Heard Island is spectacularly glacierized as a result of both its height (2745 metres at the summit of Big Ben) and its location south of the Antarctic Convergence – the meeting point of cold Antarctic surface water and less cold subantarctic surface water.
The island has extensive ice cover, with glaciers covering approximately 70% of the land (around 257 square kilometres) and permanent snow covering a further 2%.
There are twelve major glaciers and several minor glaciers, the majority of which radiate from the summit region of Big Ben, with individual glaciers separated by well-developed buttresses.
Many of the glaciers with westerly to south-westerly aspects terminate in the sea, whereas those with northerly and particularly north-easterly aspects terminate on land or in lagoons well inland from the ocean.
There are also extensive snow fields and several smaller glaciers which descend from the the summits of Mt Dixon, Mt Anzac and Mt Olsen on Laurens Peninsula. There are no glaciers on the low-lying McDonald Islands.
The largest glacier is the Gotley, which descends for over 13 kilometres from Heard Island's highest point (2745 metres at Mawson Peak) to the south coast near Cape Labuan. It covers an area of over 27 square kilometres.
Since the late 1940s, the total area covered by glaciers on Heard Island has reduced by approximately 11%. This recession is linked to regional climate warming over that time, as has also been witnessed at Îles Kerguelen approximately 400 kilometres to the north-west. Any contribution to the retreat at Heard Island from volcanic activity is considered negligible.
Four coastal lagoons have been formed as a result of the retreat of the Brown, Compton, Winston and Stephenson glaciers. Some of the lagoons are closed and allow for easy walking along the coast, but some of the lagoons are open to the sea, and present a challenge to pass.