Tasman Glacier lake and its icebergs

Tasman Lake fills the lower Tasman Valley between the glacier's ice face and the moraine walls that once held its snout. DOC says it started forming in 1974 and has grown steadily since then.¹ NIWA's Water & Atmosphere magazine of October 2018 and NASA's Earth Observatory both put the line a year earlier: before 1973, they say, the lake did not exist.^6,7 The sources differ on the year, not on the story.

A lake at the front of a glacier changes how it melts. Once a lake has formed, NIWA explained in 2008, it eats at the glacier far faster than surface melt.⁸ NIWA scientists, quoted by NASA, added that a lake at the snout makes it more likely that blocks of ice will break away.⁹ The water is both a product of the retreat and an engine of it: the water undercuts the ice face, slabs fall in, and the lake moves one step further up the valley.

Its size tells the same story. By 2017, NASA reported, the lake had swollen to 7 kilometers long within a decade.² NIWA wrote in 2008 that Tasman Lake still had to almost double in size before the glacier would shrink enough to reach equilibrium with the climate.¹⁰ DOC's walking pages describe it as growing rapidly as the glacier melts.¹¹ Anyone who returns after a few years sees a different shoreline.

For anyone who wants to be out among the bergs, the way onto the lake is a guided boat trip. Mackenzie tourism calls Glacier Explorers New Zealand's only glacial boat tour.³⁰ Its season runs from September to June, and trips leave from the Hermitage Hotel in the village.⁵ The trip includes a 1.5km walk from the Blue Lakes car park to the jetty, which guests should cover in about 25 minutes.²² Our lake boat page covers prices and booking in detail.

Out on the water, the boats cross Tasman Lake to view the glacier's ice face from a safe distance and weave among the icebergs.¹⁵ From lake level the scale reads differently than from the moraine lookout: bergs that looked like white dots become cliffs of ice, and the grey glacier front turns out to be a wall many storeys high. Dress warmly. Wind off the ice chills a boat far faster than it chills the walking track.

The boat season reflects the lake's year. DOC notes that the lake freezes over in winter,³ and the boat season ends in June and restarts in September.⁵ Book a morning trip if you can: calmer water gives sharper reflections and a gentler ride. In the heart of summer the jetty walk and the car park both get busy, and an early start keeps the lake quieter for you.

The free way to the Tasman Glacier terminal lake is on foot from Tasman Valley car park. Follow the Blue Lakes Track briefly, then fork right after the shelter onto the Tasman Lake and River Track, which ends at a lookout over the water.²⁷ The round trip is 2.6 km and takes about 50 min, in DOC's figures.^21,41 Another fork heads to the point where the Tasman River leaves the lake and spills into its braided bed.⁵⁷

The higher view is on the Tasman Glacier View track, which climbs the moraine wall to a lookout over the whole lake: 1.5 km and 30 min return.^39,40 From the top you see the lake with the glacier at its far end, which makes it easy to understand how they fit together.²⁸ From the shore you see the bergs up close and hear the water lapping the gravel. If you have the time, do both on the same visit.

The lake track crosses the ridges of rubble the glacier left at its old snout, where plants are slowly taking hold.⁵⁸ DOC describes these large moraines as marking the foot of the glacier at the time the lake formed, and as a sobering reminder of its retreat.²⁹ Standing on them and looking up the lake to the distant ice face is a direct way to feel how far the Tasman has pulled back in a single human lifetime.

From the air the lake becomes a map. Our heli hike's helicopter crosses the valley on its way up, and the trip keeps you on the glacier with a guide for as long as 2 hours, from $528. A ski plane and helicopter combination flight of 45 minutes lands on the Tasman Glacier, from $323. Both show the line where the grey, rock-covered ice ends in the water.

Higher up, scientists are watching another lake. In March 2021 NIWA described a lake that kept appearing and vanishing where the Tasman and Hochstetter glaciers meet.¹⁴ NIWA suspected that it built to a certain size and was then siphoned away, possibly under the Hochstetter Glacier, into Tasman Lake.⁶¹ The two glaciers still join above the lake, but NIWA expects ice loss to separate them eventually.⁴³

Downstream, the lake's water has a long life. NASA notes that the glacier's water ends up in Lake Pukaki, a storage lake for hydroelectric power.⁶² On the way it spreads across the braided bed of the Tasman River, where DOC says the kaki, or black stilt, lives, a bird it counts among the country's rarest.⁶³ The milky turquoise of Lake Pukaki that travellers photograph from the highway starts here.