The Northern Advocate

Quakes prompt warning to steer clear of water’s edge at reserve

- Dan Hutchinson

The Taupō District Council is asking people to stay away from the water’s edge at a popular lakeside reserve while it works out what caused about 20m of foreshore to disappear during a swarm of earthquake­s this week.

“Hey folks, we know you’re interested in what’s happened out at Wharewaka but we have serious concerns about the land stability there. We estimate we’ve lost around 20m of foreshore,” the council said in a Facebook post.

“Other agencies are investigat­ing the cause, but it may be a result of land slumping with a resultant wave on the lake, rather than a wave alone.

“Our team is working to organise a temporary fence but in the meantime, to keep everyone safe in this area we ask that you please keep yourself, your children and your vehicles well back from the edge. Thanks.”

Two large, four-person pedal boats that were pulled up onto the grass near the area of erosion, were torn from their chains, washed onto rocks and destroyed by a surge of water, thought to be a tsunami, during the swarm on Wednesday night and Thursday morning.

Aftershock­s have continued to rattle Taupō and surroundin­g areas after Wednesday night’s magnitude 5.6 earthquake.

A 3.9 quake hit 20km southwest of Taupō at 5.37am yesterday at a depth of 5km. Other tremors were too weak to be noticeable.

The series of shakes continue in the wake of a strong 5.6 magnitude quake that rattled central North Island just before midnight on Wednesday.

One of the larger aftershock­s recorded was a 4.1 magnitude tremor at 11.47pm on Thursday.

Niwa scientist Dr Emily Lane showed in a tweet the tsunami as measured by water level gauges at Acacia Bay and Tokaanu.

Lane said 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 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 f ault l i nes 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 Thursday night’s quake.

Lane said her team want to talk to locals who have seen any more inundation (the very high tide line) around Taupō so they can continue to research the quake.

GeoNet was still questionin­g if the wave was a tsunami at all.

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.

 ?? PHOTO / SUPPLIED ?? It is estimated about 20m of foreshore has been lost this week at Four Mile Bay, Wharewaka.
PHOTO / SUPPLIED It is estimated about 20m of foreshore has been lost this week at Four Mile Bay, Wharewaka.

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