Landforms associated with plate movements

Question 1

Describe the formation of ocean ridges

Answer 1

The longest continuous uplifted features on the surface of the planet, they are formed when plates move apart in oceanic areas. The space between the plates is filled up with basaltic lava upwelling from below to form a ridge. Volcanic activity also occurs along these ridges, forming submarine volcanoes which sometimes rise above sea level.

Question 2

Describe the formation of rift valleys

Answer 2

Rift valleys form when plates move apart on continental areas. The brittle crust fractures as sections of it move apart. Areas of crust drop down between parallel faults to form the valley. An area between two parallel rift valleys form an upstanding block know as a Horst.

Question 3

Describe the formation of deep sea trenches

Answer 3

Where oceanic and continental plates meet, the denser oceanic is forced underneath the lighter continental one. The downwarping of the oceanic plate forms a very steep part of the ocean known as a trench.

Question 4

Describe the formation of island arcs

Answer 4

During subduction, the descending plate encounters hotter surroundings, and this coupled with the heat generated from friction, begins to melt the plate. As this material is less dense than the surrounding asthenosphere, it begins to rise towards the surface as plutons of magma. Eventually these reach the surface and form complex, composite and explosive volcanoes. If the eruptions take place offshore, a line of islands form offshore.

Question 5

Describe the formation of young fold mountains

Answer 5

There is little subduction due to the continental crust having a much lower density than the underlying layers. As such plates move towards each other, their edges and the sediments between them are forced up into fold mountains. As there is little subduction there is little volcanic activity.