano
Nuees ardentes
A specific type of pyroclastic flow, characterised by its dense, glowing, cloud like appearance and often formed from the collapse of an eruption column or volcanic dome. They are fast moving, hot pyroclastic flows composed of ash, gas and volcanic fragments. They resemble dense, turbulent clouds of glowing mertierla racing downslope. Can travel at speeds of 100-700km/h. Extremely hot, ranging from 200-700C
How are nuees ardentes formed?
During a volcanic eruption, a column of hot ash and gas rises. If the column becomes too dense it collapses under its own weight creating a nuee ardente. When a volcanic dome (hardened mass of lava) becomes unstable it can collapse and release pyroclastic material downslope. A sudden release of pressure can violently eject material that forms a nuee ardente
Lava flows
Streams of molten rock that pout or ooze from an erupting vent. Masses of molten rock can pour from volcanoes during an eruption. Lava flows are so hot they destroy everything in their path. Most are quite slow moving and not a threat to human life
Volcanic gases
Include CO2, CO, hydrogen sulfide, SO2 and chlorine. The craters of many volcanoes can fill with rainwater forming lakes. Volcanic gases can seep up through the ground at collect at the bottom of lakes. When the water gets displaced the gases can seep out
Lahars
A destructive volcanic mudflow composed of water, ash, rock and debris that travels rapidly down a volcanoes slope often triggered by eruptions, rainfall or melting ice
Formation of lahars
Explosive eruptions can rapidly melt snow and ice on a volcanoes summit releasing large amounts of water that mix with volcanic ash and debris. Intense rain during or after an eruption can mobilise loose volcanic material creating fast moving mudflows. The sudden release of water from a volcanic lake or the collapse of unstable crater walls can trigger lahars
Impact of lahars
Can bury roads, bridges and buildings under thick layers of mud and debris, disrupting transportation and access. Their fast flow can sweep away people, livestock and farmland causing fatalities and long term economic hardship. Can choke rivers with sediment leading to flooding, water contamination and the destruction of aquatic habitats
Flooding
Caused by the melting of ice caps or glaciers by volcanic eruptions and lava flows
Tsunamis with volcanoes
Usually caused by earthquakes but can be caused by large caldera forming volcanic eruptions
Volcanic landslides
Landslides are common on volcanoes because their massive cones typically rise hundreds to thousands of metres above the surrounding terrain and are often weakened by the process that created them being the rise and eruption of molten rock. Each time magma moves toward the surface overlying rocks are shouldered aside as the molten rock makes room for itself often creating internal shear zones or over steepenidng one or more sides of the cone
Climate change and volcanoes
The ejection of vast amounts of volcanic debris into the atmosphere can reduce global temperatures and is believed to have been an agent in past climate change vents
Landslides
Occur due to earthquakes, volcanoes, floods or wildfires. The destruction depends on the speed of onset, speed of movement, slope angle, ground saturation and volume of material. Earthquakes can lead to liquefaction if flat land has a high water content. Saturated sediment loses strength undermining foundations, lowering the ground
Primary impacts of earthquakes
Possessions broken
Building collapse
Air pollution
Infrastructure destroyed
Injuries
Missing persons
Buildings lost
Secondary impacts of earthquakes
Rescue resources stretched
Psychological impacts
Homelessness
Lack of food and water
Lack of sanitation causing diseases
People leave areas
Primary impacts of volcanoes
Ash and smoke in the air
Loss of light
Ash falls
Congestion from evacuation
Lava flows destroy infrastructure
Pyroclastic flows destroy villages and farms
Neighbourhoods lost
Secondary impacts of volcanoes
Respiratory problems from ash
Homelessness
Decline in economy due to loss of agriculture and airport closures limiting aid
Overcrowding
Lack of food, water and sanitation
Psychological impacts
Primary impacts of tsunamis
Loss of homes and boats
Injuries
Deaths
Building destruction
Flattened villages
Secondary impacts of tsunamis
Homelessness
Psychological impacts
Lack of clean drinking water causing infection and disease
Loss of livelihoods
Lack of schooling
After the impacts of hazards
New employment opportunities
International aid received
Building design and location improvements
Education of locals
Improved warning systems and government policies
Government compensation
Volcanic eruption strength
Strength is measured by the Volcanic Explosive Index (VEI). Based on the amount of material ejected in the volcanic explosion, height of ash clouds and damage caused. Above 5 is very strong and 8 is a supervolcano
Supervolcanoes
Can produce an eruption with an explosive force thousands of times greater than a regular volcanic eruption leading to global consequences. Much larger than regular volcanoes with eruption craters tend to hundreds of kilometres wide. Can drastically alter the climate and ecosystems. Eruptions are rare but have the potential to cause mass extinctions and climate change
Risk
The probability of a hazard event causing harmful consequences
Vulnerability
The geographic conditions that increase the susceptibility of a community to a hazard or the impacts of a hazard event
Hazards vs disasters
A hazard refers to a potential event or phenomenon that has the capacity to cause harm to people, property or the environment. A disaster occurs when a hazard actually impacts vulnerable populations resulting in significant damage, disruption or loss of life. Without a degree of vulnerability a hazard does not become a disaster
Perception of risk factors
Experience (people who have been in a similar disaster before will cope better)
Material well being (wealthy people will have more options available)
Personality (is the person a leader, follower or risk taking impacting reactions)
Response options
Do nothing and accept the consequences of the hazard
Adjust to the situation of living in that area
Leave the area
Factors impacting the level of adjustment to a hazard
Identification of hazards
Estimation of the risk of the hazard
An evaluation of the cost casued by the hazard
Precondition stage of response
1: Lifestyle risks, routine safety measures, social construction of vulnerability, planned developments and emergency preparedness
2: Incubation period, erosion of safety measures, heightened vulnerability, signs and problems misread or ignored
The disaster stage of response
3: Beginning of crisis, threat period, impending or arriving hazard, danger seen clearly, may allow warnings, flight or evacuation and pre-impact measures
4: The disaster, concentrated impacts, impaired or destroyed security, individuals and small groups cope as isolated survivors
5: Exposure of survivors, post impact hazards, delayed deaths
6: Rescue, relief, evacuation, shelter provision, clearing dangerous wreckage, organized response, national and international humanitarian efforts
Recovery and reconstruction stage of response
7: Relief camps, emergency housing, residents and outsiders clear wreckage, salvage items, blame and reconstruction debates, disaster reports, evaluations, commissions of enquiry
8: Reintegration of damaged community with society, re-establishment of everyday life, similar to or different from pre disaster, continuing private and recurring communal grief, disaster related development and hazard reducing measures
Managing the earthquake hazard
Better forecasting and warnings
Improved building design and location
Establishing emergency procedures
Predicting and monitoring earthquakes
Small scale ground surface changes
Small scale uplift or subsidence
Ground tilt
Changes in rock stress
Micro earthquake activity
Anomalies in earths magnetic field
Changes in radon gas concentration
Changes in electrical resistivity of rocks
Requires detailed recording with specialist equipment and not reliable. Hard to be confident of exact time and location
Methods of detecting earthquakes
Includes distortion of fences, roads and buildings as well as changes in water levels of boreholes. Strain can change the water holding capacity or porosity of rocks by opening cracks. Satellites can measures the position of points on the earths surface
Difficulties in predication and risk assessment of earthqukes
Some earthquakes are irregular in time while other parts of the surface may continually slip and produce lots of small earthquakes. Different parts of a fault line may behave differently. Areas that don’t move are seismic gaps but areas with many small earthquakes may be less hazardous. The location of earthquakes is closely linked with the distribution of fault lines but timing is hard to predict. Previous patterns and frequencies have some prediction but size is hard to predict
Earthquake monitoring equipment
Seismometer to record minor earthquakes
Magnetometer to record changes in earths magnetic field
Near surface seismometer to record larger shocks
Vibroseis truck to create shear waves to probe the earthquake zone
Strain meter to monitor surface deformation
Sensors in wells to monitor changes in groundwater levels
Satellite relays to relay data to weather stations
Laser survey equipment to measure surface movement
Background of earthquakes
1.5 million people were killed by earthquakes in the 20th century. Most deaths are caused by collapsing buildings. 1/3 of the worlds largest cities are in earthquake prone areas. Earthquakes can’t be stopped so risks need to be minimised
Seismic gap theory
Suggests that sections of active fault lines having not experienced significant earthquakes for a long time are gaps where stress is building making future events more likely. Over time as tectonic plates move stress accumulates along fault lines. Stress may not be released in a seismic gap increasing the risk of a major earthquake. They are used to aid earthquake preparedness and risk mitigation
Countries preparing for earthquakes
Implement and enforce strict building regulations to ensure structures are designed to withstand seimsic activity. Establish well coordinated emergency plans including evacuation routes, communication strategies and resource allocation after. Raise awareness about earthquake preparedness through community training programmes, drills and information resources. Install advanced seismic monitoring and early warning systems to detect and alert of earthquakes to take protective measures. Reinforce essential facilities to ensure they are functional during and after an earthquake. Use seismic risk maps to guide land use decisions avoiding construction in high risk areas and promoting sustainable urban development
Land use planning for earthquakes
Prohibit construction in areas prone to earthquakes like fault lines, unstable slopes and liquefaction zones to reduce damage and casualties. Implement land use zoning laws that limit high density developments in earthquake prone regions and prioritize open spaces for emergency shelters and evacuation routes. Require seismic risk assessments before approving major construction projects ensuring urban development is safe, sustainable and resilient
Designing earthquake resistant buildings
Reinforced foundations
Base isolation systems
Shock absorbers
Flexible materials
Cross bracing and shear walls
Lightweight roofs and floors
Retrofitting older structures
LEDC building designs
Quake-resistant houses are being built of straw. The compressed bales are held together by nylon netting between layers of plastic. Heavy concrete roofs collapse on many homes, sheet metal roofs on wooden trusses are more resistant. Small, regularly spaced windows create fewer weak spots but walls are not properly reinforced. Reinforcing rods can be made of natural materials or plastic mesh. Brick walls can be framed and connected to the roof by corner columns and a crown beam of reinforced concrete. Tyres filled with stones and sand between floor and foundation can be cheap ground motion absorbers
Predictions of volcanoes vs earthquakes
Volcanoes are easier to predict because they have clear warning signs (seismic activity, ground deformation, gas emissions). Volcano prediction relies on monitoring methods (satellite imagery, seismographs, gas sensors). Earthquake prediction relies on seismic history and stress accumulation which only gives a general probability. Volcanoes provide warning days, weeks or months before due to the gradual build up of pressure and observations. Earthquake prediction is limited to short term forecasts and initial seismic wave detection
Volcano monitoring systems
Seismometers to record swars of small earthquakes as magma rises
Chemical sensors to measure increased sulfur levels
Lasers to detect physical volano swelling also with GPS
Ultrasound to monitor low frequency waves in magma due to the surge of gas and molten rock
Observations
Not possible to state exactly when earthquakes occur
Reasons for living with volcanoes
Long history of living with eruptions
People are confident there will be sufficient warning
Volcanic soils can be very fertile due to chemical weathering and leaching
Volcanic islands are important for tourism
Some are culturally symbolic
Adaptations for living with volcanoes
Advanced monitoring networks detect early signs
Land use planning and zoning. Governments designate exclusion zones around high risk areas restricting permanent settlement
Buildings are designed to withstand ashfall and earthquakes
Drills and education campaigns teach residents how to respond in emergencies
Mass movements
Large scale movements of the earth’s surface that are not accompanied by a moving agent like rivers, glaciers or the sea
Soil creep
Speed is very slow below 1 cm per year. Common in humid climates and can be nearly continuous
Solifluctuation
Very slow and of limited importance. Occurs 5-10 cm per year due to a thawed top layer moving over a frozen lower layer
Fast movements
Involve both mud and earth flows. Type is dependent on amount of water
Earth and mud flows
Occurs on slopes 5-15 degrees often after the soil has become saturated and flow then results. Vegetation can be destroyed and speeds range 1-15 km per year. Also called debris flows
Landslides
The internal structure of the slope remains stable. A chunk of a slope slides away from the rest
Rotational slump
Usually found on weaker rocks (clay) that become saturated and heavy. Undercutting of cliffs by wave action can also be a cause as human activity increasing pressure on rocks
Rockfall
Occurs on very steep slopes greater than 40 degrees. Results from extremes of physical and chemical weathering. Debris or scree slopes at cliff foot
Runoff
Fine particles move downslope through overland flow. Thin, continuous layer of silt and clay flowing called sheetflow. Happens when there is little vegetation to told the soil together. May flow straight into sea
Shear strength
The internal resistance of the slope
Shear stress
The forces attempting to pull as mass downslope
Factors increasing shear stress
Removal of lateral support through undercutting or slope steepening
Removal of underlying support
Loading of slope
Lateral pressure
Transient stresses
Factors reducing shear strength
Weathering effects
Changes in pore-water
Changes of structure
Organic efforts
Human factors increasing mass movements
Deforestation
Urban development
Mining and quarrying
Water mismanagement
Slope safety
In MEDCs slopes in densely populated areas are often assess for movement risk. The safety factor is determined by the relative shear strength of a slope compared to the shear stress
Factors determining slope movement
Gravity
Slope angle
Pore pressure (pressure of water held within soils or rocks)
Slope failure
Shear stress is increased
Shear strength is reduced
Avalanches
A mass movement of snow or ice
Process of avalanches
Can occur when newly fallen snow slips off older snow in winter. Partially thawed snow at the surface begins to move triggered by humans. Most frequency on slopes over 22 degrees especially on north facing slopes with a lack of sunshine. Exposure to energy from the sun allows some partial melting to help stabilise slopes. Very fast and dangerous usually 40-60km/h up to 200km/h
Classification of avalanches
Type of breakaway (a point formed with loose snow or from an area formed of a slab)
Position of the sliding surface (whole snow cover ot just the surface)
Water content (dry or wet)
Form (channelled in cross section or open)
Avalanche dynamics
Snow gets its strength from the interlocking of snow crystals and the electrostatic bonding between them. Snow will remain stationary as long as this shear strength is greater than the shear stress exerted on it by the weight of the snow and angle. The overlying pressure of new snowfall and the composition caused by this along with fluctuating temperatures and the movement of meltwater through the profile can quickly cause snow to be unstable
Loose avalanches
Occur after fresh snowfall
More common in winter
Tend to be less deadly
Slab avalanches
Occur sometime after heavy snowfall when it has developed more cohesion
Larger and more destructive
More common in spring following sudden increases in temperatures
The meltwater caused by this warming lubricates the slab causing instability
Timing of avalanches
Many occur in spring because the snowpack is large and temperatures are rising. The least number occur in December and April when it is either too cold for snow to move or too warm for new snow to fall. 41% occur between 2000 and 2499 m of altitude so enough sunlight can reach the slope to produce meltwater but not too much to melt all the fresh snow. Only 3% occur above 3000m and only 4% below 1500m. Temperature is affected by sunlight
Managing avalanches
Monitoring and prediction (weather monitoring, snowpack analysis, technological tools like remote sensing and forecasting)
Avalanche control (controlled explosions, snow fencing, reforestation, terrace building)
Warning systems and education
Emergency preparedness
Land use planning (zoning, defensive structures)
Monitoring slope stability (prediction of mass movement events)
Rainfall is a significant trigger for many mass movements. Instruments like rain gauges and weather radar are used to establish thresholds beyond which slopes become unstable.
Technologies such as inclinometers, piezometers and strain gauges monitor ground movement, water pressure and soil strain
Geological and geotechnical surveys (prediction of mass movement events)
Geological mapping identifies vulnerable areas based on rock type, structure and historical data. Combining this with geotechnical surveys which assess soil and rock strength provides insights into slope stability
Remote sensing and GIS (prediction of mass movement events)
Satellite imagery detects changes in vegetation, surface displacement and fractures.
LiDAR generates high resolution topographic maps to identify landslide prone areas.
GIS modelling integrates multiple datasets to produce susceptibility maps
Slope stabilisation (preparation for mass movement events)
Retaining walls reinforce unstable slopes.
Inserting steel rods into slopes stabilises the soil through soil nailing
Planting trees and shrubs stabilises slopes through root reinforcement
Drainage control (preparation for mass movement events)
Excess water is a common trigger for slope failure. Installing drainage systems such as culverts and surface drains reduces pore water pressure
Barriers and catchments (preparation for mass movement events)
Steel nets and fences catch rockfalls and falling debris
Debris flow dams are structures designed to slope or capture debris flows
Land use planning (preparation for mass movement events)
Restricting development in high risk zones reduces the vulnerability of communities
Early warning systems (preparation for mass movement events)
Rainfall and seismic monitoring is used in conjunction with hazard mapping to issue warnings
Educating residents about warning signals and evacuation routes increases resilience
Susceptibility maps (mapping mass movement events)
These maps indicate the likelihood of a mass movement occurring in a specific area based on static factors such as slope gradients, rock type and land use
Hazard zonation (mapping mass movement events)
Combines susceptibility maps with dynamic triggers like rainfall or seismic activity to identify high risk zones
Use of historical records (mapping mass movement events)
Analyzing past mass movement events helps refine hazard maps
Tropical cyclones
A rapidly rotating storm system characterised by a low pressure center, strong winds and heavy rainfall. It forms over warm ocean waters in tropical and subtropical regions and derives its energy from the heat and moisture of the ocean
Hurricanes, typhonnes and cyclones
Tropical cyclones are hurricanes in the Atlantic and northeastern Pacific, typhoons in the northwestern Pacific and cyclones in the Indian Ocean and south Pacific
Features of tropical cyclones
A central eye which is calm and surrounded by a wall of intense thunderstorms known as the eyewall. Spiral rainbands extending outwards from the center. Sustained winds of at least 74 mph
Conditions for hurricane formation
Sea surface temperatures of at least 26.5C down to a depth of 50m. Warm water provides the heat and moisture necessary for development. Wind shear is the change in wind speed and direction with height in the atmosphere. For hurricane formation, wind shear must be low to prevent the vertical structure being disrupted. A weather system like a tropical wave must already exist to act as a seed for the cyclone. It provides an initial area of low pressure around which the storm can develop. High moisture level in the mid to low atmosphere to help sustain convection and energy. The Coriolis effect due to the earths rotation provides the spin that allows the storm to develop a rotating structure so usually form at 5N/S of the equator where the Coriolis force is strong enough. Air must be able to flow outward from the top of the storm creating a vacuum that allows more warm, moist air to rise from the surface and fuel the system
Predicting tropical cyclones
Tropical cyclone forecasting relies on numerical weather predictions that simulate atmospheric conditions and cyclone behaviour. These help predict cyclone paths, intensity and landfall location. Forecasting uses satellite imagery, radar data and ocean buoys to monitor storm development and movement, enhancing prediction accuracy
Limitations of predicting tropical cyclones
Subject to forecast uncertainty due to the complex and chaotic nature of the atmosphere making precise predictions especially beyond 72 hours difficult. Factors like sea surface temperature, wind shear and atmospheric pressure can influence a cyclones strength and trajectory and slight changes in these conditions can lead to large forecasting errors
Intensifying tropical cyclones
Human induced climate change is likely to intensify TCs by warming oceans. Rising sea levels amplify the flooding caused by TCs. The proportion of severe TCs has increased and this will continue. Future severe storms are expected to have more damaging winds, higher storm surges and extreme rainfall. The total number of TCs may stay the same or decrease with a reduction in low intensity cyclones. Changes like the poleward shift of maximum storm intensity, faster intensification and slower forward motion have been observed. These may signal the influence of climate change from natural variability. Climate models project tat rapid intensification, slower forward motion and poleward shifts may increase in certain regions
Tropical disturbance
Initial stage with a cluster of thunderstorms and weak surface winds. Low pressure area, rising moist air and no organised structure. Instability creates the potential for further development
Tropical depression
The disturbance becomes more organised with a defined low pressure center. Sustained wind speeds of less than 38 mph and increased convergence of warm air and stronger updrafts. Strengthening of rotation and convection
Tropical storm
Intensified system with sustained wind speeds between 39-73 mph. Circular shape, more organised structure and named storm. Draws more energy from warm waters, setting the stage for potential hurricane formation
Hurricane
Sustained wind speeds over 74 mph. Development of an eye and eyewall, spiral rainbands and categorized on the Saffir-Simpson scale. High impact storm capable of causing significant damage
Dissipation
The storm weakens over land or colder waters losing its energy source. Decreasing wind speeds, disorganisation, heavy rain may continue causing flooding. The system eventually dies out though its remnant can still affect weather patterns
Social hurricane impacts
Loss of lives and injuries
Increased mental health issues
Potential for social unrest if recovery is slow or unequal
Disruption to daily life, including education and community services
Displacement of populations and homelessness
Economic hurricane impacts
High costs of building and repairs
Damage to homes, schools and healthcare facilities
Destruction of businesses and loss of jobs
Impact on agriculture, fisheries and industries
Loss of tourism revenue due to damaged attractions and travel disruptions
Environmental hurricane impacts
Coastal erosion and destruction of natural habitats
Pollution from debris, oil spills and chemical leaks
Alteration of ecosystems and wildlife populations
Contamination of freshwater supplies due to flooding
Uprooting of vegetation and deforestation
Political hurricane impacts
Strain on government resources and disaster response systems
Damage to infrastructure
Criticism of disaster preparedness and recovery efforts
Increased pressure on international aid and funding
Changes in policies regarding climate adaptation and disaster mitigation
Tornadoes
A rapidly rotating column of air that extends from a thunderstorm to the ground characterised by its funnel shape cloud and violent winds
Characteristics of toranodes
Form when warm, moist air meets cool, dry air creating instability in the atmosphere. They can cause significant destruction along their path with wind speeds of <100 km/h to >500 km/h
Stages of tornado formation
- Form when warm, humid air from the surface meets cooler, drier air above creating atmospheric instability
- Strong updrafts in severe thunderstorms (supercells) lift the warm air rapidly forming towering cumulonimbus clouds
- Differences in wind speed and direction at different altitudes cause the air to rotate horizontally creating a spinning column of air
- Rising air tilts the rotating horizontal column into a vertical position forming a mesocyclone
- The rotating column of air tightens and speeds up extending downwards as a funnel shaped cloud
- When the funnel cloud reaches the ground it becomes a tornado capable of damage
Measuring tornadoes
The Fujita scale to measure the intensity and area of a tornado was introduced in1971. The enhanced Fujita scale with other factor was introduced in the 1990s
EF0-EF5 scale
EF0=65-85mph
EF1=86-110mph
EF2=111-135mph
EF3=136-165mph
EF4=166-200mph
EF5=200+mph
Predicting tornadoes challenges
Develop and intensify in minutes so hard to provide timely and accurate warnings
Affect small areas needing highly detailed, real time data that is hard to collect/analyse
Precise atmospheric combination is hard to model causing uncertainty in forecasts
Long term trends in tornadoes
Activity can be shifting east from Tornado Alley to the SE USA including Alabama, Mississippi and Tennessee
The total number in the US is relatively stable but the intensity and location of activity may vary due to changing climatic patterns
Climate change is debatably changing trends with changes in timing, location and intensity of outbreaks
Primary impacts
Are the immediate and direct effects of a natural hazard as a direct result of the event (building collapse, flooding, injuries)
Secondary impacts
Are the indirect or long term effects of the primary impacts (homelessness, economic losses, disease outbreaks)
Tornado damage
Most deaths are from debris while they bring intense rain, high winds and large changes in pressure gradients. Winds cause the removal or severe damage of objects. Strong rotational movement twist objects from fixings and strong uplift carries debris upward. The low atmospheric pressure near the vortex centre causes damage since external pressure falls leading to walls and roofs exploding outward to equalise
Tornado damage vs tropical storm damage
Winds in multiple vortex tornadoes usually do less damage than smaller sub vortices. Tropical storms cause more damage than tornadoes due to larger size, longer duration and variety of damage. Tornaodes last for minutes and wind is usually the only cause of damage
Managing tornadoes
Advanced radar technology, weather monitoring and tornado sirens provide early warnings to residents, allowing time to seek shelter and reduce casualties. Public education campaigns, tornado drills and the construction of storm shelters or safe rooms improve community readiness and safety during tornadoes. Enforce stronger building codes in tornado prone areas ensures structures are more resilient to high winds, minimising damage and protecting lives
Social tornado impacts
Power outtages
Spread of waterborne diseases
Loss of cultural or historical landmarks
Disruption of education
Loss of livestock
Scarcity of clean water
Homelessness
Ruined farmland and crops
Displacement of families
Deaths and injuries
Temporary unemployment
Increase in mental health issues
Environmental tornado impacts
Disruption of wildlife habitats
Destruction of forests
Pollution of rivers from debris
Deaths of wildlife
Ground erosion caused by high winds
Economic tornado impacts
Increased demand for construction materials
Collapse of local businesses
Strain on healthcare systems
Increased insurance premiums
Economic inflation in affected areas
Loss of tax revenue for local governments
Increases public spending on rebuilding
Damage to homes and buildings
Political tornado impacts
Emergency government spending
Damage to infrastructure
Damage to emergency response systems
Protests over disaster response
Media coverage of government response
Opportunities of living near volcanoes
Volcanic rock and ash provide fertile land leading to higher crop yields. Tourists are attracted to the volcano which increases money in the economy. Geothermal energy can be harnessed providing cheap electricity for locals. Minerals are contained in lava which are mined to make money (diamonds)
Risks of living near volcanoes
Explosive eruptions release lava, ash and pyroclastic flows. Volcanic ash can cause respiratory issues and contaminate water supplies. Lava flows and ash falls can destroy homes, infrastructure and agricultural land. Volcanic activity can alter landscapes, disrupt ecosystems and affect the global climate through the release of volcanic gas
Deaths and injuries near volcanoes
500-1000 deaths annually are a direct result of volcanic eruptions. In major eruptions the deaths can rise significantly. Thousands annually suffer injuries due to pyroclastic flows, falling ash or lahars. Many experience health issues or displacement due to volcanic gases, ashfall or long term environmental damage
“Do nothing” method of dealing with environmental hazards
Accept that disasters will happen. May be more or less viable depending on the volcano and the frequency of eruption
“Protect society” method of dealing with environmental hazards
Strengthening roofs against tephra, building structural defences against lahars, pumping seawater on to lava or slowly degassing. This is not always feasible since not all gases can be averted through degassing, large lava and pyroclastic flows are hard to stop or redirect and reliance on protective measures can lead to a false sense of security
“Avoid hazards” method of dealing with environmental hazards
Not always feasible since hazards may not just be local so all places can be impacted. With a rising population, constraints on land and resources leave little option other than to live in affected areas. Moving away can also lead to exposure to other hazards and social challenges
“Live with the risk and accept that hazards are part of life” method of dealing with environmental hazards
It involves localising disaster risk reduction such as preparedness and mitigation as well as response and recovery. Most successful with support and action from locals. Long dormancy and uncertainty can reduce disaster risk reduction but are vulnerable to hazards other than volcanoes
Sustainable livelihoods approach
SLA is a framework used to understand and improve the living conditions of people particularly in developing contexts. It focuses on reducing poverty and vulnerability while enhancing people’s capacity to make a living sustainably
SLA and volcanoes
Understanding, communicating and managing vulnerability and risk and the local perceptions of vulnerability and risk beyond immediate threats to life
Maximising benefits to communities of the volcanic environment especially in inactive periods without increasing vulnerability
Managing crises
Managing reconstruction and resettlement after a crisis
SLA components
Livelihood assets
Vulnerability context
Policies, institutions and processes
Livelihood strategies
Livelihood outcomes
Sustainability focus
Reducing volcanic impacts with the SLA
Develop community based monitoring and warning systems, leveraging local knowledge and technology to enhance preparedness and response times. Encourage the sustainable use of volcanic resources like fertile soils for agriculture or geothermal energy, ensuring benefits without increasing vulnerability. Invest in resilient housing, evacuation routes and disaster shelters with input from locals to protect lives and property. Involve locals in risk assessments, planning and mitigation to ensure interventions are culturally appropriate and address perceived risks. Providing training and education to increase understanding of hazards so communities can make informed decisions and take proactive measures. Promote alternative income sources to reduce dependence on high risk areas while maintaining economic stability
Knowing when the risk is too great
Living with volcanic risk is not always possible. Sometimes doing nothing is more sensible
