Year 9 - H&G Notes - 6.5.14

Thai Sikh International School

Year 9, Geo Notes. Topic 11. [Plate Tectonics]

1.      Explain how the movements along plate boundaries give rise to earth quakes and volcanoes?

The earth’s surface, called as crust, is a collection of solid tectonic (moving) plates. Around the solid core at the centre of the earth is the layer of the molten magma. This is called the mantle. Through this layer flow convection currents. The plates float on the mantle. The convection currents move these plates away or towards each other. These movements along plate boundaries give rise to earth quakes and volcanoes.

2.      Mention the different plates that form boundaries with the plate you live on.

1. Pacific plate 2. North American plate 3. South American plate 4. African plate 5. Eurasian plate. 6. Indo Australian plate. 7. Antarctic plate. And8. Nazca plate. Thailand is in Eurasian plate.

3. What evidence suggests that the plates are moving apart?

The Red Sea is parting and creating a new ocean basin. The African and Arabian plates are pulling Apart, creating cracks in the earth’s crust. In six weeks an 8 meter crack appeared along a 60 km stretch of desert. The widening is about 30 mm per year but the rate of sea floor spreading is more rapid than that.

4...Explain how Fold Mountains are formed? Give an example for it.

Fold Mountain consists of folded sedimentary rock which can be up to 12000 meters thick. Originally the rocks were deposited beneath the sea or lake in horizontal layers. Converging plates squeezed together and raised these beds up to form Fold Mountains.

Mount Everest, in Himalayas, is the highest mountain above sea level at 8848 meters, is an example of Fold Mountain.

5. Why is Mt Everest still rising?

  Mt Everest was formed about 60 million years ago. It is still rising by a few millimeters each year as the Indian plate continues to move towards the Eurasian plate.

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Topic 11a –A volcano in Chile

  1.      Describe Chile’s location.

Chile is situated in Southern America, bordering the South Pacific Ocean and a small part of the South Atlantic Ocean. The country extends from latitude of 17degree south to Cape Horn at 56 degree. From north to south, Chile extends 4270 km and 177 km east to west.

Chile’s northern neighbors are Peru and Bolivia, and its border with Argentina to the east.

  2.      Chile is called a country of contrasts. Why?

Chile is a country of enormous contrasts. Among the Andes Mountain there are more than 2000 ash and lava volcanoes, of which 500 are active. On 2^nd May 2008, the Chaiten volcano- which was thought to be dormant –surprised everybody by suddenly erupting for the first time in over 9000 years.

  3.      How do ash and lava volcanoes erupt?

These volcanoes form at convergent plate boundaries.  The subduction plate melts and heat and pressure build up due to friction between the plates. The eruption is explosive. Hot lava flows out and lighter ash clouds settle on the lava in layers.

   4.      What is Caldera? How are they formed?

Caldera is the depression or crater found on the top of volcanic mountain. It is usually formed when the top of a volcano is blown off.

   5.      List the damages caused by the Chaiten volcanic eruption.

More than 4000 people had to flee their homes after a huge cloud of ash and lava was thrown into the sky by a long dormant volcano in southern Chile. The ash rose to a height of 20km and was still settling in Chile and Argentina five days later. Cars, houses and trees were coated with ash up to 15 cm thick. Forests were set on fire. Getting people out has been difficult due the terrain. Because the mountains rise immediately from the coast people had to queue to be evacuated by naval ships.

Topic11b- An earthquake in China.

   1.      No country has suffered natural disasters on the scale of China. Explain.

In china tens of millions died from famine, floods and earthquakes in the 20^th century alone. Just ten days after Chaiten volcano erupted, on Monday 12 May 2008 China’s most devastating earthquake in 30 year took place. The epicenter of 7.9 magnitude earthquake was in a mountainous region of Sichuan province. This earthquake killed over 87,000 people.

   2.      How do we measure earthquake energy?

Earthquake energy is measured on the Richter scale. Most are felt between 3.5 and 8 magnitudes. The higher the number the more energy is released and more damage caused. The great Chilean earthquake of 22 May 1960 was measured 9.5.

   3.      The area west of Chengdu, is vulnerable to earthquakes. Why?

The Sichuan area, west of Chengdu, is vulnerable to earthquakes because it is close to the boundary of two converging plates. These have also created many surface cracks or Faults.

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