1.1 - Distribution Of Hazards And Tectonic Plates

Question 1

Distribution of earthquakes

Answer 1

• The majority of earthquakes (about 95%) occur close to or at a plate boundary
• Many occur around the ‘Ring of Fire’ surrounding the Pacific Ocean
• The most powerful earthquakes are usually associated with convergent or conservative plate boundaries
• Intra-plate earthquakes are those which do not happen at plate boundaries, these are often linked to hot spots or old fault lines

Question 2

Distribution of volcanoes

Answer 2

• Like earthquakes, most active volcanoes occur at or near to plate boundaries
• Many (about 75%) occur around the ‘Ring of Fire’ surrounding the Pacific Ocean
• Volcanoes occur at convergent and divergent plate boundaries
• They can also be found at hot spots in the middle of plates like Hawaii in the central Pacific

Question 3

Distribution of tsunamis

Answer 3

• Over 70% of tsunamis occur around the Pacific Ocean
• They are caused by tectonic activity
• Most occur due to activity at convergent boundaries

Question 4

What are the three types of plate boundaries

Answer 4

• Divergent (constructive) - plates moving apart
• Transform (conservative) - plates moving past each other or in the same direction at different speed
• Convergent (destructive) - plates moving together

There are three categories of convergent boundaries
- Oceanic - continental
- Oceanic - oceanic
- Continental - continental (also known as a collision boundary)

Question 5

Intra-plate earthquakes

Answer 5

• Earthquakes can occur in the middle of tectonic plates
• This is usually associated with major ancient fault lines being re-activated by tectonic stresses.
• The New Madrid Seismic Zone on the Mississippi River is an example of this, it generates earthquakes up to magnitude 7.5 but is thousands of miles from the nearest plate boundary.

Question 6

Hotspot volcanoes

Answer 6

• Some volcanic eruptions are ‘intra-plate’ meaning there are far away from a plate boundary at locations called mid-plate hotspots such as Hawaii
• This can be result of the upwelling of hot molten material from the core/mantle boundary.
• It could be also as a result of plumes of convecting heat, called mantle plumes rising towards the asthenosphere (the upper layer of the earth’s mantle)
• As the tectonic plate moves over the hotspot, it can generate volcanoes

Question 7

What are the causes of earthquakes

Answer 7

• Constructive plate boundaries only result in small magnitude earthquakes from friction and strain as the plates diverge away from each other
• Transform plate boundaries have a large amount of friction, and when the energy is released, the shockwaves can be strong
• A converging plate creates large amounts of friction and strain, and usually creates high magnitude earthquakes

Question 8

What are the causes of volcanoes

Answer 8

• Volcanic activity is found at constructive plate boundaries, as mantle material moves upwards to fill the gaps left by diverging places
• Volcanoes, can also be found in fold mountains because unstable mantle material and melted oceanic plate forced their way to the surface

Question 9

What are the causes of tsunamis

Answer 9

• This is an upward or downward movement of the crust which disturbers mass of a seawater.
• It is associated with an undersea earthquake, and so is usually linked to a destructive plate boundary