Tectonic hazards

Question 1

What is an earthquake?

Answer 1

An earthquake is a sudden and violent period of ground shaking. It is most commonly caused by a sudden movement of rocks within the Earth’s crust. This occurs mainly at the margins of tectonic plates where plates are moving and enormous pressures build up and are released.

Question 2

Why is there a pattern of earthquakes?

Answer 2

Pattern of earthquakes along plate margins, for example the western coast of North and South America. The occurrence of earthquakes around the edge of the Pacific Ocean follows the plate margins. Some earthquakes may not occur at plate margins they may be caused by human activity such as underground mining or oil extraction.

Question 3

What are tectonic plates?

Answer 3

• Earth’s crust split into a number of plates about 100km thick
• two types of crust- dense, thick oceanic crust and less dense, thick continental crust
• plates move in relation to each other due to convection (heat) currents from deep within the Earth.
• At a constructive plate margin, plates move apart. New crust is formed as magma rises through the surface.
• At a destructive plate margin, where plates are moving towards each other, the denser oceanic plate may sink (subduct) beneath a less dense continental plate. Gravity pulls the oceanic plate into the mantle, dragging the plate away from the constructive margin.
• tectonic activity at plate margins causes earthquakes and volcanoes.

Question 4

Where do volcanoes happen?

What is a volcano

Answer 4

Page 11 for map c on distribution of volcanoes.
A volcano is a large and often conical-shaped landform usually formed over a long period of time by a series of eruptions. Like earthquakes the majority of volcanoes occur in long belts that follow the plate margins, for example around the edge of the Pacific Ocean. Also known as the ‘Pacific Ring Of Fire’. There is also a belt of volcanoes through the middle of the Atlantic Ocean. This is the Mid-Atlantic Ridge which includes the Azores and Iceland which are volcanic islands.

Question 5

Why is there a pattern of volcanoes?

Answer 5

Volcanoes are fed by hot molten rock (magma) from deep within the Earth. This rises to the surface at constructive and destructive plate margins. Volcanoes also forms at hot spots, where the crust is thin and magma is able to break through to the surface. The Hawaiian Islands in the Pacific Ocean are a good example of a hot spot.

Question 6

What happens at a plate margin?

Answer 6

example: Iceland
It is a country in the North Atlantic Ocean, situated on the Mid-Atlantic Ridge, a plate margin where two plates are moving away from each other. There are several active volcanoes in Iceland including EYJAFJALLAJÖKULL, which erupted in 2010. It is possible to identify three main types of plate margin (next card)

Question 7

What are the three main types of plate margin?

Answer 7

• Constructive (transform) - where two plates are moving apart
• Destructive- where two plates are moving towards one another
• Conservative- where two plates are sliding alongside each other.

Question 8

Constructive margin

Answer 8

• two plates moving apart
• page 12- diagram B - shows what is happening at the constructive margin in the mid-Atlantic. Magma is forcing its way to the surface along the Mid-Atlantic Ridge. As it breaks through the overlying crust it causes earthquakes. On reaching the surface it forms volcanoes such as Eyjafjallajökull in Iceland.
• The magma at constructive margins is very hot and fluid. Lava erupting from a volcano will flow a long way before cooling. This results in typically BROAD and FLAT SHIELD volcanoes.

Question 9

Destructive margin- subduction

Answer 9

• two plates move towards one another
• Diagram C page 13 shows what is happening on the west coast of South America.
• where the two plates meet a deep ocean trench has formed
• oceanic Nazca plate, which is relatively dense, is subjected beneath the less dense South American Plate.
• friction between the 2 plates causes strong earthquakes
• as the oceanic plates move downwards it melts
• creates magma which is less fluid than at a constructive margin, breaks through to the surface to form STEEP SIDED COMPOSITE volcanoes- eruptions are often very violent and explosive.

Question 10

destructive margin- collision

Answer 10

• Where 2 continental plates meet, there is no subduction
• instead when they collide, the crust becomes crumpled and uplifted.
• this forms mountains such as the HIMALAYAS.
• these mountain-building processes causes earthquakes but no volcanoes as at these collision margins there is no magma.

Question 11

conservative margin

Answer 11

• 2 plates moving past each other
• friction between plates causes earthquakes
• map d page 13 shows the San Andreas Fault in California
• the faster moving PACIFIC PLATE is sliding in the same direction next to the slower-moving North American Plate
• earthquakes happen along conservative plate margins as stresses gradually build up over many years.
• can be destructive as they are close to the Earth’s surface
• released suddenly when the plates slip and shift
• no volcanoes as no magma

Question 12

Effect of earthquakes-

Answer 12

Earthquakes can have devastating effects on peoples’ lives and activities. Primary effects are caused by the ground shaking and can include deaths and injuries, and damage to roads and buildings. Secondary effects are the result of primary effects (ground shaking) and include tsunami, fires and landslides.

Question 13

Chile earthquake- basic info

Answer 13

• 27th February 2010
• 8.8 on the Richter scale
• off the coast of central chile
• on a destructive plate margin where the Nazca plata subducted beneath the South American plate.
• followed by a series of smaller aftershocks
• occurred out to sea, tsunami warnings issued
• waves raced across the Pacific ocean at speeds of up to 800km per hour.

Question 14

Chile primary effects

Answer 14

• 500 people killed
• 12000 injured
• 800000 affected
• 220000 homes, 4500 schools, 53 ports, 56 hospitals and other public buildings destroyed
• ports of Talcahuanao and Santiago airport badly damaged.
• much of chile lost power, water supplies and communications
• cost estimated at US$30 billion

Question 15

Chile secondary effects

Answer 15

• 1500km of roads damaged- mainly by landslides
• remote communities cut off for many days
• several coastal towns devastated by tsunami waves
• several pacific countries struck by tsunami- warnings prevented loss of life
• fire at a chemical plant near Santiago- area had to be evacuated.

Question 16

Nepal earthquake- basic info

Answer 16

• 25th April 2015
• 7.9 richter scale
• epicentre 80 km (50 miles) to the north-west of Nepal’s capital Kathmandu in the foothills of the Himalayas
• destuctive plate margin- Indo-Australian plate colliding with the Eurasian plate at a rate of about 45mm per year
• collision and pressure responsible for the formation of the himalayas
• earthquake was very shallow, 15km below the surface
• resulted in very severe ground shaking and widespread landslides and avalanches.
• earthquake caused damage hundreds of kilometres away in India, Tibet and Pakistan.

Question 17

Nepal primary effects

Answer 17

• 9000 people died
• 20,000 injured
• 8 million people (1/3 of Nepal’s pop) affected
• 3 million homeless
• electricity, water supplies, sanitation and communications affected
• 1.4 mill people needed food water and shelter
• 7000 schools destroyed
• international airport congested as aid arrived
• 50% of shops destroyed, affecting food supplies and people’s livelihoods
• cost of damage estimated over US$5 billion.

Question 18

Nepal secondary effects

Answer 18

• ground shaking triggered landslides and avalanches, blocking roads and hampering relief efforts
• avalanches on Mt Everest killed at least 19 people
• an avalanche in the Langtang region left 250 people missing
• a landslide blocked Kali Gandaki river- 140 km (90 miles) NW of the capital Kathmandu- people evacuated in case of flooding
• earthquake occurred on land so no tsunami

Question 19

Response to earthquakes

Answer 19

immediate responses- search and rescue and keeping survivors alive by providing medical care, food, water and shelter

long- term responses - re-building and reconstruction, with the aim of returning people’s lives back to normal and reducing future risk.

Question 20

chile immediate response

Answer 20

• emergency services acted swiftly, international help needed to supply field hospitals, satellite phones and floating bridges
• temporary repairs made to Route 5 north-south highway within 24 hours, enabling aid to be transported from santiago to affected areas
• power and water restored to 90% of homes within 10 days
• national appeal raised US$60 million- enough to build 30,000 small emergency shelters.

Question 21

chile long- term responses

Answer 21

• month after earthquake, government launched a housing reconstruction plan to help nearly 200,000 households affected by the earthquakes
• chile’s strong economy based on copper exports could be rebuilt without the need for much foreign aid
• president announced it could take 4 years for chile to recover fully from the damage to buildings and to ports

Question 22

nepal immediate responses

Answer 22

• search and rescue teams, water and medical support arrived quickly from countries such as UK, India and china
• helicopters rescued many people caught up in avalanches on Mt Everest
• half a million tents needed to provide shelter for the homeless
• financial aid pledged from many countries
• field hospitals set up to support overcrowded main hospitals
• 300,000 people migrated from Kathmandu to seek shelter and support from family and friends
• social media widely used in the search and rescue operations and satellites mapped damaged areas.

Question 23

Nepal long- term responses

Answer 23

• roads repaired and landslides cleared
• lakes, formed by landslides damming river valleys, needed to be emptied to avoid flooding
• thousands of homeless people to be re-housed, and damaged homes repaired.
• Over 7000 schools to be re-built or repaired.
• stricter controls on building codes
• june 2015- hosted international conference to discuss reconstruction and seek technical and financial support from other countries
• tourism to be boosted, by july 2015 some heritage sites re-opned and tourists starting to return
• repairs to Everest base camp and trekking routes- by August 2015 new routes established and the mountain re-opened for climbers
• late 2015 blockade at indian border badly affected supplies of fuels, medicines and construction materials.

Question 24

living with the risk from tectonic hazard

Answer 24

The majority of tectonic hazards occur at plate margins which criss-cross the Earth’s surface. Some margins run through densely populated regions such as Japan, parts of China, and southern Europe.

Question 25

why do people choose to live in hazardous areas?

Answer 25

• earthquakes and volcanic eruptions don’t happen very often- not seen as a great threat to people’s lives
• people living in poverty have other things to think about- money, food, security and family
• plate margins often coincide with very favourable areas for settlement, such as coastal areas where ports have been developed
• some people may not be aware of the risks of living close to a plate margin.
• volcanoes can bring benefits such as fertile soil, ideal for farming, rocks for building, rich mineral deposits and hot water
• fault lines associated with earthquakes can allow water supplies to reach the surface, particularly important in dry desert regions
• more effective monitoring of volcanoes and tsunami waves enable people to receive warnings and evacuate before events happen.
• better building design can withstand earthquakes so people feel less at risk.

Question 26

Life of a plate margin in Iceland

Answer 26

• lies on Mid- Atlantic Ridge- constructive plate margin
• over 320000 people live on Iceland and close to 1 million people visit each year
• tectonic activity brings benefits to the country:
• hot water from within the earth’s crust provides heat and hot water for nearly 90% of all buildings in Iceland
• Volcanic rocks are used in construction for roads and buildings
• Iceland’s dramatic landscape with waterfalls, volcanos, mountain glaciers brings in huge number of people and creates many jobs in the tourism industry.
• naturally occurring hot water- reaches through cracks created by earthquakes allows for the heating of greenhouses and swimming pools
• geothermal energy is used to generate 25% of the country’s electricity (most of the rest is from hydroelectric power)
• thousands of tourists visited after the recent eruption of Eyjafjallajökull in 2010

Question 27

Reducing the risk form tectonic hazards

Answer 27

monitoring- using scientific equipment to detect warning signs of events such as volcanic eruptions

prediction- using historical evidence and monitoring, scientists can make predictions about when and where a tectonic hazard may happen

protection- designing buildings that will withstand tectonic hazards.

planning- identifying and avoiding places most at risk

Question 28

Monitoring- volcanoes

Answer 28

• as magma rises through a volcano it gives off a number of warning signs that an eruption is likely to occur.

remote censoring- satellites detect heat and change’s to volcanoes shape

seismicity- seismographs record earthquakes

ground deformation- changes to the shape of the volcano are measured using laser beams

geophysical measurements- detect changes in gravity as magma rises to the surface

gas- instruments detect gases released as magma rises

hydrology- measurements of gases dissolved in water

Question 29

monitoring- earthquakes

Answer 29

• generally occur without warning
• some evidence of changes in water pressure, ground deformation and minor tremors prior to an earthquake.
• scientists have yet to discover reliable ways to monitor and predict earthquakes

Question 30

prediction- volcanoes

Answer 30

• prediction of volcanic eruption is based on scientific monitoring.
• in 2010 an increase in earthquake activity beneath Eyjafjallajökull ice cap in Iceland enabled scientists to make an accurate prediction about the eruptions that took place in March and April that year

Question 31

prediction- earthquakes

Answer 31

• impossible to make accurate predictions about earthquakes due to the lack of clear warning signs
• scientists studying historical records of earthquakes at plate margins have identified locations that they believe are at greatest risk.
• map B page 20

Question 32

protection- volcanoes

Answer 32

• sheer power of a volcanic eruption means that there if often little than can be done to protect people and property
• possible to use earth embankments or explosives to divert lava flows away from property.
• has been done on the slopes of Mount Etna in Italy.

Question 33

protection- earthquakes

Answer 33

• main way to reduce risk
• construct buildings and bridges to resists the ground shaking associated with an earthquake
• In chile, new buildings have:
  – reinforced concrete columns strengthened by a steel frame
  Earthquake resistant building:
  – walls reinforced with steel and concrete to reduce movement
  – shock absorbers to absorb ground shaking
• rolling weights on roof to counteract shock waves
• automatic shutters come down over windows to prevent broken glass falling
• open areas for easy evacuation
  -reinforced foundations

Question 34

planning- volcanoes

Answer 34

• hazard maps have been produced for many of the world’s most dangerous volcanoes, showing the likely areas to be affected.
• can be used in planning to restrict certain land uses or to identify which areas nee to be evacuated when an eruption is about to happen

Question 35

planning- earthquakes

Answer 35

• maps can be produced to show the effects of an earthquake or identify those areas most at risk from damage. High- value land uses such as hospitals, reservoirs and office blocks can then be protected in these vulnerable areas.