Earthquakes and volcanoes: processes affecting magnitude of earthquakes

Question 1

What is the name of the part directly above the focus?

Answer 1

The epicentre.

Question 2

Where is the shaking the strongest?

Answer 2

Nearest to the epicentre

Question 3

What is used to measure earthquakes?

Answer 3

seismometer

Question 4

What are the 2 scales used to measure earthquakes?

Answer 4

1. Richter scale (ML)
2. Moment magnitude scale (Mw)

Question 5

What is a volcano?

Answer 5

It is a landform created when lava erupts onto the Earth’s surface. It accumulates over time, forming a cone-shaped mountain;a volcano.

Question 6

How does volcanic eruptions occur at divergent plate boundaries?

Answer 6

1. The plates move apart, causing the crust to stretch and fractures develop
2. There is a decrease in overlying pressure, causing parts of the underlying mantle to melt, forming magma
3. Magma contains dissolved gases and is less dense than the surrounding materials
4. Magma rises through weak areas onto the Earth’s surface to erupt as lava
5. After it erupts, the lava cools, solidifies and accumulates over time, forming a volcano

Question 7

How does volcanic eruptions occur at convergent plate boundaries?

Answer 7

1. Plates move towards each other, causing the denser plate to subduct underneath the other
2. The subducting plate sinks into the mantle, and the high pressure forces water out of the oceanic crust, lowering the melting point of the underlying mantle, causing it to melt and form magma
3. The magma contains dissolved gases, making it less dense than the surrounding materials
4. Magma rises through the weak areas onto the Earth’s surface to erupt as lava
5. As the lava cools, it solidifies and accumulates over time, forming a volcano

Question 8

Why are some volcanic eruptions more explosive than others?

Answer 8

Magma of high and low silica.
Magma of high silica is more viscous (thicker), gases cannot escape easily, more pressure built up, more explosive (associated with stratovolcanoes)

Magma of low silica is less viscous, gases can escape easily, less pressure built up, less explosive (associated with shield volcanoes)

Question 9

How are volcanic ERUPTIONS measured?

Answer 9

Volcanic Explosivity Index (VEI)