The highest unclimbed mountain in a particular region or in the world is often a matter of controversy. In some parts of the world surveying and mapping are still not reliable, and there are not comprehensive records of the routes of explorers, mountaineers and local inhabitants.
However, a major problem relates to the definition of a mountain. Any particular mountain, in addition to its highest point, will also have subsidiary "tops." Generally, a subjective view is taken of what is a mountain and what is a top. The horizontal distance between main peak and top, the difference in height, the topographic prominence of the top, as well as the general topography, all come into consideration. Although objective criteria have been proposed for distinguishing "peaks" from "tops" (a prominence of 610 m, 2,000 feet is one definition), there is no widely agreed standard.
The Peakware World Mountain Encyclopedia has a list of unclimbed 7000 m Himalayan peaks which includes tops.[1] The list is somewhat out-of-date: for example Lhotse Middle, 8430 m, was first climbed in spring 2001. Another list is provided on the Explorersweb website using a prominence cutoff of 500 m.[2]
The mountain most widely claimed to be the highest unclimbed mountain in the world in terms of elevation seems to be Gangkhar Puensum, 7570 m (24,836 feet). It is in Bhutan, on or near the border with China. In Bhutan, climbing of high mountains has been prohibited since 1994. The rationale is based on a combination of (1) the Bhutanese government's respect for local customs that consider this and similar peaks to be the sacred homes of protective spirits and (2) the lack of high-altitude rescue resources from any locale closer than India.
It is also doubtful which is the highest unclimbed non-prohibited mountain. This depends greatly on the prominence cutoff. Saser Kangri II East (7,513 m, Prom=1,450 m), until recenty considered the second highest unclimbed mountain, was climbed on August 24, 2011.[3] Labuche Kang III/East (7250 m?, Prom=570 m?), near Cho Oyu, is reportedly unclimbed, but its status is hard to verify. It also lacks significant prominence.
It is similarly troublesome to determine the most prominent unclimbed mountain. Finisterre Range HP (Prom. = 3,675 m), Sauyr Zhotasy (Prom. = 3,252 m) and Mount Siple (Prom. = 3,110 m) all have no record of successful ascents, but the status of each of these peaks is difficult to confirm. Coincidentally, Gangkhar Puensum (Prom. = 2,995 m) is perhaps the most prominent unclimbed mountain that has any reasonable degree of certainty regarding its unclimbed status.