Tectonic Processes & Hazards - EQ1 - 1.3C - Tsunamis Flashcards

1
Q

What is a tsunami

A
  • a series of larger-than-normal waves (know as a wave train) caused by seabed displacement
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2
Q

Tsunamis are usually linked to……, …% occur along ……………………- particularly ……………………. located within the ………….

A
  • tectonic events
  • 90%
  • subduction zones
  • pacific Basin’s ‘Ring of fire’
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3
Q

What is the wavelength of tsunamis

A

long (much longer than normal sea waves) typically 150- 1000 km

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4
Q

What is the waveheight of tsunamis

A
  • Wave height (amplitude) is low (0.5- 5m)
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5
Q

What is the speed of tsunamis

A
  • Velocities are fast, up to 600 kph in deep water
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6
Q

The first wave in a Tsunami is not………………………….., so often there is an……………….

A

The first wave in a Tsunami is not usually the most destructive, so often there is an escalation effect in terms of damage and loss of life

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7
Q

The amount of time between ………………waves (………………………) is only a …….. apart posing a …………… risk, as….

A

the amount of time between successive waves (wave periods) is only a few minutes apart posing a greater risk, as people have lost their lives after returning home between waves thinking it has stopped coming

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8
Q

Why are not all tsunamis a hazard

A
  • Out to sea Tsunamis do not represent a hazard since they are generally low in height (often 300 mm) and generally go unnoticed
  • It is only as they approach a coastline that they grow in height as the water becomes shallower
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9
Q

Give an example of the largest wave not being the first in tsunamis

A
  • For example, in the 1960 Chile tsunami at Hawaii, it was the third wave that did the damage
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10
Q

How does the wavelength of tsunamis vary

A

Long wavelength in open ocean but short in shallow water

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11
Q

How does the speed of tsunamis develop

A
  • Very fast speed in deep water but much slower (35 km/h) in shallow water
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12
Q

How does the waveheight of tsunamis vary

A
  • Low height in open ocean (about 3 m), but significant height in shallow water (up to 20 times higher than in deep water)
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13
Q

Causes of tsunamis

Tsunami waves are caused by….

A
  • the displacement of large quantities (columns) of water
  • The displaced water become tsunami waves as the waves reach shallower water in coastal areas (as the topography of the seabed changes) the waves become higher
  • In shallower water water, friction between the tsunami wave and the seabed increases and the tsunami waves slow down, decreasing wavelength but increasing waveheight
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14
Q

Causes of tsunamis

How can earthquakes cause tsunamis

A
  • An undersea earthquake at a subduction zone may cause a rapid movement of the seabed
  • If this movement is up or down then a column of seawater above the epicentre is displaced, creating a powerful wave motion
  • Undersea landslides displace water when material falls from a continental shelf on the seabed
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15
Q

Causes of tsunamis

What can volcanic erruptions cause tsunamis

A
  • Volcanic eruptions displace water when materials ejected from the volcano falls into the sea
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16
Q

Causes of tsunamis

how do landslides cause tsnuamis

A

Landslides displace water when large quantities of water are displaced by land falling into the sea

17
Q

What determines the impact of Tsunamis

A
  • The duration of the event
  • The wave amplitude, water column displacement and the distance travelled.
  • The physical geography of the coast, especially water depth and gradient at the shoreline.
  • The degree of coastal ecosystem buffer, for example protection by mangroves and coral reefs.
  • The timing of the event – night versus day – and the quality of early warning systems.
  • The degree of coastal development and its proximity from the coast, especially in tourist areas.
18
Q

What are tsunamis measured on

A

The Tsunami Intensity Scale

19
Q

How are tsunamis measured

A
  • Tsunamis are measured by theirrun-up, which is the difference between an observed sea level and the distance the tsunami travelled
  • Tsunamis are measured by their height, it took 20 years to fully understand properly how to measure and time tsunamis
  • Today they use wave height measured by satellites to get the height of tsunamis
20
Q

What is the diffculty of predicting tsunamis to send warnings

A
  • Since most tsunami are caused by underwater earthquakes, the lack of a way to predict earthquakes also means that there is no way to predict tsunami before they occur
    • although it is possible to give people some early warning before an activated tsunami actually reaches the coast and threatens lives
21
Q

Tsunami early warning systems are now in place in both the ……..

A

Pacific and Indian Oceans

22
Q

What are tsunami early warning systems

A
  • These systems use seismic sensors to detect undersea earthquakes
  • Yet, because not all undersea earthquakes cause tsunami, scientists use additional scientific equipment to gather more information
  • This includes a system called DART (Deep-ocean Assessment and Reporting of Tsunami)
23
Q

Describe the DART system

A
  • The DART system uses seabed sensors and surface buoys to monitor changes in sea level and pressure
  • When tsunami waves are detected, the system sends the information via a satellite to tsunami warning stations
  • These stations review the transmitted information and use computer modelling to estimate the size and direction of the tsunami, before informing the areas at risk
  • Depending on where the tsunami originates, some people might receive a warning hours in advance of any threat - giving them time to move to higher ground further inland
24
Q

Describe how early warning tsunamis sensors could have be useful at the 2004 Boxing Day Tsunami

A
  • In 2004, the Indian Ocean didn’t have an early warning system The Boxing Day tsunami took 2 hours to reach Sri Lanka, where over 31 000 people died
  • Had an early warning system been in place, many people might have had time to evacuate
  • Therefore, because of the terrible impacts of the 2004 tsunami , an Indian Ocean early warning system was developed and began operating in 2006
25
Q

…… has the most extensive earthquake and tsunami warning systems in the world

26
Q

How did Japan’s tsunami system react in 2011

A
  • When the magnitude 9.0 earthquake struck in 2011, the Japan Meteorological Agency issued a major tsunami warning within three minutes of the earthquake
  • But the system, in part, failed
  • The size of the earthquake was underestimated, which led to the size and power of the tsunami also being underestimated
27
Q

What was the consequence of the size of the tsunami being underestimated in Japan

A
  • some people thought the tsunami was going to be small, so they didn’t take steps to prepare or evacuate
28
Q

What is the name of the tectonic disaster in Japan 2011

A

Great East Japan earthquake and tsunami (Tohoku) 2011

29
Q

What caused the Great East Japan earthquake and tsunami (Tohoku) 2011

A
  • Undersea earthquake at junction of plates (e.g. Pacific and Okhotsk), multiple ruptures along Benioff zone at shallow depth (24 km), measured M. 9.0.
  • 35m vertical uplift and 50m horizontal movement displaced water column
30
Q

How close was Japan to the earthquake & tsunami

A
  • Lowland east coast of Japan only 130 km away from epicentre facing the tsunami
31
Q

What was the cost of the Great East Japan earthquake and tsunami (Tohoku) 2011

A
  • 18500 people killed
  • $220 billion of damage,
  • including failure of nuclear power plants and release of radioactivity at Fukushima
32
Q

Great East Japan earthquake and tsunami (Tohoku) 2011 was category …. on the Tsunami Intensity scale

A

6 - highest