Mount Giluwe is the second highest mountain in Papua New Guinea at 4,367 metres (14,327 ft) (Mount Wilhelm being the highest). It is located in the Southern Highlands province and is an old shield volcano with vast alpine grasslands. Ancient volcanic plugs form its two summits, with the central peak the highest and an east peak about 2 kilometres (1.2 mi) away at 4,300 m (14,108 ft). Giluwe has the distinction of being the highest volcano on the Australian continent, and is thus one of the Volcanic Seven Summits.
The original volcano on the site of Mount Giluwe formed roughly 650,000-800,000 years ago, probably as a stratovolcano of similar height to the current peak. Extensive Pleistocene glaciation eroded away much of the peak, leaving a series of volcanic plugs which form the present-day summits. A renewed episode of extensive volcanic eruptions formed the shield-like bulk of the current mountain between 220,000-300,000 year ago, and there is evidence that some of the lava erupted subglacially. During the last glaciations of the Ice Age, the upper slopes were covered by a massive ice cap over 150 m (500 ft) thick, from which only the main and east peaks protruded as nunataks above the ice surface.
At its maximum extent, the ice cap was over 15 km (9 mi) across and covered an area greater than 100 km² (40 mi²). Outlet glaciers extended down as low as 3,200-3,500 m (10,500-11,500 ft), leaving a variety of deposits including glacial till and moraines. Although the glaciers are now long gone, numerous cirques and U-shaped valleys remain visible. The present-day climate on the summit plateau above roughly 3,400 m (11,000 ft) is cold enough for nightly frosts and occasional snowfall.