Tectonics

Thursday 22nd May

The earth as a scotch eggThe crust of our earth is very shallow like the breadcrumb layer of the scotch egg. It is what we live on.

The mantle is like the meaty bit of our scotch egg. It is the largest section and is made of liquid rock called magma. It is underneath the crust and behaves a bit like jam

The outer core is what lies beneath the mantle. This is the white of our egg. This is also liquid rock but moves very slowly because it is under so much pressure.

The inner core of the earth is solid because of the pressure. It is also hotter than the surface of the sun

Cross Section of the Earth Crust – very thin like the breadcrumbs of our scotch egg.

6-70km thick

Mantle – very high temps. Looks

like jam! Between 5000 and 1300oC

Outer Core – Liquid made

mostly of iron

Inner Core – Solid made

of iron. Up to 5500oC

Distribution of Earthquakes and Volcanoes

Distributed on the plate boundaries

Mostly on the coasts or in the ocean

Around the edge of the pacific and through the middle of the Atlantic

With the exception of Hawaii which is on a hotspot

Convection Currents

Mantle

Crust

Why the plates move

• Magma from the earths core is super heated and rises towards the crust• As it rises and travels away from the core it begins to cool• When it reaches the crust it is forced sideways and because it is not colder, sinks back

down again towards the core.• Where is spreads out you will find divergent boundaries and where is sinks

downwards it full down crust from a convergent boundary.

Oceanic and Continental Crust

Continental Crust:

• 25 -100km thick

• Less dense

• Bigger crystals

• More easily eroded

• Youngest

Oceanic Crust:

• 5 -10km thick

• More dense

• Tiny crystals

• Very hard rock

• Very old rock

Divergent Plate Boundaries

The plates moving apart in this way is known as sea floor spreading.

It is the reason for Iceland's existence and the reason why volcanoes are present there.

The island of Sursey, off the coast of iceland erupted in 1963. Before then there had been no land in that place.

Convergent Plate Boundary – two continental crusts

Convergent Plate Boundaries – one oceanic, one continental crust

It is on convergent plate boundaries that you find the deepest ocean trenches and some of the most active volcanoes in the world.

The Cascade Mountain range is off the west coast of America and is a line of volcanic mountains caused by the convergent plate margin.

Because a lot of earthquakes occur under the ocean it is only destructive plate margins that cause tsunamis.

Conservative Plate Boundaries

The San Andreas Fault in California is the best known example of a constructive plate margin.

The can also be found near Fiji, Israel, South Island in New Zealand and Sumatra in Indonesia.

Type of plate boundary

Diagram Description of changes

EQ/Volcano activity

Examples

Convergent

•Oceanic plate forced downwards into the mantle forming a subduction zone.•Deep trench formed•Continental plate forced up into mountain range

Constructive

Conservative

Pacific and North American Plates along the San Andreas Fault

•Two plates move away from each other•New oceanic crust is created forming mid-oceanic ridges with volcanoes

Two plates move sideways past each other – land is neither formed nor destroyed.

•Heat from the mantle and friction from contact between the two plates causes violent earthquakes to be triggered. •These can also cause tsunamis•The melting plate creates magma which rises to the surface to form volcanoes

•Where magma builds up above the surface, volcanoes form.•In the ocean these quite often show as islands

Plates do not tend to move past each other smoothly. Friction is created and they tend to get stuck. Pressure builds until the plate flips forward creating violent EQ’s

Pacific ring of FireJapanese Island ArcNew Zealand

IcelandGreat Rift Valley Africa

Measuring Earthquakes

Richter ScaleMeasures strength using numbers

No upper limit

Mercalli ScaleMeasures effects using roman numerals. Limited because there is only so much damage that can

be done

How do earthquakes happen?

1) Pressure builds up at plate boundaries.2) The plates cannot move though due to

friction, and pressure continues to build.3) Suddenly the crust breaks along a fault.4) The plates spring apart.5) Stored energy is released in a few seconds

from the focus, and travels out from the epicentre as seismic waves on the surface.

Silicon Valley, home of IBM and Apple. 23,000 jobs and 700,000 people. On the San Andreas Fault. There has not

been a large earthquake here for over 30 years.

The Soufriere Hills on the island of Montserrat erupted in 1995 in one of the most devastating eruptions ever seen. It entirely covered the capital city of Plymouth in ash and closed the airport. It was known that the island was highly volcanic but no-one wanted to leave the island even after the

eruption. Their families and their livelihoods were there and they had nowhere else to go.

Sorrento and the Island of Capri in Italy.

Massive tourist destination and people are attracted because of the beautiful beaches and amazing weather. It also has a historic interest with many people coming to visit Pompeii; the ancient roman port that got destroyed by the volcano in 79AD.

Across the bay from Mt Vesuvius

It has not erupted violently for over 50 years.

Mount Etna in Italy, Europe's most active volcano but ‘safe’ enough for tourists to go and watch. Many farmers also grow olives, grapes and citrus fruits because the volcanic ash produces

extremely fertile soil here. Siciliy is quite a poor area of Italy too with a very close knit community.

Iceland straddles the Mid Atlantic ridge; a divergent plate boundary. The magma near the surface heats water in the rock causing warm pools of water to rise up. People visit Iceland to bathe in

these pools. The hot water can also be harnessed for geothermal energy. This is extremely environmentally friendly and renewable.

Haiti - LIC Earthquake Case Study

Effects Responses

• The main port was closed after severe damage to the docks and a crane.

• Some roads are impassable - either because of earthquake damage, or because they are blocked by rubble or smashed vehicles.

• Between 500,000 and 700,000 people are believed to have been left homeless

• Even before the earthquake only half of Haitians had access to clean water. Now most of the remaining water supply been cut off.

• Eight hospitals or health centres in the capital collapsed or suffered severe damage.

• US engineers and dive teams fixed piers, cranes, and buildings.

• Around 3,000 UN troops and police worked to clear some of the major roads.

• More than 500 makeshift camps have been identified by the Haitian government, which has requested large tents be set up as reception centres for the homeless.

• On 20 January, 755,000 litres of water were provided to 151,000 people.

• Field hospitals have been set up by teams from Russia, Israel, Colombia, Jordan and Brazil.

Causes• Haiti is located on a conservative plate margin between the Caribbean and

North America plate which are slowly moving past each other.• 7.0 magnitude which stuck on Tuesday 12th January at 16:53 (Haiti Time)

Iceland – HIC Volcano Case StudyCauses•Iceland lies on a divergent plate boundary between the North American and Eurasian plates which are moving apart at a rate of 2cm per year.•As they move apart, lava wells up in the gap in between towards the surface.•As this process continues and consecutive lava eruptions cool and build up, volcanoes are created.

Effects•The cloud of ash went 20,000ft into the atmosphere and blew on westerly winds cross Europe.•95,000 flights had to be cancelled in the UK as the ash was at the height that plans normally fly at.•The flight ban was imposed because in the high temperatures of an engine turbine, ash can turn to molten glass and cripple the engine. •The airline industry said its losses soared to over £650 million•Other transport companies benefitted as passengers looked for alternatives to flying. •Eurostar in particular saw a huge demand from and said it carried 50,000 extra passengers just on one day alone.•Kenyan farmers were forced to dump stocks of fresh food and flowers destined for European consumers which cost the Kenyan economy $3.8m a day as a result of flight cancellations to Europe.•Locally 700 farmers around the volcano were evacuated due to the melting ice cap on top of the mountain which caused flooding and property to be washed away.

Responses•Some 60 volunteers and staff of the Icelandic Red Cross provided food for the farming population living in the vicinity of the glacier. •Some 700 people were evacuated from the disaster zone three times in the past month. •A 24-hour emergency information hotline was also activated. Red Cross volunteers are also providing meals twice a day in Heimaland, as most people have not been able to stock up on food.

Prediction - VolcanoesVolcanoes can be monitored to predict eruptions with:• GPS - to see if the ground is rising up as magma approaches the surface• Gas sampling – changes to gases coming out of the volcano might mean

an eruption is coming• Geothermal monitoring – the ground gets hotter as magma rises to the

surface• Seismic monitoring – to ‘listen’ to the rising blobs of magma as they force

their way upwards and cause small earthquakes• Looking at historical records to see if there is a past pattern of eruptions that might be repeated.

Prevention - VolcanoesOnce an eruption has happened it is possible to prevent it from having major effects on the local people by;• Spraying the lava with water to cool it down and stop it flowing• Putting concrete barriers in the path of lava forcing it away from villages• Setting off explosive to divert the lava flow• Digging ditches to funnel it away from homes

Prediction - EarthquakesEarthquakes are much harder to predict because they happen underground so are not visible. Methods used to predict earthquakes include;• Noting strange animal behaviour – cats, dogs, birds and snakes are known

to behave differently before an earthquake• Monitoring electrical discharges – there is some evidence that these

increase before an earthquake. Some scientists believe that they appear in the sky as a rainbow glow, known as earthquake lights.

• Recording minor tremors as these could be small foreshocks

Planning for EarthquakesBecause so little warning can be given it is better to plan for the worse to limit the effects such as;• Providing education for local residence who

are taught how to react• Have an emergency kit ready including a

torch, bottled water, first aid kit and tinned food.

• Design buildings that can withstand earthquakes by having flexible steel frames; shutters can be used to cover windows that might shatter; rubberised foundations can be used to absorb the energy of a quake

• Planning regulations so buildings are not built too high.