1.3 Physical Impacts

Question 1

What is a P wave?

Answer 1

• primary wave
• caused by compressions in the direction of travel through the crust
• they are fastest and arrive first

Question 2

What are S waves?

Answer 2

• secondary waves
• 60% the speed of P waves and move through solid rock only
• up and down movements

Question 3

What are L waves?

Answer 3

• love waves
• only travel of the surface of the crust
• side to side movement
• causes most damage due to long wavelength and focused energy at the surface

Question 4

What are the primary and secondary impacts of volcanoes?

Answer 4

PRIMARY

• lava flows (move further away from crater if basaltic forming shield volcanoes due to lower viscosity)
• pyroclastic flows can me triggered by extreme ash clouds which are inescapable
• ash falls can blanket crops destroying agricultural systems
• gas eruption like fumaroles and geysers

SECONDARY

• Lahars are formed of ash mixing with water and mud sediment creating mud rivers which destroy rural settlements
• jökulhlaups are water flows from glaciers that have been melted by volcanic activity

Question 5

How does a tsunami form?

Answer 5

• elastic energy and tectonic strain is built up in the Benioff zone due to subduction at a locked fault
• the energy is released and the sea bed (Continental crust) is thrust upwards (mega thrust fault)
• this creates water column displacement leading to a wave train which travels across the sea in all directions
• the waves can travel over 600mph in deeper oceans
• when the waves reach the shallower sea floor the lower part of the wave slows down due to friction with sea bed meaning the wave increases in height, this is called wave shoaling
• once the energy is lost gravity drags the water and debris back into the sea