Tsunami in New Zealand
Published on LEARNZ (http://www.learnz.org.nz)
Listen: Listen to this page [1]
Listen to this page [2]
A tsunami is a series of waves in the sea caused by a movement on the sea floor.
New Zealand is at risk from tsunami because it has a long exposed coastline and
sits on the ‘Pacific Ring of Fire’ where earthquakes and volcanoes are common.
A tsunami is a series of waves in the sea caused by a movement on the sea floor.
New Zealand is at risk from tsunami because it has a long coastline and
earthquakes and volcanoes are common.
What causes a tsunami?
The most common cause of tsunami is a shallow earthquake that displaces the sea
floor. Other triggers include;
undersea landslides
undersea volcanic eruptions
meteorite impact
Sudden changes to the seafloor raises the water level locally and causes the ocean
to flow away from the movement, creating waves.
Tsunami waves
In the open ocean, tsunami waves travel at 600kph to 700kph. In the deep ocean,
waves from a large tsunami may be as little as 60cm high. They pass ships
unnoticed. As they encounter shallow water, they slow down to about 30kph and
increase in height.
Before a tsunami
The seawater may recede a long way out, sometimes hundreds of metres, before
coming back in as a tsunami. Tsunamis are not just moving lumps on top of the
ocean surface, they also include hollows. Sometimes the hollow reaches the coast
first. When this happens, the ocean first draws down and sucks water away from
coastlines. It then rushes back in with enormous speed and force as the lumps
arrive.
People who notice the receding water have as little as five minutes to flee inland to
higher ground. Other signs of a tsunami are a sudden rise or fall in sea level and
hearing loud and unusual noises from the sea.
Page 1 of 8
Tsunami in New Zealand
Published on LEARNZ (http://www.learnz.org.nz)
Tsunami in New Zealand
In New Zealand there here have been about 10 tsunami higher than 5 metres since
1840. Some were caused by distant earthquakes, but most by seafloor earthquakes
not far off the coast.
Some tsunamis are turbulent, foaming walls of water filled with debris and sand that
crash ashore and sweep inland. Others are just rapidly rising or falling water levels
over minutes to an hour. Both are dangerous. Both can travel over land at speeds
faster than a person can run.
Risk of tsunami
The risk of tsunami in the Pacific Ocean is higher than for other oceans because of
the Pacific Plate boundary or ‘Ring of Fire’. This zone has frequent earthquakes due
to movement of the tectonic plates. New Zealand is therefore at risk of tsunami.
Sources of tsunami
Tsunami can come from local sources or far off sources. If a tsunami is generated
close to shore then there may be very little warning. Tsunami generated by local
earthquakes can arrive at the nearest coast before scientists can calculate the
location of the earthquake and issue a warning and activate tsunami sirens. A
strong earthquake may be the only warning of a tsunami.
Warnings
If an earthquake lasts for more than a minute or is strong enough that it is difficult
to stand then you need to move to higher ground. If you are at the beach and notice
the sea suddenly recedes you also need to move to higher ground.
For tsunamis caused by distant earthquakes such as in South America there will be
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Tsunami in New Zealand
Published on LEARNZ (http://www.learnz.org.nz)
warnings. Warnings from the Pacific Tsunami Warning Centre PTWC, will be issued
by the Ministry of Civil Defence and Emergency Management if needed. Tsunamis
from South America, Alaska and Japan take more than 12 hours to reach New
Zealand.
What causes a tsunami?
Tsunami are usually caused by earthquakes that move the sea floor. Other causes
include;
undersea landslides
undersea volcanic eruptions
meteorite impact
Sudden changes to the seafloor raises the water level above and causes the sea to
flow away from the movement, creating waves.
Tsunami waves
In the open ocean, tsunami waves travel at 600 to 700 kilometres per hour (kph). In
the deep ocean, waves from a large tsunami may be as little as 60cm high. They
pass ships unnoticed. As they reach shallow water, they slow down to about 30kph
and gain height.
In low-lying coastal areas waves can travel a long way inland.
Before a tsunami
The seawater may recede a long way out, sometimes hundreds of metres, before
returning as a tsunami. Tsunamis are not just moving lumps on top of the ocean
surface, they also include hollows. Sometimes the hollow reaches the coast first.
When this happens, the ocean first draws down and sucks water away from the
beach. It then rushes back in with great speed and force as the lumps arrive. People
who notice the receding water have as little as five minutes to get inland to higher
ground.
Other signs of a tsunami are a sudden rise or fall in sea level and hearing loud and
unusual noises from the sea.
Tsunami in New Zealand
In New Zealand there have been about 10 tsunami higher than 5 metres since
1840. Some were caused by earthquakes that happened a long way away, but most
were from seafloor earthquakes closer to New Zealand.
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Tsunami in New Zealand
Published on LEARNZ (http://www.learnz.org.nz)
Risk of tsunami
The risk of tsunami in the Pacific Ocean is higher than for other oceans because of
the Pacific Plate boundary or ‘Ring of Fire’. This zone has lots of earthquakes
because of the movement of the tectonic plates. New Zealand is therefore at risk of
tsunami.
Sources of tsunami
Tsunami can come from close or far off sources. If a tsunami is formed close to land
then there may be very little warning. Tsunami formed by local earthquakes can
reach the nearest coast before scientists can work out the location of the
earthquake and issue a warning or start tsunami sirens.
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Tsunami in New Zealand
Published on LEARNZ (http://www.learnz.org.nz)
A strong earthquake may be the only warning of a tsunami.
If an earthquake lasts for more than a minute or is strong enough that it is
difficult to stand then you need to move quickly to higher ground.
If you are at the beach and notice the sea suddenly recedes you also need
to move to higher ground.
For tsunamis caused by far off earthquakes such as in South America, there will be
warnings. Tsunamis from South America, Alaska and Japan take more than 12 hours
to reach New Zealand.
Māori keywords:
tai āniwhaniwha
ngaru
waipuke
hoepapa
Tangaroa
tsunami
wave of the sea
flood
destroy
god of the sea
Audio Maori keywords:
tai aniwhaniwha - tsunami [3]
ngaru - wave of the sea [4]
waipuke - flood [5]
hoepapa - destroy [6]
Tangaroa - god of the sea [7]
Find out which areas of New Zealand are at most risk from tsunami.
Find out which areas of New Zealand are at most risk from tsunami.
[8]
A tsunami is formed by rapid movement of the ocean floor, often caused by
an earthquake. A series of waves travel outwards from this movement. Why
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Tsunami in New Zealand
Published on LEARNZ (http://www.learnz.org.nz)
do the waves increase in height as they move close to land? Image: Steven
Stankiewicz.
[9]
The 2004 Indian Oean tsunami hitting Ao Nang in Thailand. Can you find out
how large the earthquake was that generated this tsunami? Image: Public
Domain.
[10]
Many people live close to the coast and need to know what to do if there is a
tsunami. What warning will people get that a tsunami is coming? Image:
LEARNZ.
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Tsunami in New Zealand
Published on LEARNZ (http://www.learnz.org.nz)
[11]
Long distance tsunamis can be large events but there will be several hours
warning. This map shows how long it could take for waves to reach New
Zealand. What is your emergency plan if there is a tsunami near you?
Image: Christchurch City Council.
[12]
The main sources of locally generated tsunamis are from earthquakes in the
Kermadec Trench, Hikurangi Trench or Puysegur Trench. Why do you think
these areas are of greater risk than some other closer off-shore faults?
Image: GNS Science.
Source URL: http://www.learnz.org.nz/geohazards163/tsunami-in-new-zealand
Links
[1] http://www.learnz.org.nz/sites/learnz.org.nz/files/bg-tsunami_0.mp3?uuid=5945d
e00550b6
[2] http://www.learnz.org.nz/sites/learnz.org.nz/files/bg-easy-tsunami_0.mp3?uuid=
5945de0054a5c
[3] http://www.learnz.org.nz/sites/learnz.org.nz/files/tai-aniwhaniwha_3.mp3?uuid=5
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Tsunami in New Zealand
Published on LEARNZ (http://www.learnz.org.nz)
945de005521f
[4] http://www.learnz.org.nz/sites/learnz.org.nz/files/ngaru_1.mp3?uuid=5945de005
5333
[5] http://www.learnz.org.nz/sites/learnz.org.nz/files/waipuke_0.mp3?uuid=5945de0
055440
[6] http://www.learnz.org.nz/sites/learnz.org.nz/files/hoepapa_3.mp3?uuid=5945de0
05554a
[7] http://www.learnz.org.nz/sites/learnz.org.nz/files/tangaroa_0.mp3?uuid=5945de
0055651
[8] http://www.learnz.org.nz/sites/learnz.org.nz/files/b-gh163-01-tsunami.jpg
[9] http://www.learnz.org.nz/sites/learnz.org.nz/files/b-gh163-02-tsunami.jpg
[10] http://www.learnz.org.nz/sites/learnz.org.nz/files/b-gh163-03-tsunami.jpg
[11] http://www.learnz.org.nz/sites/learnz.org.nz/files/b-gh163-04-tsunami.jpg
[12] http://www.learnz.org.nz/sites/learnz.org.nz/files/b-gh163-05-tsunami.jpg
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