The entirety of Lake Wānaka has been mapped in incredible detail by NIWA scientists in a bid to better understand its underwater structures – and its future potential for earthquakes and tsunamis.
It comes after an active fault was discovered at the lake three years ago.
NIWA marine geology technician Sam Davidson said the institute could now visualise the entire lakebed and its structures.
“Lake Wānaka is one of the most photographed locations in the country but, until now, its depths have remained a mystery,” Davidson said today in a statement.
NIWA marine geology technician Sam Davidson said the institute could now visualise the entire lakebed and its structures.(Source: NIWA)
Researchers studying the lakebed “discovered some really interesting features”, he said, “including complex channel systems from the rivers that feed into it”.
“We also saw dramatic steep slopes that plummet to the deepest parts of the lake.
“Wānaka sits in a U-shaped valley which was carved by an ancient glacier during the last ice age over 10,000 years ago; these features and the lake’s geological history came to life in front of our eyes.”
Davidson and his team retrofitted a multibeam echosounder – a form of underwater sonar – onto a small dive vessel, which they steered up and down the lake over several weeks.
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 built a full 3D model of the entire area.
NIWA hydrodynamics scientist Dr David Plew was also 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. Nutrient loads, the volume of water, and the amount of sediment going into Lake Wānaka have all been impacted,” Plew said.
“Climate change is also affecting our lakes and will do so even more in the future.”
Predicting seismic activity
![Mapping of Lake Wānaka.](https://tvnz-1-news-prod.cdn.arcpublishing.com/resizer/v2/mapping-of-lake-wanaka-HHPSBLI2X5F7NKFGQP2JX4FPDU.jpg?auth=62d9b7e5daa23f475e31d6efb45d9f6455e42b13c44edde3560a41441a64e1da&quality=70&width=767&height=431&focal=947%2C471)
To predict how Lake Wānaka would change, NIWA was using their new insights to develop computer models of the catchment and lake.
NIWA will be using accurate bathymetry data collected from their research – a long overdue update after working from charts created in the ’70s.
“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,” Plew said.
Could a tsunami occur at Wānaka?
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,” Davidson said.
Otago Regional Council’s manager natural hazards, Dr Jean-Luc Payan, said the new data is “invaluable to inform natural hazards investigations and to understand the consequences of natural hazards events on people and infrastructure in the Lake Wanaka area”.