Global Distribution of Tectonic Hazards (Edexcel A Level Geography)

Global Distribution of Tectonic Hazards

Earthquake distribution

• 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

Volcano distribution

• 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

Tsunami distribution

• Over 70% of tsunamis occur around the Pacific Ocean

  • 15% Mediterranean Sea, 9% Caribbean Sea and Atlantic Ocean, and 6% Indian Ocean

• They are caused by tectonic activity 

• Most occur due to activity at convergent boundaries

Plate Boundaries

• Plate boundaries are the locations where the tectonic plates meet

• Due to the movement of the plates, these are areas where a range of processes take place

• There are three main types of plate boundary:

  • Divergent - plates moving apart

  • Convergent - plates moving together

  • Transform - plates moving past each other or in the same direction at different speeds

• There are three categories of convergent boundaries:

  • Oceanic - continental

  • Oceanic - oceanic

  • Continental - continental (also known as a collision boundary)

Intra-plate Earthquakes & Volcanoes

• Some earthquakes and volcanic eruptions occur away from the plate boundaries

• These are intra-plate earthquakes and hot spots

Intra-plate earthquakes

• These can occur anywhere

• The cause is not fully understood but is thought to be:

  • Tectonic stresses causing ancient fault lines to reactivate

  • The plates are moving over a spherical surface and this causes zones of weakness

• The New Madrid earthquake in 1812 and the 2011 Virginia earthquake are examples of intra-plate earthquakes

Hotspot volcanoes

• These occur over stationary magma plumes (columns of rising magma) in the asthenosphere

• The tectonic plate moves over the plume leading to the formation of a chain of volcanic islands (Hawaii)

• The oldest island is the one furthest away from the plume