KEY POINTS:
The newly formed lake in the South Island could become the newest attraction at the Mt Aspiring National Park.
GNS geologist and engineer Stuart Read said there was a chance the lake's dam could hold.
"When you look at the history of these sorts of dams, they have a tendency to fail. But there are exceptions. A lot depends on the type of land slide that forms," Mr Read said.
The 2.5km long, 500m wide and 100m deep lake in the Young Valley was created after a large land slip blocked the river in August.
Geologist Chris Massey and surveyor Neville Palmer told NZPA that it was the biggest landslide in New Zealand in 16 years.
Water has been flowing over the top but there were concerns last month that heavy rain could burst through the dam, causing millions of cubic metres of water to rush down the valley.
Mr Read said New Zealand's best known example of these types of lakes was Lake Waikaremoana, in the Urewera National Park.
He said the survival of the dam was dependent on the type of rock in the landslide and whether the landslide blocks the waterway with large masses of rock or sediment.
Department of Conservation spokesman John Gordon said the multiple earthquakes that struck the South Island last week had strengthened the dam.
Mr Gordon said the tracks in the Young River Valley remained closed and would remain that way until snow in the area melts and the Spring rains pass.
He said geological consultants would make a decision on the lake's safety.
Gavin Palmer from the Otago Regional Council visited the lake on Friday afternoon.
He said water was seeping through the dam but that had now dried up. Dr Palmer said water was still flowing over the top but he confirmed the dam could hold.
He said the council would continue to monitor the lake, recording the river flow and another visit to the lake will take place early next week.
The lake has not yet been given a name and Land Information New Zealand spokeswoman Julia Hodge said the geographic board would need scientific evidence to prove that the lake was a permanent feature.
"The Board has no written criteria on how long a feature has to be in place," Ms Hodge said.
- with NZPA
