Lecture 3 Flashcards
Tsunami is Japanese for:
harbour wave
How are Tsunamis produced?
by the sudden displacement of water
Events capable of triggering tsunamis:
- earthquakes that cause uplift of the seafloor
- landslides
- volcano flank collapse
- underwater volcanic eruptions
- meteorites
What earthquake caused the greatest human casualties?
Sumatra Earthquake, Indonesia 2004
Earthquakes can cause tsunamis in two ways:
- By displacement of the seafloor
2. By triggering a landslide that enters water
An earthquake must be at least ______ in order to trigger a tsunami
M 7.5
Describe the stage 1 of the 4-stage process of a Earthquake-Triggered Tsunami Development
Stage 1: Displacement of the seafloor sets waves in motion that transmit energy upward and outward
- when the waves reach the surface of the water, they spread outward
Describe the stage 2 of the 4-stage process of a Earthquake-Triggered Tsunami Development
Stage 2:
The waves move rapidly across the open ocean (can reach speeds of over 500km/h)
The spacing of the wave crests are very large (can be more than 100km)
The height (amplitude) of the waves is often small (less than 1 m)
Passengers on ships in the ocean rarely even notice tsunamis passing beneath them
Describe the stage 3 of the 4-stage process of a Earthquake-Triggered Tsunami Development
- As the tsunami approaches land, the water depth decreases
- This results in the water ‘piling up’ and causes these effects:
- a decrease in wave speed
- a decrease in spacing of the waves
- an increase in wave amplitude
Describe the stage 4 of the 4-stage process of a Earthquake-Triggered Tsunami Development
- As the tsunami impacts land, waves can reach heights of dozens of metres
- the wave speed at this time can be up to 50km/h making them impossible to outrun
Tsunami Event:
consists of a series of large waves reaching shore that can last for several hours
Run-Up:
The maximum vertical distance that the largest wave of a tsunami reaches as it travels inland
Types of Tsunamis
Distant Tsunami:
A tsunami that travels thousands of kilometres across the open ocean
On remote shorelines across the ocean, reduced energy lessens its impact
Also called tele-tsunamis
Regional tsunami:
A tsunami that affects shorelines 100km to 1000km from its source
Local Tsunami:
A tsunami that affects shore lining within 160 km from its source. They are the most dangerous types
What Regions are most at Risk?
- coasts located near subduction zones or across oceans from subduction zones
- areas at greatest risk are the Pacific Ocean and the Mediterranean Sea
Primary Effects of Tsunamis:
- Flooding and erosion destroy beaches, coastal vegetation and infrastructure
- After the tsunami retreats to the ocean, scattered debris is left behind
- most tsunami deaths are from drowning, injuries result from physical impacts with debris
Secondary Effects of Tsunamis:
These are effects that generally occur after the event is over
- fires may develop due to ruptured gas lines or from ignition of flammable chemicals
- water supplies may become contaminated and water-borne diseases (cholera) may spread
Indian Ocean Tsunami 2004
- source was a M 9.1 earthquake off the west of coast Sumatra
- 3rd strongest earthquake in world history
Tsunameters
Sensors electronically connected to buoys verify that a tsunami was produced
- they rest on the seafloor and measure changes in water pressure passing over them
Inundation Maps
showing the geographic area that can be potentially impacted by tsunamis are created to help plan for future events
Prospect Theory
people are more willing to protect against a loss than gamble for an equivalent gain
Cultural Adjustment
may result from changes in an environment
Purposeful Adjustment
is specifically designed to reduce loss or damage
Incidental Adjustment
not primarily hazard-related but they have the effect of reducing potential loss
