Living with Tectonic Hazards KQ2 - Landforms At Different Plate Boundaries and How They Are Formed

We have learned about the movement of plates at different plate boundaries. Now let's look at how these movements will result in the formation of various landforms.

Convergent plate movements will result in fold mountains, where converging plates move towards each other and collide. The resultant compression force create immense pressure, which causes layers of rock to buckle and fold. This process is also known as folding.

Locations of Fold Mountains Around the World

Divergent plate movements will result in rift valleys and block mountains, where diverging plates move away and are pulled apart from each other, giving rise to faults. A fault is a fracture in the rocks along where it is displaced. The tension resulting from the movements of the plates causes the crust to be fractured, in a process known as faulting.

Locations of Rift Valleys and Block Mountains

Around the World

Volcanoes is a landform found at both divergent and convergent plate boundaries where there is subduction.

1. At these subduction zones, magma rises and accumulates in the magma chamber which is a reservoir of molten rock beneath the earth's crust.
2. Pressure builds up until the magma forces its way onto the earth's surface through vents which are openings in the earth's surface with a 'pipe' leading into the magma chamber. 
3. Magma is ejected onto the surface as lava.
4. When volcanic eruptions occur, pyroclastic flow (i.e. movement of pyroclasts - rock fragments and gases down the slope of a volcano) and lahars (i.e. mixture of pyroclasts and melted ice) may result.

The figure below shows a typical volcano and how it forms from eruptions of ash and lava,

\

The shapes and sizes of volcanoes vary due to the characteristics of the lava. 

• Low-silica lava has low viscosity and High-silica lava and high viscosity
• Viscosity refers to the stickiness of the lava (i.e. resistance to flow)

Low-silica lava has low viscosity that allows gas to escape easily and results in less explosive volcanic eruptions, forming shield volcanoes that has gentle sloping sides and a broad summit. They are common near divergent plate boundaries (e.g. Mount Washington, USA).

*Constructive (also known as Divergent) boundaries.

High-silica lava is more viscous that traps has and result in a build of pressure as magma rises towards the earth's surface, causing an outward explosion. The volcanic eruption ejects lava, ash, rock fragments and gases into the environment. 

This type of lava will form stratovolcanoes, which are develop from successive eruptions of lava and ash.This type of volcanoes is steeper at the top and gentler at the base, secondary cones may also develop as magma from the vent seeps into the sides of the cone and erupts. (e.g. Mount Pinatubo, Philippines)

*Destructive (also known as Convergent) boundaries.

Distribution of Volcanoes Around the World