The Tasman Glacier lake at Mt Cook has its largest iceberg ever following an overnight "calving" whch left 20 huge icebergs on the lake.
The entire 650-metre-wide front face of the Tasman Glacier is believed to have broken away into various-sized sections in the early hours of Saturday morning.
One of the icebergs is the "largest ever" by quite some way, according to Glacier Explorers operations manager Bede Ward.
"The last major calving we had was just over a year ago which was estimated at 30 million tonnes of ice breaking off the glacier," he said.
"This is much, much larger. There's one iceberg that surpasses the last largest-ever single iceberg [nicknamed Taniwha] we've ever had on the lake."
The sheer walls of this iceberg reach 40m to 50m in height and are likely to go 200m to 250m below the water.
Mr Ward said the timing was a huge coincidence, as the Tasman Glacier lake experienced a similar calving of this scale just five minutes after the huge Christchurch earthquake two years ago.
"The Tasman Glacier has been unusually quiet for the past 12 months with only small calvings, suggesting the glacier had maybe started to slow down," he said.
"It's an extraordinary opportunity to view nature in action, simply spectacular. Guests who have been out with us today couldn't believe their luck."
- The Timaru Herald