Ch 8 Flashcards
Geographical occurrence of tsunamis
- Major tsunami ~1/decade
- 59% in Pacific Ocean, 25% Mediterranean Sea, 12% Atlantic, 4% Indian
Fukushima Daiichi Nuclear Disaster
- Tsunami flooded the Fukushima Daiichi nuclear power plant in japan, 2011
- Power loss = cooling system failed, fuel rods melt through containment
- During next several days, released H2 gas exploded through the reactor buildings, allowing release of radioactive I-131, Xe-133, and Cs-137 into the atmosphere and ocean
2016
- Radiation decreasing but still high
- Water circulation tool damaged reactor contaminates surface water, groundwater, and ocean
- Residents are beginning to move back
2011 Tokohu, Japan, Earthquake and Tsunami
- Longer term - tsunami debris drifting in the Pacific are a hazard to navigation and marine ecosystems
- Travelling east pushed by the North Pacific current and prevailing westerlies, 18mil tons of debris are predicted to wash up along the coast of BC in 2014 and the following years
What is a tsunami created/caused by?
- Created most often by earthquakes with shallow hypocentres at subduction zones
- Reverse faulting of ocean floor displaces water mass (mostly in the Pacific Ocean)
- Also caused by volcanic eruptions, caldera collapses, underwater landslides, meteorite or comet impacts
Wind waves
- Velocity depends on the period of the wave
- 17mph for 5sec wave; 70mph for 20sec wave
- Prograde rotational movement (tsunamis do not have this)
Tsunami
- Huge mass of water with tremendous momentum
- Velocity: v = (g*d)^1/2
- Average: d = 5500m and v = 232m/sec (518mph)
- Actual observations of tsunami speed peak at 420-480mph
- Wave will slow as it approaches shore
Waves in Water and on the Coast
- Waves are energy fronts passing through water, causing water particles to rotate in place - rotational movement becomes insignificant at depths greater than 1/2 the wavelength
- As a wave moves into shallower water, it rises higher. Rotating water touches the bottom, gradually causing a flattening into ellipses and a back-and-forth motion
Tsunami Height
- <1m in the open ocean (not v noticeable b/c super long wavelength and such small height)
- 6-15m in shallow water
- Higher in narrow topography
- Series of waves separated by 10-60min
Tsunami at the shoreline
- Very rapidly rising tide, rushing inland
- Water may retreat first
Wavelength and Period vs. Height
- Destructive period due to momentum of large mass
- 60min period tsunami rushes inland for 30min before water pulls back to form next wave
- Can bend around islands
As the tsunami waves become compressed near the coast, the wavelength is
shortened and the wave energy is directed upward - thus increasing their heights considerably. The energy of the tsunami waves must be contained in a smaller volume of water, so the waves grow in height.
How does the wavelength and wave height of a tsunami in the deep ocean far from land compare to wind-generated ocean waves in the deep ocean?
The longer the wave, the greater the volume of water involved. Though they appear smaller in height (distance b/w trough and crest) in the deep ocean than some wind waves, tsunamis can grow to much greater heights and cause much more destruction than wind waves at the coast.
Earthquake-caused Tsunami: Indian Ocean, Dec 26 2004
- 14 countries affected
- 245k deaths
- 1,200km fault rupture
- Indian-Australian plate
- Either side of the fault rupture is where the tsunami propagates. IF a country is pointed right at the strike (Bangladesh), no tsunami!
Fault movements with pronounced vertical
offsets of the seafloor that disturb the deep ocean-water mass
- Water will support shear in large scale (normally opposes shear)
Landslide-caused Tsunami, Volcano collapses: Hawaii in Pacific Ocean
- Slump and debris-avalanche deposits cover more than 5x the land area of the island
- Flank-collapses = where entire side of volcano breaks off and falls into the sea
- Huge tsunami when island collapses into the ocean
- Coastal area SE of Kilauea slides up to 25cm/yr into the ocean; a major movement would create a tsunami up to 30m high directed to SE
