1.9 Making Waves

Question 1

Where do subduction zones form?

Answer 1

Dense oceanic crust descends under less dense continental crust
An ocean trench forms, and because if the sea water, the crust does not need to be that hot in order to melt
Earthquake hypocentres are found in the contact point between 2 plates (Benioff zone)

Question 2

How do tsunamis start?

Answer 2

An earthquake causes the seabed to thrust upwards
This displaces the water above it, creating a wave
The displaced water becomes a tsunami wave
The wave could also be formed by a landslide (underwater)

Question 3

How do tsunamis grow (develop)?

Answer 3

Waves radiate outwards from the epicentre
In open water the amplitude (height) is low
As waves move towards shallower coastal water, there is increased friction with the sea bed, so the wave slows down
This causes wavelengths to shorten as the following wave catches up, and the amplitude to increase

Question 4

How do tsunamis become disasters?

Answer 4

Distance from source (waves lose energy)
Offshore batty metro (shallow or deep)?
Coastline orientation
Shape of coastline
Coastal topography and geology