Restless Earth The lithosphere is the upper most layer of the Earth. It is cool and brittle and includes the top part of the mantle and above this the crust. The asthenosphere is a ‘lubricating’ layer beneath the lithosphere. How do we know what the layers are like? There are several clues:
1) Meteorites from space 2) Volcanic eruptions 3) Earthquake waves
How do the tectonic plates move?
Convection currents in the mantle move the tectonic plates a few centimetres a year. The heat that ‘drives’ the plates is caused by radioactive decay of uranium and thorium in the core and mantle. Plumes are concentrated zones of heat. They bring magma to the surface. When magma reaches the surface it is known as lava.
Pangea was a ‘super continent’ (when all the land masses were joined together). This diagram shows the position of the continents 250 million years ago. They are still moving apart today!
Make sure you learn how each of the plate boundaries works and know what sort of tectonic activity occurs at each one!
Volcanoes!
So why do people live so close to active volcanoes? Minerals - minerals such as tin, silver, gold, copper and even diamonds
can be found in volcanic rocks. Geothermal power - heat from underground is used to heat water turning
it into steam to drive turbines and produce electricity, or to heat water supplies that are then used to provide household heating and hot water.
Tourism – Volcanoes attract millions of visitors a year. Around the volcano may be warm bathing lakes, hot springs, bubbling mud pools and steam vents.
Fertile soils – Cool lava needs hundreds of years to become weathered and broken down before they form rich soils. When they do become soils though, they form some of the richest ones on the planet.
Poverty – Some people in LEDC’s are not able to move away from a potentially dangerous volcano as they are too poor.
Religious beliefs – e.g. the Aetas who live around Mt Pinatubo believe the volcano is a ‘God’
Case study: Mt Pinatubo (Indonesia - LEDC)
Case Study: Sakurajima (Japan - MEDC)
Sakurajima is a stratovolcano so is dangerous and explosive. Why do you think people in an MEDC such as Sakurajima live close to it? (write your ideas below)
What effects do volcanic eruptions have?
Social Effects Economic Effects Environmental Effects People are killed by the explosion / pyroclastic flows / lahars and poisonous gases! Homes are destroyed People can be injured from harmful gases / debris etc.
Tourism can be affected (positively and negatively) Crops can be destroyed by lava / ash and pyroclastic flows Communications can be destroyed (e.g. roads / railways)
The environment can be severely altered e.g. forests completely blown away in the blast of the eruption Wildlife will not survive a violent eruption
So how can volcanic eruptions be predicted?
Are there different types of volcano?
There are three different types of volcanoes. The different types of volcanoes are: composite (or stratovolcanoes), shield and cinder cones.
Layers, or strata, of rock and lava form the Composite or Stratovolcanoes. These volcanoes come in a number of shapes. A composite volcano resembles a helmet. The sides of this type of volcano are usually steep, some reaching a pointy peak at the top. This is because the lava is
viscous and so ‘plies’ up quickly forming steep layers. Sakurajim in Japan and Mt Pinatubo in Indonesia are both good examples. Eruptions are particularly intense. As magma rises to the eruption point, it tends to get clogged due to high viscosity. The pressure needed to force the magma out of the volcano is huge, and the result is an explosion of both rock and lava. It is quite dangerous to witness such an eruption up close.
Shield volcanoes are huge in size. They are built by many layers of runny lava flows (the lave is not very viscous). Lava spills out of a central vent or group of vents. A broad shaped, gently sloping cone is formed. This is caused by the very fluid, basaltic lava which can't be piled up into steep mounds. Shields erupt frequently, but tend not to be highly explosive. These are some of the best volcano eruptions to witness at a relatively close, but still safe, range, since lava spray is uncommon. Both Mauna Loa and Kilauea in Hawaii are examples of the shield volcano. Shields also form on the ocean floor, gradually building height through a steady stream of magma.
Cinder cones are likewise relatively gentle in eruption. They tend to occur in mountain ranges with other types of volcanoes. A central vent forms a volcano made up of lava fragments. Cinders grow quickly but tend not to exceed about 800 feet (243.84m) in height. Occasionally, cinders form on ground with no known history of volcanic activity. In 1934, Paricutín erupted out
of a Mexican cornfield and in approximately five days, grew to 300 feet (91.44m) tall.
Tip: You will need to be able to explain how each of the volcano types above
forms.
http://www.wisegeek.com/what-is-magma.htmhttp://www.wisegeek.com/what-is-viscosity.htmhttp://library.thinkquest.org/17457/glossary/glossary.html#lavahttp://library.thinkquest.org/17457/glossary/glossary.html#lavahttp://library.thinkquest.org/17457/glossary/glossary.html#venthttp://library.thinkquest.org/17457/glossary/glossary.html#venthttp://library.thinkquest.org/17457/glossary/glossary.html#basalthttp://library.thinkquest.org/17457/glossary/glossary.html#lava
A comparison of two different volcanoes:
Philippines - Mt Pinatubo Iceland - Eyjafjallajokull Type of volcano: Composite
Type of volcano: Shield
The lava is viscous. This means that as is solidifies the cone becomes steep sided. It erupts with violent force due to the viscosity of the lava (the main vent can often get blocked).
The lava is less viscous and ‘runny’. This means that it flows freely. It will cover a larger surface area and as the lava solidifies it will create a gently sloping volcano.
Tectonic plates responsible: The Philippines plate (oceanic) subducted beneath the Eurasian plate (continental). This is a destructive plate boundary.
Tectonic plates responsible: The Eurasian plate and the North American plates are pulling apart. This is a constructive plate boundary.
Date last erupted: June 1991
Date last erupted April 2010.
Social effects: 1500 people died 50,000 people made homeless Water contaminated
Social effects: 500 – 600 people evacuated Roads closed / travel made difficult People stranded around world due to travel chaos Schools closed in parts of Iceland
Economic effects: 200,000 buildings destroyed Lahars devastated rice harvest 1 million farm animals died 650,000 people lost their jobs
Economic effects: Millions of pounds lost in travel industry Thick layer of ash erupted has made farming impossible in parts of Iceland
Earthquakes!
The focus is the point at which the earthquake starts.
The epicentre is the point directly above the focus point.
Earthquakes are measured using a seismometer.
The magnitude of an earthquake is sown on the Richter Scale.
A comparison of two different earthquakes:
Kobe (Japan) 1995 Sichuan (China) 2008
Magnitude: 7.2
Magnitude: 8.0
Plates responsible: The Philippine plate is subducted beneath the Eurasian plate. This is a destructive plate boundary.
Plates responsible: The Indian plate and the Eurasion plate colliding (Making the Himalayas). This is a collision plate boundary.
Depth of Focus point: 14km
Depth of Focus point: 19km
Location of epicentre: Awaji Island
Location of epicentre: Wenchuan
Deaths: 5,477 Injuries: 35,000 Buildings collapsed: over 172,000 Total damage: 10 billion yen!
Deaths: 70,000 Injuries: 400,000 Building collapsed: 420,000 Total damage: $75 billion
Other facts: Soft ground (unconsolidated land) made the shaking worse.
Other facts: 700 schools collapsed! – This should not have happened due to strict building codes.
Japan is an MEDC whereas China has only recently become an NIC (Newly Industrialised Country) and is still comparatively poor. How do you think their level of development affected the way in which they prepared themselves for earthquakes / coped with the event itself?
Battle for the Biosphere
Restless Earth Question Checklist – make sure you can
answer these using this guide and your exercise books!
1. Draw a diagram to show the layers of the earth.
2. State two differences between oceanic and continental crust.
3. Explain why plates move.
4. Explain the term “ subduction “ when does it occur? You can draw a
diagram if you wish.
5. Why are no volcanoes found at collision boundaries?
6. Describe the main features of shield volcanoes. ( mention shape,
frequency of eruption and type of lava)
7. Describe the main features of composite volcanoes. ( mention shape,
frequency of eruption and type of lava)
8. Which type of country developed or developing is more vulnerable when
experiencing tectonic hazards? Why, use examples you have studied.
9. Compare the effects of a volcanic eruption is a developed and developing
country ? Use named examples.
10.Why are some areas of the world more likely to experience tectonic
hazards than others?
11.Why do earthquakes occur?
12.How are they measured?
13.Explain the terms, epicentre, focus, seismometer, seismograph
14.What is the differences between primary and secondary impacts of a
volcanic eruption or earthquake?
15.Why do earthquakes occur at destructive plate margins?
16.How can earthquakes and volcanoes be predicted and planned for?
17.How can buildings be protected from earthquakes?
