To understand how the Himalaya were formed it seemed logical to start at the actual zone of plate collision, the Indus suture zone. Most of this collision zone runs across southern Tibet, which in the 1970s was almost impossible to travel through. Following Mao Tse-tung’s Red Army’s invasion and occupation of Tibet in October 1950, that region had remained firmly closed to all foreigners. In the western Himalaya the Indus suture zone runs right across the northernmost province of Ladakh. Ladakh used to be a part of southwestern Tibet before the British annexed it during the Raj. Leh, the ancient capital of Ladakh at 3,500 metres in the Indus Valley, was the final outpost of British India before the great trans-Himalayan barrier of the Karakoram Range. Only the Nubra Valley and the Tangtse Valley north of Leh were beyond the Indus, and these valleys led directly up to the desolate high plateau of Tibet. Leh was a major caravan route and a crossroads of high Asia, with double-humped dromedary camel caravans coming south from the Silk Route towns of Yarkhand and Khotan; Kashmiris and Baltis came from the west and Indian traders from the Hindu regions of Himachal and Chamba to the south. Ladakh, Zanskar, and Zangla were three ancient Himalayan kingdoms ruled by a Giapo, or King, each from a palace that resembled a small version of the Potala Palace in Lhasa. In 1978, when we were climbing in the mountains of Kulu, I had looked from our high summits across to the desert mountains of Lahoul and Zanskar, north of the main Himalayan watershed. Here, in the ancient Buddhist kingdoms of Zanskar and Ladakh lay wave upon wave of unexplored and unclimbed mountains. They lay north of the monsoon limits and in the rain shadow of the main Himalaya, so the vegetation was sparse, and the geology was laid bare. Flying north from Delhi, or east from Kashmir into Leh, the views were simply mesmerizing.
Erosion in southern Tibet shut down at ∼10 Ma due to enhanced rock uplift within the Himalaya