Tsunamis
What are tsunamis?
Do we get tsunamis on the Gold Coast?
Tsunamis are a series of long, ocean waves generated
by large-scale physical disturbances to ocean water.
Earthquakes generate most tsunamis, but volcanic
eruptions, landslides, explosions and meteorites can
also cause physical effects. Tsunamis are sometimes
confused with tides and storm surges; however these
are influenced by quite different coastal processes.
Tides are the result of the gravitational pull on the earth
by the moon causing regular changes in ocean water
levels. On the other hand, weather events—such as
tropical cyclones—can cause storm surges. See Storm
Surges and Cyclones information sheets for more
information.
Tsunamis are recorded in Australia about once every
two years with most being small and presenting little
threat to the coastal zone. Despite this, even relatively
small tsunamis can cause abnormal waves, tides and
currents that can be dangerous to swimmers and
mariners. This is why all tsunami warnings must be
taken seriously. In recent years, the Gold Coast has
experienced the minor effects of a tsunami on
27 February 2010, from a Chilean earthquake with a
magnitude of 8.8. The Gold Coast observed increases in
wave heights of 42cm, seven hours after the initial
shock (see Figure 1). There was another tsunami
warning on 15 July 2009, from an offshore earthquake,
this time near the south coast of New Zealand,
measuring 7.9 on the Richter scale. There were no
visible effects on the Gold Coast.
How are tsunamis formed?
When deep ocean water is disturbed, ocean wave
characteristics change. This causes a ripple effect at the
starting point of the disturbance (the epicentre), and
can create a series of waves that increase in height and
speed. As a tsunami approaches the coast and
shallower water, the waves become slower and
compressed, causing them to grow in height. This effect
is called shoaling, and a tsunami that is barely visible at
sea may grow several metres or more in height as it
approaches the coast.
What happens if a tsunami reaches the
coast?
Tsunamis may cross a coastline thousands of kilometres
away from the epicentre, travelling across the world’s
oceans. In a best-case scenario, a tsunami may come
onshore like a quickly rising tide and cause inundation
of low-lying areas, virtually undetected. In a worst-case
scenario, a tsunami can result in 40m waves thrusting
inland through coastal regions.
Figure 1. Sea level fluctuation at the Gold Coast Seaway from the
Chilean earthquake in February 2010.
Who issues the warning?
Australia has a comprehensive, independent tsunami
warning service—the Joint Australian Tsunami Warning
Centre— that is operated 24-hours a day to ensure all
media, public and emergency authorities are notified of
any tsunami threat to the Australian coastline. This is
jointly undertaken by the Bureau of Meteorology,
Geoscience Australia and Emergency Management
Australia.
“It doesn’t matter how
experienced or how long you have
been surfing in the same spot, the
fear is with a tsunami you are
going to get very unusual
conditions and rips and it will form
gutters and so on...”
(Emergency Management Queensland acting
chief officer, Bruce Grady)1
Types of tsunami warnings
The Joint Australian Tsunami Warning Centre assesses
the level of threat posed by any potentially tsunamicausing earthquakes that occur and issues a warning
accordingly:
1.
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No threat – an undersea earthquake has
been detected, however it poses no threat of
a tsunami to Australia and its offshore
territories.
Marine and immediate foreshore threat –
warning of potentially dangerous waves,
strong ocean currents in the marine
environment and the possibility of some
localised ocean overflow onto the immediate
foreshore.
Land inundation threat – warning for
low-lying coastal areas of major land
inundation, flooding, dangerous waves and
strong ŽĐĞĂŶĐƵƌƌĞŶƚƐ͘
What is Gold Coast City Council doing to
prepare for tsunamis?
♦ In case of a major threat, the Gold Coast City
Council Disaster Management Response Unit
coordinates our city’s emergency response
♦ A unique Disaster Management Centre streamlines
the city’s emergency response
♦ Earthquakes in our region are continuously
monitored and interpreted
♦ The centre corresponds with key stakeholders, such
as the Joint Australian Tsunami Warning Centre and
Emergency Management Queensland, to ensure
disaster preparedness
During a tsunami...
♦ Move to higher ground
♦ Do not stay on the beach
♦ If on a boat, come into shore, shelter behind a
headland or enter a harbour
To find out how you can prepare for a tsunami, visit
goldcoastcity.com.au/disaster
For more information
Visit the Bureau of Meteorology website
www.bom.gov.au/tsunami or call 1300 TSUNAMI
(1300 878 6264)
Figure 2. Australian tsunami warning service map
(Source: Bureau of Meteorology 2010)
1
Lappeman, S. 2010, ‘Coast’s tsunami warning “confusing”’, Gold
Coast Bulletin 2 March, goldcoast.com.au/
article/2010/03/02/194135_gold-coast-news.html/