Complex sentence: Tilman and Wigram went up the main Rongbuk Glacier to Lho La from where they decided that the West Ridge provided no way to the summit and that from the Lho La itself there was no means of descent to the Western Cwm.
Split into simpler sentences: Tilman and Wigram went up the main Rongbuk Glacier to Lho La. The West Ridge, they decided, provided no way to the summit and Lho La provided no means of descent to the Western Cwm.