What are tsunami?
Tsunami are a series of waves caused by a displacement of water.
• Are long-period waves – up to 100 kilometres
• Travel quickly in the open ocean – up to 700 kilometres per hour
• Slow down and increase in height as they approach land
• Behave like a rapidly rising/falling tide
What causes tsunami?
Tsunami are mainly caused by earthquakes, landslides and volcanic
activity under the ocean.
Types of tsunami
There are three main types of tsunami:
Local source
Travel time between
the source, such as
an earthquake just
offshore, and impact is
one hour or less.
Regional source
Travel time between
the source, such as
the Southern Tonga –
Kermadec Trench and
impact is between one
and three hours.
Distant source
Travel time between the
source – such as South
America or Japan – and
impact is greater than
three hours, often over
twelve hours.
Where do most of Tauranga’s
tsunami come from?
Tsunami that impact Tauranga may be from distant sources, such as South
America; regional sources, such as the Tonga-Kermadec Trench or from local
sources such as earthquakes on the east coast.
What are we most
concerned about?
We are most concerned about tsunami
events generated from large earthquakes
along the Tonga-Kermadec Trench
subduction zone – the tectonic plate
boundary between the Pacific and
Science behind Tsunami
in Bay of Plenty
Initial modelling by GNS
identified the Kermadec
trench off the East
Cape as source of
greatest risk for the Bay
of Plenty.
Based on fault
characteristics and
learnings from Japan
a Magnitude 9.0
earthquake has been
identified as maximum
potential event.
Tsunami wave terminology
AMPLITUDE
Inundation
line or limit
Crest
Wave
height
Sea level
at the time
Run-up
Shoreline
Trough
Inundation horizontal flooding
Flow modelling for
Tauranga City
Timing of tsunami flow from generation
• 50 – 60 mins to reach coast
• Then 10 mins to move over first 1km inland
• Up to 6 hours to reach maximum inland extents
How deep?
Flow depth
Future development
scenario at Wairakei
A major earthquake is the most reliable way to know that a devastating
tsunami might be on the way from a local source (like the Kermadec Trench).
This is confirmed by the Ministry of Civil Defence Emergency Management and
GNS Science.
Formal warning systems will not be able to be activated in time to help you
survive such a tsunami.
Natural warning signs
• A big earthquake that knocks you over.
• Any earthquake that lasts more than a minute.
• Strange ocean behaviour (loud or strange noises, sudden change in sea
level, ocean drawing away from the shore).
The first tsunami wave may arrive at Tauranga’s coastline
50 minutes after a major earthquake. Don’t wait for an
official warning. Get inland or to high ground.
What do the maps show?
Safe zones
Safe zones are coloured green and indicate areas outside
potential tsunami flow, or safe assembly areas.
Tsunami evacuation zones
Each map shows three different tsunami evacuation zones.
Red zone – Every tsunami will affect this part of the coastline. You should
always evacuate this area if there is any sort of tsunami warning, whether
that warning comes from unofficial sources (like text messages or social
media), official warnings, or natural warning signs. Orange zone – In a formal Civil Defence evacuation you may be asked to
move from the orange zone into the yellow zone. Tsunami from regional or
distant sources (further away than 1000km) could take anywhere from 2 to
12 hours to arrive. You won’t feel an earthquake for this type of tsunami so
this is where things like warning systems, text alerts, emails, TV/radio and
social media are really important.
Yellow zone – The most devastating tsunami, similar to the big one that
hit Japan in 2011, is predicted to flood the yellow zone. There is a very low
chance this will happen in our lifetime but if it does happen there will be
no time for official warnings. After a major earthquake it would take about
50 minutes for this tsunami to reach the coast, plus maybe another 30
minutes to flood the yellow zone. The further into the yellow zone you get,
the shallower and slower moving the water will be. If you plan ahead and
evacuate as soon as you can after that first earthquake you have a very good
chance of surviving this devastating tsunami.
Evacuation Strategy
Safe Evacuation
Prioritise evacuation
1. Evacuate from higher to lower hazard (within 40 minutes)
Get people out alive
2.Evacuate from hazard to safety (within 60 minutes)
Get people to safety
Assume evacuation by foot
Keep roads free for emergency and evacuation of less mobile
People take 10 minutes to feel earthquake and
decide to self-evacuate and 10 minutes to depart
Aim to have high hazard zones evacuated within 40 minutes
All zones evacuated within 60 minutes
Evacuation modelling
Time to evacuate to safety
•Most within 40 minutes
•All within 60 minutes
Emergency Alerts
There are different ways you can be alerted during an emergency by
subscribing to emergency updates. You will be notified any time there is
a change to the emergency status or advice on a specific event.
What about alert systems
and sirens?
Alert systems are the topic of earnest, ongoing conversation – but a big
earthquake is the best warning for the tsunami we are most concerned about.
The most important thing is to be aware of the natural warning signs so that
you can make your own decision to evacuate if there is an earthquake. Warning
systems are useful for tsunami that come would from regional or distance
sources (greater than 2 hours away).
Civil Defence has a suite of warning systems.
Subscribe to emergency alerts at www.bopcivildefence.govt.nz
How to evacuate:
Use your feet. Help your neighbours.
It’s natural to think you’ll be able to leap into the car and get away before everyone
else. But what if everyone else is thinking the same thing?
Consider this: if everyone tries to drive out of Papamoa at the same time, traffic
modelling undertaken by NZTA show that it will take at least 6 hours to get everyone
clear. That’s on a good day with no emergency.
The best plan is to walk
Learnings from the Japan tsunami of 2011 confirm this fact.
The evacuation maps we have provided show safe locations and zones that can be
reached by foot from every part of the coast within 60 minutes. The distances are
modelled on a very conservative walking pace.
Plan with your neighbours
With less than an hour after a major earthquake before a tsunami
arrives, emergency services will not be able to get you out in time.
The reality is that you’re on your own.
The community’s best chance to survive a tsunami is to work together as a
community. Make an evacuation plan with your neighbours, especially if you know
they will need assistance getting to a safe area.
Take your emergency pack
A tsunami is a large volume of water that surges across the
ocean, usually caused by an underwater earthquake. It is
like ripples in a pond but on a much larger scale. Tsunami
can arrive in several waves over a long period of time. The
first wave is not always the biggest. That is why you need
your emergency pack. You must be prepared to wait for many
hours before the water subsides.
This is a local community plan for the
escape of tsunami in Tauranga, Mount
Maunganui and Papamoa. It is specifically
targeted toward “local source tsunami”
and the actions required from first
awareness to an official response.
Be Prepared
•
•
•
•
Create and practice your household emergency plan
Have your getaway kit prepared for fast evacuations
Identify safe places in your community and know how to get there
Make sure each member of your family knows where the safe zones are
Earthquake, think Tsunami
•
•
•
•
•
Shaking strong enough to knock you off your feet
Prolonged shaking (greater than one minute)
Sea level suddenly rising or falling
The sea makes loud and unusual noises or roars like a jet engine
Don't wait for sirens
Get inland and move to higher ground
•
•
•
•
Walk or cycle. Don't rely on cars, expect traffic chaos
Natural high points (hills or inland)
Use strong muli-story Buildings if you can't get to natural high points
Signs or blue lines on the road indicate safe evacuation zones
After the Tsunami
• Check yourself for injuries and get first aid if needed
• Turn on your radio for civil defence advice
• Stay where you are until you’re given the official all clear, a tsunami
consists of multiple waves over many hours,
• Use text messages for contacting family members, save voice calls for
emergencies only
• Register at a welfare centre for assistance and to help locate your family
and friends
3 things you need
What
do
the
maps
show?
to know to survive
a tsunami
1
WHEN TO EVACUATE
The best tsunami warning
is an earthquake
The first tsunami could arrive 50 minutes after a major
earthquake. Don’t wait for an official warning to evacuate.
2
WHERE TO EVACUATE
Inland or high ground
We have taken the best possible scientific information to show
where tsunami flooding is predicted to go and where you will
be safe. Use the map on the other side of this flyer to plan your
escape route.
3
HOW TO EVACUATE
Use your feet
In a big tsunami emergency there will be crippling traffic jams.
Most people should be able to walk to a safe area or safe
location shown on the map within 60 minutes.
Sign up for text and email alerts at www.bopcivildefence.govt.nz