The Challenge of Natural Hazards - Plate Tectonics

The Challenge of Natural Hazards Plate Tectonics Use pages 17 - 23 in your Blue revision guide Sarah Bullough

Explain what the term ‘natural hazard’ means.

The term natural hazard means a severe event which makes a change to the environment and occurs naturally.

Give 5 examples of natural hazards.

Mudslides, volcanic eruptions, hurricanes, earthquakes, tsunamis.

What are the factors that affect the risk of hazards? ● Urbanisation: denser areas puts a larger concentration of people at risk. ● Poverty: houses are expensive, cheaper houses may be built on risky and unsafe ground, so more damage could take place after a natural hazard occurs. ● Farming: the attraction of nutrient-rich floodplains put more people at risk of floods and building/crop damage. ● Climate Change: global warming causes sea level increase and generates more extreme weather. This can lead to more natural hazards, such as floods, to take place.

What is a plate margin? What happens at plate margins?

Plate margins are borders between the 7 major and 7 minor tectonic plates.

Between plates there are different types of margins such as constructive margins, destructive margins and conservative margins. Constructive margins cause 2 plates to move apart, destructive margins cause 2 plates to move together and conservative margins cause 2 plates to move past each other.

There are two types of crust on plate margins, oceanic crust and continental crust. Oceanic crust is dense and thin compared to continental crust. The plates all move due to convection currents in the mantle.

Describe the structure of the earth’s interior (find a diagram to help you!).

On the outer layer of the earth there is the crust, the crust is hard and can either be continental or oceanic. After the crust is the mantle, the mantle is hard, solid magma rock, this is where convection currents are. After the mantle there is the outer core, the outer core is the only liquid layer and consists of mainly metals. The outer core is the reason for the earth's magnetic field. The inner core is the middle of the earth and is mostly solid metal.

How do convection currents move the earth’s plates?

Heat rising and falling inside the mantle causes convection currents.

Convection currents are generated by radioactive decay in the core.

When the convection currents diverge near the earth’s crust the plates move apart and when the convection currents converge near the earth’s crust the plates move away.

Describe the global distribution of the earth’s plates (a map might help here!).

The earth is made up of 7 major and 7 minor tectonic plates. Earthquakes and volcanoes usually can be found at plate boundaries. The 7 major plates are African, Antarctic, Eurasian, Indo-Australian, North American, South American and Pacific.

What are the differences between continental plates and oceanic plates?

Continental plates are thicker and less dense than oceanic plates. Continental plates also have greater buoyancy than oceanic crust.

What happens at a DESTRUCTIVE margin?

A diagram might help!

Two plates move towards each other due to convection currents, one continental and the other oceanic crust. The denser oceanic crust is pushed underneath the lighter continental crust causing friction between the two plates. This friction, which takes place in the subduction zone, can cause earthquakes. As the oceanic crust moves further down it pushes the continental crust forming fold mountains.

The oceanic crust sinks further into the mantle and melts, turning into magma. The magma in the mantle begins to rise up the continental crust creating a volcano and erupting violently.

What happens at a CONSTRUCTIVE margin?

A diagram might help!

Two plate margins move apart and magma is forced to the surface, due to convection currents. As the magma rises the crust breaks apart causing mild earthquakes. The magma rises even more forming a volcano, The hot lava flow takes a while to cool, this typically leads to a broad and flat shield volcano, e.g.

Mid-Atlantic ridge.

What happens at a CONSERVATIVE margin?

A diagram might help!

Two plates move past each other creating friction. The friction between the two plates triggers earthquakes. The plates can either move along with each other or in opposite directions.

Investigate the Nepal and Chile Earthquakes for the next set of slides!

Use pages 20 and 21 in your revision guide

Wealth, Cause and Size Chile:

Nepal:

Wealth- 38th out of 193 countries

Wealth- 109th out of 193 countries

Cause- Nazca Plate subduction beneath the South American Plate

Cause- Indo-Australian Plate colliding with the Eurasian Plate

Size- Magnitude 8.8

Size- Magnitude 7.9

Primary Effects Chile:

Nepal:

-500 killed, 12000 injured and 800000 people affected

-9000 killed, 20000 injured, 8000000 people affected

-Significant destruction of buildings and infrastructure

-Widespread destruction of buildings and infrastructure

-Power,water and communications cut.

-Power, water, sanitation and communications cut

Secondary Effects Chile:

Nepal:

-Communication cut off by landslide

-Communications cut off by landslides and avalanches

-Coastal towns devastated by tsunami

-Avalanches on mount Everest killed at least 19 people

-Chemical plant fire near Santiago forced evacuations.

-Flooding caused by (landslide) blocked rivers

Immediate Responses Chile:

Nepal:

-Swift and effective response by emergency services

-Overseas aid included widely active NGOs(e.g Oxfam)

-key roads repaired within 24 hours

-Aid included helicopters for search, rescue and supply drops in remote areas, such as Mount Everest

-Most power and water restored within 10 days -60 million dollar national appeal built 30000 emergency wooden shelters

-300000 people migrated from Kathmandu for shelter and support from friends and family.

Long-term Responses Chile:

Nepal:

-Strong economy reduced need for foreign aid

-Roads repaired, landslides cleared and flood lakes drained

-Government reconstruction plan to help 200000 households

-International conference to seek technical and financial support

-Full recovery within four years likely

-Indian border blockade in 2015 caused crippling fuel, medicine and construction material shortage.

Why do people continue to live in areas at risk from tectonic activity? (page 22) -Poor people have no choice in where they live- money, food and family are more important than where they live -Earthquakes and volcanic eruptions are rare- not seen as a threat -Earthquake-resistant buildings -some people have no knowledge or experiences of the risks -volcanoes can bring benefits such as fertile soil, rich mineral deposits and hot water.

How does geothermal power help people in Iceland?

Geothermal power generates 25% of Iceland’s electricity

How can EARTHQUAKES be monitored?

A number of events can occur before an Earthquake strikes such as: -microquakes before the main tremor, -bulging of the ground, -raised groundwater levels.

How can EARTHQUAKES be predicted?

Historical records can help determine probability of where and when earthquakes will occur and help to plan for them.

How people be protected from EARTHQUAKES? Earthquake drills help keep people alert and prepared for an earthquake.

Earthquake-resistant construction is the best way to reduce the risk.

How can EARTHQUAKES be planned for?

RIsk assessment and hazard mapping can help to identify areas where buildings and infrastructure need extra protection.