Mount Sidley

Mount Sidley, tallest volcano in Antarctica, with a summit of 14,058 feet (4,285 meters), and located on the continent’s Pacific Coast near the Thwaites Glacier. Mount Sidley is a shield volcano and one of five major volcanoes in the 50 mile- (80 km-) long Executive Committee Range in Marie Byrd Land (see also volcano: shield volcanoes). It is also considered one of the Volcanic Seven Summits, the highest volcanic peaks on each of Earth’s seven continents; however, Mount Sidley is the shortest member of the group—its elevation being comparable with that of the volcano Mount Giluwe in Papua New Guinea (14,331 feet [4,368 meters]) and the nonvolcanic peak Mount Whitney (14,494 feet [4,418 meters]) in the 48 conterminous United States.

Mount Sidley has a relatively flat peak that contains a 3-mile- (5-km-) wide caldera and a sheer amphitheater (that is, a caldera wall), which is thought to have been created by an eruption about 4.7 million years ago that collapsed the volcano’s south-facing slope. Studies have determined that Mount Sidley was active for a period of about 1.5 million years, during which its vent and caldera formed Sidley’s plateau and caldera, both of which are covered in ice. Although Sidley and its neighboring volcanoes are thought to be dormant, at least one seismology study in 2010 detected underground earthquakes nearby (some 18 miles [29 km] away from Mount Sidley), which could indicate the presence of a new volcano.

American naval officer and explorer Richard E. Byrd discovered Mount Sidley during an Antarctic expedition on November 18, 1934. Byrd named his finding after Mabelle E. Sidley, the daughter of his benefactor American manufacturer William Horlick. Prior to the volcano’s discovery, the expedition nearly ended with Byrd’s death during the Antarctic winter (that is, the period spanning from March to August) of 1934; he spent five months alone in a hut buried beneath the ice shelf before being rescued. The other mountains in the Executive Committee Range were not discovered until 1940, by members of the U.S. Antarctic Service who were flying overhead.

Though Mount Sidley’s gentle slope makes it a straightforward climb for experienced mountaineers, the volcano’s remote location and forbidding climate conditions make reaching the volcano difficult. New Zealand researcher Bill Atkinson became the first recorded climber to reach Sidley’s peak in 1990, and only 11 other groups have successfully climbed the volcano as of 2020.