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 20m to 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.
Latest M4.1 earthquake at 1:53pm today is the 3rd M4.0+ aftershock since the main shock of M5.6 late yesterday within the volcano's caldera. Here is the summary and locations of the Taupō Volcano's M4.0+ shock sequence for the 2022 episode....so far pic.twitter.com/Ep6gtNRDOP
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.
This is the #tsunami as measured by the @niwa_nz water level gauges at Acacia Bay (near Taupō township) and Tokaanu (southern end of the lake) - see second image for locations. It's in NZST which is why it looks like it comes in an hour early. https://t.co/W7PfhJFgVlpic.twitter.com/FPScHYSV1n
She referenced the complex Kaikōura earthquake when referring to what it might look like under Lake Taupō at the moment.
During the 7.8 magnitude shake in 2016, parts of the land in Kaikōura were jolted several metres upwards because of the many fault lines that were activated.
Although it may not be as extreme under Lake Taupō, the ground shifting is what would have 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 its website, it said researchers were “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.
A lake surge at Taupō's Four Mile Bay after an earthquake destroyed boats and caused damage to the foreshore. Photo / Dan Hutchinson
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.
