The night before Mallory left Camp IV (North Col), he had a conversation with Norton. Norton had just returned from his own summit attempt where he reached an altitude record of 28,126 at the top of the Great Couloir. Norton told Mallory that the route was climbable at that point but that he turned around because (1) he was out of energy, (2) he was out of time, and (3) he was climbing unassisted, as his climbing partner, Somervell, had fallen ill, and Norton climbed on ahead without him.
Mallory communicated his final decision on the routes to the expedition photographer, John Noel, so he would know where to point his camera: “Mallory told me himself, when he talked to me of his possible routes up the final pyramid and told me where to watch for him, that he expected to go up the northeast of the final pyramid, but if he found the Gully particularly difficult, or if the west wind were particularly bad, he would take the eastern ridge, missing the Gully by passing across the head of it and gaining better protection from the west wind.”
These two potential routes were identified by Norton: a small gully off to the right and a “zig-zag” route to the left. The “small gully” route was eventually climbed by the Swedish in 1987 and is shown in blue below. Norton also noted that there is the “possibility of breaking through the lower strata of these two bands east of the great couloir, and traversing along slabs between it and the upper band until it is possible to break through the latter.” This is essentially a zig-zag route across the top of the couloir to meet up with the Third Step. One potential for this route is shown in red below (photo from modern Camp 3). In all these photos, east is to the left.
(Please note that a popular website describing the “Routes of Everest” gives simplifications of the routes in order to categorize them. However, the image of the routes has numerous errors as a result. The graphic is fine as an overview of different routes, but when analyzing exactly where an expedition climbed, it is of little use. For instance, the graphic shows the “The Great Couloir aka Norton Couloir (White Limbo) – 1984 Australian” as climbing out of the Couloir at the route marked in blue below. However, the expedition reports a significantly different route, climbing out well below, which is on page 196 of the book “White Limbo“. )
Mallory would not spend an hour on a speculative climb up to inspect the Second Step because he would have lost too much time to continue on with the easier couloir routes he had already seen. Mallory was not on a reconnaissance climb. Mallory was on a summit bid and had made plans: Plan A: Climb the “small gully” out of the couloir. Plan B: Climb a “zig-zag” route to the east of the couloir. It is ultimately this Plan B that matches up with Odell’s sighting. Potential routes for Plan B are shown here:
A close-up shows a variety of ways it could be climbed. Note the climbers descending the Third Step. However, this perspective, known as “foreshortening,” makes the angle appear less steep than it actually is:
The general angle of the route as compared to the First and Second Steps can be seen in this photo taken from modern Camp 3. Note that the terrain blocks some of the view of the area directly below the Second Step.
Mallory and Irvine followed one of these routes when they are spotted by Odell. (See video on Odell’s view of Mallory and Irvine heading towards summit.)
Mallory and Irvine would not be traversing across the ridge at that “Y” snow slope, but heading back towards the crest of the ridge. The logical attack point is the saddle between the “a” and “b” portions of the Third Step. They would crest the ridge and be visible against the skyline. This is one of the few locations where this occurs. For instance, at the top of the Second Step ladder, you are still about 15-20 below the top of the ridge and not easily visible from below. At the “top” of the First Step, you are nowhere near the top of the step but only at the top the the lower section. You are not easily visible at that section from below, and the First Step is entire blocked from view in the picture above — a potential spot for Odell’s sighting.
This leaves the issue of why Mallory did not climb the “small gully” route, as he stated that was his preferred route if there was no wind, and there was little to no wind that morning. A likely reason is that the “small gully” route looks like the best route when viewed from far away. However, once you get closer to the ridge, it is apparent that the “small gully” will require a great deal of back tracking. Not only will it require about 150ft of altitude to be given up, but even if you did mange to traverse across without giving up altitude, you would still traverse away from the summit for a good distance — far more than in the “zig-zag” route. In any case, Odell’s sighting does not match up with them climbing the “small gully.”