Hazards Flashcards
Explain the distribution and causes of most tectonic hazards.
Generally occur on plate boundaries, and are caused by the movement of plates, sticking together to buildup pressure, and release of magma through subductive boundaries and constructive ones.
What are intra-plate processes?
Processes occurring in the middle of a plate. This can be from (generally minor) earthquakes on ancient faults, and volcanic activity in hotspots where there is an upwelling of magma from the mantle, or a large mantle plume.
What is convection?
The process by which heat radiates outwards from the earth’s core. The hot magma rises, and cools further away from the core, sinking as the now hotter magma rises again. This cycle creates a convection current which moves the plates where it makes contact with the base of the crust through frictional drag.
What is ridge push/slab pull?
Older, denser plates are subducted at cooler downwellings of magma at destructive boundaries. Meanwhile, at constructive boundaries, new plates are formed through the upwelling of magma to the surface.
What are constructive/divergent boundaries?
Plates move apart, creating shield volcanoes and mid-ocean ridges, e.g the Mid-Atlantic ridge.
What are destructive/convergent boundaries?
Plates move together, with one being subducted under the other, causing earthquakes, tsunamis, and composite volcanoes, e.g Cascadia
What are collision boundaries?
Plates of similar densities move together, causing folding or crumpling of the land, creating fold mountains, and earthquakes, e.g the Himalayas.
What are conservative/transform boundaries?
Plates move past eachother, either in opposite directions, or the same directions at different speeds, causing earthquakes. e.g the San Andreas Fault.
What evidence is there to support the theory of plate tectonics?
Alignment of continental coastlines, matching geology and fossils found on these coasts. surveyal of seafloor found evidence of seafloor spreading, and correct predictions of the movement of hotspots.
What is the physical process resulting in an earthquake?
Stress and strain due to plates moving and catching on each other results in a buildup of friction. The focus is the place where this is released. Seismic waves are sent out in all directions, but are strongest at the shortest distance from the surface, directly above it (the epicentre).
What are P-waves?
Primary waves, the first to arrive as they are quicker through the crust and have a shorter wavelength. They don’t generally cause too much destruction.
What are S-waves?
Secondary waves, slightly slower to reach the surface and have a longer wavelength. These cause most of the shaking and destruction.
What secondary hazards can occur from an earthquake?
Tsunamis which can have far reaching impacts; landslides when rock is loosened on a steep slope and is pulled downwards; and liquefaction where loose rock in lowland areas is shaken an sorted to the point where it begins to act as a liquid.
What happened in the Christchurch Earthquake?
- Shallow focus earthquake in New Zealand, where shockwaves were amplified by nearby solid rock.
- Waterlogged silt lost cohesion and began to behave like a fluid, including eruptions of ‘sand volcanoes’.
- Buildings lost their foundations and one of the main roads was damaged.
- Afterwards cone penetrometer testing (CPT) used to study soil and test susceptibility to liquefaction, to make resistant foundations.
How are Tsunamis created?
Water column displacement occurring after the seabed is thrust up or down due to undersea plate movement. They can also occur due to an explosive eruption on a volcanic island (where there is a cone collapse or landslide falling into the sea), or an underwater landslide.
What are supervolcanoes?
Volcanoes that, if they exploded, would have a significant impact on the world. E.g Yellowstone in the US.
What are the 3 main types of lava and their qualities?
- Basaltic: Hottest, low gas content and thin/runny so eruptions are gentle and effusive. Occurs at volcanic hotspots, mid-ocean ridges, and shield volcanoes.
- Andesitic: Medium temp, mid gas content and intermediate viscosity so eruptions are violent and moderately explosive. Occurs at composite cone volcanoes and subduction zones.
- Rhyolitic: Coolest temp, high gas content and high viscosity so eruptions are very violent, explosive and cataclysmic. Occurs at supervolcanoes and composite cone volcanoes.
What are the hazards associated with volcanic eruptions?
Lava flows and gas/steam emissions (phreatic eruption) close to the volcano. Further away the hazards are pyroclastic flow, and ash (tephra). Secondary hazards are lahars and jokulhlaups.
What is a jokulhlaup?
A flood of meltwater from under an icecap or glacier when a volcano erupts underneath, forming a lake dammed by ice. when the water bursts through, it creates a high speed flood down to lowland areas and has the power to change the course of rivers. E.g Icelandic eruptions like Eyjafjallajokull created jokulhlaups like the river Makarfljot (this was anticipated and the road was closed so no harm was done).
What is a pyroclastic flow?
A mixture of superheated tephra (ejected material) and hot, poisonous gases moving rapidly down composite volcanoes. Occurs at explosive eruptions of molten or solid tephra, or cone collapse or thick lava flows. Gravity means large solids e.g boulders move slowly while lighter particles occur as a fast moving ash cloud. Will destroy anything in its path through burning, burying, or poisoning. E.g Mt Merapi in Indonesia.
What are the impacts associated with volcanic ash?
Locally can cause roof collapse, and breathing difficulties, and bury vegetation and crops. Roads may shut due to poor visibility, and there may be issues with air transport (ash in jets can cause engine failure) globally in its wake e.g Eyjafjallajokull disrupted European flights for a week.
What are lahars?
Water mixed with volcanic deposits flowing through valleys. Fast velocity and material carried (e.g 10m diameter boulders) makes them dangerous. E.g town of Amero, Columbia was buried by a lahar, and 23,000 people were killed (it occurred at night), people were sleeping in homes so could not escape. Buried by 2-5m of deposits, and survivors killed/unable to escape due to a further 10 surges.
What scales can be used to measure earthquakes?
Richter Scale - A logarithmic scale that measures the magnitude of the earthquake based on the P and S waves, and the distance from the epicentre. It’s less accurate than the MMS.
Moment Magnitude Scale - (MMS) A logarithmic scale that measures magnitude based on the energy released by the shockwaves, and the area of rupture and movement. It’s more accurate than the RS. Unit is Mw.
Mercalli Scale - Measures intensity based on the amount of damage caused (and also takes into account any secondary hazards).
What is the hazard risk equation?
Risk = Hazard x Vulnerability
What is the pressure and release model?
- A model suggesting what should be tackled to decrease risk of disaster.
- Root causes: dysfunctional cultural, political, and economic systems.
- Dynamic pressures: lack of resources, development, training, organisations, ect. as well as factors like rapid population change, urbanisation ect.
- Unsafe living conditions: dangerous living conditions, lack of resistant infrastructure, disparity, lack of preparation, disease, ect.
- Geographical modification: distribution, hazard zones, magnitude, timing, frequency. Hazards and opportunities.
- Natural tectonic processes: Earthquake, tsunami, landslide, liquefaction, volcano, pyroclastic flow, lahar, and ash.
What is risk?
The probability of harm or loss taking place.
What is hazard?
The tectonic event itself, including secondary hazards and the characteristics of the event.
What is vulnerability?
Human geography in the area of the tectonic event that determines the amount of disaster occurring. E.g location of settlement, knowledge, warning systems, infrastructure, training and plans, ect. This is the thing that can be used to mitigate the effects of the hazard and therefore best reduce risk.
What is the general tectonic situation in the Middle East?
- The Eurasian and African continental plates have a long history of seismic activity in this region.
- There is a general lack of knowledge surrounding the situation for the civilians of these countries, they do not know how to prepare or mitigate.
What is the situation in Iran?
The Bam earthquake (6.6Mw) in 2003 killed 31,000+ people as clay houses collapsed. UNESCO heritage site Arg-e Bam was also destroyed.
What is the situation in Turkey?
- In Turkey’s rural areas there was a growing aseismic culture with resistant buildings being built. However rapid urbanisation is reversing this process.
-The Izmit earthquake (7.4Mw) in 1999 killed 17,000 and badly damaged 245,000 buildings. - Afterwards there was a focus on training locals for impact reduction strategies, raising community awareness. leaflets with maps of the seismic risk zone were handed out with advice for making homes safer.
What is the situation in Egypt?
- Whilst ancient structures are partially earthquake proof, recent attempts to adapt this for modern housing were met with resistance, as the low frequency means the community has poor risk perception.
- The government has produced a free booklet being distributed through schools. Scientific explanations were reinforced with Qur’an quotes so people would more readily accept it.
- However this info was more focused on response than mitigation, and so there are still big issues.
- E.g Nile Valley villages destroyed in 1992 were not given any info on how to ‘build back better’.
What is the situation in Vanuatu?
- It’s the most at risk country in the world with earthquakes, volcanoes, tropical cyclones, and sea-level rise.
- E.g Cyclone Pam (2015), Frequent strong earthquakes (e.g 7.1Mw in October 2015), and Volcanic eruptions (e.g Mt Yasur).
- Its make up of isolated islands make it more vulnerable, as well as poverty and a lack of access to resources, poor education, and lack of investment into healthcare and sanitation infrastructure (only 57% of the population have an adequate sewage system).
What is the trend in fatalities in disasters from the 20th century?
Since the 20th century only 2.2% of fatalities from natural hazards were due to earthquakes, volcanic eruptions, and associated secondary hazards. The vast majority were instead due to slow onset events like drought and famine.
It is important to remember that most deaths are caused by an intersection of factors e.g poverty forcing people to live in risky areas like the side of a volcano, or in slums where unstable housing exaggerates the impacts of seismic activity.
What may bias our understanding of hazard frequency?
The media is often more likely to report ‘sudden onset’ events as they are seemingly more shocking and dramatic than starvation.
Additionally, there is more reporting of these events via social media, therefore we are more likely to hear about events happening in developed countries with widespread internet access.
What happened in the Philippines in 1991?
- Mount Pinatubo erupted an ash and sulphur dioxide cloud to a height of 32 km and this ash was deposited far away in the Indian ocean.
- The ash caused some damage to aeroplanes despite warnings, but the main impact was the SO2 cloud which circulated the earth in the stratosphere and decreased the earth’s temperature by 0.6 degrees celsius between 1991-93.
What were the global impacts of the 2010 Eyjafjallajokull earthquake in Iceland?
- 110 million m3 of ash in 1 week, much was distributed across main flight paths causing major disruption in Europe and North America.
- Tourists were stranded, airlines lost $200 million per day, perishable agricultural products rotted in warehouses, workers were temporarily unemployed, ect.
What happened in Japan in 2011?
- The Tohoku tsunami destroyed any docks and boats in various places around the Pacific Ocean, and killed 1 person in California.
- Buildings destroyed in Japan led to the release of chemicals increasing global warming to the atmosphere, and decline in Japan’s manufacturing exports.
- Encouraged other countries to make their nuclear reactors less susceptible to damage in case of natural hazards (Japan had issues with radioactive seawater after explosions at Fukushima).
- Changed earth’s wobble by 17cm and rate of spin by 1.8 microseconds.
What happened with the 2004 ‘Boxing day’ tsunami?
- Occurred in the Indian Ocean, deaths in Indonesia, Thailand, Sri Lanka, India, and Tanzania.
- However fatalities were from 46 other countries as well due to tourism, including many European countries (interestingly this is what the textbook focuses on despite the fact that whilst the highest death toll in Europe was Sweden at 543, Indonesia’s was over 160,000).
- E.g there were 143 deaths from the UK.
Why is the Philippines a multi-hazard country?
- Situated on the Ring of Fire, with 18/37 volcanoes currently active, and a subduction zone that produced frequent earthquakes (due to its islands this has caused many deaths from tsunamis).
- 74% of the population is exposed to 2 or more hazards. Poverty increases the effects of these.
How can natural hazard events be modified?
Most cannot be modified e.g earthquakes. However some volcanic activity can be modified through the building of lava diversion barriers (spraying seawater on lava to cool and solidify it), diversion channels, and draining crater lakes to reduce the risk of lahars. Additionally coastal management strategies like mangroves can mitigate the impacts of tsunamis. Monitoring and predicting technologies can also help.
How can vulnerability and resilience be modified?
- Risk mapping can be useful to predict areas where liquefaction is likely or lahar routes might occur.
- This can produce land use zoning and planning laws that remove people and property from large risk areas, and encouraging an increase in food production and stockpiling.
- Warning systems can be produced and hazard resistant buildings can be designed and built.
How can loss be modified?
- Loss can be modified through fully equipped rescue efforts followed by relief aid including water, blankets, food, shelter, and sanitation.
- Developing countries may rely on external assistance from NGOs.
- In some cases whole settlements will be moved away from risky areas and rebuilt safer e.g Balakot was moved 23km after the 2005 Kashmir earthquake.
What is the IDNDR?
The international decade for national disaster reduction, created by the general assembly of the UN, emphasised the need to combine ‘top down’ government approaches with ‘bottom up’ community and NGO responses.
