A tsunami in Lake Taupō sparked by last night’s strong earthquake has destroyed boats and caused damage to the township’s foreshore as more than 180 aftershocks have been detected.
The central North Island is continuing to be rattled by tremors in the wake of a strong 5.6 magnitude quake.
The shallow quake struck about 20km southwest of Taupō shortly before midnight, at a depth of 5km.
One of the larger aftershocks recorded was a 4.1 magnitude tremor at 1.53pm today.
Coastguard Lake Taupō skipper Mike Hughes said the earthquake caused a surge of water to sweep up some beaches.
In Four Mile Bay at the southern end of Taupō township, the water had surged about 20-30m up the beach, destroying two boats belonging to Taupō Pedal Boats, ripping wooden bollards from a park area nearby and eroding about 2m of soil away from the foreshore.
Hughes said it was the same concept as a tsunami at sea – if it is long and strong, with an earthquake lasting more than a minute then it was best advised to get away from the water’s edge. In this case, Four Mile Bay shelves off sharply into deep water which could have been a factor.
Niwa hydrodynamic scientist Dr Emily Lane showed in a tweet the tsunami as measured by water level gauges at Acacia Bay and Tokaanu.
Lane told the Herald it was interesting a tsunami resulted from an earthquake of this size.
“With these volcanic earthquakes, you will get deformation, it actually deforms the ground underneath the lake,” Lane explained.
She referenced the complex Kaikoura earthquake when referring to what it might look like under Lake Taupo at the moment.
During the 7.8 magnitude shake in 2016, parts of the land in Kaikoura were jolted several metres upwards due to the many fault lines that were activated.
Although it may not be as extreme under Lake Taupō, the ground shifting is what would’ve caused the wave.
However, Lane said the tsunami was bigger than scientists would have guessed given the magnitude of last night’s quake.
“One of the interesting things is that an earthquake of this size, in terms of generating tsunamis, that’s pretty small,” Lane said.
“We sort of think that maybe the amount of movement you got was more than what you would expect for an earthquake of that size.”
Lane said she and her team are very interested in talking with locals who have seen any more inundation (the very high tide line) around Taupō so they can continue to piece together the science around last night’s quake.
GeoNet is still questioning if the wave was a tsunami at all.
In a post on their website, they said that their researchers are “still looking into the evidence of a potential seiche or small tsunami” which have both occurred on the lake previously.
“At this point, we don’t know if this is due to a seiche, where the lake moves back and forth and “sloshes” or a tsunami, caused by a landslide, or some combination of both,” GeoNet wrote.
Taupō Pedal Boats owners Jess Ratana and Kiripiti Bowden were down at the lake’s edge pulling the two four-person pedal boats off the rocks with a 4WD ute.
Jess said they were fortunate all of their pedal bikes were intact but the larger pedal boats were the only two they had.
”We pulled them right up last week because of the wind. It was really windy down here.
They were on the grass, they weren’t really near the water at all.
”It’s just pulled them out and the wind direction has taken them this way and they have ended up being smashed against the rocks.”
She said they were insured.
”It’s not something we ever thought would happen – an earthquake, and a lake tsunami. I don’t think anyone would have expected that.”
She said their summer season kicks off in about two weeks but it would likely take at least two months to get replacement boats bought and shipped in from overseas.
The business had been going great since they started in January last year and they had also expanded the pedal bikes into Pilot Bay in Mt Maunganui.
Taupō mayor David Trewavas said it was a pretty big earthquake but so far they had not identified any damage to infrastructure, although teams were out checking pipes this morning.
“It was a juicy one alright.”
GeoNet said 150 quakes had been recorded since the initial shock that saw items fall from walls and shelves and gave residents across the central region a sleepless night.
GNS seismic duty officer John Ristau and volcanic duty officer Steve Sherburn said last night’s quake was by far the largest tremor recorded since May when activity ramped up under the lake.
The previous largest was a 4.2 magnitude quake on September 10.
The scientists said this week was now regarded as the most active of this year but most of this was down to aftershocks.
“The current week, is the most active this year, and it is twice as active as the next most which was in early September, but this activity is almost all aftershocks of the M5.6 earthquake.”
While there was a small possibility an even more powerful quake would strike, the likely scenario was a repeat of an earlier September sequence which saw activity decrease.
“While it is impossible to predict earthquakes – we can only calculate statistical forecasts – however when an earthquake occurs there is always a small possibility that a larger earthquake will occur.
“The most likely scenario is there will be a number of smaller aftershocks which will taper off, much like we experienced with the M 5 in September 2019 with a similar aftershock sequence.”
Sherburn said locals shouldn’t be overly concerned about the latest swarm, though.
The volcanic risk remained low with “no concerns at this time”.
He said there was likely to be “potentially many years of unrest” as forewarning before any future volcanic eruption at Lake Taupō.
However, he said that “we live in a country where earthquakes are part of everyday life” and this meant following Civil Defence advice around being prepared for natural disasters, and following the “drop, cover, hold” mantra when quakes happen.
Meanwhile, Countdown Taupō Central was closed on Thursday while earthquake risk assessments were carried out.
“It’s probably one of the oldest buildings still standing in Taupō so there is an abundance of caution in inspecting the site,” said store manager Chris Partridge.
“Our priority is making sure we’re safe for staff and customers”.
There was no visible damage or disruption inside the store so he was optimistic that they would be given the go-ahead to reopen before the anticipated busy upcoming weekend.
This morning Oruanui resident Beth told Newstalk ZB: “Never felt anything like it before. Things fell down and next thing I could hear water.
“It shook the hot boiler so violently it’s ruptured all the pipes at the top. Water was spraying all over the floor down and through the carpet.
“First thing I did was dive into the room and get my grandson - he looked quite frightened. And then I ran outside in the dark to turn the water off.”
Another Taupō resident, Karen, said her family was “shaken up pretty badly”.
”We’ve been through the big quake in Whakatāne years ago and this was not nice. It was a complete reminder of what we went through back then.”
Taupō local Stacey Fox, whose house is on a hill, said it shook all night; breaking glass and spilling books and cans from the pantry onto the floor.
Shop security footage captured the moment the quake hit at the Asian Sari-sari store.
Just after 11.48pm items on the shelves started shaking before falling on the floor.
By 5.23am, there had been at least 29 aftershocks.
The biggest aftershock was reported at 12.40am with a 4.5 magnitude quake hitting at a depth of 5km about 20km southwest of Taupō.
On the GeoNet Facebook page, Taupō local Brittany Rose said: “Was that a good one. Still rumbling here for [the] past hour and hasn’t stopped.”
Katie Howie said over at her house, drawers “flew open” when the quake struck.
That was “a biggie”, she wrote.
Taupō resident Les Pepper said the shakes brought back memories of being in the 1987 Edgecumbe earthquake.
Pepper, who lives in the Rangatira Park area, said they usually get regular small earthquakes. But last night was different.
“This one woke me up in a real rush. Our two-storey house was rocking and creaking. I could hear things falling off of shelves,” he said.
”I hope this isn’t the volcanic events in the lake starting to ramp up. We lived through the Edgecumbe earthquakes whilst based at Matahina hydro power station. It’s brought a lot of those memories back.”
Pepper said things had settled down this morning and there appeared to be no major damage on his street.
Taupō Volcano’s seismicity - the occurence or frequency of earthquakes in a region - had “sharply increased” overnight, as a result of the 5.6 magnitude quake.
Hauraki Gulf Weather reported about 6.30am that there had been over 150 earthquakes in the area in the last 12 hours.
“Since April’s unrest started, 1000 (plus) earthquakes have been recorded,” according to the site.
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