The islands belong to Australia and are located 4,000 kilometres (2,485.5 mi) southwest of the mainland in the Southern Ocean.

The island's area is now reported as 2.45 square kilometres (0.9 sq mi) and the highest summit is at least 230 metres (750 ft) high.

[5] It is dominated by Mawson Peak, a 2,745-metre (9,006 ft) high complex volcano which forms part of the Big Ben massif.

A July 2000 satellite image by the University of Hawaii showed an active 2-kilometre (1.2 mi) long and 50–90-metre or 164–295-foot wide lava flow trending southwest from the summit.

Glaciers have carried the eroded sediment to the downstream end of the island and formed the low land of the Nullarbor (gravel isthmus) between the two volcanoes, and further to the east in the Elephant Spit.

Measurements between 1947 and 1980 show that glacial retreat, particularly on the eastern flanks, is correlated with changes in weather patterns.

[9] The volcano Big Ben, from which all the glaciers drain, has shown no sign of changing geothermal output to cause the melting;[9] a 1 °C or 1.8 °F warming has occurred over the same time period.

[9] Monitoring of climatic conditions continues, with emphasis on the impact of Foehn winds on glacier mass balance.

An expedition by scientists from the Australian Antarctic Division visited the volcanic island in 2009, observing glaciers that had retreated 50 metres (160 ft) in three years.

[8] Glaciologist Dr. Ian Allison states that the latest aerial surveys, in 2009, showed continuous rapid melt.

It was sighted from the air by Lieutenant Malcolm Smith, RAAF, pilot of the ANARE (Australian National Antarctic Research Expeditions) seaplane that made the first reconnaissance flight over the island in 1948.

In view of his death in an aircraft accident shortly afterward, this proposal was adopted by Australian Antarctic Names and Medals Committee (ANCA) with only a change of generic term.

At Atlas Cove (at the northwestern end of Heard Island) the monthly average temperatures reported lie in the range from 0.0 °C (32.0 °F) to 4.2 °C (39.6 °F).

Annual precipitation at sea level on Heard Island is in the order of 1,300 to 1,900 mm (51.2 to 74.8 in); rain or snow falls on about 3 out of 4 days.

[13] This is reported to have caused glacial retreat and as result lagoons and freshwater lakes are getting formed, and flora and fauna have emerged in the new land.

[5] The inscribed area is 658,903 ha (which includes both terrestrial and marine land) and under Criteria: (viii)and (ix) with the title "Territory of Heard Island and McDonald Islands", stating that it will "‘open a window into the earth’, thus providing the opportunity to observe ongoing geomorphic processes and glacial dynamics.

The distinctive conservation value of Heard and McDonald – one of the world's rare pristine island ecosystems – lies in the complete absence of alien plants and animals, as well as human impact.