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KS3 Geography - Tectonic Hazards: Plate Tectonics

A guide to tectonic hazards for your Year 9 course, compiled by your Librarians.

Plate tectonics of the earth

   Earth was formed 4.6 billion years ago from the same nebula cloud of gas and dust that the sun and the other planets were formed. Earth's rocky core formed first, with heavy elements colliding and binding together. Dense material sank to the center, while the lighter pieces created the crust. 

 The flow of the mantle beneath the crust causes plate tectonics, the movement of the large plates of rock on the surface of the Earth. Collisions and friction gave rise to mountains and volcanoes, which spew gases into the atmosphere. Today the earth is still developing due to the plate activities.

Plate tectonics videos

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Theory of plate tectonics

   The theory of continental drift was first suggested by the German meteorologist Alfred Wegener in 1912. Wegener contended that the relative positions of the continents are not rigidly fixed but are slowly moving—at a rate of about one yard per century. This idea laid the groundwork for the modern plate tectonics theory. Scientists believe that Earth's surface is broken into a number of shifting plates, which average about 50 miles in thickness. As years passed, more and more evidence was uncovered to support the idea that the plates move constantly over geologic time. Many of the dramatic geological phenomena we experience on earth — volcanic eruptions, earthquakes, tsunamis, and more — are caused by the plate movements

   The following presentation explains the history of the plate tectonics theory.

The world's tectonic plates

   The movement of the plates, and the activity inside the Earth, is called plate tectonics.

   Plate tectonics cause earthquakes and volcanoes. The point where two plates meet is called a plate boundary. Earthquakes and volcanoes are most likely to occur either on or near plate boundaries.

   Today the earth is generally considered to have 15 major plates, 7 or 8 of which are primary plates and the others are smaller, secondary plates.

   Play with the interactive map to see the world's tectonic plates and the distribution of earthquakes and volcanoes.

Simulation of plate boundaries

   Explore how plates move on the surface of the earth. You can change temperature, composition, thickness, types and movements of the plates. Discover how to create new mountains, volcanoes, or oceans!

Plate Tectonics
 
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Test your knowledge about plate tectonics!

1Which part of the Earth is directly below the crust?

2Which part of the Earth is the hottest?

3What material makes up the mantle?

4A constructive or divergent plate boundary is when:

5A destructive or convergent boundary is when:

6At a conservative plate boundary land is:

7What occurence is common along a conservative plate boundary?

8Which of these statements about a constructive boundary is NOT true?

9The Himalayas were formed on what kind of plate boundary?

10The Mid-Atlantic Ridge or chain of volcanoes formed underneath the Atlantic Ocean is created by what kind of plate boundary?

Structure of the earth

   In the early part of the 20th century, geologists studied the vibrations (seismic waves) generated by earthquakes to learn more about the structure of the earth's interior. They discovered that it is made up of these distinct layers: the crust, the mantle, and the core.

Animation of plate tectonics

   The following animation shows how the earth's surface changed over miliion years time.

Plate boundaries

   The earth's continents are constantly moving due to the motions of the tectonic plates. The border between two tectonic plates is called a boundary. All the tectonic plates are constantly moving — very slowly — around the planet, but in many different directions. Baed to their moving directions, ectonic plate boundaries are grouped into three types and sub types:

 

 

   The following animation explains the motions of three types of plate boundaries.

 

Plate movements

Subduction Zones and Volcanoes

   When an oceanic plate collides with a continental plate, the denser oceanic crust gets bent and subducted beneath the lighter and thicker continental crust. This forms what is called a subduction zone. As the oceanic crust sinks, a deep oceanic trench, or valley, is formed.

   The magma formed at a subduction zone rises up toward the earth's surface and builds up in magma chambers, where it feeds and creates volcanoes on the overriding plate.

   A subduction zone is also generated when two oceanic plates collide - the older plate is forced under the younger one - and it leads to the formation of chains of volcanic islands known as island arcs.

   Since the collision and subduction of plates is not smooth, earthquakes are result from this type of interaction. Earthquakes generated in a subduction zone can also give rise to tsunamis.

Collision Zones and Mountains

   When two continental plates collide, because the rock making up continental plates is generally lighter and less dense than oceanic rock, it is too light to get pulled under the earth and turned into magma. Instead, a collision between two continental plates crunches and folds the rock at the boundary, lifting it up and leading to the formation of mountains and mountain ranges.

   An example of this mountain-building process is the Himalayan range in southern Asia. Containing the highest mountain peaks in the world and traversing the modern-day countries of India, Pakistan, China (Tibet), Bhutan, and Nepal, the Himalayas were formed by the collision of the Indian and Eurasian Plates. This process began after the breakup of Pangaea, when India became an island continent and began traveling northward toward Asia. The island of India slammed into Asia about 40 to 50 million years ago near modern-day Tibet, crushing and folding the plates to form the Himalayan mountain range.

Seafloor Spreading

   Divergent boundaries in the middle of the ocean contribute to seafloor spreading. As plates made of oceanic crust pull apart, a crack in the ocean floor appears. Magma then oozes up from the mantle to fill in the space between the plates, forming a raised ridge called a mid-ocean ridge.

Rifts

   When two continental plates diverge, a valleylike rift develops. This rift is a dropped zone where the plates are pulling apart. As the crust widens and thins, valleys form in and around the area, as do volcanoes. Early in the rift formation, streams and rivers flow into the low valleys and long, narrow lakes can be created. Eventually, the widening crust along the boundary may become thin enough that a piece of the continent breaks off, forming a new tectonic plate.

Faults and Earthquakes

   Transform boundaries and the resulting faults produce many earthquakes because edges of tectonic plates are jagged rather than smooth. As the plates grind past each other, the jagged edges strike each other, catch, and stick, "locking" the plates in place for a time. Because the plates are locked together without moving, a lot of stress builds up at the fault line. This stress is released in quick bursts when the plates suddenly slip into new positions. The sudden movement is what we feel as the shaking and trembling of an earthquake.

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Plate tectonics map

   Roll your mouse over each boundary name in the KEY section to see the world's major plates and where the three types of plate boundaries are found.

Plate interactions challenge

Are you ready to take the challenge to test how well you know about plate interactions?

Plate tectonics activity

The continents are slowly moving away from each other. Find out about continental drift and plate tectonics in this activity.

Plate tectonics game

Find the tectonic features associated with plate boundaries. Click anywhere to start in a new window.

Plate tectonics Q&A

Play this plate tectonics game to sharpen your knowledge on this topic!


zondle - games to support learning

This Dynamic Planet

Explore This Dynamic Planet, a complete interactive world map of volcanoes, earthquakes, impact craters, plate tectonics and notable hazard events. Please zoom in and choose from the Layers options to view detail information!