Week 5 Flashcards
What are Tsunamis
Tsu - Habor
Nami - Wave
What is the important distinction between normal ocean waves and tsunami
- Wave length
- Wind driven waves have short wavelength (tens of meters)
- Tsunami waves lengths are long (up to more than a hundred kilometers)
Initiation of a Tsunami
- reverse faults are responsible for earthquake included tsunami by uplifting/ subsiding a large area of the sea floor
- tsunami waves propagate away from the source
Two fundamental physical parameters of water waves
- Wavelength (distance from peak to peak)
- Period (time for passage of one wave)
Tsunami propagation speed
As it enters shallow water, tsunami waves speed will slows and its height increases creating destructive, life threatening waves
What are the causes of tsunamis
- Undersea rupture of normal, thrust, megathrust faults
- Undersea landslide
- Undersea volcanic eruptions
- Asteroids
How do we calculate velocity of the tsunami
velocity = sqr (gravity x water depth)
Undersea rupture of normal, thrust, megathrust faults
- if the rupture is 100 km wide, so is the initial tsunami wavelength
- the waves get steeper and higher as they come into shallower and shallower water
- often become a chaotic front
Example of Undersea rupture of normal, thrust and megathrust faults
- 2004 Indian Ocean and 2011 Tohoku
- 1933 Sanriku (normal fault)
Factors affecting height of tsunami waves
- earthquake magnitude
- area of rupture zone
- rate and volume of water displaced
- sense of ocean floor motion
- depth of water above rupture
Undersea landslides
- tsunami from fast moving landslides or rock falls can displace immense amounts of water and generate tsunami
- the height of fall has more effect than volume of mass that displaces water
- heavily dependent on the speed and volume of the landslide
Examples of undersea landslides
- 1958 Lituya bay
- Hawaiian islands
Tsunami generate by volcanic eruptions
- volcanic processes can displace large volumes of water and trigger tsunami:
1. fast-moving flows of hot volcanic ash
2. submarine volcanic explosions
3. collapse of volcano in giant landslide - tsunami generated by volcanic eruptions are poorly understood; maximum in size unknown
Examples of undersea volcanic eruptions
- 1883 Krakatau
- 1628 BC Santorini
- 2022 Tonga Eruption
Three plausible causes (1883 Krakatau eruption)
- an enormous explosion displaces large quantities of seawater
- the underwater portions of the volcano subside quickly during the eruption, greatly disturbing the seafloor
- large volumes of volcanic material enter the sea and displace sea water