Volcanoes and earthquakes are among hazards Bay of Plenty residents are advised to prepare for

Earthquake activity in the central volcanic region often signalled low-level volcanic unrest. Photo / Andrew Warner

There are "unique" hazards in every region of the country and Bay of Plenty residents are being advised to be prepared.

Emergency Management Bay of Plenty director Clinton Naude said every region had its own unique hazardscape — "like the landscape, but for dangerous things."

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", he said.

Emergency Management Bay of Plenty director Clinton Naude. Photo / Supplied

Each community faced different risks. The potential hazards in Rotorua varied from those down the road in Maketū.

Naude's advice was to learn about the local hazards for that area.
Sometimes risks can be predicted but others could not, he said.

"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."

He said scientists were able to put probabilities on quakes, but nobody can actually tell when one will hit.

Android users may get a few seconds warning, as part of the Android Earthquake Alerts System trial, but this had caused confusion in the recent past.

"Large and small emergencies happen all the time, and often we don't see it coming.
"That's not meant to scare people, it's just a fact of life. That's why a lot of people and organisations work hard to get people in the best possible position to survive and get through whatever comes along."

The National Emergency Management Agency was 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' with essentials 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.

Volcanoes and quakes - last year's activity

Last year, GeoNet located more than 22,000 earthquakes in and offshore of New Zealand.
More than 3500 of these were in the Bay of Plenty and Waikato.

GNS Science duty seismologist Sam Taylor-Offord said they were in a region of tectonic extension — where the Earth's crust is being stretched thin from the movement of the subducting Pacific Plate.

GNS Science duty seismologist Sam Taylor-Offord. Photo / Supplied

As well as hosting the active central volcanic region, there were many faults and associated structures running through the region.

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.

This area includes the Taupō Volcanic Zone and extends from Ruapehū to Whakaari/White Island. It is dominated by the caldera volcanoes of Ōkataina and Taupō, large geothermal systems and the Taupō Fault Belt.

There were 1047 quakes in the central volcanic region less than 30km deep, and two of three more than magnitude 4 happened in a sequence east of Rotorua in January last year.

The largest, an M4.9, procured an "impressive" 5235 felt reports from across the Bay of Plenty and Waikato region.

GNS Science volcano information specialist Brad Scott said activity in the area was largely in the central volcanic region.

GNS Science volcano information specialist Brad Scott. Photo / Supplied

Whakaari had an elevated level of unrest last year and was the most active volcano in the greater Bay of Plenty-Waikato area.

This activity included volcanic fog that 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.

Tsunami sirens

Many in the region live and work along coasts at risk from tsunami waves.

Plans for tsunami warning systems in various forms have come and gone over the years and 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, and in April the council seek public feedback on whether the expected $3,120,508 project should go ahead.

The Council's emergency management manager Paula Naude said there were a number of ways the community was informed of an emergency, including natural warnings as well as official warning systems and informal warnings.

Its key message was to not wait for an official warning.