Mount Sidley is the highest volcano in Antarctica, a member of the Volcanic Seven Summits, with a summit elevation of 4,181-4,285 metres (13,717-14,058 ft). It is a massive, mainly snow-covered shield volcano which is the highest and most imposing of the five volcanic mountains that comprise the Executive Committee Range of Marie Byrd Land. The feature is marked by a spectacular 5 km wide caldera on the southern side and stands NE of Mount Waesche in the southern part of the range.
The mountain was discovered by Rear Admiral Richard E. Byrd on an airplane flight, November 18, 1934, and named by him for Mabelle E. Sidley, the daughter of William Horlick who was a contributor to the 1933-35 Byrd Antarctic Expedition. Despite its lofty status, the volcano languishes in obscurity due to its extremely remote location. It is little known even in the mountaineering world compared to the far more famous Mount Erebus, the second highest Antarctic volcano which is located near the U.S. and New Zealand bases on Ross Island. The first recorded ascent of Mount Sidley was by New Zealander Bill Atkinson on January 11, 1990, whilst working in support of a USAP scientific field party.
- Elevation: 4,285 m (14,058 ft)
- Prominence: 2,517 m (8,258 ft)