[4][5] It was discovered in 1775 by James Cook and initially named "Cape Montagu" as he thought it was a promontory of a larger landmass;[6] Thaddeus von Bellingshausen in 1815 determined that it was actually an island.

[14] The name has also been applied to the a peak on the southern caldera rim, which is the high point of Montagu Island[15] at 1,370 metres (4,490 ft).

[16] The submarine structure of Montagu Island is characterized by a largely regular, oval edifice with the pointy end to the west.

[17] A shallow shelf, which probably formed through erosion during glacial sea level lowstands, surrounds the island with widths of 14 kilometres (8.7 mi) to the west.

[19] A smaller submarine volcanic edifice merges into the western end of the Montagu Island volcano.

[21] It is much older than the main volcanic arc; potassium-argon dating has yielded ages of 32–28 million years.

[2] The few outcrops indicate that Montagu Island is formed by alternating layers of lava flows, scoria, tuffs and volcanic ash.

[28][29][30] Montagu Island largely lacks vegetation, although mosses (mostly Drepanocladus uncinatus) grow in drainages[31] and algae in penguin colonies.

[2] Satellite images observed an eruption at Mount Belinda, commencing in September or October 2001[37] and ending in 2007,[38] although heat anomalies from the cooling of the flow continued into 2010.

Initially it consisted of the emission of tephra, volcanic plumes[2] and a 600 metres (2,000 ft) long lava flow.

[40] In August 2003, a larger lava flow was observed, which extended down the northern flank of Mount Belinda over a length of 2 kilometres (1.2 mi), cutting down into the ice.

[12] Steam columns rose from the site where lava entered the seawater, and a lagoon filled with hot water.

[8] The island was named by Cook after John Montagu, 4th Earl of Sandwich, at the time First Lord of the Admiralty.