Research into understanding Lake Wānaka’s underwater structure and potential for earthquakes and tsunamis has resulted in NIWA scientists mapping Lake Wānaka in more detail.  

An active fault was discovered under the lake three years ago.

“Lake Wānaka is one of the most photographed locations in the country but until now its depths have remained a mystery,” NIWA marine geology technician Sam Davidson said. 

“We discovered some really interesting features, including complex channel systems from the rivers that feed into it.”

Sam said features from the lake's geological history came to life in front of the researcher's eyes.

“Wānaka sits in a U-shaped valley which was carved by an ancient glacier during the last ice age over 10,000 years ago,” Sam said.

“We … saw dramatic steep slopes that plummet to the deepest parts of the lake.” 

Sam and his team retrofitted a multibeam echosounder onto a small dive vessel, which they steered up and down the lake over several weeks.

The Lake Wānaka mapping project team onboard RV Rukuwai II with multibeam echosounder attached to the bow of the research vessel. PHOTO: Lana Young, NIWA

It calculated the water depth by bouncing soundwaves off the lakebed at a rate of 10 per second and timing how long they took to return. From this data, NIWA have built a full 3D model of the entire area.

NIWA hydrodynamics scientist Dr David Plew is using the map to study the lake’s water quality.

“New Zealand has experienced dramatic changes in land use over the past century, which has had big impacts on our freshwater systems,” David said. 

“Nutrient loads, the volume of water, and the amount of sediment going into Lake Wānaka have all been impacted. And climate change is also affecting our lakes and will do so even more in the future.”

Map showing extent of mapped area. IMAGE: Sam Davidson, NIWA

To predict how Lake Wānaka will change, NIWA is developing computer models of the catchment and lake. These need accurate bathymetry data, and up until now NIWA has been working from charts created in the 1970s.

“This new depth data that we've captured is more accurate and detailed. This is especially important in shallow parts of the lake like Roys Bay and Stevensons Inlet, but also where rivers flow into the lake because these areas have seen some of the biggest impacts and changes since the 1970s,” David said.

NIWA’s work will also be used to study hazards from future seismic activity.

Lake Wānaka is at risk of experiencing a tsunami-like event due to its location on an active fault and its specific geological features, such as steep slopes that could create a landslide and pose a risk to lakefront communities.

“Now we have a clear picture of the lake’s structure, we can better inform hazard modellers and councils to better prepare for these events,” Sam said.

Go deeper: 

• Risk of major earthquake more than doubled
• Tsunami risk identified for Wānaka
• Active fault under Wānaka identified