The largest glacier in aotearoa. The glacier remained at a constant 28 km (17 mi) in length for all of its recorded history in the 20th century before starting its current period of rapid melting in the 1990s. Between 2000 and 2008 alone, the glacier terminus receded 3.7 km.

Since the 1990s the terminus has retreated about 180 metres (590 ft) a year on average. The glacier is now in a period of faster retreat where the rate of retreat is calculated to be between 477 to 822 metres (1,565 to 2,697 ft) each year. It is estimated that the Tasman Glacier will eventually disappear and the terminal Tasman Lake will reach a maximum size in 10 to 19 years time.

In 1973 Tasman Glacier had no terminal lake and by 2008 Tasman Lake was 7 kilometres (4.3 mi) long, 2 kilometres (1.2 mi) wide, and 245 metres (804 ft) deep.