Tekapo tsunami a real threat

Work is under way to discover if landslides on Tekapo’s lake bed could generate a destructive tsunami.

The first complete mapping of the Tekapo lake bed has found ‘‘astounding’’ large landslides cover more than half of the lake.

The Niwa research of the South Canterbury hydro lake was collected over the past month using state-of-the-art sonar equipment.

The team, led by Niwa marine geologist Dr Joshu Mountjoy, mapped the lake and then used seismic reflection survey equipment to get images of the sediment beneath the lake floor.

Mountjoy said the data revealed an astounding and unexpectedly dynamic lake bed.

More than half of the 83 square kilometre lake floor was covered in landslide deposits, some spreading more than 1km across the lake bed.

‘‘Landslides on the lake floor are just one part of the story,’’ Mountjoy said.

‘‘The seismic surveying will give us images more than 100m under the lake floor that reveal the long history of landslides in the lake.’’

Analysis is now under way with the aim of discovering if the landslides can cause tsunamis within the lake and whether they are a hazard to the Lake Tekapo township and also the hydro power infrastructure.

This will be done by mathematically simulating landslides generating tsunami and assessing how big they will be at the lake edge.

The two-year study is funded by the Natural Hazards Research Platform and is a joint NIWA-GNS Science project with input from Otago University and Environment Canterbury.

A 2015 GNS Science tsunami and seiche hazard scoping study found that landslides on steep slopes around Tekapo, as well as the more sparsely populated Lake Pukaki and Lake Ohau, had the potential to create tsunamis as low as 0.5m and as high as 25m.