Because of the persistent presence of the ice sheet, the island is sometimes taken to be part of the Antarctic mainland. Its area is 2,460 square kilometres (950 sq mi); only a small portion of the island is free of ice and snow. The planet's southernmost active volcano, Erebus (3,794 m or 12,448 ft), as well as the dormant volcano Terror (3,230 m or 10,597 ft), are situated on the island. They were named by Captain James Ross after his ships HMS Erebus and HMS Terror. The third highest elevation is Mount Bird, with Shell Glacier and Endeavour Piedmont Glacier on its slopes. Abbott Peak stands between Mount Erebus and Mount Bird. Gamble Cone and Kyle Cone stand in the east of the island.
Despite its relatively small size, Ross Island is the world's 6th highest island. It has the highest average elevation of any island.
The Alcorta Rocks (77°30′S 166°22′E / 77.500°S 166.367°E / -77.500; 166.367) is a nunatak on the east shore of Maumee Bight, Ross Island, 2.6 kilometres (1.6 mi) east-northeast of Rocky Point. The feature rises to about 100 metres (330 ft) and is distinctive because three ridges radiate from the center. The rocks were named by the Advisory Committee on Antarctic Names in the year 2000 after Jesse J. Alcorta, a year-round support employee with eight field seasons at McMurdo Station from 1992–93 and many trips to South Pole Station; hazardous waste handling specialist at both McMurdo Station and South Pole Station; and cryogenic technician in support of the United States Antarctic Program laboratories.
Sir James Clark Ross discovered it in 1840, and it was later named in honour of him by Robert F. Scott.
Ross Island was the base for many of the early expeditions to Antarctica. It was and still is the southernmost island reachable by sea. Huts built by Scott's and Shackleton's expeditions are still standing on the island, preserved as historical sites.
Today Ross Island is home to New Zealand's Scott Base, and the largest Antarctic settlement, the U.S. Antarctic Program's McMurdo Station. Greenpeace established World Park Base on the island and ran it for five years, from 1987 to 1992.
Ross Island lies within the boundaries of Ross Dependency.
Ross Island supports a colony of approximately half a million Adélie penguins.