Reasons why Earthquakes and Volcanoes Occur Where they Do

2. Why do earthquakes and volcanoes occur where they do?

Earthquakes

An earthquake is caused by the movement of two or more plate boundaries and the pressure that builds up during the movement. When this pressure is released, an earthquake is created.

Earthquakes can occur wherever there is a plate boundary because all plates move in a direction and pressure can build up easily.

*earthquakes occur on all plate boundaries*

All plates move because of convectional currents that cause hot air to rise and cooler air to sink. In the mantle, which Earth's crusts float on, these convectional currents cause the magma in the mantle to move. The hotter magma rises and the cooler sinks, this movement causes the Earth's crust to move as well since it is floating on the magma.

1. When the crusts collide or move past one another
2. Pressure is built up
3. Pressure is released
4. The plates continue to move
5. The release of pressure and plate movement cause earthquakes

Volcanoes

Volcanoes are caused by magma in the mantle moving up to the surface and escaping.

They can occur at convergent (excluding the collisional boundary with continental to continental plates) plate boundaries, divergent plate boundaries or hotspots

At a convergent plate boundary, fold mountains and volcanoes (where there is subduction) are produced

• Oceanic plate subducts
• Crust melts to form molten rock / magma
• Magma escapes to the surface and forms a volcano (or island in some cases)
• Volcanic eruption happens when the magma forces its way up the volcano

Hotspots

Hotspots are areas where the crust is weak and an island chain is formed

1. A superheated plume of magma escapes the crust
2. It rises until sea level
3. It then creates an island and volcano
4. As long as this island remains above the hotspot, the volcano will be active (large supply of magma)
5. However, because over time the crust moves, a new island will be formed (the hotspot NEVER MOVES)

*volcanoes occur on divergent, convergent (destructive and ocean to ocean) boundaries and hotspots*