1.3 - Causes And Impacts Of Tectonic Hazards Flashcards
(13 cards)
Primary waves
- Body waves
- Fastest
- Reach the surface first
- Travel through liquids and solids
- Cause backwards and forwards shaking
- Least damaging
Secondary waves
- Body wave
- Slower than P waves
- Only travel through solids
- Cause a sideways motion
- More damaging
Love waves
- Surface wave
- Slowest
- Larger and energy is focussed on the surface
- Most damaging
- Only travel through solids
- Horizontal movement (side to side)
Rayleigh waves
- Surface wave
- Only travel through solids
- Focus all energy on Earth’s surface
- Spread the furthest from focus
- The ground moves in an elliptical pattern causing shaking
Earthquake hazards
Primary
- Ground shaking
- Crustal fracturing (when the movement causes the Earth’s crust to crack)
Secondary
- Landslides and avalanches - the movement of the Earth may trigger the collapse of material down steep slopes
- Liquefaction - when the shaking causes particles in the ground to move further apart causing them to act like a liquid rather than a solid
- Flooding - caused by a tsunami
Earthquake case study - Haiti 2010
On the 12th of January 2010 an earthquake measuring 7 on the Richter scale struck Haiti
Haiti is situated at the northern end of the Caribbean Plate, on a transform (slip/conservative) plate boundary with the North American Plate. The North American plate is moving west. This movement is not smooth, and there is friction between the North American Plate and the Caribbean Plate. Pressure builds between the two plates until released as an earthquake.
Primary impacts
- 3 million people were affected by the earthquake
- between 217,000 and 230,000 people died
- an estimated 300,000 were injured
- an estimated 1,000,000 were made homeless
- also estimated that 250,000 residences and 30,000 commercial buildings had collapsed or were severely damaged.
Secondary impacts
- Two million people were left without water and food.
- Regular power cuts occurred.
- Crime increased - looting became a problem and sexual violence escalated.
- People moved into temporary shelters.
- By November 2010 there were outbreaks of cholera.
Immediate responses
- Due to the port being damaged, aid was slow to arrive.
- The USA sent rescue teams and 10,000 troops.
- 235,000 people were moved away from Port-au-Prince to less-damaged cities.
- £20 million was donated by The UK government.
Long term responses
- As one of the poorest countries on Earth, Haiti relied on overseas aid.
- Although the response was slow, new homes were built to a higher standard. Over one million people still lived in temporary shelters one year after the earthquake.
- The port needed rebuilding, which required a large amount of investment.
Volcanic hazards
Primary
- Pyroclastic flow - a mix of dense, hot, rock, ash and gases
- Lava flow - most move slowly enough that they are not a risk to human life but can reach over 1000oC
- Ash falls - can travel many km, causing injuries, damage, deaths and disruption to transport
- Gas eruptions - gases trapped in the magma are released during an eruption, they may form gas clouds which are hazardous to health
Secondary
- Lahars - a mixture of rocks, mud and water which flow down the volcano. They are fast-flowing and destroy everything in their path
- Jökulhlaups - floods caused by a sudden release of water and rocks when glacial ice is melted by the eruption
Volcano case study - Eyjafjallajökull, Iceland 2010
Eyjafjallajokull erupted between March and June 2010. It erupted three times in 2010 - on 20 March, April–May, and June. The volcano is situated on a constructive plate boundary between the North American and Eurasian plate. The two plates move apart due to ridge push along the Mid-Atlantic Ridge. As the plates move apart, magma fills the magma chamber below Eyjafjallajokull - several magma chambers combined to produce a significant volume of magma below the volcano. It erupts basaltic lava and there is a glacier above the volcano.
Primary impacts
- As a result of the eruption, day turned to night, with the ash blocking the sun. Rescuers wore face masks to prevent them from choking on ash clouds
- The ash plume stopped 100,000 jet engines, just in Europe
- During the eruption, a no-fly zone was imposed across much of Europe, meaning airlines lost around £130m per day
- The price of shares in major airlines dropped between 2.5 and 3.3% during the eruption.
- 700 people evacuated due to the flooding from the melted glacier as the river’s capacity increased by over 100x
- Homes and roads were damaged
- services were disrupted
- crops were destroyed by ash
- roads were washed away
Secondary impacts
- Sporting events were cancelled or affected due to cancelled flights
- Fresh food imports stopped
- industries were affected by a lack of imported raw materials
- Local water supplies were contaminated with fluoride
- Flooding was caused as the glacier melted
- Ash caused respiratory illnesses for some local
Immediate response
- 700 locals evacuated
- 100,000 European flights cancelled during 6-day ban
- Exclusion zone created
Long term responses
- Government rebuilt riverbanks even high than before
What triggers a tsunami
- volcanic eruptions or underwater earthquakes, because they’re usually linked to tectonic events, they tend to occur along plate boundaries
- tsunamis are caused by underwater landslides
- meteor or asteroid strikes which suddenly displace large amounts of seawater
How does a tsunami form
- After the trigger event, water is displaced
- The displaced water increases the height of the water column and waves radiate in all directions
- Waves travel through the water very quickly however the waves are very small in shallow water
- When the waves reach shallow coastal areas, they slow down and increase in height. This process is known as shoaling
What factors influence the impact of a tsunami
- Whether an earthquake is relatively close to the shore or not
- The degree of coastal ecosystem buffer, for example protection from mangroves and coral reefs
- The extent to which warnings can be given
- The duration of the earthquake event
- The wave amplitude, water column displacement and the distance travelled
- The degree of coastal development and land use and population density
- The physical geography of the coast, especially water depth and gradient at the shoreline (e.g. where there is a quick change from deep ocean to shallow shore this will cause rapid shoaling)
- The timing of the event - night versus day and the quality of early warning systems
Characteristics of a tsunami
- Open water: up to 250km wavelength, under 1m wave height, 800km/hr
- Shallow water: short wavelength, wave height 3-10 m, 30-50km/hr
Tsunami case study - Indian Ocean 2004
On 26 December 2004 there was a massive and sudden movement of the Earth’s crust under the Indian Ocean. This earthquake was recorded at magnitude 9 on the Richter Scale and as it happened under the ocean, caused a devastating sea wave called a tsunami. The rupture of the Sunda Megathrust fault caused the seabed to rise by 15m for over 1500 km. This caused a 30m wave.
Primary impacts
- Some smaller islands in the Indian Ocean were completely destroyed.
- 1.7 million people were made homeless
- 230,000 people died
- Electricity power lines and lines of communication were cut off
- Roads and railways were destroyed
- 120,000 people lost their jobs as tourist hotels in Thailand were destroyed and fishing vessels were washed ashore.
Secondary impacts
- There was an outbreak of diseases such as cholera due to a lack of fresh water supplies.
- There was a lack of food as many fish died and farms were destroyed and most vegetation and top soil was removed up to 800m
- ecosystems such as coral reefs and forests were severely damaged
Immediate responses
- Fresh water, water purification tablets, food, sheeting and tents poured in aid
- Medical teams and forensic scientists arrived
- The UK government promised £75 million and public donations of £100 million followed
- The US provided aircraft for Search and Rescue, surveying, and transport of aid cargo.
Long term responses
- A year later £372 million had been donated by the British public, but only £128 million had been spent by the Disasters Emergency Committee (DEC) - there were organisational issues following the collection of such a large sum of money.
- Rebuilding is progressing, and the DEC has spent more than £40 million on projects in Sri Lanka and Indonesia, and plans were made to spend a further £190 million the following year building 20,000 houses.
- The Indian Ocean Tsunami Warning System was set up in June 2006, as before there had been no early-warning system.
- Ensuring people know how to respond, and that local authorities have plans in place are essential to its success.
