Mount Kosciuszko

The land here is high but rolling, like big, smooth waves.

Long ago, when the world was colder, glaciers slid down the mountains and dug lakes.

Geoscience Australia describes the Snowy Mountains as undulating tablelands: high, gently rolling land. They are part of the Great Dividing Range.

During the last ice ages, glaciers formed in a small area of the southeastern highlands, on the Kosciuszko massif. Scientists at the Australian National University dated rocks they left behind and found glaciers advanced more than once, the last time about 16,800 years ago. Their ice scooped out bowl-shaped hollows that now hold lakes.

Geoscience Australia places the mainland's highest mountains in the Snowy Mountains and the Victorian Alps, part of the Great Dividing Range, and describes the Snowy Mountains as typically undulating tablelands.

Barrows and colleagues (Quaternary Research, 2001) report that Late Pleistocene glaciation of the Australian mainland was restricted to a small area of the southeastern highlands. Using cosmogenic beryllium-10 exposure dating, they found an Early Kosciuszko glaciation (the Snowy River Advance, before 59,300 ± 5,400 years ago) and a Late Kosciuszko glaciation of three progressively smaller advances: 32,000 ± 2,500 (Headley Tarn), 19,100 ± 1,600 (Blue Lake) and 16,800 ± 1,400 years ago (Mt. Twynam).

Blue Lake sits in a round, bowl-shaped valley that ice dug long ago.

In spring and autumn, the water can mix all the way through the lake.

Blue Lake, in Kosciuszko National Park, is one of only four cirque lakes on mainland Australia, says the New South Wales government. A cirque is a bowl-shaped valley carved by a glacier.

Twice a year, in spring and autumn, the lake's cold and warm layers reach the same temperature and can mix. Blue Lake and Hedley Tarn, a smaller lake just downstream, became a Ramsar wetland of international importance in 1996.

NSW Environment and Heritage describes Blue Lake as one of only 4 cirque lakes on mainland Australia, in an amphitheater-shaped valley formed by glacial erosion. It has a dimictic thermal regime: its layers reach the same temperature in spring and autumn and can mix throughout, which helps regulate the temperature of the water flowing out.

The site, with Hedley Tarn about 400 m downstream, was listed under the Ramsar Convention in 1996 as a rare example of near-natural alpine wetlands, surrounded by alpine herb fields, heaths, fens and bogs.

A pygmy possum and a rare frog live in these mountains.

Special plants grow where snow stays late.

Kosciuszko National Park protects rare and endemic plants and animals, including the mountain pygmy possum and the corroboree frog. Around Blue Lake live threatened species such as the alpine tree frog and the anemone buttercup.

On the Main Range, a special plant community called Snowpatch Feldmark grows only where snow lies late. It was listed as critically endangered in 2018: it covers only a small area, and snow in the Snowy Mountains has been getting shallower and lying for less time.

A NSW National Parks education program describes the park as home to rare, endangered and endemic plants and animals, including the mountain pygmy possum and the corroboree frog. The Blue Lake Ramsar site supports the mountain pygmy possum, alpine tree frog and anemone buttercup, and alpine-only plants such as the snow buttercup and snowpatch cushion-plant.

In 2018 the NSW Threatened Species Scientific Committee listed Snowpatch Feldmark as a critically endangered ecological community. It is restricted to late-lying snowpatches, with an extent of occurrence of 104 km², and the committee cites evidence that snow depth and cover duration in the Snowy Mountains have declined since the late 19th century.

The weather on the mountain can change very fast. Snow can fall at any time.

Check the weather first, and stay with your grown-up.

NSW National Parks says the walk from Thredbo to the summit is 13 kilometers return and takes 4 to 5 hours, with steep bits and many steps. Weather can change quickly in the Snowy Mountains, and snow can fall at any time, so check the forecast and don't set out if bad weather is coming.

In winter the track is buried in snow, and walking it is not recommended. Mobile phone coverage is limited.

NSW National Parks grades the Thredbo-to-summit walk as Grade 3: 13 km return, 4-5 hours, short steep hills and many steps. Its safety messages: weather can change quickly and snow can fall at any time; alpine conditions can be extreme and change rapidly, particularly in winter, when the track is snowbound and walking is not recommended; mobile reception is limited; recreational drones are prohibited.

National Geographic Education notes that a chairlift takes hikers most of the way up, leaving a walk of about 6 km to the summit.