Tsunami evacuation information sign in Pilot Bay, Mount Maunganui. Photo / George Novak
With "no silver bullet" in emergency warnings and alerts, Bay of Plenty residents are advised to be prepared.
Living in the Bay of Plenty, as in any part of New Zealand, comes with risks. Be it earthquake, landslide, flooding or volcano, the message from those who work in emergency management is to plan ahead.
With many of the region's residents living and working along the coast, the risk of a tidal wave hitting our coast is real.
Plans for tsunami warning systems in various forms have come and gone over the years.
In 2019 Tauranga City Council gave the go-ahead for up to 12 tsunami sirens to be installed between Pāpāmoa East and Ōmanu over the next two years. None have been installed, however.
In April the council will look for public feedback on whether the expected $3,120,508 project should go ahead.
Tauranga City Council emergency management manager Paula Naude said the Long-Term Plan 2021-31 included the installation of sirens in the budget for 2022/23, and depending on public consultation outcome, the sirens could be installed in the 2022/2023 year.
She said they were not budgeted for installation until after June 2022, and annual costs would sit at $299,000.
A project was being undertaken to increase community awareness about being tsunami-prepared and included the employment of six tsunami awareness ambassadors.
"Whilst council's Emergency Management Team and Emergency Management Bay of Plenty prepare for many different eventualities, how the community fares in an emergency will depend a great deal on the community's level of preparedness."
She said there were a number of ways the community was informed of an emergency, including natural warnings such as earthquakes and sea-level change as well as official warning systems and informal warnings.
Its key message was to not wait for an official warning, however.
The public consultation would ask if the community felt current mechanisms were sufficient.
She said there was no silver bullet in alerts and warnings, and increasing awareness and preparedness were critical.
Planned consultation was prompted by the council needing to balance community desire for sirens with "the best information available at the time", she said.
This included during the recent Tongan volcanic eruption, when Tūtūkākā sirens did not activate, "signifying the short-comings inherent in this style of warning".
Napier City Council approved the removal of its sirens on Thursday.
Emergency Management Bay of Plenty director Clinton Naude said sometimes risks and emergencies could be predicted, other times, not.
"Just the other weekend we were preparing for ex-cyclone Cody to hit our region hard, but it tracked off to the East instead. We also have had examples of potential tsunami waves that, fortunately, didn't end up posing a danger on land."
Scientists were able to put probabilities on quakes, but nobody could actually tell when one would hit, he said.
Android users may get a few seconds warning, as part of the Android Earthquake Alerts System trial, but this had caused confusion in the past.
"The fact is large and small emergencies happen all the time, and often we don't see it coming."
Naude said every region had its own unique collection of things to be prepared for.
Bay of Plenty's hazardscape was "really varied", as it included a long stretch of coastline, geothermal fields, a caldera and "Aotearoa New Zealand's most active volcano".
Naude's advice was to learn about the local hazards for your area.
"People living in Maketū face very different potential hazards compared with people who live in Edgecumbe or Rotorua."
He suggested the National Emergency Management Agency offered a good starting point for a plan.
"Once you have thought about how you will look after yourself and each other, the next step is to gather together things that will help you."
This included a "grab bag", which should have some essentials for if there was a need to evacuate in a hurry.
The other aspect of preparedness was thinking about how you would manage for the first couple of days after an emergency if you were at home, he said.
GNS Science volcano information specialist Brad Scott said activity in the area was largely in the "central volcanic region" that included the Taupō Volcanic Zone. This extended from Ruapehu to Whakaari/White Island.
Whakaari had an elevated level of unrest last year; activity included minor "intermittent ash emissions" for periods of days to weeks that typically didn't extend far from the island.
More unusually, volcanic fog was driven onshore. This was noted across the coast and is "quite a rare occurrence for New Zealand".
Mt Ruapehu also had minor volcanic unrest which was reflected as temperature changes in the crater lake Te Wai ā-moe.
Last year, GeoNet located more than 22,000 earthquakes in and offshore of New Zealand, more than 3500 of them in the Bay of Plenty and Waikato.
GNS Science duty seismologist Sam Taylor-Offord said the areas were situated in a region of tectonic extension – where the land (Earth's crust) is being stretched thin from the movement of the subducting Pacific Plate.
As well as hosting the active central volcanic region, there were many faults and associated structures.
Of the 3500 quakes last year, however, only 1200 were within the top 30km of the crust and only three were above magnitude 4. Most earthquakes were too small to feel.
Earthquake activity in the central volcanic region often signalled low-level volcanic unrest and sometimes occurred in the form of earthquake swarms (or clusters) that lasted hours to weeks.
Tectonic-induced earthquakes were also common but often happened in characteristic mainshock-aftershock sequences.
"In the central volcanic region, it can be difficult to say whether an earthquake relates to volcanic or tectonic forces, or whether it was caused by both," Taylor-Offord said.
There were 1047 quakes in the central volcanic region less than 30km deep, and two of three more than magnitude four happened in a sequence east of Rotorua in January last year.
This area is dominated by the caldera volcanoes of Ōkataina and Taupō, large geothermal systems and the Taupō Fault Belt.
The largest, a M4.9, procured an "impressive" 5235 "felt" reports from across the Bay of Plenty and Waikato region.
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