Tectonic Plates

A German meteorologist, Alfred Wegener, suggested that the continents may not have always been in the same place as we see them today. He believed that they had once all been joined together in a single landmass. He made his claim in the early part of the 20th century but scientists of the time dismissed his ideas as being silly.

Less than fifty years later, scientists realised that all of the evidence suggested that Wegener was correct and in the 1960s, evidence of seafloor spreading was the final piece of evidence that showed he was correct. This led to the development of the theory of plate tectonics and we now take these ideas for granted. For your GCSE, you are expected to know how this theory explains how the natural hazards of volcanoes and earthquakes occur as well as understanding how humans deal with them.

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This quiz is only concerned with the physical geography of what has been termed the Restless Earth.

The Earth is made from distinct layers, one of which is the crust. This is the outer solid and cool layer of rocks. It is broken into large segments called plates. Some plates are comparable in size to the size of a small country whilst others are several times larger than any continent. Beneath the crust lies the mantle. The rocks here are extremely hot and slowly flow in giant convection currents. It is believed that these currents are the 'engine' that moves the plates around the surface of the Earth, carrying the continents with them.

Where plates meet, we say there is a plate boundary. There are three types of plate boundary (also called plate margins), constructive, destructive and conservative. Each type of plate boundary creates its own unique landforms - fold mountains, ocean trenches, shield and composite volcanoes, fissure volcanoes to name just a few.

At a constructive boundary, the plates move apart, magma pushes up between the plates, solidifies and so new material is added to the plates. There are non-explosive volcanoes and small earthquakes associated with this type of plate boundary. An example is the mid-Atlantic ridge.

Where plates slide past each other, no new material is added and no material is lost. This is why it is called a conservative boundary. There are no volcanoes of any type created by this type of plate movement but there are earthquakes, including some really big ones. The usual example of this sort of boundary is the San Andreas fault of North America.

When two plates meet head-on, you get a destructive boundary. One plate is pushed below the other and destroyed by melting in the mantle. The sediments lying on the plates are crumpled up to form mountain ranges. OK, the situation is much more complex than that but keeping that picture in your mind works at GCSE. At this type of boundary there are big earthquakes and explosive volcanoes. A good example of this is the Andes mountain range in South America.

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  1. It is said that Yellowstone Park in the USA is the site of a supervolcano that could erupt at some point in the future. A supervolcano eruption:
    It is very possible that a supervolcano eruption would cause global climate change as the dust and gases would block the heat from the sun. There would be a mass extinction of life on Earth
  2. Plates do not move smoothly. The rocks on either side become jammed together and incredibly large forces build up as the plates either side continue to move. When the plates finally become 'unstuck', which of the following natural hazards occurs?
    The tricky part of this question is that you associate both composite volcanoes and earthquakes with this type of plate boundary but it is earthquakes that are formed when rocks move in this way, not volcanoes
  3. What part of the Earth is broken into 'plates'?
    Make sure that you know the different layers of the Earth
  4. What is the name given to the places where the plates meet?
    They are also known as plate margins
  5. What is thought to move the plates around?
    The forces required to move continents are huge
  6. Which pair of words correctly describes the point at which the earthquake occurs and the point on the Earth's surface directly above where it occured?
    Make sure that you are familiar with these terms, the examiners love to test you on them!
  7. At which type of plate boundary do you get only earthquakes?
    Plates slide sideways past each other so there is no melting of rocks or gaps through which molten magma can squeeze up from below
  8. Earthquakes are formed in:
    This happens at differing depths. A large earthquake that occurs at shallow depths will have a greater effect at the surface of the Earth
  9. At which type of plate boundary are fold mountains created?
    Good examples of these are the Alps (African plate colliding with the Eurasian plate), the Himalayas (Indian plate hitting the Eurasian plate) and the Andes (the Nazca plate hitting the South American plate)
  10. At which type of plate boundary is one plate pushed down into the mantle?
    The plate that is pushed down into the mantle is the one that is destroyed

Author: Kev Woodward

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