Why is K2 not one of the 7 summits, and are the second-highest mountains harder?

K2 is not one of the 7 summits because it is the second-highest mountain in Asia, 238 m781 ft lower than Everest, and the challenge takes only the highest peak on each continent.

The second-highest summits of the seven continents, sometimes called the Seven Second Summits, are K2, Ojos del Salado, Mount Logan, Mount Kenya, Dykh-Tau, Mount Tyree and, depending on the list, Puncak Mandala or Mount Townsend. Some of them are harder than the highest peak on their continent and some easier; taken as a set they are more technical, more remote and less often climbed than the 7 summits, which is why fewer than a handful of people have completed them.

Continent by continent

• Asia: K2, 8,611 m28,251 ft, on the China and Pakistan border. Widely considered the hardest of the 8,000 m26,247 ft peaks, with no easy route and a fatality rate far above Everest's.

• South America: Ojos del Salado, 6,893 m22,615 ft, on the Argentina and Chile border and the highest volcano on earth. Harder to reach than Aconcagua but a walk-up by its normal route.

• North America: Mount Logan, 5,959 m19,551 ft, in the Yukon. As cold and remote as Denali, with a non-technical but very long normal route and hard routes elsewhere.

• Africa: Mount Kenya, 5,199 m17,057 ft. The true summits, Batian and Nelion, need rock climbing; only Point Lenana, 4,985 m16,355 ft, is a trek. Harder than Kilimanjaro in every way except altitude.

• Europe: Dykh-Tau, 5,205 m17,077 ft, in the Caucasus. Technically far more demanding than Elbrus, though 437 m1,434 ft lower. Mont Blanc, often assumed to be Europe's second summit, is the highest in the Alps only.

• Antarctica: Mount Tyree, 4,852 m15,919 ft, more technical than Vinson, with the cold and the logistics making it the hardest of the set to arrange. Mount Shinn, 4,661 m15,292 ft, is a close third.

• Oceania: Puncak Mandala, 4,760 m15,617 ft, in Papua, on the Carstensz list; Ngga Pulu, next to Carstensz Pyramid, was once higher but its ice cap has melted. On the Kosciuszko list, Mount Townsend, 2,209 m7,247 ft, a short walk from Kosciuszko.

The comparison

The question is usually asked to belittle the 7 summits, and it does not do that. Difficulty on the 7 summits depends on the route: the South Face of Aconcagua, the Cassin Ridge on Denali and the Kangshung Face of Everest are as hard as anything on the second summits. By their normal routes, K2, Mount Kenya, Dykh-Tau and Tyree are harder than their taller neighbours, Ojos del Salado and Logan are about the same, and Townsend is a stroll. Christian Stangl is recorded as the first person to climb the seven second summits, a claim Guinness World Records confirmed with the case closed as of October 2013; Hans Kammerlander's claim was challenged over his Mount Logan ascent, and a second fraudulent claim on Puncak Trikora confirmed he never completed the set. Only a handful of climbers have followed.