the red line shows the Great Couloir or Norton Couloir; in 1924 Norton crossed the north face between the light blue and the green lines; (b) marks the highest point on west face of the couloir, up to which Norton ascended in 1924;
the light blue line shows the 1980 Messner Traverse;
the green line shows the normal route, which largely corresponds to the 1924 Mallory Route, with high-altitude camps at about 7,700 and 8,300 m, although today's 8,300 m camp is somewhat more to the west (2 triangles).
The Norton Couloir or Great Couloir is a steep gully high on the north face of Mount Everest in Tibet which lies east of the pyramidal peak and extends to within 150 m below the summit.
Its companion to the west of the summit is the Hornbein Couloir.