Base

As you can see, volcanoes and earthquakes:

• Tend to lie along lines
• Are often together
• Occur in the ocean as well as on land
• There is a high concentration around the Pacific ocean - 'The Pacific Ring of Fire'
• The earthquakes in India and Nepal seem more randomly arranged.

Why?

The answer begins with Alfred Wegener in Germany

Wegener analyzed either side of the Atlantic Ocean for rock type, geological structures and fossils. He noticed that there was a significant similarity between matching sides of the continents, especially in fossil plants.

It is important not to confuse the crust with land. Whilst some of it is land (continental crust), most of it is the sea bed (oceanic crust). So the oceans and seas lie on top of the oceanic crust. This diagram may help:

These convection currents tore the crust apart into sections that we call 'tectonic plates'. Those plates are still being moved around by the currents today. Sometimes the plates are being pulled apart, sometimes they are being pushed together, and other times they grind past each other.

Remember this map from last lesson?

Using your knowledge from last lesson, try to suggest why volcanoes and earthquakes are arranged in this way.

The floor of the Atlantic Ocean is getting wider as the plates pull apart and new ocean floor forms. Does this mean the Earth is getting bigger?

• Yes, but by so little that it is not really noticeable.
• No, because the sea eroding the land makes up for it.
• No, because at destructive plate boundaries the ocean floor is being destroyed.
• Yes but beacuse aeroplanes and boats are getting faster, we don't notice it.

The safest place to live is:

• At a conservative boundary.
• At a destructive boundary.
• At a constructive boundary.
• At a collision boundary.

Nobody should live on a destructive plate boundary do you agree?

• Yes, it is much too dangerous.
• Yes, but some people don't have a choice.
• No, there are reasons to live there BECAUSE of the tectonic activity
• No there are some very developed countries on destructive plate boundaries - they seem to be doing ok!

Copy the diagram, on the board, to show the causes of volcanoes in Chile. Add the following labels:

a) Label the oceanic plate, the continental plate and a volcano. b) Mark in melted rock that feeds the volcano. c) Use an x symbol to mark in where earthquakes might happen.

Read the paragraph on the board about how the volcano is caused. Agree, with a partner on which synchronised sentence you could use to explain the causes in your own words. (There is a list of geography synchronised sentences at the end of the workbook).

This is a destructive margin, where the more dense Nazca plate is subducted beneath the Less dense, continental, South American plate. As the plate descends it causes earthquakes, and volcanoes occur here because of melting of the plate in the mantle. These are the causes of this volcano

Use your netbook to find definitions of the following volcanic activity:

Volcanic Plume, Pyroclastic Flow, Lahars, Ash Fall.

At the start of May 2008, Chaitén began erupting violently, producing numerous plumes, pyroclastic flows, minor earthquakes and lahars. The ash cloud was up to 17 kilometers high and was visible on satellite images for hundreds of kilometers over the Atlantic. When the volcano began erupting, it produced high eruption columns of ash, gas and rock. These columns were accompanied by pyroclastic flows, lahars, and abundant ash fall.

Read the information about the effects of the 2008 eruption and complete a secondary effect for 3 of the primary effects below:

The eruption has had serious consequences for the nearby town of Chaitén, even disrupting travel and agriculture in surrounding countries.

The town of Chaitén, located about 10 kilometers southwest of the eruption site, was blanketed with ash.

The ash plume was so thick that Chaitén was a major concern to both the airline industry and the neighbouring country of Argentina. In the first week of the current eruption, five aeroplanes encountered eruption-cloud ash, and several sustained significant engine damage. Airports in Chile, Argentina and Uruguay, up to 2,300 km from the volcano, were forced to close or cancel flights.

Lahars (volcanic ash mud flows) had cut communications in areas and made access difficult whilst ash falls up to 15cm deep had blocked rivers and contaminated water supplies. By 14/05/08 it was confirmed that 90% of Chaitén was flooded due to increased flows of the Rio Blanco or Rio Chaitén but casualties were low with just one death caused by stress. The major impact was on farming, and many farm animals were killed by suffocating on the ash.

Between 80-90% of the town of Chaitén reported damaged, 20-30% being completely destroyed and there was extensive damage to the airport and marine facilities.

Plenary:

Which 2 responses do you think was the most effective and why?

Read the following information and see if you can explain why Iceland was not part of the super-continent Pangaea.

The eruption began on 20th March as a lava eruption. Lava erupted out of a

fissure on the flank of the volcano. However on the 14th April 2010, lava pushed up through the midle of the volcano which was covered with ice. The lava was quickly cooled by the ice and became like a glass plug, blocking the vent. Pressure built up behind the volcanic plug until eventually it exploded through causing ash like tiny fragments of broken glass.

The Icelandic Meteorological Office monitors earth movements as well as the

weather and issues warnings.

The IMO worked closely with the London VAAC (Volcanic Ash Advisory Centre) and the ash cloud was tracked by satellite by many nations.

Local people were warned via social media, TV, radio and text message.

Sirens are sounded when eruptions are imminent.

Locals wore masks when outside to avoid breathing in the ash.

500 farmers and their families were evacuated from the area around the volcano.

Farm animals were prevented from drinking from ash contaminated streams.

Plenary

5 million people in Sichuan Province were left homeless; many people were forced to live in makeshift shelters for many weeks/months using whatever they could get their hands on.

The landslides caused the rivers to fill with mud, which caused them to burst their banks and flood towns and cities downstream. This mud then solidifies around already damaged buildings.

Huge boulders that fell from mountains blocked roads. Many other roads were damaged from the earthquake itself. What added problems did this cause?

Some people received aid and assistance from organisations such as the International Red Cross who came into the area with tents, clean water and food parcels.

Plenary

How did China’s population management policies make the impact of this disaster even more devastating?

Take note - the diagrams continue on the next page.

Only watch this if you have time!

Do any of those advantages explain why people live in earthquake zones?

Do any of these? Circle any that do:

Cross bracing is a really simple, but very effective way of giving a building stability...

Or you can make changes to existing buildings to make them more resistant:

Due to outcries by the parents of the schoolschildren, the government had to investigate and many officials were either sacked from their jobs or put into prison.

Deep ocean trenches of the sea floor showed that Oceanic plates were colliding with continental plates and sliding down under them (subduction)

In the middle of the Atlantic Ocean, scientists found evidence, from the age of the rocks either side of a split in the crust, that the sea floor was spreading. This is the Mid-Atlantic Ridge.

The Continental shelf of the Americas fit closely to Africa and Europe, and Antarctica, Australia, India and Madagascar fit next to the tip of Southern Africa.

Wegener's ideas have now been accepted and we now have detailed maps of the earths tectonic plates and the way that they are moving. There are 4 kinds of plate boundary (the edges of plates, where they come into contact with other plates). Your map shows the types of plate boundaries, the direction the plates are moving and how much they move every year.

Describe the pattern of volcanoes and earthquakes on this map.

Hints:

Where are they?

• Which continents?
• On land or sea?
• Compass points?

How are they arranged?

• Randomly?
• In clusters?
• In lines?
• Are there any anomalies to the pattern?