The Icefall is a frozen river.
Gravity drags the ice downward.
The pull is constant. The slow, steady flow of ice is imperceptible, but not all of the Icefall's movements are slow, some are sudden. On the Nepal side, the side from which Byron is approaching, is the Khumbu Glacier. The upper end of this great river of ice is high in the Western Cwm, around 7,000 m. Here the glacier separates from the steeper wall immediately above, leaving a gap where it pulls away from the rock.