The best route from Waimakariri Falls Hut to the Rolleston River does not cross Waimakariri Col itself, but crosses the main divide higher and further to the northwest. The actual crossing point under Mt Armstrong cannot be seen from Waimakariri Falls Hut. From Waimakariri Falls Hut you can see a ravine and two lines of bluffs to its left. Travel up the true left to the ravine in the middle of the valley and cross the Waimakariri River below the ravine. Go up the scree between the two bluffs. This will take you above the lower bluffs. Sidle to the right to get around the upper bluffs. The low point in the ridge where you cross is between Point 1845 and Mt Armstrong. Make your own way through bluffs to this point well to the northwest of Waimakariri Col. Time: 2–3 hours.
From the ridge, travel down the stream draining the small glacier on the slopes of Mt Armstrong. The gully running parallel to the stream develops into a steep chute and should not be entered. Leave the stream where it begins to level out in the basin below. Time: 3–4 hours