Unit 8:  Internal dynamics of the Earth                                    1   2   3

3.4. Mountain ranges formation

Mountain ranges or orogens are formed when two tectonic plates collide.

The plates are subject to enormous pressure, which compresses the sediments deposited on the ocean floor between them and deforms the rocks provoking their rising up.

Earthquakes and volcanic activity are frequent in mountainous regions because mountains are formed where two tectonic plates meet.

There are two types of mountain ranges:

       - Thermal orogens are located in the margin of some continents, where a plate

          collides and sink below another (subduction zone). The marine sediments

          located on the subducting plate are folded and pushed up against

          the other plate. And this plate is also deformed and pushed up.

          This type of mountain range has an intense volcanic activity.

          (E.g. Andes)

       - Collision orogens are located in the middle of a continent, where two plates

          collided and fused (obduction zone). This type of mountain range is much bigger

          than the thermal orogens and they do not have volcanic activity.

          (E.g. Himalayas)

3.5. Indicate the differences between thermal orogens and collision orogens.